June 2001/ BULLETIN 10-9 Thermostatic Expansion Valves · Page 2/ BULLETIN 10-9 THERMOSTATIC...

ThermostaticExpansion

Valves

June 2001 / BULLETIN 10-9

• Theory of Operation

• Application

• Selection

®

/ BULLETIN 10-9

THERMOSTATIC EXPANSION VALVES

OutstandingFeatures &

Benefitsof Sporlan

ThermostaticExpansion

Valves

Refer to Bulletin 10-10 for complete specifications ofThermostatic Expansion Valves, with Selective Thermostatic Charges.

Refer to Bulletin 10-11 for a complete discussion onInstalling and Servicing Thermostatic Expansion Valves.

FOR USE ON REFRIGERATION and/or AIR CONDITIONING SYSTEMS ONLYBulletin 10-9, June 2001 supersedes Bulletin 10-9 dated October 1995 and all prior publications.

© Copyright 2001 By Sporlan Valve Company, Washington, MO

10

The Refrigeration System . . . . . . . . . . . . . . . . . . . .3Types of Expansion Devices . . . . . . . . . . . . . . . . . 3How the Thermostatic Expansion Valve Works . . . .3

Basic Operation . . . . . . . . . . . . . . . . . . . . . . . . .3Effect of Pressure Drop Across the Valve Port . . 4Balanced Port TEVs . . . . . . . . . . . . . . . . . . . . . 5Equalization Method . . . . . . . . . . . . . . . . . . . . . 5Thermostatic Charges . . . . . . . . . . . . . . . . . . . . 6

Sporlan Thermostatic Expansion Valves . . . . . . . . . . . 7 Alternative Refrigerants . . . . . . . . . . . . . . . . . . 7Sporlan Selective Charges . . . . . . . . . . . . . . . . 7 Air Conditioning and Heat Pump Applications . . 7Refrigeration Applications . . . . . . . . . . . . . . . . . 8Special Selective Thermostatic Charges and

Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Thermostatic Expansion Valve Applications . . . . . . 9

System Design Factors . . . . . . . . . . . . . . . . . . . 9Balanced Port TEVs . . . . . . . . . . . . . . . . . . . .10

System Design For Part-Load Conditions . . . . .11Two or more evaporators sections

handling the same load . . . . . . . . . . . . . . . .11Single evaporator controlled by two TEVs . . . . . . .11Hot gas bypass and desuperheating TEVs . . . .12Off-Cycle Pressure Equalization . . . . . . . . . . . .12R-717 (Ammonia) Applications . . . . . . . . . . . . .13Thermostatic Charges for Ammonia Valves . . .14

Factors Affecting TEV Operation and Performance 14Superheat . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Valve Setting . . . . . . . . . . . . . . . . . . . . . . . . . .15Evaporator Temperature . . . . . . . . . . . . . . . . .15Subcooling . . . . . . . . . . . . . . . . . . . . . . . . . . . .15Refrigerant Liquid Temperature and Pressure

Drop Across TEV . . . . . . . . . . . . . . . . . . . .16Thermostatic Charge . . . . . . . . . . . . . . . . . . . .16

Selection Procedure . . . . . . . . . . . . . . . . . . . . . . .16Recommended Thermostatic Charges . . . . . . . . .18

TABLE OF CONTENTS

• SELECTIVE THERMOSTATIC CHARGESDesigned to provide optimum performance for all applications—air conditioningand heat pump, medium and low temperature refrigeration.

• THERMOSTATIC ELEMENT DESIGNLong lasting and field proven stainless steel diaphragm and welded elementconstruction.

• DIAPHRAGM DESIGNLarge flat diaphragm permits precise valve control.

• REPLACEABLE THERMOSTATIC ELEMENTSField replaceable elements on all standard valves.

• BALANCED PORT DESIGN [TYPES (E)BF, EBS & O] Provides perfect pin and port alignment, and prevents changes in pressure dropacross the valve from influencing valve operation. Provides excellent control onapplications having widely varying operating conditions.

• PIN CARRIER DESIGN (CONVENTIONAL VALVES)Provides precise pin and port alignment, and better seating.

• ACCESSIBLE INTERNAL PARTSDurable, leakproof body joint construction allows the valve to be disassembled,and the internal parts cleaned and inspected.

• MATERIALS OF CONSTRUCTIONPin and port materials offer maximum protection against corrosion and erosion.

• SILVER SOLDERED CONNECTIONSFor leakproof, high strength connection-to-body joints.

• ADJUSTABLE SUPERHEAT DESIGNAll standard valves are externally adjustable except the Type Nl, which isinternally adjustable through its outlet connection.

BULLETIN 10-9 /

THE REFRIGERATION SYSTEM

To understand the function of the thermostatic expansionvalve, a short discussion of the refrigeration system is nec-essary. The refrigeration system can be defined as a closedsystem in which the process of absorbing and rejecting heatis performed by flowing a refrigerant in a vapor compressioncycle. In its simplest form, the refrigeration system consistsof five components: the compressor, condenser, evaporator,expansion device, and interconnecting piping.

The heart of the system is the compressor since it causes therefrigerant flow. Its function is simply to receive low pres-sure (and temperature) refrigerant vapor from the evapora-tor and compress it into high pressure (and temperature)refrigerant vapor. The high pressure vapor is then con-verted to a liquid phase in the condenser. The condenserperforms this function by removing heat from the vapor andrejecting the heat to the air, or to water in the case of awater cooled condenser. The liquid, which remains at a highpressure, passes through the expansion device and becomesa low pressure two phase (liquid and vapor) mixture. Thisrefrigerant mixture returns to its vapor phase in the evapo-rator by absorbing heat from the medium being cooled.

The selection of the expansion device is of particular impor-tance to the operation of the refrigeration system because itregulates refrigerant flow into the evaporator. An expansiondevice which is misapplied or incorrectly sized will ordinar-ily result in operational difficulties and poor system perfor-mance. For example, an undersized expansion device willprevent sufficient refrigerant from flowing into the evapora-tor causing a reduction in the design cooling capability ofthe system. An oversized expansion device may allow toomuch refrigerant into the evaporator causing liquid refrig-erant to flow back to the compressor. The latter condition isreferred to as floodback. Both conditions will invariablyresult in compressor damage if not quickly remedied.Therefore, the expansion device requires attention to itsselection and application.

TYPES OF EXPANSION DEVICES

Expansion devices can be divided into four general categories:the fixed area restrictor, the automatic (constant pressure)expansion valve, the thermostatic expansion valve, and the elec-tric expansion valve. The fixed area restrictor expansion deviceis simply a precisely formed restriction through which liquidrefrigerant flows. Two common examples of this type of deviceare the capillary tube, or cap tube, and the short tube restrictor,or plug orifice. These devices are typically used on certain smallair conditioning and refrigeration systems where operating con-ditions permit moderately constant evaporator loading and con-stant condenser pressures. The drawback associated with thesedevices is their limited ability to efficiently regulate refrigerantflow in response to changes in system operating conditions,since they are sized based on one set of conditions.

Like the fixed area restrictor, the automatic expansionvalve (AEV) is best suited for applications having moder-ately constant evaporator loading. The AEV regulatesrefrigerant flow by simply maintaining a constant evapora-tor or valve outlet pressure. As the heat load on the evapo-rator rises, the AEV decreases refrigerant flow to maintainevaporator pressure at the valve's setting. Conversely, theAEV increases refrigerant flow when the evaporator heatload decreases to maintain evaporator pressure at thevalve's setting. As a result, the AEV starves the evaporatorat high load conditions, and overfeeds it at low load condi-tions.

The thermostatic expansion valve provides an excellentsolution to regulating refrigerant flow into a direct expan-sion type evaporator. The TEV regulates refrigerant flowby maintaining a nearly constant superheat at the evapo-rator outlet. As superheat at the evaporator outlet risesdue to increased heat load on the evaporator, the TEVincreases refrigerant flow until superheat returns to thevalve's setting. Conversely, the TEV will decrease refriger-ant flow when superheat lowers as a result of a decreasedheat load on the evaporator. The effect of this type of reg-ulation is it allows the evaporator to remain as nearly fullyactive as possible under all load conditions. The concept ofsuperheat, and the proper method of measuring it is fur-ther explained on Page 14, TEV Operation andPerformance.

The thermostatic expansion valve provides an additionalbenefit when charging the system with refrigerant. When aTEV is used, the system refrigerant charge is usually not ascritical as with the other expansion devices. The properoperation of a fixed restriction and, to a lesser extent, anautomatic expansion valve depends on having an exactamount of refrigerant in the system.

The electric expansion valve (EEV) provides a means bywhich applications can be designed with sophisticated sys-tem control functions. This type of valve is controlled by anelectronic circuit which is often designed to allow the valveto control some aspect of system operation in addition tosuperheat at the outlet of the evaporator. For example,evaporator discharge air temperature or water tempera-ture from a chiller could be monitored by the EEV's con-troller. See Bulletin 100-9 for details on electric valves forrefrigerant control or contact Sporlan Valve Company foradditional information.

