Boiler Room

Glossary, Terminology & Definitions

Terminology:

Absolute Pressure: Atmospheric pressure added to the gauge pressure. Indicated as “psia”

Acidic: A condition of liquid, opposite from alkaline on the pH scale, which is represented by

sulfuric, carbonic acids, etc. contained within it.

Air Changes: The number of times in an hour that a volume of air within a space is exchanged.

Alkaline: A condition of liquid, opposite from acidic on the pH scale, which is represented by

carbonates, bicarbonates, phosphates, silicates or hydroxides contained within it.

Ambient Temperature: The temperature of the air immediately surrounding a device.

Angle Valve: A variant of the globe valve design, having pipe openings at right angle to each other.

ASME Code: Codes adopted by American Society of Mechanical Engineers for the construction

and operation of boilers and related pressure vessels and equipment. ASME Sections I, VII and VIII

are the most significant Codes that cover recommendations, rules and formulas that apply to the

corrugator industry.

Atmospheric Pressure: the weight of the atmosphere measured in pounds per square inch. At sea

level it is 14.7 psia, or 29.9 IN. Hg. ABS.

Atomization: The process of reducing a liquid fuel into a fine spray (mist) so that it may be

surrounded by air for better combustion.

Backwash: The backflow of water through the resin bed of a water softener during the cleaning

process.

Baffle: A structure or partition used for directing the flow of gasses or liquids.

Balanced Draft: A fixed ratio of incoming air to outgoing products of combustion.

Ball Valve: A quick opening valve providing tight shut off. Name is derived from its spherical

shaped gate.

Blister: A raised area on the surface of metal caused by overheating.

Blowdown: The removal of water from a boiler in the process of lowering its chemical

concentrations.

Boiler Horsepower: The evaporation of 34.5 pounds of water per hour from a temperature of 212OF

into dry saturated steam.

Boiling Out: A process whereby an alkaline solution is boiled within a vessel to rid its interior of oil

or grease.

Boiling Point: The temperature at which a liquid is converted to a vapor corresponding to its

pressure.

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British Thermal Unit (BTU): A unit of measurement of heat. The amount of heat needed to raise

the temperature of one pound of water, one degree Fahrenheit.

Carryover: A condition whereby water or chemical solids enter the discharge line of a steam boiler,

contaminating the steam.

Cavitation: The formation of vapor pockets in a flowing liquid. The imploding bubbles can damage

internal surfaces.

CFM: Abbreviation for Cubic Feet per Minute. Measurement unit for gas flows.

Combustion Efficiency: The ratio of the heat released from a fuel as it burns, to its heat content.

Concentrations: The number of times that dissolved solids increase in a body of water as a one-to-

one multiple of the original amount due to the evaporation process.

Condensation: The process of returning a vapor back to its liquid state through the extraction of

latent heat.

Conduction: Transfer of heat from a hotter portion of a body to a cooler part of the same body or to

another body at a lower temperature in direct contact with it.

Continuous Blowdown: A process whereby solids concentrations within a body of water are

controlled through the constant removal and replacement of the water. Also referred to as “Surface

Blowdown”

Convection: A process of heat transfer resulting from movement within fluids due to the relative

density of its warmer and cooler parts. Only occurs in fluids; liquids, gases, and vapors: not solids.

Corrosion: The wasting away of metals due to physical contact with oxygen, carbon dioxide, or

acids.

Damper: A mechanism used to create a variable resistance within a gas or air passage in order to

regulate its rate of flow.

Deaeration: The removal of entrained air from a liquid.

Degree of Superheat: The difference between the saturation temperature of a vapor and its actual

temperature at a given pressure.

Demineralization: Deionization, the removal of ionizable salts from solution.

Economizer: A heat recovery device that utilizes waste heat for preheating fluids.

Entrainment: The inclusion of water or solids in steam, usually due to the violent action of the

boiling process.

Evaporation: The transformation of a liquid into its vapor state through the application of latent

heat.

