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ARMY TM 5-814-2

AIR FORCE AFM 88-11, Vol. 2

SANITARY AND INDUSTRIAL

WASTEWATER COLLECTION--

PUMPING STATIONS AND FORCE MAINS

D E P A R T M E N T S O F T H E A R M Y A N D T H E A I R F O R C E

MARCH 1985


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TM 5-814-2/AFM 88-11, Vol. 2

REPRODUCTION AUTHORIZATION/RESTRICTIONS

This manual has been prepared by or for the government and, except to the extent indicated below, ispublic property and not subject to copyright.

Copyrighted material included in the manual has been used with the knowledge and permission of theproprietors and is acknowledged as such at point of use. Anyone wishing to make further use of anycopyrighted material, by itself and apart from this text, should seek necessary permission directly fromthe proprietors.

Reprints or republications of this manual should include a credit substantially as follows: "JointDepartments of the Army and Air Force, USA, Technical Manual TM 5-814-1/AFM 88-11, Volume 2,Sanitary and Industrial Wastewater Collection--Pumping Stations and Force Mains."

If the reprint or republication includes copyrighted material, the credit should also state: "Anyone wishingto make further use of copyrighted material, by itself and apart from this text, should seek necessarypermission directly from the proprietors."


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*TM 5-814-2AFM 88-11, Vol. 2

Technical Manual DEPARTMENTS OF THE ARMYNo. 5-814-2 AND THE AIR FORCEAir Force ManualAFM 88-11, Volume 2 Washington, DC, 15 March 1985

SANITARY AND INDUSTRIAL WASTEWATER COLLECTION-

PUMPING STATIONS AND FORCE MAINS Paragraph Page Chapter 1. GENERAL

Purpose and scope.................................................................................. 1-1 1-1Special wastes ........................................................................................ 1-2 1-1Pump Station alternatives ....................................................................... 1-3 1-1

Chapter 2. LOCATION OF PUMPING STATIONSService area............................................................................................ 2-1 2-1Site selection .......................................................................................... 2-2 2-1Building and site requirements ................................................................ 2-3 2-1

Chapter 3. TYPE AND CAPACITY OF PUMPING STATIONSRequired pumping capacity..................................................................... 3-1 3-1Type of construction................................................................................ 3-2 3-1

Chapter 4. WASTEWATER PUMPING EQUIPMENTWastewater pumps ................................................................................. 4-1 4-1Pump drives............................................................................................ 4-2 4-2Drive mechanisms .................................................................................. 4-3 4-3Pump speed controls............................................................................... 4-4 4-3

Chapter 5. PUMPING SYSTEM DESIGNForce main hydraulics............................................................................. 5-1 5-1Pump analysis and selection................................................................... 5-2 5-3Wet well design....................................................................................... 5-3 5-5Pump controls and instrumentation ......................................................... 5-4 5-6

Surge phenomena................................................................................... 5-5 5-7Screening and comminuting devices....................................................... 5-6 5-9

Chapter 6. PIPING, VALVES AND APPURTENANCESPipe materials, fittings, joints................................................................... 6-1 6-1Valves and appurtenances...................................................................... 6-2 6-2Installation............................................................................................... 6-3 6-2

Chapter 7. PUMP STATION COMPONENTSConstruction requirements ...................................................................... 7-1 7-1Heating and ventilation............................................................................ 7-2 7-1Electrical equipment and lighting............................................................. 7-3 7-2Standby power ........................................................................................ 7-4 7-2

Water supply........................................................................................... 7-5 7-2Flow measurement.................................................................................. 7-6 7-2Paints and protective coatings................................................................. 7-7 7-3

Appendix A. References....................................................................................................................................... ....A-1Bibliography ....................................................................................................................................................... ..BIBLIO-1

*This manual supersedes TM 5-814-2 dated 1 September 1958.

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LIST OF FIGURES

Figure Page5-1. Chart for Hazen-Williams formula ....................................................................................... 5-25-2. Typical pump-system curves............................................................................................... 5-55-3. Pump suction connections to wet well ................................................................................. 5-7

LIST OF TABLESTable Page3-1. Classification of pumping stations ....................................................................................... 3-15-1. Minimum pump cycle times................................................................................................. 5-65-2. Required submergence depth to prevent vortexing ............................................................. 5-65-3. Water hammer wave velocities . ......................................................................................... 5-8

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TM 5-814-2/AFM 88-11, Vol. 2

CHAPTER 1GENERAL

1-1. Purpose and scope. This manual providesguidance, instructions and criteria for the design of

sanitary and industrial wastewater pumping facilities atfixed Army and Air Force installations, and anyapplicable special projects. Facilities covered in thismanual include pump and ejector stations required for(1) removal of sanitary and industrial wastes fromremote or low lying areas of the installation whichcannot be served hydraulically by gravity sewers, (2)controlled introduction and lifting of raw wastewater intothe waste treatment plant, (3) transfer of recycled andbypassed flows throughout the plant, and (4) dischargeof treated effluent. Pumping systems for the handling ofsludge, grit and scum are presented in TM 5-814-3/AFM88-11, Vol. 3. The design of a wastewater pumpingstation will typically include site improvements,structures, screening and flow monitoring devices,pumping units, pump drives, system controls andinstrumentation, mechanical and electrical components,interior piping, underground force mains, valves andappurtenances.

1-2. Special wastes. Pumping systems forhazardous and explosive wastes, corrosive acids oralkalies, high temperature or other industrial typewastes, will generally require the selection of highlyresistant pumps, valves and piping materials. Design ofthese systems will be in accordance with special criteriadeveloped for the particular situation. Selection of

materials for pumps, piping, valves and controls, etc.,will be based on manufacturers' recommendations,product specifications, and any other appropriate designmanuals or applicable criteria.

1-3. Pump stations alternativesa. Gravity sewer system. Pumping stations and

pneumatic ejectors will normally be required to removewastes from areas which cannot be served hydraulicallyby gravity sewers. In certain situations however, a

gravity sewer system can be utilized, but only at the

expense of deep trench excavation, jacking, boringtunneling, or construction of long sewer runs to avoid

high terrain. In those cases, both wastewater pumpingand gravity flow sewers will be technically feasible andcapable of meeting service requirements. Howeverthey may not be equivalent in economic terms. When iis not readily apparent which solution would be moreeconomical, the decision to use one or the other will bebased on a life cycle cost analysis. Initial capital andconstruction costs for pumps, ejectors, structures, forcemains, etc., plus operation and maintenance costs, wilbe compared with the costs of deep trench excavationor other special construction methods required for agravity system. Generally, a gravity sewer system wilbe justified until its cost exceeds the cost of a pumpedsystem by 10 percent. TM 5-814-8 contains criteria foeconomic evaluation of wastewater pumping. TM 58141/AFM 88-11, Vol. 1 provides criteria for engineeringand design of sanitary and industrial wastewatecollection systems.

b. Grinder pumps and vacuum systems. Theremay be areas so limited by high groundwatersubsurface rock, unstable soil or steep topography, thaneither gravity sewers nor centralized pumping stationswill be feasible. In these cases, the use of grindepumps or vacuum systems will be investigated. Seeparagraph 1-4b of TM 5-814-1/AFM 88-11, Vol. 1Design criteria for grinder pumps are contained in thismanual.