HOW THE THERMOSTATIC EXPANSION VALVE WORKS

Basic Operation

In order to understand the principles of thermostatic expansionvalve operation, a review of its major components is necessary.A sensing bulb is connected to the TEV by a length of cap-

The thermostatic expansion valve (TEV) controls the flow ofliquid refrigerant entering the direct expansion (DX) evapora-tor by maintaining a constant superheat of the refrigerantvapor at the outlet of the evaporator. Superheat is the differ-ence between the refrigerant vapor temperature and itssaturation temperature. To measure the superheat the TEVcontrols, the difference between the actual temperature at thesensing bulb and the saturation temperature corresponding

to the suction pressure at the sensing bulb location is deter-mined. By controlling superheat, the TEV keeps nearly theentire evaporator surface active while not permitting liquidrefrigerant to return to the compressor. The ability of the TEVto match refrigerant flow to the rate at which refrigerant canbe vaporized in the evaporator makes the TEV the idealexpansion device for most air conditioning and refrigerationapplications.

SPORLAN THERMOSTATIC EXPANSION VALVES

illary tubing which transmits bulb pressure to the top of thevalve's diaphragm. The sensing bulb, capillary tubing, anddiaphragm assembly is referred to as the thermostaticelement. The thermostatic element on all standard SporlanTEVs is replaceable.

The diaphragm is the actuating member of the valve. Itsmotion is transmitted to the pin and pin carrier assemblyby means of one or two pushrods, allowing the pin to movein and out of the valve port. The superheat spring islocated under the pin carrier, and a spring guide sets it inplace. On externally adjustable valves, an external valveadjustment permits the spring pressure to be altered.

There are three fundamental pressures acting on the valve'sdiaphragm which affect its operation: sensing bulb pressureP1, equalizer pressure P2, and equivalent spring pressureP3 (see Figure 1). The sensing bulb pressure is a function ofthe temperature of the thermostatic charge, i.e., the sub-stance within the bulb. This pressure acts on the top of thevalve diaphragm causing the valve to move to a more openposition. The equalizer and spring pressures act togetherunderneath the diaphragm causing the valve to move to amore closed position. During normal valve operation, thesensing bulb pressure must equal the equalizer pressureplus the spring pressure, i.e.:

P1 = P2 + P3

Equivalent spring pressure is defined as the spring force dividedby the effective area of the diaphragm. The effective area of thediaphragm is simply the portion of the total diaphragm areawhich is effectively used by the bulb and equalizer pressures toprovide their respective opening and closing forces. Equivalentspring pressure is essentially constant once the valve has beenadjusted to the desired superheat. As a result, the TEV functionsby controlling the difference between bulb and equalizer pres-sures by the amount of the spring pressure.

The function of the sensing bulb is to sense the temperatureof the refrigerant vapor as it leaves the evaporator. Ideally,the bulb temperature will exactly match the refrigerantvapor temperature. As the bulb temperature increases, bulbpressure also increases causing the valve pin to move awayfrom the valve port, allowing more refrigerant to flow intothe evaporator. The valve continues in this opening direc-tion until the equalizer pressure increases sufficiently suchthat the sum of the equalizer and spring pressures balancewith the bulb pressure. Conversely, as the bulb temperaturedecreases, the bulb pressure decreases causing the valve pinto move toward the valve port, allowing less refrigerant toflow into the evaporator. The valve continues to close untilthe equalizer pressure decreases sufficiently such that thesum of the equalizer and spring pressures balance with thebulb pressure.

A change in refrigerant vapor temperature at the outlet ofthe evaporator is caused by one of two events: (1) the springpressure is altered by means of the valve adjustment, and(2) the heat load on the evaporator changes. When springpressure is increased by turning the valve adjustment clock-wise, refrigerant flow into the evaporator is decreased.Vapor temperature at the evaporator outlet increases sincethe point where the refrigerant completely vaporizes movesfurther back within the evaporator, leaving more evaporatorsurface area to heat the refrigerant in its vapor form. Theactual refrigerant vapor and bulb temperature will be con-trolled at the point where bulb pressure balances with thesum of the equalizer and spring pressures. Conversely,decreasing spring pressure by turning the valve adjustmentcounterclockwise increases refrigerant flow into the evapo-rator and decreases refrigerant vapor and bulb tempera-ture. Spring pressure determines the superheat at whichthe valve controls. Increasing spring pressure increasessuperheat, decreasing spring pressure decreases superheat.

An increase in the heat load on the evaporator causesrefrigerant to evaporate at a faster rate. As a result, thepoint of complete vaporization of the refrigerant flow ismoved further back within the evaporator. Refrigerantvapor and bulb temperature increase, causing bulb pressureto rise and the valve to move in the opening direction untilthe three pressures are in balance. Conversely, a reductionin the heat load on the evaporator will cause the vapor andbulb temperature to fall and the valve to move in a closeddirection until the three pressures are in balance. Unlike achange in the spring pressure due to valve adjustment, achange in the heat load on the evaporator does not appre-ciably affect the superheat at which the thermostatic expan-sion valve controls. This is due to the fact that the TEV isdesigned to maintain an essentially constant differencebetween bulb and equalizer pressures, thus controllingsuperheat regardless of the heat load.

Effect of Pressure Drop Across the Valve Port

An additional pressure affecting valve operation, which isnot considered fundamental, arises from the actual pressuredrop across the valve port. This pressure P4 can be relatedto the three fundamental pressures as the product of pres-sure drop across the valve port and the ratio of the port areato the effective area of the diaphragm, i.e.:

P4 = Pressure Drop x (Port Area / Effective Diaphragm Area)

With Sporlan's conventional TEV design, this pressure is anopening influence since refrigerant flow tends to move thevalve in an opening direction. As a result, our original equa-tion is modified as follows:

P1 + P4 = P2 + P3

/ BULLETIN 10-9

SuperheatEvaporator Temperature

Bulb Temperature

Clo

sin

g F

orc

e

2 3

2

C

losin

g Forc

e 2 +

3

Ope

ning

For

ce 1

2

1 BulbPressure

SpringPressure

EvaporatorPressure

Refrig.Curve

1

Figure 1

P4 becomes more significant to TEV operation the greaterthe port area to effective diaphragm area ratio, and thegreater the pressure drop varies across the valve port.

Balanced Port TEVs

Sporlan introduced the concept of the balanced port thermo-static expansion valve in 1946 on large tonnage Types T andW valves. This concept provided the means to either largelyreduce or eliminate the effect of pressure drop across the valveport. This design utilized a double seating piston operated bya single pushrod. The two port construction divided the refrig-erant flow in opposite directions, thereby providing a semi-balanced pressure differential across the piston.

Improved balanced port designs resulted in a fully balancedType O valve, and then the Types (E)BF, SBF, and EBSvalves for smaller capacity applications. For additionalinformation on the types and applications of balanced portTEVs, refer to Page 9, Thermostatic Expansion ValueApplications.

Equalization Method

As previously discussed on Pages 3 and 4, the operation ofthe thermostatic expansion valve is determined by the rela-tionship between three fundamental pressures: bulb pres-sure, equalizer pressure, and equivalent spring pressure.These pressures are illustrated in Figure 1. The equalizerpressure is the evaporator pressure the valve senses. Themeans used to transmit this pressure from the refrigerationsystem to the underside of the valve diaphragm is referredto as the equalization method.

Evaporator pressure is transmitted to the underside of thevalve diaphragm by one of two methods. If the valve isinternally equalized, the evaporator pressure at the valveoutlet is transmitted to the diaphragm via a passagewaywithin the valve body or through a clearance around thepushrods. If the valve is externally equalized, the under-side of the valve diaphragm is isolated from the valve outletpressure by the use of packing material around thepushrods or with pushrods which are closely fitted.Evaporator pressure is transmitted to the diaphragm by atube connecting the suction line near the evaporator outletto an external fitting on the valve. The external fitting isconnected to a passageway which leads to the underside ofthe valve diaphragm. See Figure 2.

Internally equalized TEVs should be limited to single circuitevaporator coils having a pressure drop no greater than theequivalent of a 2°F saturated temperature change. Refer toTable 1 for recommended maximum allowable pressuredrop values for internally equalized valves.

Externally equalized TEVs, however, are not affected by pres-sure drop across the evaporator, including pressure drop fromrefrigerant distributors employed by multi-circuited evaporator

IMPORTANT: The External Equalizer must be used on evaporatorswhich employ a refrigerant distributor.

coils. An externally equalized TEV may be used for allrefrigeration applications. It provides no operational disad-vantages with respect to an internally equalized valve otherthan requiring an external equalizer line be connected.Figures 3, 4, and 5 illustrate the effects of evaporator pres-sure drop on an internally and externally equalized TEV.

When an externally equalized TEV is used, the equalizerconnection on the TEV must be connected to the outlet ofthe evaporator, and not capped!

Figure 3 shows an internally equalized valve feeding a sin-gle circuit evaporator which has no pressure drop. The sys-tem refrigerant is R-22 and, for the purpose of illustration,R-22 is also used as the thermostatic charge. The evapora-tor pressure at the valve outlet and at the sensing bulb loca-tion is 52 psig. The sum of this pressure and the 12 psispring pressure produces a 64 psig pressure in the closingdirection. For the valve to properly operate, a 64 psig open-ing bulb pressure is required to balance pressure. Since thesensing bulb consists of liquid R-22, its pressure-tempera-ture characteristic is identical to the saturation curve ofR-22, and a 37°F bulb temperature is required. The super-heat at which the valve is controlling is calculated by sub-tracting the saturation temperature of the evaporatorpressure at the sensing bulb location by the bulb tempera-ture. In this case, the superheat is 9°F.