Excess Air: The air supplied for the combustion process in excess of that theoretically needed for

complete oxidation. High flow of excess air reduces boiler efficiency.

Feedwater Treatment: The conditioning of water with chemicals to establish wanted characteristics

desired for use in a boiler.

Firetube Boiler: Uses tubes to direct the hot gases of the combustion process through the boiler to a

discharge flue. The tubes are submerged within the boiler water, which is held in a large drum type

shell, and transfer heat from the hot gases to the water. Typical boiler used for pressures below about

250 psig.

Flue: A pipe or conduit used for conveying combustion exhaust fumes to the atmosphere.

Foaming: The continuous formation of bubbles having a high surface tension, which are hard to

disengage from a surface. In a boiler this results in steam vapor not separating from the boiler water

properly causing carryover. Commonly caused by very high concentrations of soluble or insoluble

solids such as alkilies, oils, fats, greases and other certain organic matters.

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Forced Draft: The process of moving air mechanically by pushing or drawing it through

combustion chamber with fans or blowers.

Fouling: The accumulation of refuse in gas passages or on heat-absorbing surfaces, which results in

undesirable restrictions to flow.

Gate Valve: Valve characterized by a disc or wedge inserted between to seating surfaces to close.

Faces are typically angled to improve closure, though many seating methods are used depending on

service. On or off service only, not suitable for throttling service.

Gauge Pressure: Absolute pressure minus atmospheric pressure. Indicated as “psig”.

Gauge Siphon: Also know as a “pigtail”. Used to protect a pressure gauge’s bourdon tube from the

direct contact of steam. A small amount of water forms in the “pigtail” and thus prevents steam from

being directly in the gauge.

Globe Valve: Characterized by the perpendicular movement of a valve disc from the seat or orifice

of the valve body. High friction component due to a “Z” shaped flow path, but highly suitable for

throttling and high-pressure drop service. With non-metallic insert in disc or seat, it can be

considered bubble tight upon closure.

Hardness: A term used to describe the calcium and magnesium content of water. Measured as PPM

or grains per gallon.

Header: A manifold to which multiple branch lines are connected. Usually a means of connecting

multiple boilers to the outgoing process and heating steam mains.

Heating Surface: That portion of a heat exchange device which is exposed to the heat source and

transfers heat to the heated medium.

High Fire: The firing rate at which a burner consumes the most fuel thus producing the most heat.

Hydrostatic Test: A procedure in which water is used to determine the integrity of pressure vessels.

Induced Draft Fan: A fan or blower located in the breeching of gas passages that produces a

negative pressure in the combustion chamber causing air to be drawn through it.

Ion Exchange: A process for removing impurities from water on the atomic level through the

selective repositioning of electrons. Commonly, a sodium ion exchange process of operation is used

in a water softener to remove calcium and magnesium ions, which cause “hardness”.

Latent Heat of Condensation: The heat extracted from a vapor in changing it to a liquid with no

change in temperature.

Latent Heat of Evaporation: The heat added to a liquid in changing it to a vapor with no change in

temperature.

Latent Heat: Transferable heat in steam, the energy given up for use, when steam condenses.

Low Pressure Boiler: A steam boiler whose maximum allowable working pressure does not exceed

15 p.s.i.

Low Water Cutoff: A mechanism used for shutting off the supply of fuel to a furnace when a

boiler’s water level falls to a dangerously low level.

Makeup Water: Water added to a system to replace that which was lost during operations due to

leaks, consumption, blow down, and evaporation.

Manual Reset: Reset switch that must be manually activated by a person. Used on critical boiler

room sensors, which interrupt the boiler controls if hazardous conditions are detected. Operator must

determine reason for failure and correct before resetting a “Manual Reset”.

MAWP: Abbreviation for Maximum Allowable Working Pressure. The maximum allowed pressure

a pressure vessel is design to operate at safely. Typically stamped on the shell or nameplate of the

equipment and is recorded on National Board documents.

Modulating Fire: Varying the firing rate with the load thereby decreasing the on off cycling of

burners.