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CHAPTER 2LOCATION OF PUMPING STATIONS

2-1. Service area. The requirement that an area beserved by a wastewater pumping facility will in mostcases be determined by topography. Building and grade

elevations in the area generally will be too low for propergravity drainage to an existing or proposed sewersystem, or waste treatment facility. Thus, collection andpumping of wastes from these low lying areas will benecessary. In addition to topographic considerations,natural boundaries like waterways, rivers, streams, etc.,and property lines of Federal, state and local

jurisdictions, also play a role in determining the size andlimits of service areas.

2-2. Site selection. The location of pumpingfacilities within a service area will be based primarily ontopographic considerations and the need to provide forfuture development. Pump stations will be located sothat all points within the intended service area can bedrained adequately by gravity sewers. Any planneddevelopment within the service area, such asconstruction of new buildings or modifications to existingones, or any projected shifts in population and/orworkforce will be considered. This type of information isgenerally obtained from the installation master plans, orfrom personnel staffing requirements. It is a relativelysimple matter to design a pumping station with capacityfor future development by providing room for additionalor larger pumps, motors, impellers, etc. However, thephysical location of the station is more critical since itcannot be moved to accommodate new buildings or

population increases. The following general guidelinesfor site selection and location of pumping stations will beused:

-Pumping facilities will not be constructedbeneath buildings, streets, roadways, railroads, aircraftaprons or runways, or other major surface structures, tothe maximum extent practical.

-Pump stations will not be located closer than500 feet to buildings, or other facilities to be occupied byhumans, unless adequate measures are provided forodor and gas control.

-Pumping stations at wastewater treatmentfacilities will normally be located adjacent to, or in

connection with, other plant elements as required forproper functioning of the treatment systems.

-The location of pumping stations will be madewith proper consideration given to the availability of

required utilities such as electric power, potable waterfire protection, gas, steam and telephone service.

2-3. Building and site requirementsa. Floor and building elevations. The inverelevations of incoming sewers will determine the depthsof underground portions (substructure) of the pumpingstation. It is common practice to set the maximumliquid level in the wet well equal to the 80-90 percenflow depth of the lowest incoming sewer. Subsurfaceand soil conditions at the site will dictate the structuradesign, excavation depths, and top of footing elevationsrequired for the foundation. Surface conditions such asadjacent buildings and site grading will determine theelevations of floors above ground (superstructure)except that the elevation of the ground floor will be seabove the maximum expected flood level.

b. Architectural and landscaping. For pumpingstations located in built-up areas, the architecturaexterior of the buildings should be made similar to, orcompatible with, surrounding buildings. When thestation is located in a remote area, building appearanceis not important, but the possibility of futuredevelopment in the vicinity will be considered. Pumpstations and facilities will be provided with fencing wherenecessary to prevent vandalism, and to protect peoplefrom hazardous contact with electrical transformers andswitching equipment. Landscaping should beconsidered in built-up areas, and will be required inresidential communities. Where stations must be

constructed in close proximity to residences or othequarters, buffer zones of planted shrubbery should beprovided for noise reduction.

c. Access. All pump stations will be readilyaccessible from an improved road. For stations that arenot enclosed, access will be provided for directmaintenance from a truck equipped with hoisattachments. For enclosed stations, provisions will beincluded in the structure to facilitate access for repairand to provide a means for removal and loading ofequipment onto a truck.

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CHAPTER 3TYPE AND CAPACITY OF PUMPING STATIONS

3-1. Required pumping capacity. Proper selectionof the number and capacity of pumping units isdependent upon the quantity and variation of

wastewater flows to be handled. Except as indicatedbelow for small stations, pumping units will be selectedto handle the normal daily range of wastewater flowsgenerated in the service area. The number andcapacity of pumps provided will be sufficient todischarge the minimum, average, peak daily andextreme peak flowrates as calculated in TM 5-814-1/AFM 88-11, Vol. 1. Pumping capacity will beadequate to discharge the peak flowrates with thelargest pump out of service. Pumps utilized fortreatment plant processes, recycling and bypassing offlows, etc., will be based on criteria developed in TM 5-8143/AFM 88-11, Vol. 3. Consideration will be given tofuture conditions which may occur during the life of thestation. Normally, where future development andpopulation increases are projected for the area, pumpswill be designed for initial conditions only, and thestation will be provided adequate room for expansion ofpumping capacity at a later date. Expansion of pumpingcapacity can be accomplished with the installation ofadditional pumping units, larger pumps, impellers, driveunits, adjustable or variable speed drives. However,some situations may warrant provision of capacity forfuture increases initially, for economic or other reasons.Each case will be analyzed individually.

a. Small stations. Pumping stations required forsmall remote areas which generate extreme peak

flowrates of less than 700 gpm, and where the possibilityof future expansion is unlikely, and grinder pumpinstallations serving three or more buildings, will beprovided with two identical pumping units. Eachpumping unit will be of the constant speed type, and willbe capable of discharging the extreme peak wastewaterflowrate. The station will be designed to alternatebetween zero discharge and peak discharge. Thisarrangement will provide 100 percent standby capacityto allow for necessary maintenance and repairs.Pneumatic ejector stations will be provided with duplexejectors each sized for the extreme peak flowrate.

b. Large stations. Pumping stations serving large

areas of the installation, and especially stations wherethe entire wastewater flow or major portions thereofmust be pumped to the treatment facility, will bedesigned so far as practicable to operate on acontinuous basis. The rate of pumpage must change inincrements as the inflow to the station varies. This

mode of operation will normally require two or morewastewater pumps of the constant or variable speedtype, operating in single or multiple pump combinations

as required to match the incoming flowrates.

3-2. Type of construction. A classification opumping stations by capacity and the method ofconstruction normally utilized for that capacity isprovided in Table 3-1. Factory assembled pumpingstations, commonly referred to as package type stationsare manufactured in standard sizes and are shippedfrom the factory in modules with all equipment andcomponents mounted, installed, and ready foconnection. These type stations will be suitable for lowflows, and where the need to protect pumps fromclogging is minimal. Conventional field erectedpumping stations are designed for a particular locationand to meet specific requirements. Field constructedstations will be used where the quantity of flow or itsvariation, or both, exceeds the capacity of availablefactory assembled stations, or where site conditionsrequire the use of special designs or constructionmethods.

Table 3-1. Classification of pumping stations.