Valve with INTERNAL Equalizer

Close Tolerance

FitInternal Equalizer

External Equalizer

Fitting

PushRods

ValveOutlet

Pressure

EvaporatorOutlet

Pressure

PushRods

Valve with EXTERNALEqualizer

BULLETIN 10-9 /

Figure 2

tnaregirfeR

erutarepmeTgnitaropavE F°

04 02 0 – 02 – 04

porDerusserP — isp

431,21 a 00.2 05.1 00.1 57.0 —

22 00.3 00.2 05.1 00.1 57.0

705,205,A404 00.3 05.2 57.1 52.1 00.1

A(717 ainomm ) 00.3 00.2 05.1 00.1 —

TABLE 1

37°5252

52

64

Bulb Pressure64 psig

EvaporatorInlet Pressure

52 psig

Evaporator Outlet Pressure

52 psig

Diaphragm

Spring Pressure12 psi

Closing Pressure............................................................................= 52 + 12 = 64 psig (Evaporator Inlet Pressure Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve..........................................................64 psig

Bulb Pressure Equivalent to 64 psig.....................................................................37°F

Saturated Temperature Equivalent to Evaporator Outlet Pressure.........................28°F

SUPERHEAT......................................................................................................9°F Bulb Temperature Minus Saturated Evaporator Temperature

12

Converted to Temperature = 37°F

Figure 3

Figure 4 shows the same internally equalized valve on a sys-tem having the same evaporator pressure at the sensingbulb location. The evaporator coil, however, now has a pres-sure drop of 6 psi. Since an internally equalized valve sensesevaporator pressure at the valve outlet, the total pressure inthe closing direction becomes 58 psig plus the 12 psi springpressure, or 70 psig. A bulb pressure of 70 psig is nowrequired for proper valve regulation, which translates to a41°F bulb temperature. The superheat becomes 13°F, or 4°Fhigher than the superheat calculated in Figure 3. This risein superheat is due to the pressure drop in the evaporator.Consequently, pressure drop between the valve outlet andthe sensing bulb location causes an internally equalizedTEV to operate at a higher than desired superheat.

/ BULLETIN 10-9

Figure 5 shows the same system as in Figure 4, but with anexternally equalized TEV installed. Since an externallyequalized TEV senses evaporator pressure at the evaporatoroutlet, it is not influenced by pressure drop through theevaporator. As a result, the TEV senses the correct pres-sure, and controls at the desired superheat.

These diagrams can be used to show the influence evaporatorpressure drop has on internally equalized TEVs as evaporat-ing temperatures fall. Table 1 provides general recommenda-tions for maximum pressure drops that can be safelytolerated by internally equalized valves. These recommenda-tions are suitable for most field installed systems. Use exter-nally equalized TEVs when pressure drops exceed valuesshown in Table 1, or when pressure drops cannot be deter-mined. An externally equalized TEV should be usedwhenever a refrigerant distributor is used with theevaporator.

Refer to Bulletin 10-11, TEV Installation, Field Service andAssembly, regarding recommendations for the location ofthe sensing bulb and external equalizer connection to thesuction line.

Thermostatic Charges

As previously mentioned, the TEV's sensing bulb transmitspressure to the top of the diaphragm by a length of capillarytubing. The thermostatic charge is the substance in theTEV's sensing bulb which responds to suction line tempera-ture to create the bulb pressure, and it is designed to allowthe TEV to operate at a satisfactory level of superheat overa specific range of evaporating temperatures. The subject ofthermostatic charges is best approached by describing thecategories into which charges are classified. These cate-gories are the following:

1. Liquid Charge2. Gas Charge3. Liquid-Cross Charge4. Gas-Cross Charge5. Adsorption Charge

The conventional liquid charge consists of the same refriger-ant in the thermostatic element that is used in the refrigera-tion system, while the liquid-cross charge consists of arefrigerant mixture. The term cross charge arises from thefact that the pressure-temperature characteristic of therefrigerant mixture used within the sensing bulb will crossthe saturation curve of the system refrigerant at some point.

Both the liquid and liquid-cross charges possess sufficient liq-uid such that the bulb, capillary tubing, and diaphragm cham-ber will contain some liquid under all temperature conditions.This characteristic prevents charge migration of the ther-mostatic charge away from the sensing bulb if the sensing bulbtemperature becomes warmer than other parts of the thermo-static element. Charge migration will result in loss of valvecontrol. An additional characteristic of these charges is theirlack of a maximum operating pressure (MOP) feature. Athermostatic charge with an MOP feature causes the TEV toclose above a predetermined evaporator pressure, therebyrestricting flow to the evaporator and limiting the maximumevaporator pressure at which the system can operate.

Similarly, the gas charge consists of the same refrigerant inthe thermostatic element that is used in the refrigeration sys-tem, while the gas-cross charge consists of a refrigerant mix-ture. Unlike the liquid type charges, both gas charges aredistinguished by having a vapor charge in the thermostaticelement which condenses to a minute quantity of liquid whenthe TEV is in its normal operating range. This characteristic

41°52

58

58



58 psig

EvaporatorOutlet Pressure

52 psig

Diaphragm


Closing Pressure............................................................................= 58 + 12 = 70 psig (Evaporator Inlet Pressure Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve.........................................................70 psig

Bulb Temperature Equivalent to 70 psig................................................................41°F

Saturated Temperature Equivalent to Evaporator Outlet Pressure..........................28°F

SUPERHEAT....................................................................................................13°F Bulb Temperature Minus Saturated Evaporator Temperature

12

70


37°5258



58 psig

EvaporatorOutlet Pressure

52 psig

Diaphragm


Closing Pressure.............................................................................= 52 + 12 = 64 psig (Suction Pressure at Bulb Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve..........................................................64 psig

Bulb Temperature Equivalent to 64 psig.................................................................37°F

Saturated Temperature Equivalent to Evaporator Outlet Pressure...........................28°F SUPERHEAT............. ......................................................................................... 9°F Bulb Temperature Minus Saturated Evaporator Temperature

52

Suction Pressureat Bulb 52 psig

12

64


Figure 5

Figure 4

�KLEA is a trade name of ICI FLUOROCHEMICALS.

Sporlan Selective Charges

Sporlan introduced Selective Charges for TEVs over 50years ago, recognizing that a single thermostatic chargecannot work effectively over the useful range of evaporatingtemperatures of many standard refrigerants. The presentuniversal acceptance of Selective Charges is evidence oftheir many operational advantages. An explanation of theirapplications, design features, and advantages of eachSelective Charge follows. Recommended Sporlan thermo-static charges for various applications are listed on Page 18.

The thermostatic expansion valve's static superheat ver-sus evaporator temperature is referred to as the superheatcharacteristic curve. This curve is helpful in under-standing TEV operation since its shape describes thevalve's operation at a given setting over a range of evapo-rating temperatures. Figure 6 illustrates the superheatcharacteristic curves of standard Sporlan thermostaticcharges. The concept of static superheat is described onPage 14, Factors Affecting TEV Operation and Performance.

Air Conditioning and Heat Pump Applications

These applications usually require a pressure limiting(MOP type) thermostatic charge to limit compressor loadingduring system pulldown. The pressure limiting chargecauses the TEV to remain closed until the system evapora-tor pressure is reduced below the MOP of the charge, per-mitting rapid pulldown.

The Sporlan thermostatic charges listed on Page 18 underthe air conditioning and heat pump section are gas-crosscharges.

Figure 6 illustrates the superheat characteristic curves ofthe Sporlan VCP100 and VG charges, a gas-cross charge

BULLETIN 10-9 /

provides an MOP for the valve at the bulb temperature ofwhich the liquid component of the charge becomes vapor.Above this bulb temperature, a temperature increase doesnot significantly increase thermostatic charge pressure, lim-iting the maximum evaporator pressure at which the sys-tem can operate. A disadvantage of this type of thermostaticcharge is the possibility of charge migration.

The adsorption charge consists of a noncondensable gas andan adsorbent material located in the sensing bulb. As thetemperature of the bulb increases, gas is expelled (desorbed)from the adsorbent material increasing bulb pressure.Conversely, as the temperature of the bulb decreases, gas isadsorbed thus decreasing bulb pressure. Like the liquid andliquid-cross charges, the adsorption charge does not providean MOP, and it will not migrate.

SPORLAN THERMOSTATIC EXPANSIONVALVES

Sporlan manufactures thermostatic expansion valves for allair conditioning and refrigeration applications. For applica-tions using refrigerants R-12, R-22, R-134a, R-404A, R-502,and R-507, Sporlan's standard line of TEVs are available withSAE flare, ODF solder, ODF solder flange, and FPT flangeconnections. For refrigerant R-717 (ammonia) applications,Sporlan TEVs are available with FPT flange connections.Socket weld flanges can also be obtained for selected valvetypes. Specifications for the standard line of Sporlan TEVs areprovided on Pages 12 to 35, Bulletin 10-10. Materials anddetails of construction are provided on Page 36, Bulletin 10-10.