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Non-Condensable Gases: Naturally incurring air introduced into a steam system through make-up

water, poor deaeration, vacuum breakers, packing glands, rotary joints, etc. Reduces heat transfer

efficiency and is detrimental to steam spaces, piping and condensate return systems due to possible

formation of corrosive acids.

Oil Temperature Limit Switch: Sensors that are used in the same manner as the low or high gas

pressure switches. Detect abnormal fuel oil temperatures and shuts off burner if not within pre-

selected temperature range. (Used with heavy fuel oils only.)

Orsat: A device used to analyze gases by absorption into chemical solutions. Typically used for

combustion analysis. Electronic versions are becoming predominant in the industry, today.

Oxygen Scavenger: A chemical treatment such as sulfite used for releasing dissolved oxygen from

water.

O2 Trim: An oxygen trim system designed to continuously monitor oxygen concentrations in the

boiler flue gases. It adjusts the fuel or air flow to the burner (usually through the burner management

equipment) to maintain the oxygen level at a set point. This reduces excess air and thus improves

combustion efficiency and reduces polluting emissions

Package Boiler: One that is shipped from the assembly plant completely equipped with all the

apparatus needed for its operation.

pH: A value that indicates the intensity of the alkalinity or acidity of a solution.

Pilot: A small burner used as in igniter to light off a main burner.

PPM: Abbreviation for Parts per Million. Measurement of a substance diluted in a liquid.

Pressure Regulator A mechanism used to maintain constant pressure within a feeder line regardless

of fluctuations above the setting in the supply line.

Primary Air: Combustion air that is introduced into a furnace with the fuel.

Priming: The discharge of water particles into a steam line causing carryover. This is caused by a

rapid change in load on the boiler resulting in a sudden surge of boiler water.

PRV: Abbreviation for Pressure-Regulating Valve.

PSI: Abbreviation for Pounds per Square Inch. Can also be considered indication of differential

pressure. If differential pressure, it should be designated as: “∆psi”

Radiation Loss: The loss of heat from an object to the surrounding air.

Refractory: Heat-resistant material used to line furnaces, ovens, and incinerators.

Relief Valve: Also known as a Pressure Relief Valve. A device used to relieve excess pressure from

liquid-filled pressure vessels, pipes, and hot water boilers. Often used to divert excess pressure on

the outlet of a pump back to the suction side of a pump. Re-closes after normal conditions have been

restored. May only open by an amount required to relieve pressure.

Safety Relief Valve: A self operated quick opening valve used for fast relief of excessive pressures.

Due to internal design characteristics, they “pop” to a full open position. Sized to prevent any further

increase of pressure within a vessel once it opens. Requires a manual lift (test) lever on steam service

or if used on hot water that is over 140OF service, per ASME codes.

Saturated Steam: Dry steam that has reached the temperature corresponding to its pressure.

Saturated Temperature: Temperature at which the change in state takes place at a given pressure.

Scale: A hard coating or layer of chemical materials on internal surfaces of pressure vessels, piping,

and fluid passages. 1/16” scale increases fuel consumption 15%, 1/4” scale deposits requires 39%

more fuel.

Sedimentation: Settling out of particles from suspension in water.

Sensible Heat: Heat, which changes the temperature but not the state of a substance.

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Sensible Heat: The energy that remains in the condensate, when the steam condenses.

Set Point: A pre-determined value to which a device is adjusted that, when reached, causes it to

perform its intended function.

Specific Heat: A measure of the heat required in Btu’s to raise the temperature of one pound of

substance, one degree Fahrenheit, the specific heat of water is 1.0.

Static Head: The pressure exerted by the weight of a fluid in a vertical column. For cold water it is

equal to one psi for every 2.31 feet or 27.7 inches of height.

Static Pressure: The force exerted per unit area by a gas or liquid measured at right angles to the

direction of the flow.