RecommendedCapacity

Range Class/Type Gallons Per Minute

Factory Assembled (PackageType)Pneumatic Ejectors 30-200Wet Pit SubmersiblePumps

100-500

Dry Pit Pumps 100-2,000Conventional Field Erected

Small 300-1,500Intermediate 1,500-10,000Large over 10,000

Note: Package type, dry pit pump stations in thecapacities shown are generally available off-the-shelf. However, station capacities up to 5,000gallons per minute can be obtained by specia

order.

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CHAPTER 4WASTEWATER PUMPING EQUIPMENT

4-1. WASTEWATER PUMPSa Centrifugal pumps. The centrifugal pump is the

predominate type of wastewater pump used. Thesepumps are available in three variations, radial flow,mixed flow, and axial flow. Centrifugal pumps will notbe used in capacities of less than 100 gallons perminute.

(1) Radial flow pumps. The radial flowcentrifugal pump is the major type used for pumping rawwastes. In a radial flow pump, the fluid enters theimpeller axially and is discharged at right angles to theshaft. Two types of radial flow pumps are available,single suction and double suction. In a single-endsuction pump, fluid enters the impeller from one side.The shaft does not extend into the suction passage, andbecause of this, rags and trash do not clog the pump.The single-end suction pump will be suitable forhandling untreated wastewater. For a double suctionpump, fluid enters the impeller from both sides, howeverthe shaft extends into the suction passage, therebylimiting its use to handling only clear water. Radial flowcentrifugal pumps are available in discharge sizes of 2to 20 inches. However, pumps with a capacity to pass3-inch minimum solids will be required. Therecommended capacity range for these pumps is 100 to20,000 gpm. Pumps are available in discharge heads of25 to 200 feet total dynamic head (TDH). Peak designefficiency ranges from 60 percent for smaller pumps to85 percent for larger pumps. Radial flow pumps are

suitable for either wet well or dry well applications. Theycan be installed with horizontal or vertical shafting,however, vertical shaft pumps require considerably lessspace.

(2) Mixed flow pumps. The mixed flowcentrifugal pump is an intermediate design between theradial flow type and the axial flow type, and hasoperating characteristics of both. The mixed flow pumpis designed with wide unobstructed passages, and istherefore suitable for handling wastewater or clearwater. Mixed flow centrifugal pumps are available in 8-inch through 84-inch discharge sizes. Therecommended capacity range for these pumps is 1,000

to 80,000 gpm. Pumps are available to operate at 10 to60 feet TDH. Peak design efficiency depends on thesize and characteristics of the individual pump, butgenerally ranges from 80 to 90 percent. The mixed flowcentrifugal pump is normally used only in dry wellapplications, with either horizontal or vertical shaftingconfiguration.

(3) Axial flow pumps. Axial flow centrifugalpumps will not be used to pump raw untreatedwastewater. This pump is designed primari ly for clearwater service and for wet well installations. The pump is

furnished with vertical shaft having a bottom suctionwith the propeller mounted near the bottom of the shaft

and enclosed in a bowl. The propeller is totallysubmerged and can be clogged by large solids, rags ortrash. Therefore, this pump will only be used for cleawell applications. Axial flow centrifugal pumps areavailable in 8-inch through 72-inch discharge sizes. Therecommended capacity range for these pumps is 500 to100,000 gpm. Pumps are available to operate from 1 to40 feet TDH.

(4) Pump construction. Centrifugawastewater pumps will normally be constructed of castiron with bronze or stainless steel trim, and with eithercast iron or bronze impellers. When operating' ilwastewater containing substantial quantities of gritimpellers made of bronze, cast steel or stainless steewill be required. Enclosed impellers will be specified fowastewater pumps required to pass solids. Pumpcasings of the volute type will be used for pumping rawuntreated wastes and wastewaters containing solidsDiffusion of turbine type casings may be utilized foreffluent or clear water service at waste treatmenfacilities. Pump shafts will be high grade forged steeland will be protected by renewable bronze or stainlesssteel sleeves where the shaft passes through thestuffing box. Stuffing boxes will utilize either packingglands or mechanical type seals.

(5) Stuffing box seals. The stuffing box wilbe lubricated and sealed against leakage of wastewater

(into the box) by grease, potable water, or another cleafluid. The lubricating and sealing sealing medium wilbe supplied to the stuffing box at a pressure of 5 to 10psi greater than the pump shutoff head. Grease sealsare usually provided by cartridges which are eitherspring loaded or pressurized by connections off thepump discharge. These arrangements generally do nomaintain sufficient seal pressure on the stuffing boxHowever, they will be acceptable for low head pumpsand where the wastewater contains little grit, as whenpumping treated effluent. When pumping raw untreatedwastes containing the usual quantities of grit, a potablewater seal system with seal pump will be required if a

potable water line is assessable within a reasonabledistance. The Later seal system will be capable osupplying 3 gpm per pump minimum. The principaadvantage of a water seal over a grease seal is thepositive pressure maintained on the stuffing box by theseal pump, and small amount of water which flows fromthe stuffing box into the pump casing. Grit and otheabrasive materials that may be in the wastewater are

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thereby prevented from entering the stuffing box, thusreducing wear on the shaft and packing. The advantageof less frequent repairs to the shaft and less frequentrepacking should be considered in relationship to thecost of providing the water line and other necessaryfacilities for the water seal. Where freezing of sealwater is likely to occur, protective measures will betaken. There must not be, under any circumstances, adirect connection between wastewater pumps and thepotable water system, nor any possibility of backflow ofwastes into the potable water system. Air Forcefacilities will comply with AFM 85-21.

b. Screw pumps. The screw pump is classified asa positive displacement pump, and as such, maintainstwo distinct advantages over centrifugal pumps. It canpass large solids without clogging, and can operate overa wide range of flows with relatively good efficiencies.Screw pumps are normally available in capacitiesranging from 150 to 50,000 gpm with a maximum lift of30 feet. Because of its nonclog capabilities and wide

pumping range, the screw pump is best suited for liftingraw untreated wastewater into the treatment facility, andfor the pumping of treated effluent. Its use in sludgepumping is discussed in TM 5-814-3/AFM 88-11, Vol. 3.Also, when treatment plants are upgraded, screw pumpsmay be installed to overcome the additional head lossescreated by new treatment units, so that existingdischarge facilities can be retained. Screw pumps areusually driven by a constant speed motor with gearreducer, and are inclined at angles of 30 to 38 degreesfrom the horizontal. In most instances, screw pumps willbe installed outdoors with only the drive unit enclosed.

c. Pneumatic ejectors. Pneumatic ejector stations

will generally be used only in remote areas wherequantities of wastes are small, and where futureincreases in waste flows are projected to be minimal. Apneumatic ejector consists of a receiving tank, inlet andoutlet check valves, air supply, and liquid level sensors.When the wastewater reaches a preset level in thereceiver, air is forced in ejecting the wastewater. Whenthe discharge cycle is complete, the air is shut off andwastewater flows through the inlet into the receiver.Generally, duplex ejectors operate on a 1-minute cycle,filling for 30 seconds and discharging for 30 seconds.Thus, each receiver tank will be equal in volume to 30seconds of the extreme peak flowrate. Pneumatic

ejector stations are available in capacities ranging from30 to 200 gpm with recommended operating heads up to60 feet TDH. A typical ejector installation will includeduplex units with two compressors, receivers, levelsensors, etc.

d Grinder pumps. Grinder pumps shred solidsnormally found in domestic wastewater, including rags,paper and plastic, into a slurry. The slurry can be

pumped under low head through pressure sewers assmall as 1 inches in diameter. Grinder pumps are fosubmersible installation, with a recommended operatingrange of 10 to 100 gpm. These pumps are available indischarge heads of 10 to 150 feet TDH. The peakdesign efficiency is generally very low. Grinder pumpswill be used only to handle domestic type wastes fromone or more individual buildings, and only in remoteareas or areas where gravity sewers and centralizedpumping facilities are not feasible (see paragraph 1-3b).