Valve capacity ratings for refrigerants R-12, R-22, R-134a,R-401A, R-402A, R-404A, R-407A, R-407C, R-408A, R-409A,R-502, R-507, and R-717 are provided on Pages 4 to 9, Bulletin10-10. The capacity tables on these pages specify valve ratingsat selected evaporator temperatures. Contact Sporlan ValveCompany for applications not specifically listed in Bulletin10-10.

In addition to the standard line of TEVs listed in this bulletin,Sporlan also manufactures special valve types to fill specificrequirements for OEM customers. These OEM valve typesinclude the Type BI, I, FB, and X TEVs. Special features suchas bleed ports, nonadjustable construction, and extra lengthcapillary tubing are available for many standard and OEMvalves. Automatic expansion valves are also available on spe-cial order. If you have a special refrigerant flow control appli-cation, contact Sporlan Valve Company for assistance.

Alternative Refrigerants

Current efforts by refrigerant manufacturers to develop alterna-tives to chlorofluorocarbons (CFCs) are being closely followed bySporlan Valve Company. At the time this bulletin is being pub-lished, hydrofluorocarbon (HFC) alternatives are available toreplace R-12 and R-502. In addition, a number of hydrochlorofluo-rocarbons (HCFCs) have been developed as intermediate or servicereplacements for R-11, R-12, R-114, and R-502.

Several HFC alternative refrigerants are also being evaluated bymanufacturers of air conditioning equipment to replace R-22, anHCFC refrigerant. These alternatives include R-407C and R-410A.

Sporlan has an ongoing program to evaluate alternative refriger-ants and, when applicable, their associated refrigerant lubricantsto assess compatibility with our materials of construction. For addi-tional information on this subject, contact Sporlan Valve Company.The table below lists some of the major HFC and HCFCreplacement refrigerants for R-11, R-12, R-114, and R-502.

CFC )CFCH(sevitanretlAetaidemretnI mreTgnoLsevitanretlA ( )CFH

11-R 321-R –

21-R)93PM(A104-R)66PM(B104-R)65-XF(A904-R

a431-R

411-R 421-R –

205-R )08PH(A204-R)01-XF(A804-R

)26PH(A404-R)06*AELK(A704-R

)05-ZA(705-R

(*VGA)

Evaporator Temperature °F

No

rmal

Su

perh

eat Ran

ge

* Ballasted

-20 -40 0 20 40 60

Su

per

hea

t °F

0

5

10

15

20 * Gas-CrossCharge (ZP)

Sporlan SelectiveThermostatic Charges

LiquidCross Charge (Z)

* GasCharge (VG)

LiquidCharge (L)

* Gas-CrossCharge (VCP100)

Liquid

Cross Charge (C)

Figure 6

and a gas charge respectively for R-22 applications. TheVCP100 charge has a flatter operating range which allowsthe TEV to maintain a more constant superheat withchanges in evaporating temperature. This characteristic isgenerally desired since many air conditioning and heatpump systems operate over a significant range of evaporat-ing temperatures. The VG charge has limited applicationexcept for our WVE-180 valve. The vertical portion of thecurves is the MOP region of both charges.

Sporlan pressure limiting charges also help reduce the prob-lem of the TEV alternately overfeeding and underfeedingthe evaporator, which is usually termed hunting orcycling. The amount of hunting in a system is influencedby the design of the evaporator coil, suction line piping atthe valve's sensing bulb location, and the variability of theheat load on the evaporator. Hunting may cause a reductionin total system capacity, and a noticeable variation of evap-orator pressure on systems having one evaporator. If hunt-ing is severe, occasional floodback may result.

To help reduce or eliminate valve hunt, many Sporlan pres-sure limiting thermostatic charges feature the FLOWMAS-TER design introduced by Sporlan in 1948. This designincorporates a thermal ballast with the charge to help sta-bilize valve control.

Originally, it was felt that a highly temperature sensitiveTEV would best be able to reduce hunting. This concept hasproved to be incorrect for the majority of air conditioningand heat pump applications and, in fact, it was found tooften aggravate hunting problems. A less temperature sen-sitive TEV using specifically designed pressure limitingthermostatic charges has been proven to be the best solu-tion for these applications.

Type VGA Thermostatic Charge � The VGA charge is aspecially designed pressure limiting charge for R-22 air con-ditioning and heat pump applications. The constituents andthermal ballast used with this thermostatic charge provideexceptional anti-hunt characteristics, which makes it therecommended charge for the majority of these applications.Due to its design, the MOP of the VGA charge is not asdefined as the VCP100 charge, our alternate standard ther-mostatic charge for R-22 air conditioning and heat pumpapplications. Therefore, if a defined MOP is notrequired, the VGA charge may be used in place of theVCP100 charge.

Maximum operating pressures for standard Sporlan pres-sure limiting charges are listed in Table 2. The factory airtest pressure represents the valve MOP determined by aSporlan air test fixture. The nominal system pressure is theactual system MOP. If an application requires a pressurelimiting charge with an MOP not shown, contact SporlanValve Company for assistance.

Due to the design of pressure limiting charges, the valvediaphragm and capillary tubing must be kept at a tempera-ture warmer than the bulb during system operation.Otherwise, migration of the charge away from the bulb willoccur, and cause loss of valve control.

A properly selected and applied pressure drop type distrib-utor is effective in preventing charge migration. Figure 7illustrates how the pressure drop across this type of distrib-utor keeps the TEV outlet pressure and temperature higherthan the suction gas temperature.

Pressure drop at the refrigerant distributor does not affectsystem capacity. The refrigerant distributor simply lowersthe pressure drop across the TEV by a small amount. If theTEV is properly sized, it will maintain desired superheat(and system capacity) with the remaining pressure dropavailable to the valve.

When applying a TEV and distributor, the two componentsperform together to provide stable system operation.Application of these components is much more critical onsystems that operate at part-load conditions much of theiroperating time, e.g., variable air volume (VAV) systems andrefrigeration systems with compressor unloading. SeeBulletin 20-10 for complete information on refrigerant dis-tributors.

Refrigeration Applications

Ordinary refrigeration applications may be divided into thefollowing three categories: commercial refrigeration, lowtemperature refrigeration, and extremely low temperaturerefrigeration. For each of these categories, Sporlan hasdeveloped a Selective Charge to provide optimum valve per-formance. These charges are described below.

Type C Charges � The charges listed under the commer-cial refrigeration section in the Recommended ThermostaticCharges table on Page 18 are collectively known as CCharges. These charges are liquid-cross charges and havean operating range from an evaporating temperature of50°F to �10°F. Figure 6 illustrates a typical superheat char-acteristic curve of the C Charge. For comparison purposes,the superheat characteristic curve of a straight liquidcharge is also shown. The flatter curve of the C Chargeallows the valve to respond in a more stable manner tochanges in evaporator pressure.

/ BULLETIN 10-9

R-22

196 psig(100°F)

P1 = 94 psig (56°F)

P2 = 69 psig (40°F) 66 psig (Superheat to 50°F)

66 psig(38°F)

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TABLE 2

Figure 7

BULLETIN 10-9 /

Types Z and ZP Charges � The charges listed under thelow temperature refrigeration section are the Types Z andZP Charges. The Z Charges (FZ, VZ, SZ, RZ, and PZ) are liq-uid-cross charges having an operating range from an evap-orating temperature of 0°F to �40°F. A typical superheatcharacteristic curve of the Z Charge is illustrated in Figure6. Since the curve slopes upward to the right, the valve willcontrol at lower superheat values as evaporator tempera-ture decreases, providing operational advantages for lowtemperature refrigeration. This characteristic preventsfloodback during compressor startup, reduces the load onthe compressor after startup, and permits rapid pulldown.Since the majority of low temperature systems operate at ornear a specific evaporating temperature, the TEV can be setfor optimum superheat at the design temperature permit-ting the system to operate as efficiently as possible.

The Types ZP Charges (FZP, VZP, SZP, RZP, and PZP) aregas-cross charges having the same operating range as theType Z Charges. A typical superheat characteristic curve ofthe ZP Charge is illustrated in Figure 6. The Z and ZPCharges are essentially the same with the exception of theZP Charge providing an MOP. Type ZP Charges are notintended as replacements for Z Charges. Each shouldbe selected for its unique purpose. A ZP Chargeshould only be used for low temperature refrigera-tion systems where it is necessary to limit evaporatorpressure during pulldown.

During and after a hot gas defrost cycle or after a shutdownperiod, evaporator pressure may rise to a level the compres-sor motor cannot handle. In such cases, a pressure limitingcharge is often effective in limiting suction pressure at thecompressor. For systems employing long suction lines, acrankcase pressure regulating (Sporlan CRO type) valvemay be required to limit suction pressure at the compressorquickly. While a pressure limiting charge can be used witha CRO valve, pulldown time may be adversely affected if thecharge MOP and the CRO valve setting are close to oneanother. Therefore, Sporlan does not recommend a CROvalve and a pressure limiting TEV be used on the same sys-tem.