Steam: The gaseous form of water. Water converts into steam by adding volumes of heat. The vapor

formed contains a large volume of BTUs (averaging about 850-900 BTUs/lb.) that is easily

transferred from the steam to a medium to be heated. The steam vapor is easily transferred from one

location to another by simple piping and pressure drops.

TDS: Abbreviation for Total Dissolved Solids. Measured as “ppm” on a conductivity meter.

Temperature Regulating Valve: An automatic valve used to control flow of liquids or steam to a

process or line. Senses the temperature of the item to be controlled and varies the flow of a medium

into the controlled medium.

Thermistor: A solid-state device whose electrical resistance varies with temperature.

Thermocouple: A mechanism comprised of two electrical conductors made of different metals

which are joined at a point which, when heated, produces an electrical voltage having the value that

is directly proportional to the temperature of the heat being applied.

Vacuum: Any pressure less than that of the surrounding atmosphere.

Vented Receiver: Tank that is vented to atmosphere, which receives and stores condensate and

fresh make-up water. May supply it to the feedwater pumps or to a high pressure receiver.

Watertube Boiler: Uses tubes to direct the boiler water through the hot gases of the combustion

process, allowing the hot gases to transfer heat through the tube walls into the water. The water

circulates by convection from the lower portions of the boiler or mud drums to the upper portion or

steam drum. Typically for high boiler pressure needs.

“Y” pattern Globe Valve: Characterized by the perpendicular movement of a valve disc from the

seat or orifice of the valve body. Valve bonnet is angled over from the piping centerline so as to

reduce the high friction losses common in a globe valve with the bonnet perpendicular to the

centerline. Highly suitable for throttling and high-pressure drop service.

Items on the Boiler: (Many are installed on the Demo Boiler at WTEC)

Alarm Bell: Provides a loud audible ringing sound to alert the boiler operator of a problem. The

boiler alarm bell is connected to the burner management controls and signals all potentially

hazardous problems.

Atomizing Air Pump: Provides a typically high-pressure air supply to the burner gun for the

atomizing of fuel oils.

Atomizing Air Pump Lube Oil Tank: Provides lubrication to the vanes of the atomizing air pump.

Atomizing Air (Steam) Proving Switch: Pressure switch that senses adequate pressure of the

atomizing media is available. Steam or air is used to atomize liquid fuels correctly. Switch opens

burner control circuit if atomizing media/pressure is not available. (Used only when firing fuel oils.)

Atomizing Air Supply Line: Provides a high-pressure air supply to a fuel oil burner nozzle. The

mixing of air with the liquid fuel breaks the liquid into minute droplets, atomizing the fuel for best

combustion efficiency. (Fuel oil firing only.)

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Auxiliary Low Water Cutoff Probe: (ALWCO) A float operated or probe operated control.

Similar arrangement as the LWCO, however it is located to sense a lower than allowable water

level. Main function is to act as the backup safety device and de-energize the burner control circuit.

It will shut down the burner if a low boiler water condition is detected and the LWCO failed to work

properly. (Must be reset manually after determining failure reasons.)

Blower Motor Starter: Heavy duty contact switches controlling electrical power to the forced draft

fan motor. Typically the switches are opened or closed by an electromagnetic coil controlled by the

burner management system.

Combustion Air Proving Switch: An air pressure-sensing switch. Typically includes a large

diameter sensing diaphragm to be sensitive to air pressures measured in inches of water column. The

contacts of this switch close upon proving of sufficient combustion air pressure supply from forced

draft fan. (Adjustable only by a qualified technician.)

Flame Detector: An infrared sensor aimed through a port at the burner front to detect a pilot flame

and/or a main burner flame. Signals the Flame Safeguard unit to shut down the burner or startup

sequence of the burner if a proper flame is not detected within certain time parameters.

Flame Safeguard/Programming Control: The important part of a burner management system.

This control unit monitors the burner start-up sequence, pilot burner control, main burner flame

management and firing rates. Most all safety device switches are connected to this control such that

if a problem is detected, the programmer shuts down the burner, thus protecting the boiler. They can

be electro-mechanical, solid state electronic and/or micro-processor type devices.