4-2. Pump drivesa Electric motors. As a general rule, electric

motors will be provided as the primary drive unit insanitary and industrial wastewater pumping stationsSmall pump stations serving remote areas whereelectric power is not available, will usually requireengine drives. The three types of electric motors moscommonly used in wastewater pumping are (1) squirrelcage induction, (2) wound-rotor induction, and (3)

synchronous. Squirrel-cage induction motors wilnormally be selected for constant speed pumpapplications because of their simplicity, reliability andeconomy. They can also be used for variable speedoperation when provided with the proper speed controlSynchronous motors may be more economical for largecapacity, low rpm, constant speed pumps. Wound-rotoinduction motors are most commonly used for pumpsrequiring variable speed operation. For a 60 cyclealternating current power supply, the maximumsynchronous motor speed allowed for wastewater pumpswill be 1800 rpm (approximately 1770 rpm inductionspeed). The normal range of speeds is from 600 to

1200 rpm, with speeds below 450 rpm unusual atmilitary installations. Lower speed pumps and motorsare larger and more expensive, but generally are morereliable. The selection of electric motors will dependupon the type, size and location of the pumps, type ofspeed control used, and the power available at the sitePump location will determine the type of motorenclosure. For dry pit pump installations, motoenclosures will normally be the open, drip proof typePumps installed outdoors, or in dirty or corrosiveenvironments, will require totally enclosed motorsSubmersible pumps will have motor enclosures whichare watertight. Motors installed outdoors will have

temperature ratings adjusted to suit ambient operatingconditions. For pumps designed to operate on anintermittent basis, space heaters will be provided inmotor housings to prevent condensation. Motorsinstalled in wet wells will be explosion proof. Motostarting equipment will be selected in accordance withparagraph 7-3, and will be suitable for the type of motor

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required voltage. Motor starters will be designed forlimiting the inrush current where shocks or disruptions tothe electrical supply are likely to occur as a result ofpump start-up. Where low starting inrush current isrequired for constant speed pumps, such as when usingengine driven generator sets, wound-rotor motors will beconsidered as an alternative to squirrel-cage motors.The voltage required for operation of motors and otherequipment will be determined in accordance withparagraph 7-3.

b Internal combustion engines. Internalcombustion (I.C.) engines will be used primarily at largepumping stations where electric motors are the primarydrive units, and where emergency standby facilities arerequired. Conditions which dictate the use of fixed,standby power at wastewater pumping stations areoutlined in paragraph 7-4. I.C. engines will be requiredfor small pump stations in remote locations where noelectric power source exists. At large wastewatertreatment plants where abundant digester gas is

produced, it will generally be more feasible to use I.C.engines which are fueled by the waste gas. I.C.engines may be arranged to drive horizontal pumps bydirect or belt connections, or they may drive verticalpumps through a right angle gear drive with an electricmotor as the primary drive unit (dual drive). It is morecommon however, and will be the general rule at largepump stations, to provide fixed emergency generatorsets powered by I.C. engines. Generators produceelectric power not only for pumps, but also for auxiliaryequipment such as heaters, lights, alarms, etc., and forcritical pump control systems. The types of internalcombustion engines normally used include (1) diesel, (2)

gasoline, (3) natural gas, primarily digester gas, and (4)dual-fuel diesel. The use of gasoline engines foranything except small, remotely located pumpingstations is not recommended due to the hazardsassociated with fuel handling and storage. Dual-fueldiesel engines fire a mixture of diesel oil and naturalgas, with a minimum of 10 percent diesel fuel requiredto ignite the mixture. Propane is usually provided as abackup fuel for gas and dual-fuel diesel units. Theselection of I.C. engines will be coordinated with theinstallation's Facility Engineer to insure that adequateoperation and maintenance can be made available.

4-3. Drive mechanismsa Direct drive. Direct drive, with the shaft of thedrive unit directly connected to the pump shaft, is themost common configuration. This connection can beeither close-coupled or flexible-coupled. When using aclose-coupled connection, the pump is mounted directlyon the drive shaft. This is the normal arrangement for avertical pump driven by an electric motor. A horizontalpump will usually have a flexible connection, with the

engine mounted adjacent to the pump. A vertical motomounted above, and at a distance from a vertical pumpwill be connected to the pump with one or more lengthsof flexible shafting. Direct drive offers the most efficienoperation because no power is lost between the driveunit and the pump.

b Belt drive. Belt drives may be utilized if thepump speed is different from those available withstandard drive units, or if speed adjustment is requiredSpeed adjustment is accomplished by changing pulleyor sheave ratios. Belt drives used with horizontal pumpsrequire more floor space than a direct drive unit. Thereis power loss through the belt, which results in loweefficiency, and belt wear increases maintenancerequirements. Belt drives will be used only when it isnot possible to choose single speed equipment to coveservice conditions, or where pump speed adjustmentsmay be required, but variable speed operation is not.

c Right angle drive. Right angle drives will beused on vertical pumps being driven by horizonta

engines. If the engine serves as emergency standby, acombination gear box will be installed on the angle driveto allow operation of the pump by the primary drive unitwhich is normally an electric motor. A clutch odisconnect coupling disengages the right angle geawhen the motor drives the pump. When the enginedrives the pump, the clutch is engaged and the motorrotates freely. In case of a power failure the engine isautomatically started, and after reaching partiaoperating speed is engaged to drive the pump.

4-4. Pump speed controlsa Mode of operation. Wastewater pumps will be

designed to operate in one of the following modes: (1constant speed, (2) adjustable speed, or (3) variablespeed. The type of speed control system will beselected accordingly. As indicated in paragraph 4-2athe type of speed control required will influence the typeof electric motor to be used.

(1) Constant speed. Constant speed drive isthe simplest, most reliable, and most economical modeof operation, and will be suitable for the majority ofwastewater pumping applications at militaryinstallations. However, where there is a need to matchpumping rates with the incoming wastewater flowrates, avariable speed drive will usually be more appropriate.