Type X Charge � The charges listed under the extremelylow temperature refrigeration are known as the X Charges.The X Charges are liquid-cross charges having an operatingrange from an evaporating temperature of �40°F to �100°F.This curve is similar to the Z Charge curve since the perfor-mance characteristics of the Z Charges previously discussedapply very well to extremely low temperature refrigeration.Contact Sporlan Valve Company for assistance in selectingTEVs for applications requiring the X Charge.

Special Selective Thermostatic Charges andElements

Sporlan Valve Company manufactures a number of specialthermostatic charges and elements designed for specificapplications. A few of these are described below:

Type N Charge � This charge is an adsorption type chargewhich has a superheat characteristic curve similar to the CCharge but tends to be less responsive. The N Charge is anoncondensable charge, and it has no MOP feature. The NCharge is used on special medium and high temperatureapplications such as chillers which are located outdoors andmust operate while exposed to cold temperatures.

Hydraulic Elements � These thermostatic elements arespecially designed double diaphragm elements which pro-vide a pressure limiting feature without the problems asso-

ciated with charge migration from the bulb when the ele-ment becomes cooler than the bulb. The hydraulic elementis often used on chillers which require a TEV with an MOPtype charge, but experience problems with charge migra-tion caused by cold ambient temperatures. For additionalinformation on the hydraulic element, contact SporlanValve Company.

Mechanical Pressure Limit Elements � These thermo-static elements may use either liquid or liquid-cross charges,and they employ a mechanical means to limit suction pres-sure (PL-type). A collapsible member is used to limit evapo-rator pressure when it exceeds a specified value. Thismethod of limiting evaporator pressure is currently consid-ered obsolete, and replacement valves and thermostatic ele-ments are no longer available. A cross reference is availablefrom the obsolete PL element to the thermostatic elementwith the MOP charge, please refer to Bulletin 210-10-17.

Special Refrigerants � Thermostatic charges for usewith special refrigerants are available. These refrigerantsinclude: R-13, R-23, R-13B1, R-124, and R-503. ContactSporlan Valve for assistance in valve selection for specialrefrigerant applications.

Desuperheating Charges � Special thermostaticcharges have been developed for applications requiring suc-tion gas desuperheating. The subject of hot gas bypass anddesuperheating TEVs is discussed on Page 12.

THERMOSTATIC EXPANSION VALVE APPLICATIONS

Due to its superior operating characteristics, the TEV iscurrently used on a wide variety of applications. Theseapplications include both large and small capacity air con-ditioning and heat pump systems; commercial refrigerationsystems including refrigerated display cases, ice cubers,and soft drink dispensers; and low temperature refrigera-tion systems.

Most air conditioning and refrigeration systems use somemethod of capacity reduction to match the capacity of thesystem to a reduced heat load condition, commonly referredto as partload operation. The simplest method of capacityreduction is cycling the compressor, usually in response toa thermostat. Other methods of capacity reduction includeusing compressors equipped with cylinder unloaders,bypassing hot gas, or some combination of the above. A dis-cussion on these capacity reduction methods and theireffect on TEV operation is presented later in this section.

The thermostatic expansion valve is a modulating type flowcontrol device with the capability to adjust to low load con-ditions and maintain reasonable refrigerant flow control.The range of effective TEV control, however, has limits andmay not be capable of operating properly on a systemrequiring a high degree of capacity reduction. As a result,systems using capacity reduction methods require the useof proper design and installation practices.

System Design Factors

Predicting TEV performance at reduced system capacitiesis difficult due to the many influencing design factors pre-sent in any system. These factors include: TEV sizing,refrigerant distribution, TEV setting, evaporator coildesign, suction line piping, and bulb location. General rec-ommendations which address these factors are providedbelow. By observing these recommendations, a conventional

/ BULLETIN 10-9

TEV can be expected to operate satisfactorily down toapproximately 35 percent of its rated capacity. The Types(E)BF, SBF, EBS, and O valves, featuring the balanced portdesign, can be expected to operate satisfactorily down toapproximately 25 percent of its rated capacity.

Valve Size � The TEV should be sized as close as possible tothe system's maximum designed heat load condition. A valvewith a capacity rating up to 10 percent below the full load con-ditions may be selected if the system is to operate at reducedloads for long periods of time, and if slightly higher than nor-mal superheats can be tolerated at full load conditions.

Distributor Sizing � The proper sizing of the distributor isextremely important for systems using methods of capacityreduction. The function of the refrigerant distributor is toevenly distribute refrigerant to a multi-circuited evaporator. Ifthe distributor cannot perform its function at all load condi-tions erratic TEV operation can be expected. For the pressuredrop type distributor, the distributor nozzle and tubes must bechecked for proper sizing at both minimum and maximum loadconditions. See Bulletin 20-10 for further information.

Superheat Adjustment � The superheat setting of the TEVshould be set at the highest possible superheat that can be tol-erated at full load conditions. A high superheat setting willreduce problems associated with mild TEV hunting at low loadconditions. High superheats are more acceptable on air condi-tioning systems where the wide temperature differencebetween the refrigerant and the air allows the TEV to operateat higher superheats without a significant loss in coil capacity.

Evaporator Coil Design � When the evaporator is cir-cuited to provide counterflow of the refrigerant relative to thedirection of the air flow, superheat will normally have theleast effect on evaporator capacity and suction pressure fluc-tuations will be minimized.

Refrigerant velocity inside the evaporator should be highenough to prevent excessive trapping of liquid refrigerant andoil, which may cause TEV hunting. Multi-circuited coilsshould be designed in such a manner that each circuit isexposed to the same heat load. Air flow across the coil must beevenly distributed.

Large capacity air conditioning evaporator coils are often splitinto multiple sections so that one or more of these sections canbe shut off for capacity control during part-load operation.Therefore, a TEV is required to feed each of these sections.The methods used to split these coils are referred to as: rowsplit, face split, and interlaced. Generally, TEVs will oper-ate best on interlaced coils.

Suction Line Piping � Approved methods of suction linepiping including recommended bulb locations and use of trapsare covered in Bulletin 10-11. Where system designers andmanufacturers have tested and approved other methods ofpiping, these methods should be used when installing or ser-vicing their systems.

Sensing Bulb Location � The TEV's sensing bulb shouldbe located on a horizontal section of suction line near the evap-orator outlet and, in the case of an externally equalized valve,upstream of the equalizer connection on the suction line. Referto Bulletin 10-11 for additional information on bulb locationand installation.

Vapor Free Liquid Refrigerant � Another importantaspect in assuring proper TEV operation is providing vaporfree liquid refrigerant to the inlet of the TEV. Vapor in the liq-uid line may severely reduce the capacity of the TEV hinder-ing proper refrigerant flow to the evaporator. An adequately

sized liquid-to-suction heat exchanger will help assure vaporfree liquid by providing some amount of subcooling to the liq-uid. In addition, the heat exchanger provides an added advan-tage to the system by vaporizing small quantities of liquidrefrigerant in the suction line before the liquid reaches thecompressor. A Sporlan See•All Moisture-Liquid Indicatorinstalled near the TEV inlet offers a visual check for vaporfree refrigerant.

Balanced Port TEVs

One of the factors limiting a TEV's ability to operate at part-load conditions is a variation in pressure drop across theTEV during normal system operation due to changes in headpressure. As previously discussed on Page 3, How TheThermostatic Expansion Valve Works, pressure drop acrossthe TEV influences valve operation, particularly with thelarger capacity valves which possess larger port areas. Tocounteract the effects of this force Sporlan has incorporatedbalanced port design features into selected valve types.

Sporlan introduced this feature in 1946 using a double portconstruction on two large capacity valves: the Types T andW. The Type T valve later became our Type V valve whenthe valve design was modified. This double port constructionfeatures a piston which seats against two ports, and signifi-cantly reduces the effects of pressure drop across the valve.

The refrigerant flow entering these valve types is dividedbetween the two ports, the force of the refrigerant flow beingtransmitted to the midsection of the piston. The force of theflow heading to the lower port is largely canceled out by theforce of the flow heading to the upper port due to the designof the piston. A semi-balanced valve is achieved, allowingthe valve to operate at a lower percentage of its rated capac-ity than a conventionally designed valve.

Sporlan introduced a patented discharge bypass valve witha fully balanced design in 1965, the Type ADRHE-6. Thisdesign was later used with the Type O TEV, which wasintroduced in 1971.

The Type O valve is designed to eliminate the effects of pres-sure drop across the valve. The Type O valve features a pis-ton which seats against the valve's single port. See Figure 8.A passageway drilled through the piston allows liquid linepressure to be transmitted to the bottom side of the piston.A synthetic cup seal encircling the piston traps this pressureunderneath the piston, which causes the force due to the liq-uid line pressure on top of the piston to be canceled.Satisfactory operation down to 25% or lower of rated capac-ity can be expected with the Type O valve provided that theaforementioned design recommendations are followed.

Recent efforts by system manufacturers to reduce operatingcosts of refrigeration systems by allowing condenser pres-sures to fall or float with lower ambient temperatures hascreated a need for a small capacity TEV with a balanced portdesign and superior modulating characteristics. This effortis particularly apparent with supermarket applications.Sporlan introduced the Types (E)BF and EBS valves in 1984to meet this need.