Forced Draft Fan: Supplies large volumes of air to burner that is required to maintain proper

balance of air to fuel for good combustion.

Fuel Oil Metering Block: Used on burners fired with fuel oils. This is a metering valve assembly

with an adjustable flow rate control. Valve uses a cam that has an adjustable ramp, by way of

setscrews, over the entire arc of the cam. Flow is adjusted to provide the best combustion efficiency

and emissions over the entire range of burner firing rates. (Linkage and cam adjustable only by a

qualified technician using combustion analysis equipment.)

Fuel Oil Pressure Switch: Pressure switch designed to open the burner control circuit if the fuel oil

pressure drops below a pre-selected minimum pressure that is required for proper burner operation.

(Not allowed to be adjusted except by authorized technician.)

Fuel Oil Valve: Main shutoff valve for fuel oils to the burner. Normally a solenoid type valve that is

normally closed unless energized by the burner management controller.

Gas Pressure Sensor: Pressure sensor connected to the fuel gas supply train. (Natural Gas,

Propane, etc.) Senses gas pressure and sends signal to burner management system. In turn, this

controls operation of burner by detecting high or low gas pressures, which would result in improper

firing of the burner or dangerous conditions. Replaces multiple mechanically operated low and high

gas pressure switches. (No internal adjustments.)

Gas Vent Valve: Solenoid operated vent to outside atmosphere. Located between the two main gas

valves. Opened when the two main gas valves are closed, thus venting the section of pipe between

the two main gas valves.

High Gas Pressure Switch: Pressure sensing switch that is normally closed whenever the gas line

pressure is below a pre-selected pressure. It de-energizes the main gas valve(s) and energizes the gas

vent valve, if the gas pressure exceeds what is considered suitable for proper combustion and safety.

Requires a “manual reset”.

High Pressure Steam Control: Pressure switch connected to steam space. Senses high steam

pressure and opens burner control circuit to shut off burner if boiler pressure exceeds pre-selected set

point. (Must have manual reset to assure problem is checked before restarting of boiler.)

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Igniter: Electrical probe used with the ignition transformer to provide a spark necessary for ignition

of fuel. Similar to a spark plug, though the spark from this jumps from the core wire of the igniter to

the shell of the pilot burner.

Ignition Transformer: Provides a high-energy spark to the pilot gas burner or main fuel oil burner

such as to ignite the fuel.

Low Gas Pressure Switch: Pressure sensing switch that is normally closed whenever the gas line

pressure is above a pre-selected pressure. It de-energizes the main gas valve(s) and energizes the gas

vent valve, if the gas pressure falls below what is considered suitable for proper combustion, safety

and maintainability of a fire. Requires a “manual reset”.

Modulating Damper Motor: Electric motor controlled by the burner management system.

Modulating action provided by signals from the burner management adjusts the damper assembly in

the burner front and controls the flow of combustion air for the best combustion efficiency and

emissions over the entire range of burner firing rates. (Linkage is adjustable only by service

technician with combustion analysis equipment.)

Main Gas Butterfly Valve: A valve that is modulated and controlled by linkage connected to the

burner management equipment. This provides control of the natural gas flow to the main burner and

is adjusted to provide the best combustion efficiency and emissions over the entire range of burner

firing rates. (Only a qualified technician, using combustion analysis equipment adjusts the linkage to

this valve.)

Main Gas Valve Actuator: (1st valve) Motorized or solenoid actuated bubble tight closure valve on

the inlet to the gas regulator train to a burner. Actuated by the burner management controller, low

gas pressure and high gas pressure switch.

Main Gas Valve Actuator: (2nd

valve) ) Motorized or solenoid actuated bubble tight closure valve

on the gas train located closest to the burner. Actuated by the burner management controller, low gas

pressure and high gas pressure switch. Proof of closure switch is usually contained in this valve.