(2) Adjustable speed. By changing pulley osprocket ratios on a belt driven pump, the speeds canbe adjusted to accommodate several constant speedpumping rates. This type of system will be used mainlyin sludge pumping, but can be a good alternative

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control offers the best efficiency, while the other unitsare considerably less efficient and require moremaintenance. In general, variable speed controldevices are more expensive, less efficient, and require

a higher degree of maintenance than constant speedcontrols.

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CHAPTER 5PUMPING SYSTEM DESIGN

5-1. Force main hydraulicsa. General . The pipeline which receives

wastewater from a pumping station, and conveys it tothe point of discharge, is called a force main. Forcemains will be designed as pressure pipe, and must beadequate in strength to withstand an internal operatingpressure equal to the pump discharge head, plus anallowance for transient pressures caused by waterhammer. The internal operating pressure is maximumat the pumping station, and is reduced by friction toatmospheric, or near atmospheric, at the point of forcemain discharge. The primary consideration in thehydraulic design of force mains is to select a pipe sizewhich will provide the required minimum velocitieswithout creating excessive energy losses due to pipefriction. The most economical size of force main shouldbe determined on the basis of power costs required forpumping, and capital investment costs of piping andequipment. In practice however, the size is usuallygoverned by the need to maintain minimum velocities atlow flows to prevent deposition of solids, and to developsufficient velocity at least once a day to resuspend anysolids which may have settled in the line. However,regardless of pipe sizes required for minimum velocities,the minimum diameters to be used are 1Y4-inch forpressure sewers at grinder pump installations, 4-inch forforce mains serving small pump stations and pneumaticejectors, and 6-inch for all other force mains.

b Design formula and chart. Force mains will be

designed hydraulically with the use of the Hazen-Williams formula as follows:

V = 1.32 C R0.63

S0.54

whereV = velocity in feet per secondC = coefficient of pipe roughnessR = hydraulic radius in feet, andS = slope of energy grade line in feet per foot

(1) Roughness coefficient. Values of C to beused in the formula range from 100 for older forcemains which have been in service a number of years(usually over 10), to 140 for force mains which arenewly constructed. Some manufacturers of plastic andasbestos-cement pipe report C values as high as 150

However, due to uncertainties in design andconstruction, plus a desire to provide a margin of safetyC values greater than 140 will not normally bepermitted. At some installations, force mains may bevery old (40 to 50 years) and in extremely bad conditionwith offset joints broken pipe, or materials encrusted onpipe walls. For these cases, lower C values may be

justif ied. However, values lower than 80 will not ballowed unless verified by flow and pressure tests. Asolution to the Hazen-Williams formula is given in figure5-1.

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TM 5-814-2/AFM 88-11, Vol. 2

Source: Design and Construction of Sanitary and Storm Sewers WPCF Manual of Practice No. 9by Water Pollution Control Federation, 1970, p. 83.

Figure 5-1. Chart for Hazen-Williams formula.

(2) Velocity. Velocity criteria for force mainsare based on the fact that suspended organic solids donot settle out at a velocity of 2.0 foot per second orgreater. Solids will settle at velocities less than 1.0 fps

and when wastewater pumps are idle. However, avelocity of 2.5 to 3.5 fps is generally adequate toresuspend and flush the solids from the line. Forcemains serving small pump stations, which are designedto operate on an intermittant basis, will be sized toprovide a minimum velocity of 3.5 fps at the peakdischarge rate. For small stations having flows too low

to warrant a minimum velocity of 3.5 fps with one pumpoperating, the design may call for both pumps to beoperated manually once a week for a sufficient period oftime to flush out the line. Larger stations having three

or more pumping units, which operate a major portion ofthe time, will require minimum force main velocitiesranging from 2.0 fps with one pump operating, to 5.0 fpswith several pumps operating. In these cases, it is onlyrequired

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that a minimum velocity of 2.5 to 3.5 fps be providedonce or twice daily. Large pumping stations which servethe entire installation or major portions thereof, andwhich are designed to pump continuously, will usuallyhave a greater number of pumps operating over a widerrange of flowrates. Since the pumping range may varyfrom 7 or 8 to 1, it will generally be sufficient to designfor velocities of 0.5 up to 7.0 or 8.0 fps. Maximumvelocity is set at 10.0 fps.

(3) Slope. The value of S in the formula isequivalent to the kinetic energy loss due to pipe frictiondivided by the length of conduit, or S = Hf /L. Minorenergy losses from fittings and valves will be convertedto equivalent lengths of conduit for use in the formula.Conversion tables for fitt ings and valves can be found instandard hydraulics textbooks. The total kinetic energyloss in a force main will be computed by multiplying theslope of the energy grade line by the total length ofconduit including equivalent lengths, or Hf = S x L.

5-2. Pump analysis and selectiona. Total dynamic head. The head in feet against

which a pump must work when wastewater is beingdischarged is termed the total dynamic head (TDH).The two primary components of TDH in wastewaterapplications are the static discharge head and thekinetic losses due to pipe friction. Velocity and pressureheads are also present, but are usually insignificant.The TDH will be calculated with the use of the Bernoullienergy equation which can be written as follows:

TDH = (Pd /W + V2d /2g + Zd) -(P8 /W +

V

2

8/2g + Z8) + Hf

where

Pd, P8 =gage pressures in pounds per

square foot

Vd, V8 =velocities in feet per second

Zd, Z8 =static elevations in feet

Hf = kinetic energy loss from pipe

friction, fittings, and valves, ascalculated in paragraph 5-1b (3).

w = specific weight of fluid in poundsper cubic foot, and

g = acceleration due to gravity 32.2

ft/sec2)

All head terms are in feet. Subscripts d and 8 representforce main discharge and pump suction, respectively. Inorder to determine hydraulic conditions at the pumpsuction, it will be necessary to write an energy equationfrom the liquid level in the wet well to the pump suctionnozzle.

b. System head-capacity curve. To determine thehead required of a pump, or group of pumps, that woulddischarge at various flowrates into a force main systema head-capacity curve must be prepared. This curve isa graphic representation of the total dynamic head, andwill be constructed by plotting the TDH over a range offlowrates from zero to the maximum expected valueFriction losses can be expected to increase with timethus affecting the capacity of the pumping units andtheir operation. Therefore, system curves well reflecthe maximum and minimum friction losses to beexpected during the lifetime of the pumping units, aswell as high and low wet well levels. The typical set osystem curves will generally consist of two curves usinga Hazen-Williams coefficient of C = 100 (one formaximum and one for minimum static head), and twocurves using a Hazen-Williams co-efficient of C = 140(for maximum and minimum static head). Thesecoefficients represent the extremes normally found inwastewater applications.

c. Pump head-capacity curve. The head that aparticular pump can produce at various flowrates isestablished in pump tests conducted by the pumpmanufacturer. The results of these tests are plotted ona graph to form the pump characteristic curve. Alongwith the discharge head developed, the pumpsoperating efficiency, required power input, and nepositive suction head are generally included on thesame diagram.(1) Efficiency and power input. Pump efficiency is theratio of the useful power output to the input, or brakehorsepower, and is given by:

E = wQ TDH(bhp)(550)

whereE = pump efficiency (100 E =

percent)w = specific weight of fluid in poundsper cubic footQ = pump capacity in cubic feet pe

secondTDH = Total dynamic head, andbhp = brake horsepower

Pump efficiencies usually range from 60 to 85 percentMost characteristic curves will indicate a best efficiencypoint (BEP) at which pump operation is most efficientWhere possible, pumps will be selected to operatewithin a range of 60 to 120 percent of the BEP.