The Types (E)BF and EBS valves feature a single pushrodwhich extends through the port of the valve. See Figure 8.The port and pushrod cross sectional areas are identical sothat the opening force created by pressure drop across theport is canceled by the pressure drop across the pushrod.Furthermore, excellent pin and port alignment is providedby this design. Refer to the section, Effect of Pressure DropAcross the Valve Port, on Page 4 for additional information.

rator shares half of the total common load. The liquid linesolenoid valve ahead of each TEV is electrically connected tothe compressor capacity modulating system. When the com-pressor capacity is reduced to 50%, one of the two solenoidvalves closes stopping refrigerant flow to one TEV. The TEVremaining in operation will then have a rated capacityapproximately equal to the compressor capacity operating50% unloaded.

This technique may be carried further by using additionalevaporator sections, each controlled by a separate TEV andrefrigerant distributor. Using multiple evaporator sectionswill let highly reduced loads to be properly controlled.

Single Evaporator Controlled by Two TEVs

For evaporator coils which are not split by design, i.e., rowsplit, face split, or interlaced, the following techniques maybe employed to improve part-load operation.

Figure 10 illustrates the use of two TEVs and two distribu-tors feeding a single evaporator. Each evaporator circuit isfed by two distributor circuits, one from each distributor.The solenoid valves are connected to the compressor capac-ity modulating system as mentioned before. Using this con-figuration, TEV and distributor capacities can be reduced inthree stages. As an example, assume that TEV and distrib-utor combination A are sized to handle 67% of the load andcombination B 33% of the load. The three stages of valveand distributor capacity reduction result from opening orclosing the solenoid valves according to the following table:

Another variation of this technique is to have each evapora-tor circuit fed by a single distributor circuit and size theTEVs and distributors on the expected load of the totalnumber of circuits fed by each TEV. Reducing evaporator

The Type (E)BF valve with the 'AA' port was developed bySporlan in 1988. Its original design used a patented twopushrod construction (U.S. patent 4,750,334) similar to theconventional Type F valve, and the balanced design wasachieved by the use of a third floating rod located above thevalve port. As with the single rod balanced port construc-tion, the floating rod causes the pressure drop across it tooffset the opening force created by the pressure drop acrossthe port.

The 'AA' port Type (E)BF valve was later redesigned in1993 to a single pushrod construction like the other Type(E)BF valve sizes. All 'AA' port valves carrying a '3393' datecode or later will have the single pushrod construction.

System Design For Part-Load Conditions

On systems where the compressor can unload to 50 percentof its rated capacity, care must be exercised when selectingexpansion valves and refrigerant distributors. If the com-pressor can unload below 33 percent of its rated capacity,special design considerations may be necessary to assureproper TEV operation. Figures 9, 10, and 11 are pipingschematics illustrating three possible methods of balancingthe capacity of the TEV and distributor with the compres-sor during low load operation. Recognized piping referencessuch as the equipment manufacturer's literature and theASHRAE Handbooks should be consulted for further infor-mation on this subject. Sporlan cannot be responsiblefor damages arising from improper piping practicesor the improper use of its products.

Two or More Evaporator Sections Handling theSame Load

Figure 9 illustrates two parallel evaporators each controlledby a separate TEV and refrigerant distributor. Each evapo-

BULLETIN 10-9 /

Pin Guide

Seal Cartridge

Pushrod

Pushrod Seal

Piston Assembly

Types (E)BF, SBF, and EBFType O

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TEV and Distributor

SolenoidValve

Figure 9

Solenoid Valve"A" TEV and Distributor

"A"

TEV and Distributor"B"

SolenoidValve"B"

Capacity Reduction – Single evaporator controlled with 2 TEVs and 2 Solenoid Valves.

capacity is accomplished by closing a solenoid valve whichdeactivates the circuits being fed by the TEV and distribu-tor downstream of the solenoid valve. This method of capac-ity control, however, requires a degree of care since the heatload on the evaporator circuits will be affected in the man-ner in which circuits are deactivated.

Hot Gas Bypass and Desuperheating TEVs

Systems which are required to operate at load conditionsbelow the unloading capabilities of their compressors pre-sent an additional design problem. To balance the systemunder these conditions, bypassing a controlled amount ofhot gas to the suction side of the system provides a practicalsolution. Bypassing hot gas is accomplished with a modu-lating control valve known as a discharge bypass valve.Sporlan manufactures a complete line of these valves. Fordetails, refer to Bulletin 90-40.

For close coupled systems, the preferred method of hot gasbypass is bypassing to the inlet of the evaporator. Thismethod has three advantages: (1) the TEV will respond tothe increased superheat of the vapor leaving the evaporatorand will provide the liquid required for desuperheating; (2)the evaporator serves as an excellent mixing chamber forthe bypassed hot gas and the liquid vapor mixture from theTEV; and (3) oil return from the evaporator is improvedsince the refrigerant velocity in the evaporator is kept highby the hot gas.

For multi-evaporator or remote systems, bypassing hot gasdirectly into the suction line in the manner illustrated inFigure 11 may be necessary. In addition to the dischargebypass valve, an auxiliary TEV known as a desuperheatingTEV is required to supply the necessary liquid refrigerant tocool the discharge gas entering the suction line. Compressormanufacturers generally rate their air conditioning compres-sors for a 65°F return gas temperature, and this temperatureis usually appropriate for selecting desuperheating TEVs.Many refrigeration and low temperature compressors, how-ever, require lower suction gas temperatures to prevent dis-charge gas temperatures from rising too high and damagingcompressor parts and carbonizing oil. Consult the compressormanufacturer if the maximum permissible suction gas tem-perature for a compressor is not known.

Sporlan has developed special desuperheating thermostaticcharges. See table below. Each charge will allow the desu-perheating TEV to control the listed suction gas superheat.For suction gas temperatures that require superheats otherthan those listed, contact Sporlan Valve or the compressormanufacturer for assistance.

Sizing a desuperheating valve involves determining theamount of refrigerant liquid necessary to reduce the suctiongas temperature to the proper level. For hot gas bypassapplications, a desuperheating valve can be properly sizedfrom the selection procedure provided in Bulletin 90-40.

An externally equalized TEV is recommended for mostdesuperheating applications. If the piping of the desuper-heating TEV is close coupled, an internally equalized valvemay be used. Figure 11 illustrates the use of an externallyequalized desuperheating TEV. Refer to the section,Equalization Method on Page 5 for further information onthis subject.

When piping the discharge bypass valve and the desuper-heating TEV, remember that good mixing of the dischargegas and liquid must be obtained before the mixture reachesthe sensing bulb of the desuperheating TEV. Improper mix-ing may produce unstable system operation causing thedesuperheating TEV to hunt. Proper mixing can be accom-plished in two ways: (1) install a suction line accumulatordownstream of both valve outlet connections with the desu-perheating TEV bulb downstream of the accumulator; or (2)tee the liquid vapor mixture from the desuperheating TEVand the hot gas from the bypass valve together before con-necting a common line to the suction line. The latter methodis illustrated in Figure 11.

Off-Cycle Pressure Equalization

Certain applications utilizing low starting torque singlephase compressor motors (e.g., a permanent split capacitormotor) require some means of pressure equalization duringsystem offcycle. Pressure equalization is necessary sincelow starting torque compressors are not capable of restart-ing against a large pressure differential. Typical applica-tions requiring pressure equalization are small airconditioning and heat pump systems which frequently cycleon and off in response to a thermostat.

Permanent Bleed Port � Any Sporlan thermostaticexpansion valve may be ordered with a bleed port.Standard bleed port sizes are: 5%, 10%, 15%, 20%, 30%, and40%. Bleed ports are designated by the percentage theyincrease nominal valve capacity at 40°F evaporator temper-ature. For example, a 2 ton TEV with a 30% bleed will havethe capacity of: 2 x 1.3 = 2.6 tons. Refer to Page 17 forOrdering instructions. Please contact Sporlan for assistancein selecting appropriate bleed port sizes.

The subject of pressure equalization during system off-cycleshould not be confused with the external equalizer of theTEV. System pressure equalization is accomplished by

/ BULLETIN 10-9

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Hot GasSolenoid Valve

DischargeBypassValve

Figure 11

BULLETIN 10-9 /

allowing a certain amount of refrigerant to leak through amachined notch or hole in the valve seat during system off-cycle. The external equalizer of the TEV, however, simplyallows the valve to sense evaporator pressure. The externalequalizer does not provide pressure equalization during sys-tem off-cycle.

The Rapid Pressure Balancer (RPB) Feature � Thethermostatic expansion valve with the Rapid PressureBalancer (RPB) feature was developed by Sporlan inresponse to an industry demand for a TEV which wouldequalize system pressures during off-cycle more rapidlythan a TEV with a permanent bleed port. In some cases, thebleed port has proved somewhat slow at equalizing systempressures creating restart problems for low starting torquecompressor motors. The RPB feature, however, has beenproven to reduce equalization times, normally to within twominutes after system off-cycle.

The RPB feature is actuated following system off-cycle.Immediately after compressor shutdown, the evaporatorpressure rises forcing the valve's pin carrier to a more closedposition. When the RPB feature is used, the pin carrier con-tinues its motion and opens a secondary spring loaded bleedport allowing rapid pressure equalization to occur. Uponcompressor restart, evaporator pressure falls closing thespring loaded bleed port. The bleed position and the normaloperating position of the RPB are illustrated in Figure 12.