Modulating Feedwater Valve: Motorized valve located in feedwater supply line to boiler. Used

where proportioning water level control is required. Valve opens and closes per a signal from the

boiler water level control unit (usually a potentiometer located in the LWCO assembly) thereby

controlling the flow of feedwater into the boiler and thus maintaining the proper water level.

Oil Burner Drawer Switch: Used on dual fuel burners to assure the proper location of a burner

nozzle gun. Gun must be fully forward into the burner front when firing fuel oils. Switch will close

when gun is locked in correct position and by way of the fuel oil solenoid will allow flow of fuel oil

to burner gun.

Oil Burner Gun: Typically a metal tube that holds a burner nozzle, on the inner end, at a proper

location within the combustion chamber of the boiler. It supplies the fuel oil and atomizing media to

the nozzle tip for proper atomization as the fuel is sprayed into the combustion area. It provides a

convenient means of connecting fuel oil and atomizing media hoses to the burner unit. The gun is

removable for nozzle cleaning purposes.

Pilot Gas Solenoid Valve: Small electric solenoid valve that opens to provide a fuel gas to a pilot

burner used to ignite the main fuel supply. Controlled by the Flame Safeguard/Programmer controls.

Pilot Gas Regulator: Reduces gaseous fuel supply pressure to a pressure suitable for use in the

pilot burner. (Adjustable only by a qualified technician.)

Primary Low Water Cutoff: (LWCO) Generally a float operated or probe operated control,

located on boiler and piped so as to sense the actual water level above the firetubes or level of water

in the steam drum of a watertube boiler. Main function is to de-energize the burner control circuit

and shut down the burner if a low boiler water condition is detected. Usually includes a set of

switches or a potentiometer designed to control a feedwater pump or modulating feedwater valve

control.

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Sight Glass: Also called a water column or gage glass. Device allows an operator to observe the

level of water or a liquid within a vessel. In the boiler room it is the most important item to observe

on the boiler. Used in the boiler room on the boiler, deaerator, feedwater tanks, chemical tanks to

indicate levels.

Slow Opening Valve: Typically an “Y” pattern globe valve, located between the “quick opening

valve” and drain or blowdown receiver. This valve is used to control the duration and flow of

blowdown during a boiler bottom blowdown program.

Stack: Ductwork or flue that carries hot combustion gases out of the boiler’s interior to be vented to

atmosphere.

Stack Temperature Monitor: A probe and/or switch within the outlet flue of the boiler’s

combustion side. This monitors the stack temperature of the exiting flue gases. Connected through

the burner management controller, it will shut off the burner if a stack temperature exceeds a preset

limit. Requires a “manual reset”.

Steam Generator: Uses a pump to push feedwater through a series of tubes or coils that are in the

combustion space like a watertube boiler. Heat is directly transferred to the feedwater and it is piped

to a steam drum where steam bubbles separate from any water still remaining. Pumps must maintain

the water flow through the tubes, which contain only a small volume of water.

Steam Pressure Sensor: Pressure sensor connected to the boiler steam area. Senses pressure and

sends signal to burner management system. In turn, this controls set pressure and detects variations

and high steam pressure. Replaces multiple mechanically operated pressure switches. (No internal

adjustments.)

Quick Opening Valve: Typically a gate type valve that is lever operated, by moving the lever in

about a 75-90O arc. Located after the bottom boiler drain. Acts as the stop valve between the boiler

and the “Slow Opening Valve”. Not used as the means of controlling duration and flow in

performing a bottom blowdown.

Around the Boiler room:

Blowdown Receiver: Also known as a Blowdown Separator. Boiler blowdown is directed into this

receiver where the energy is dissipated and temperature is reduced to levels suitable for discharge to

drains or sewers. As a separator it separates water and flash steam.

Blowdown Tempering Valve: Usually a temperature regulating valve used to automatically inject

water into the blowdown separator. The water is usually raw water, which cools the blowdown water

to acceptable levels for drains or sewers.

Boiler Feedwater Pump: Pump(s) devoted to supplying boiler feedwater to the boiler. Usually

designed to handle high temperature water for improved boiler efficiency. Pump feedwater from the

deaerator or a high-pressure receiver/feedwater tank to the feedwater inlet valving of the boiler.