(2) Net positive suction head. When pumpsoperate at high speeds and at capacities greater thanthe BEP, the potential exists for pump cavitationCavitation can reduce pumping capacity and may intime damage the pump impeller. Cavitation occurswhen

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the absolute pressure at the pump inlet drops below thevapor pressure of the fluid being pumped. To determineif cavitation will be a problem, the net positive sunctionhead (NPSH) available will be computed, and comparedwith the NPSH required by the pump. The NPSH is notnormally a problem when discharge heads are less than60 feet. However, when heads are greater than 60 feet,or when the pump operates under a suction lift, or farout on its curve, the NPSH will be checked. The NPSHavailable at the eye of the impeller in feet will becalculated with the following formula:

NPSHA = H8 + Pa/w - Pa/wwhereH8 = total energy head at pump suction

nozzle= P8/w + V2 /2g + Z,

Pa = atmospheric pressure in poundsper square foot absolute, and

Pv = vapor pressure of fluid being

pumped in pounds per square footabsolute

All head terms are in feet.(3) Affinity laws. A set of relationships

derived from flow, head and power coefficients forcentrifugal pumps, can be used to determine the effectof speed changes on a particular pump. Theserelationships are known as affinity laws and are asfollows:

Q1/Q2 = N1/N2H1/H2 = N

21/N

22

P1/P2 = N31/N32whereN1, N2 = pump speeds in revolutions per minute

(rpm)

Q, H and P terms represent pump capacity, dischargehead, and power output respectively, at speeds N1 andN2. These relationships will be used in analyzing

variable speed pump operation in the absence ofmanufacturer's characteristic curves, or wherecharacteristic curves do not show performance at thedesired speeds.

d Pump selection. System analysis for a pumpingstation will be conducted to select the most suitablepumping units which will meet service requirementsand to determine their operating points, efficiencies, andrequired horsepower.

(1) Single pump operation. A system headcapacity curve will be prepared showing all conditionsunder which the pump is required to operate. Thesystem curve will then be superimposed onto a pumphead-capacity curve, or characteristic curve, to definethe pump operating point. The point where the twocurves intersect represents the head and capacity atwhich the pump will operate in the given piping system.

(2) Multiple pump operation. Where two omore pumps discharge into a common header, the headlosses in individual suction and discharge lines will be

omitted from the system head-capacity curve. This isbecause the pumping capacity of each unit will varydepending upon which units are in operation. In order toobtain a true picture of the output from a multiple pumpinstallation, the individual suction and discharge lossesare deducted from the pump characteristic curves. Thisprovides a modified curve which represents pumpperformance at the point of connection to the dischargeheader. Multiple pump performance will be determinedby adding the capacity for points of equal head from themodified curve. The intersection of the modifiedindividual and combined pump curves with the systemcurves shows total discharge capacity for each of the

several possible combinations. Pumps will be selectedso that the total required capacity of the pumpinstallation can be delivered with the minimum level inthe wet well and maximum friction in the discharge linePump efficiency will be a maximum at averageoperating conditions. A typical set of system curveswith pump characteristic curves is shown in figure 5-2.

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Figure 5-2. Typical pump-system curves.

5-3. Wet well designa General . Wet wells will be constructed at

pumping stations for the purpose of storing wastewaterflows prior to pump operation. The storage volumerequired depends upon the method of pump operation,i.e., whether pumps are constant, adjustable or variablespeed. In addition to providing adequate storagevolume, wet wells will be designed to (1) allow for properpump and level controls, (2) maintain sufficientsubmergence of the pump suction inlet, (3) prevent

excessive deposition of solids, and (4) provideventi lation of incoming sewer gases. In smaller stations,bar racks or comminuting devices may be installedwithin the wet well in order to reduce costs. Overflowsfrom wet wells are prohibited in all cases.

b Storage volume. If pumps are of constant oradjustable speed type, the wet well volume must belarge enough to prevent short cycling of pump motors.

For pumps driven by varible speed drives, the storagevolume may be small provided pumping rates closelymatch the incoming flowrates. The volume required fothe wet well will be computed with the following formula:

V = tq/4whereV = required volume in gallons

between start and stop elevationsfor a single pump, or a single

speed step increase for adjustableor variable speed operation

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t = minimum time in minutes of one pumpingcycle (time between successive pumpstarts), or time required for a speed orcapacity change, and

q = pumping capacity, or increment in capacitywhere one or more pumps are operatingand an additional pump is started, or wherepump speed is increased, in gallons perminute

Constant or adjustable speed pumps driven by squirrel-cage induction motors will be designed for minimumcycle times as shown in the following table.

Table 5-1. Minimum pump cycle times.

More size, bhp t, minutesLess than 20 10 to 1520 to 100 15 to 20100 to 250 20 to 30Over 250 as recommended by

manufacturer

The storage volume calculated for small stations

(capacities less than 700 gpm) which utilize two identicalconstant speed pumps, may be reduced one half byproviding a control circuit to automatically alternate thepumps. The storage volume required for variable speedpumps will be based on providing sufficient time for achange in capacity when a pump is started or stopped.When a pump is started, the motor must be ramped tothe desired speed, and the pumps already in operationmust be reduced in speed. The time required for this isusually less than 1 minute. A considerable amount ofstorage is normally available in large sewers whichserve stations utilizing variable speed pumps. Thisvolume may be considered in design by calculating

backwater curves for the various operating levels. Themaximum retention time in the wet well will not exceed30 minutes to prevent septicity.

c. Suction pipe connections. Pump suction pipingwill be selected to provide a velocity of 4 to 6 feet persecond. Pipe should be one or two sizes larger than thepump suction nozzle. Vertical pumps installed in a drywell which is adjacent to the wet well, will be fitted with a90 degree suction elbow, followed by an eccentricreducer and a gate valve. The suction line will beextended through the wall into the wet well, andterminated with either a 90 or 45 degree flared elbow, oran elbow with a flared fitting. The most commonly used

piping arrangements are illustrated in figure 5-3, where Dis the diameter of the flared inlet, and S is thesubmergence depth.Adequate submergence of the suction inlet is critical toprevent air from being drawn in by vortexing. Minimumrequired submergence depths are given in table 5-2 as afunction of velocity. The net positive suction head(NPSH) will also be considered when determining S.See paragraph 5-2c (2).