The RPB feature has a specific application. The featureshould only be used on small air conditioning and heat pumpsystems which use a low starting torque single phase com-pressor motor. On heat pump applications, the RPB featureshould only be used on the indoor coil. Since the outdoor coilmay be exposed to cold ambient temperatures, there exists apossibility the evaporator pressure may fall too slowly uponcompressor restart to reset the RPB feature. In addition, theRPB feature is not recommended nor is it required for anysystem employing electrical hard start components.

The RPB feature is available with the Type RI TEV, and itcan be specified on a special order basis for Types C and STEVs up to and including 4 tons R-22 nominal capacity.Refer to the valve specification sheets for further informa-tion. For OEM type TEVs, contact Sporlan Valve Companyregarding the availability of the RPB feature. A Catch-AllFilter-Drier should be installed near the inlet of a TEVhaving the RPB feature to assure proper valve operation.

The normal capacity of the valve is increased by 15% whenthe rapid pressure balancer is used. A cross drilling is partof the internal construction of the RPB feature and thisdrilling provides the additional refrigerant flow.

R-717 (Ammonia) Applications

Thermostatic expansion valves for ammonia applicationsrequire special design considerations due to the erosiveeffects of ammonia vapor. For this type of application,Sporlan has developed the Types D and A thermostaticexpansion valves. Like other components of any ammoniasystem, the Types D and A valves are made from steel andsteel alloys. The materials used in the manufacture of thesevalves are listed on Page 32, Bulletin 10-10.

With ammonia systems, the formation of flash vapor at theexpansion valve port causes valve seat erosion or wire draw-ing to occur. This effect is further aggravated by high veloc-ity ammonia mixed with dirt or scale passing through theport of the expansion valve. Fortunately, seat erosion can beminimized and valve life extended if the following steps aretaken:

1. Maintain vapor-free liquid at the TEV inlet at all times.2. Maintain clean ammonia through effective filtration.3. Reduce the velocity of the ammonia through the TEV

port by reducing the pressure drop across the port.

Step 1 can be accomplished through proper system design.Liquid line vapor is prevented by adequately sizing liquidlines and providing sufficient subcooling. Step 2 can beassured with the use of a Sporlan Catch-All Filter-Drier.This filter-drier is an effective scale trap when used onammonia systems. For further information on the use of theCatch-All Filter-Drier with ammonia systems, refer toBulletin 40-10 or Catalog 717.

Step 3 is accomplished through the use of a removable dis-charge tube located in the outlet of all Type D valves andthe nominal 20, 30, and 50 ton Type A valves. This dis-charge tube represents the principal difference betweenSporlan ammonia TEVs compared to TEVs used with otherrefrigerants. The discharge tube functions by removing aportion of the total pressure drop across the valve resultingin a lower pressure drop across the valve port. Liquid veloc-ities and the formation of flash vapor at the valve port arereduced, extending the life of the valve. Discharge tube sizesare listed in the Types D and A valve specifications locatedon Pages 30 and 31, Bulletin 10-10.

The discharge tube should be removed and discarded whena Sporlan refrigerant distributor is used with the ammoniaTEV since the function of the discharge tube is accom-plished by the distributor nozzle. If the discharge tube is notremoved from the valve, the combination of the dischargetube and distributor nozzle may create an excessive pres-sure drop resulting in a substantial loss of TEV capacity.Refer to Bulletin 20-10 for further information on ammoniadistributors or Catalog 717.

The nominal 75 and 100 ton Type A valves do not employ adischarge tube since their valve outlets are designed to

Typical Valve Cross Section

Bleed or EqualizingPosition

Normal OperatingPosition

RIVEWithRPB

Figure 12

example, the superheat of R-22 vapor at 50°F and 68.5 psigat the sensing bulb location is calculated as follows:

saturation temperature of R-22 vapor at 68.5 psig = 40°Fsuperheat = 50°F - 40°F = 10°F

Another method of measuring superheat the TEV is con-trolling is the two temperature method. With thismethod, saturation temperature is measured directly byplacing a temperature probe on the evaporator surface, nor-mally at a location one-half to two-thirds the distancethrough the evaporator coil. Since this method can onlyapproximate true saturation temperature, it is not as reli-able as the pressure-temperature method, and it should beavoided whenever possible.

The TEV is designed to control superheat at a constantvalue at the location of its sensing bulb. The level of super-heat determines to what extent the valve is open. A TEVcontrolling at a high superheat will be further open than aTEV controlling at a low superheat. Refer to the section,How the Thermostatic Expansion Valve Works, on Page 3 foradditional information. Figure 13 shows a plot of valvecapacity versus superheat for a typical TEV, illustrating theeffect superheat has on valve capacity. For the purpose ofunderstanding the relationship between superheat andvalve capacity, superheat may be described as follows:

Static Superheat � static superheat is the amount ofsuperheat necessary to overcome the spring and equalizerpressures so that any additional superheat will cause thevalve to open.

Opening Superheat � opening superheat is the amountof superheat required to move the valve pin away from theseat after the spring and equalizer pressures have beenovercome to permit refrigerant flow.

Operating Superheat � operating superheat is thesuperheat at which the TEV operates on a refrigeration sys-tem. Operating superheat is the sum of static and openingsuperheats. The valve capacity versus operating superheatcurve is referred to as the valve gradient.

The most desirable operating superheat for a particular sys-tem largely depends on the temperature difference (TD)between the refrigerant and the medium being cooled. Thebasic definition of TD is the difference between evaporatortemperature and the entering temperature of the mediumbeing cooled, i.e., air or water. Systems with a high TD, suchas air conditioning and heat pump systems, can toleratehigher superheats without appreciable loss in system capac-ity. Refrigeration and low temperature systems require lowsuperheats due to their lower TDs. The table below providesgeneral recommendations for superheat settings for differ-ent evaporator temperature ranges. These settings areonly estimates for typical system designs and shouldonly be used if setting guidelines are unavailablefrom the system manufacturer:

When a Sporlan TEV is properly selected and applied, thefactory superheat setting will usually provide an operating

/ BULLETIN 10-9

serve as a secondary orifice to reduce pressure drop acrossthe valve port.

Thermostatic Charges for Ammonia Valves

Thermostatic charges C, Z, and L are available for the TypeD thermostatic expansion valve. The Type L thermostaticcharge is the only charge available for the Type A valve.

The Types C and Z thermostatic charges provide operatingadvantages for systems that cycle in response to a suctionpressure switch or thermostat. These charges are also rec-ommended for systems using a small capacity compressor.The table below lists the recommended temperature rangefor each charge.

Cold storage plants will often have large centralized ammo-nia systems. These systems will consist of many evaporatorsconnected to one or more large compressors. With manythermostatic expansion valves operating at a common evap-orator pressure, a change in flow rate made by one valvewill not have a significant effect on the evaporator pressure.This operating characteristic makes it more desirable forthe thermostatic expansion valve to be more responsive tochanges in bulb temperature. This is the feature of theSporlan Type L charge. Therefore, for large ammonia sys-tems consisting of multiple evaporators, the Type L chargeis recommended.

FACTORS AFFECTING TEV OPERATION ANDPERFORMANCE

There exists many factors which influence TEV operationand performance. The following discussion lists the majorfactors:

Superheat

Superheat is defined as the difference between the refriger-ant vapor temperature and its saturation temperature. Toproperly measure the superheat the TEV is controlling, thepressure-temperature method is used. This method con-sists of measuring the suction pressure at the sensing bulblocation, converting this pressure to its saturation tempera-ture by using a pressure temperature (PT) chart, and sub-tracting the saturation temperature from the vaportemperature measured at the sensing bulb location. For

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Figure 13

BULLETIN 10-9 /

superheat in the range of 8 to 12°F. A precise determinationof the valve's operating superheat from a factory setting isnot possible since factory settings are determined on thebasis of static superheat, and opening superheat of the valveis influenced by several design factors within the system.Once the TEV has been placed on the system and set to thedesired operating superheat, however, the valve's staticsuperheat can be measured on a test fixture permitting thedesired setting to be duplicated for production runs.

All Sporlan TEVs have reserve capacity in addition to thecapacity shown in the rating tables on Pages 5 to 11,Bulletin 10-10. This reserve capacity should not be consid-ered when selecting a valve and, in most cases, will not beutilized if the valve is properly selected and applied. Reservecapacity, however, is an important and necessary character-istic of any well designed TEV. Reserve capacity enables thevalve to adjust for a temporary increase in load, periods oflow condensing pressure, and moderate amounts of flashgas in the liquid line.

Valve Setting

All Sporlan TEVs will produce rated capacity at the stan-dard factory setting. If the valve adjusting stem is turnedclockwise, the additional spring pressure created willincrease static superheat and decrease the valve's capacity

to a limited degree. Turning the adjusting stem counter-clockwise will decrease static superheat and increase thevalve's capacity to a limited degree. Figure 14 illustratesthe effect setting has on valve capacity.