Pressure output must exceed the operating pressures of the boiler.

Centrifugal Pump: A rotating pump, which produces fluid velocity and converts it to pressure.

Typically, an impeller draws the liquid towards its center or “eye” and through a set of radial vanes

flings the liquid outward at high velocity into a volute. The volute then directs flow to pump

discharge outlet. Horsepower of the drive source is converted to kinetic energy within the fluid.

These pumps require a positive suction head to avoid cavitation at their impellers.

There are three basic designs:

Overhung impeller: Impeller is located at one end of drive shaft, with motive force at the

opposite end. Suction or inlet is typically at the central end of the pump casing and outlet is on

the peripheral of the casing. An example is a Gould’s model “3196”.

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Impeller between bearings: As the name implies, the impeller is located on a shaft with bearings

on either side of the impeller. Motive force can be at either end. Suction can be to one or either

side of the impeller. Typically these pumps have a horizontally split casing, with inlet and outlet

on opposite sides. Worthington and Aurora are representative of companies making some of

these.

Turbine type: Another rotary pump with stages using impeller(s) similar to a basic centrifugal

pump, however stationary vanes direct the flow from stage to stage. Pressure builds increasingly

from one stage to the next. Flow characteristics are similar to a positive displacement pump and

one must be careful to not dead-end it. Requires less NPSH than the centrifugal pumps above.

More suited for low flow and high head pressure outputs. Grunfos and Aurora manufacture some

examples of turbine pumps.

Cochrane Feedwater Pump: A special feedwater pump, which is designed to receive hot

condensate directly and pump it directly to a boiler. Consists of a jet pump portion that feeds

returning condensate to a centrifugal pump portion. The jet pump can handle a mixture of steam and

water typical of condensate returns. A recirculation loop section provides a depression, which allows

venting, and correct conditions for the centrifugal pump suction. An air separator section discharges

non-condensable gases present in a system. More efficient than a vented receiver (only) system, but

does not react to varying water levels within a system well.

Conductivity Meter: A small electronic meter that measures the total dissolved solids (TDS)

present in a sample of water. Reads as a function of the conductivity of electricity through water that

has impurities. Unit of measure is “µMhos”. Often includes “pH” measurement ability.

Deaerator: A tank into which condensate and make-up water is sprayed and heated by steam.

Usually the steam pressure is between 5-15 psig. This heats the potential feedwater and

simultaneously removes undesirable gases from the water. Gases are theoretically insoluble in water

that has reached saturation temperature. Gases, also, diffuse to a surrounding atmosphere when

dissolved gases, in the water, experience a low partial pressure. The steam introduced to the

deaerator serves as a heating agent and a scrubbing agent effecting the water saturation temperature

and partial pressures of the entrapped gases.

High Pressure Receiver (HPR): A high-pressure tank that receives high temperature condensate

returned from the steam system and/or hot deaerated water for storage. Typically becomes the

supply source for the suction side of feedwater pumps.

Make-up water: Fresh or raw water that has been pretreated by filters, softeners and/or chemicals.

The treated water is added to a system to replace that which was lost during operations due to leaks,

consumption, blow down, and evaporation.

Make-up water control valve: Motorized valve used to meter make-up water into the system.

Controlled by a float type switch or potentiometer located on a deaerator, feedtank or possibly a

boiler.

Metering Pump: Small pump used to precisely meter amounts of a fluid into a process. Usually

have a means of making minute flow rate adjustments. In a boiler room they are used to feed water

treatment chemicals into a boiler, deaerator, steam line, etc. on an automatic basis.

Pressure Regulator: A valve that is used to automatically reduce and maintain pressure below that

of the incoming source. Also called a pressure-reducing valve.

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Raw Water: Water as received from an outside water source, such as municipal water supplies,

wells, ponds, etc. It has not been softened, demineralized, polished or otherwise cleaned for use in a

boiler system.