Table 5-2. Required submergence depth to preventvortexing.

Velocity at diameter D, fps S, feet2 1.04 2.65 3.4

6 4.57 5.78 7.1

Larger, conventional type pump stations will normally beconstructed with wet wells divided into two or moresections, or compartments, so that a portion of thestation can be taken out of service for inspection omaintenance. Each compartment will have individuasuction pipes, and will be interconnected with slide osluice gates. The floor of the wet well will be level fromthe wall to a point 12 to 18 inches beyond the outeedge of the suction bell, and then will be sloped upwardat a minimum 1:1 slope.

5-4. Pump controls and instrumentationa. General . Instrumentation at a pumping station

includes automatic and manual controls used tosequence the operation of pumps, and alarms foindicating malfunctions in the pumping systemAutomatic control of pumps will usually be based on theliquid level in the wet well. Paragraph 4-4 contains adiscussion of the various modes of pump operationpump control systems, and a description of levedetection devices. Manual control of pumps is alwaysrequired in order to operate the pumps duringemergencies, for maintenance purposes, or whenautomatic systems fail. Manual override will be set to

bypass the low level cut-off, but not the low level alarm.b. Selection of control points. A control range of a

least 3.0 feet is required between maximum andminimum liquid levels in the wet well. A minimum of 6inches will be required between pump control pointsused to start and stop successive pumps, or to changepump speeds. For small stations, the control range maybe less, however control points will not be set closerthan 3 inches.

(1) Constant or adjustable speed pumpsrequire simple on-off switches to start or stop pumps, orto change from one speed step to the next.

(2) Variable speed pumps require a more

complex control arrangement. The two basic types olevel control for variable speed operation are (a)variable level, and (b) constant level. For variable levecontrol, a narrow band of control points is established inthe wet well. Pump speed is then adjusted in steps bythe level detection system (usually a bubbler tube) asthe level varies. Pumps operate at maximum

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Figure 5-3. Pump suction connections to wet well.

speeds near the HWL, and at minimum speeds near theLWL. However, pumps are started and stopped by levelswitches. Constant level control is seldom used, butmay be required where a very narrow band of operationis necessary. In a constant level system, one level isset as the control point, and pump speed is adjusted in astepless fashion as the liquid level rises above, or falls

below this point.c. Alarms. Alarms will be provided to signal high

and low liquid levels in the wet well, pump failure, or amalfunctioning speed control system. The high levelalarm will be set above the start point of the last pumpin the operational sequence, but below the start point ofthe standby pump, if used. The low level alarm will beset below the shutoff point of the lead pump. Anemergency, low level pump cutoff will be set below thelow level alarm.

5-5. Surge phenomenaa. Water hammer. Sudden changes in flow and

velocity in force mains can occur as a result of pumpstartup, pump shutdown, power failure, or rapid closingof a valve. These velocity changes can produce largepressure increases or surge phenomena known as wate

hammer. The most severe water hammer conditionsare usually caused by a pump shutdown or powerfailure. An analysis of water hammer will includecalculating the critical time, determining the maximumpressure increase, and selecting a method of control.

b. Critical time. When flow is suddenly changed ina force main, a pressure wave is generated whichrapidly travels the entire length of conduit, and back

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to the point of change. The time required for thisroundtrip is given by:

Tc = 2L/awhereTc = critical time in secondsL = length of force main between

point of flow change and point ofdischarge in feet, and

a = velocity of pressure wave in feetper second

When flow is completely stopped (Q = O) in a timeinterval greater than Tc, the maximum theoreticalpressure increase is not fully developed. However,when flow is stopped in a time interval less than or equalto Tc, the change is said to be instantaneous, and themaximum pressure increase is developed as givenbelow.

c. Maximum pressure increase. The maximumtheoretical pressure increase or surge caused by waterhammer is calculated from the following:

hw = aV/gwherehw = pressure increase in feetV = velocity of f luid in the pipeline

prior to flow change in feet persecond

g = acceleration due to gravity, or32.2 ft/sec2 at sea level, and

a = velocity of pressure wave in feetper second

Some typical values of a are given in table 5-3 below.Table 5-3. Water hammer wave velocities.

Pipe Material a, ft/sec

Asbestos-cement 2700--400Ductile iron 3100--4200Steel 2700--3900Concrete 3300--3800Plastic 1100--1500Fiberglass 1200--1600

d. Methods of control. Whenever a pump is shutdown, or power to the station fails, the pump motor issuddenly cut off. Pump speed along with flow andvelocity in the force main are quickly decelerated bypressure waves, which travel up the pipeline and back inaccordance with Newton's second law of motion. Whenthe velocity is reduced to zero, reverse flow through the

pump would occur if a gravity operated check valve oran automatic control valve were not installed on thepump discharge line, and did not close properly.Reverse flow fully accelerated through the pump couldcause transient flows and pressures well abovemaximum design conditions. A swing check valvewhich stuck open temporarily, and then slammed shutunder these conditions, would re5-8 suit in a largepressure surge as given by paragraph c above. In order

to control and limit these surge phenomena, thefollowing practices will be followed.

(1) Gravity check valves. For simple casesinvolving small to medium sized pump stations withgradually rising force mains (no intermediate highpoints) of less than 1000 feet in length, and with staticdischarge heads of less than 50 feet, a gravity operatedcheck valve will usually be sufficient. Gravity typecheck valves may be either swing checks utilizingoutside lever and weight (or spring) set to assist closureor then may be ball checks. Swing check valves areusually installed horizontally, while ball check valvesmay be either vertical or horizontal. For additionaprotection, a pressure relief valve may be installed inconjunction with check valves to allow reversing flow toreenter the wet wall. Pressure relief valves must bespecially designed for sewage applications. As analternative to relief valves, a hydro-pneumatic tank maybe utilized.