Referring to Gradient Curve A in Figure 14, Capacity C2 isachieved with a static superheat setting of A and an operat-ing superheat of C. Turning the adjusting stem clockwisewill increase the static superheat and shift the curve to theright. This new curve, identified as Gradient Curve B, showsthat valve capacity will decrease to capacity C1 at the sameoperating superheat C. Capacity C2 can only be achieved atthe expense of a higher operating superheat designated as D.

On an operating system where a given valve capacity isrequired, any valve adjustment will merely change thesuperheat at which the valve is operating.

Evaporator Temperature

The pressure-temperature curves for all refrigerants havea flatter slope at lower temperatures. Figure 15 illustratesa P-T curve using R-22 as an example. The P-T curve for athermostatic charge will also be flatter at lower tempera-tures. As a result, a given bulb temperature change causesa smaller bulb pressure change at lower evaporator tem-peratures. A given change in superheat will result in lesspressure difference across the valve diaphragm at lowerevaporating temperature causing a reduction in valveopening and valve capacity.

Subcooling

Subcooling is defined as the difference between the refrig-erant liquid temperature and its saturation temperature.For example, the amount of subcooling of R-22 liquid at85°F and 196 psig is calculated as follows:

saturation temperature of R-22 liquid at 196 psig = 100°F subcooling = 100°F - 85°F = 15°F

Adequate subcooling of the refrigerant liquid is necessaryto prevent the formation of liquid line vapor due to pressurelosses in the liquid line. Vapor in the liquid line, even insmall quantities, will measurably reduce valve capacity.Several methods by which liquid line vapor can be pre-vented in spite of relatively high liquid line pressure lossesare explained in Bulletin 10-11.

�See Sporlan Bulletin 20-10 for pressure drop data as related topercent loading.

Pre

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Figure 14

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TABLE 3

TABLE 4

86°F. For other liquid temperatures, apply the correction factorgiven in the tables for each refrigerant.

3.Select valve from the capacity tables — Select a valve based onthe design evaporating temperature and the available pressuredrop across the valve. If possible, the valve capacity should equalor slightly exceed the design rating of the system. Be sure to applythe appropriate liquid temperature correction factor to the valveratings shown in the tables. Once the desired valve capacity hasbeen located, determine the nominal capacity of the valve from thesecond column of the tables. On multiple evaporator systems,select each valve on the basis of individual evaporator capacity.

4. Determine if an external equalizer is required — Theamount of pressure drop between the valve outlet and bulblocation will determine if an external equalizer is required.Refer to the section, Equalization Method, on Page 5 for fur-ther information on this subject.

5. Select body type — Select the body type from Table 5according to the style connections desired. For completespecifications on each TEV type including nominal ratings,refer to Bulletin 10-10 for valve's specifications.

6. Select the Sporlan Selective Thermostatic Charge — Selectthe charge according to the design evaporating temperature fromthe Table on Page 18. Refer to Pages 7 thru 9 for a complete dis-cussion of the Sporlan Selective Thermostatic Charges available.

Selection ExampleRefrigerant 22Application: air conditioning

Design evaporator temperature . . . . . . . . . . .40°FDesign condenser temperature . . . . . . . . . .105°FRefrigerant liquid temperature . . . . . . . . . . . .90°FDesign system capacity . . . . . . . . . . . . . . .2 tons

Available pressure drop across TEV:Condensing pressure (psig) . . . . . . . . . .211Evaporating pressure (psig) . . . . . . . . . . .69

____142

Liquid line and accessories loss (psi) . . . . .7Distributor and tubes loss (psi)1 . . . . . . .35

____100

Refrigerant liquid correction factor . . . . . . . . .1.06

The SVE-2 has valve capacity of: 2.00 x 1.06 = 2.12 tons at40°F evaporating temperature, 100 psi pressure drop, and90°F liquid temperature.

Thermostatic charge (from Table on Page 18): VGA �

Pressure losses in the liquid line result from friction and sta-tic pressure losses. Minimizing these pressure losses as muchas possible is necessary for proper system design. Frictionlosses may be minimized by properly sizing the liquid lineand liquid line accessories such as a solenoid valve and filter-drier. Static pressure losses, however, are solely the result ofthe weight of the vertical height of refrigerant liquid. As aresult, static pressure losses can only be minimized by reduc-ing the upward vertical height refrigerant liquid must travel.Table 3 may be used to determine the static pressure loss ofa liquid line. When the sum of the static pressure and frictionlosses are known, the amount of subcooling necessary to pre-vent vapor from forming in the liquid line can be determined.For example, if the sum of the static and friction losses is 14psi for an R-22 system, and the condensing temperature is100°F, the subcooling necessary is as follows:

saturation pressure of R-22 at 100°F condensing = 196psig pressure at TEV inlet = 196 -14 = 182 psigsaturation temperature of R-22 liquid at 182 psig = 95°Fsubcooling required = 100 - 95 = 5°F

Refrigerant Liquid Temperature and Pressure DropAcross TEV

The refrigerant liquid temperature entering the TEV and thepressure drop available across the TEV influence valve capac-ity. The valve capacity ratings displayed on Pages 4 to 9,Bulletin 10-10, are based on 100°F vapor free liquid enteringthe valve for R-12, R-22, R-134a, R-401A, R-402A, R-404A, R-407A, R-407C, R-408A, R-409A, R-502, and R-507. R-717(ammonia) valve capacity ratings are based on 86°F vapor freeliquid entering the valve. Liquid correction factors for other liq-uid temperatures are included in Bulletin 10-10 along with theratings tables for each of the refrigerants listed above. Thetables also provide valve capacities for typical pressure dropsacross the TEV.

Thermostatic Charge

The pressure-temperature curves of the various Sporlan SelectiveCharges have different characteristics. The same amount ofsuperheat will not produce equal valve openings for each type ofcharge. The valve capacity ratings shown in this Bulletin specifythe thermostatic charges which they are based on.

SELECTION PROCEDURE

The following procedure should be used when selecting aSporlan TEV:

1. Determine pressure drop across valve — Subtract theevaporating pressure from the condensing pressure. The con-densing pressure used in this calculation should be the mini-mum operating condensing pressure of the system. From thisvalue, subtract all other pressure losses to obtain the netpressure drop across the valve. Be sure to consider all of thefollowing possible sources of pressure drop: (1) friction lossesthrough refrigeration lines including the evaporator and con-denser; (2) pressure drop across liquid line accessories suchas a solenoid valve and filter drier; (3) static pressure loss(gain) due to the vertical lift (drop) of the liquid line; and (4)pressure drop across a refrigerant distributor if used. Table 4specifies typical pressure drops across Sporlan type refriger-ant distributors at design load conditions. Refer to Bulletin20-10 for further information on refrigerant distributors.

2. Determine the liquid temperature of the refrigerant enteringthe valve — The TEV capacity tables on Pages 5 to 11, Bulletin10-10, are based on a liquid temperature of 100°F for R-12, R-22,R-134a, R-401A, R-402A, R-404A, R-407A, R-407C, R-408A, R-409A, R-502 and R-507. R-717 (ammonia) capacities are based on

/ BULLETIN 10-9

The valve capacityshould equal or slightlyexceed the tonnage rat-ing of the system

a Designevaporatingtemperature

b Available pressuredrop

BULLETIN 10-9 /

Selection:

SVE-2-GA 1/2” x 5/8” ODF— 5’, 1/4” ODF equalizer

� An externally equalized valve must be used on evapora-tors employing a refrigerant distributor due to the pressuredrop created by the distributor.

� Refer to the section, Sporlan Selective Charges, on Page7 for information regarding the differences between theVGA and VCP100 charges. Please note that the refrigerantcharge designation in the thermostatic charge ("V" in thiscase) is dropped when it is incorporated into the valvemodel designation.

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TABLE 5

R-12R-13R-13B1R-22R-23R-114R-124R-134aR-401A

—Yellow—Blue—Blue—Green—Blue—Blue—Blue—Blue—Pink

R-402AR-404AR-407CR-410AR-500R-502R-503R-507R-717

—Sand/Beige—Orange—Lt.Brown—Pink—Orange—Purple—Blue—Teal—White

For the complete valve specification, also include all con-nection sizes and capillary tube length.

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7. Ordering instructions — Combine the letters and numbers in the following manner to obtain the complete valve desig-nation. Also include all connection sizes and the capillary tube length.

Refrigerant Color Code Used on decals

/ BULLETIN 10-9

SAEFlare

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*Application Factors:

1. The Type ZP charges have essentially the same characteristics as the Type Z charge with one exception: They produce a pressurelimit (MOP). ZP charges are not intended as replacements for Z charges. Each should be selected for its own unique purpose. SeePage 8 for additional application discussion.

2. All air conditioning and heat pump charges are intended for use with externally equalized valves. See Page 5 for complete discus-sion on when to use an external equalizer.

3. Type L Liquid charges are also available for most commonly used refrigerants in most element sizes.

4. If in doubt as to which charge to use, review discussion on Pages 7 and 8 or contact Sporlan Valve Company, Washington, MO withcomplete system data.

SPORLAN SELECTIVE CHARGES ENGINEERED for PEAK PERFORMANCE for EACH SPECIFIC APPLICATIONRecommended Thermostatic Charges*

Printed in U.S. of A. 50-601

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