Sample Cooler: A smaller shell and tube heat exchanger used to cool water samples taken from the

boilers, deaerator or other high temperature water sample source in the boiler room.

STEAM TRAP: An automatic condensate removal device. They allow condensate resulting from

steam giving up its latent to flow to a collection system. They vent air and other non-condensable

gases, thus maintaining steam temperatures and reducing corrosion of steam system components.

They prevent the escape of steam, which would result in the undesirable loss of latent heat.

Float & Thermostatic style: Uses a float to easily detect a level of formed condensate and by

way of a simple orifice, and in most models a linkage connected to a valve plug, discharges the

condensate to a return system. A thermostatically controlled vent valve, located in the upper

portion of the steam trap body, carries out the necessary process of venting non-condensable

gases. Modulating discharge characteristics and considered a very reliable trap design, especially

in services below 250 psig.

Inverted Bucket style: An open ended can or bucket is inverted within the trap chamber.

Condensate and/or steam and non-condensable gases enter into the trap and are directed to the

underside of the bucket. When condensate is present the bucket looses buoyancy and sinks to the

bottom of chamber thereby opening the trap’s discharge valve, by way of connected linkage.

Condensate is pushed through the trap to the return system by pressure differentials. If air or

steam is present the trap bucket floats upward and closes the valve. Bucket sinks as the steam

condenses under the bucket, or as air (non-condensable) escapes through a small bleed hole in

the top of the bucket. The cycle repeats as condensate arrives and or steam condenses in trap.

Considered a cyclic operation mode steam trap.

Thermostatic style: A thermal element senses the difference in temperature of steam as

compared to condensate. Cooler condensate or non-condensable gases will cause the element to

contract and open the discharge orifice by pulling a valve plug away from the orifice. Steam or

very hot condensate entering the trap will expand the thermostatic element and force the valve

closed. Considered a modulating type discharge design.

Thermodynamic style: Most common version is a Disc type trap. Operates based on velocity

differences of gases and liquids. A small round flat disc rests on a valve seat sealing it closed.

Condensate flowing to the trap will exert a force on the underside and push the disc open. It will

remain open until steam enters the trap. Due to a gases’ much higher velocity, and as a result of a

180O turn of the flow path directly under the disc, a pressure drop occurs and pulls the valve disc

down towards the seat. The theorem of the Bernoulli equation concerning expanding gases is

applied. Internal pressure from the steam is present on top of the disc and holds it down against

the seat. The steam above the disc condenses with time and the cycle repeats when the force of

the entering condensate or steam against the underside of the disc exceeds the force of the

condensing steam on top of the disc. Poor air and non-condensable gas discharge as these gases

act like steam (also a gas) within the trap, locking the disc down against the seat (air binding).

Characterized as a cyclic discharge design.

Water Meter: A meter, which measures volume and registers water amount in a readable manner.

May be read as “Gallons”, but can also register as “cubic feet” or “pounds of water” and may

include flow rates such as GPM.

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Water Softener: A mechanism used to remove calcium and magnesium impurities from water, thus

reducing “hardness” or PPM of impurities. Many different designs are capable of performing this

task, however the most common is a sodium based ion exchange unit. These utilize a bed of resin

beads to which the calcium and magnesium ions will adhere upon an exchange with sodium ions.

When the resin bed is saturated with the calcium and magnesium ions, the unit regenerates by first

rinsing away dirt and broken resin beads to drain. Then rinsing the resin beads with a sodium brine

solution, which displaces the calcium and magnesium ions. Then final rinses flush the brine solution

out of the bed leaving it ready the calcium and magnesium ions to adhere to the resin again.

References: Boiler Room Guide, Cleaver Brooks, 1997

Boiler Water Treatment - An Introduction, Nalco Chemical Company, 1998

Stationary Engineering Handbook, Petrocelly, Fairmont Press, 1989

Managing Steam, Jason Makansi, Leslie Company, 1985

Low Pressure Boilers, Fred M. Steingress, American Technical Society, 1977