(2) Automatic control valves. In situations

where long force mains are required, pipe profiles musconform to existing ground elevations for economicreasons. This normally will result in high points in theforce main, with the possibility of water columnseparation at the high points in the force main, with thepossibility of water column separation at the high pointsduring pump shutdown or power failure. The pressuresgenerated when these separated columns come to resagainst closed valves or against stagnant columns maybe large, and are again determined by paragraph cabove. In general, where force mains are greater than1000 feet in length or contain intermediate high pointsand where pumping stations are large in capacity, o

static discharge heads are greater than 50 feet, controvalves will be automatically operated (1) cone, (2) plug(3) ball, or (4) butterfly valves. Normal operation othese valves upon pump shutdown, is to slowly close thevalve while the pump continues to run. When the valveis closed, a limit switch then stops the pump motor. Onpower failure, an emergency hydraulic or other typeoperator closes the valve slowly. The time of valveclosure is of utmost importance. Valves should be halclosed when the velocity in the force main has droppedto zero. The time required to reach zero velocity can becalculated with the following formula:

t = LV/g Hav

wheret = time in secondsL = length of force main in feetV = velocity of fluid in pipeline in fee

per second, andHav = average decelerating head

including pipe friction in feet

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The types of valve operators most often utilized arehydraulic, electric and pneumatic. Valves and operatorsspecified for use will be fully adjustable for closure timesranging from t to 4t minimum. In some large pumpingstations, the use of automatically controlled valvesalone will not be sufficient. Extremely long force mains(over 1 mile) may require very long valve closing times,and thus result in excessive backflow to the wet well andreverse rotation of the pump and motor. To solve theseproblems, a pump bypass with surge relief valve willgenerally be required. Valves used for surge relief willbe automatically controlled cone or butterfly valves,similar to the pump discharge valves. Normal operationupon pump shutdown now will require the pumpdischarge valve to be fully closed when the velocity hasdropped to zero. The surge relief valve will be fullyopen allowing backflow to enter the wet well at areduced rate. As before, the relief valve must closeslowly to avoid water hammer. Most cases involvinglarge pump stations with long force mains, which contain

several intermediate high points, will be too complex tosolve by hand using conventional methods such asgraphical solutions, arithmetic integration, or waterhammer charts. Many computer programs are now

available for water hammer analysis, and arerecommended for use in those instances.

5-6. Screening and comminuting devicesCentrifugal pumps are susceptible to clogging by ragstrash, and other debris normally found in wastewaterTo protect pumps from clogging, equipment will beinstalled to screen or cut up these materials prior topumping. Small pump stations with capacities of lessthan 200 gpm, including grinder pumps and pneumaticejectors, are exempt from this requirement. The typesof equipment to be used include bar racks, screens, andcomminutors which are installed in the wet well, or in aseparate influent channel. The design of these facilitiesis covered in TM 5-814-3/AFM 88-11, Vol. 3. At mosmedium to large sized pump stations, the use ofmechanically cleaned bar screens or comminutors wilbe required. However, at smaller stations in remoteareas, manually cleaned racks may be more feasibleThe smallest clear opening between bars is normally 1

inch, and spacings of less than 3/4 inch will not bepermitted. All electrically operated equipment in wewells will have explosion proof motors.

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CHAPTER 6PIPING, VALVES AND APPURTENANCES

6-1. Pipe materials, fittings and jointsa. General . Factors to be considered in the

selection of pipe materials and piping systems for forcemains are: -Flow characteristics or friction coefficient.-Life expectancy and history of use.-Resistance to scour and abrasion.-Resistance to acids, alkalis, high temperature

or corrosive wastes, and corrosive soils.-Ease of handling and installation.-Physical strength and pressure ratings.-Joint watertightness and ease of installation.-Availability of pipe in required sizes, strengths,

etc.-Availability of fittings, connections and

adapters.No pipe manufactured is suitable for all installationrequirements and conditions. The pipe materialscovered in this paragraph are the ones most often usedfor force mains carrying sanitary and industrial wastes.Each type of pipe will be evaluated to determine itssuitability for the particular design. Where iron orconcrete pipe are to be considered, special attention willbe paid to subsurface and soil conditions. Thecharacteristics of the soil in which a pipe is placed affectthe rates of corrosion, with the most corrosive soilsbeing those having poor aeration and high values ofacidity, electrical conductivity, dissolved salts, andmoisture content. The relative potential for corrosionmay be estimated by evaluating the degree of corrosion

of existing metallic or concrete pipelines previouslyburied in the soil. Facili ty engineer personnel willnormally have knowledge of these matters. When thisinformation is not available, or is nonconclusive,resistivity tests of the soil will be conducted and resultsevaluated as required in TM 5-811-4/AFM 88-11, Vol.4. Pipe materials found inappropriate for use will bedeleted from the project specifications.

b Ductile iron. Ductile iron (D.I.) pipe is suitablefor force mains used at pumping stations andwastewater treatment facil ities. Special uses includeriver crossings, pipe located in unstable soil, highwayand rail crossings, and piping installed above ground.

D.I. pipe is susceptible to corrosion from acid wastesand aggressive soils. Cement linings, bituminouscoatings or polyethelene linings are usually provided forinterior protections. For extremely corrosive soils, apolyethelene encasement is recommended for externalprotection. Pipe is available in 3-inch through 54-inchdiameters, and with mechanical, push-on or flanged

joints. Flanged joints are restricted to interior piping.

The Handbook of Ductile Iron Pipe, Cast Iron Pipepublished by the Cast Iron Pipe Research Association

(CIPRA) will be used for guidance in designing ductileiron force mains.c. Steel . Steel pipe may be used for force mains

when lined with cement mortar or bituminous materialsto provide internal protection. A bituminous coatingmust be applied for external protection also. Lined andcoated steel pipe is available in diameters 6-inchthrough 144-inch. Galvanized steel pipe will be used fosmall diameter force mains and pressure sewers from1/4-inch to 4-inch in size. Joints for steel pipe less than6-inch will be threaded. Pipe 6-inch in diameter andlarger will have mechanical, push-on, or flanged jointsThreaded and flanged joints will be used only for interiorpiping. Steel pipe will be installed in accordance withthe manufacturer's recommendations, and Manual NoM11-Steel Pipe Design and Installation published by theAmerican Water Works Association (AWWA).

d. Concrete. Concrete pressure pipe will generallybe used where high strength or large diameter forcemains are required. The type of cement used foconcrete will be selected in accordance with paragraph6-5a of TM 5-814-1/AFM 88-11, Vol. 1. Pretensionedreinforced concrete pressure pipe is available indiameters 10-inch through 42-inch, prestressed concretepressure pipe in diameters 16-inch through 144-inchand reinforced concrete pressure pipe in diameters 24-inch through 144-inch. Each type utilizes bell and spigo

joints with rubber gaskets. The Concrete Pressure PipeManual, Manual No. M9 published by the AmericanWater Works Association (AWWA) will be used fordesign of force mains.

e. Asbestos-cement. Force mains constructed oasbestos-cement (A.C.) pressure pipe are durable andlight in weight. However, A.C. pipe is affected bycorrosive wastes and aggressive soils, and must beprovided with plastic linings for protection. The type omaterial required for A.C. pipe will be type II inaccordance with ASTM C 500. Pipe is available indiameters 4-inch through 42-inch, and will be joined bymeans of couplings utilizing rubber gaskets. Design o

A.C. force mains will conform to the manufacturer'srecommendations.

f. Plastic . Characteristics which make plastic pipehighly desirable for force main use include highcorrosion resistance, light weight, and low coefficient offriction. Disadvantages include the possibility oexcessive pipe wall deflections when installed

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improperly or subjected to high temperature wastes, andchemical breakdown caused by prolonged exposure tosunlight. The following types of plastic pipe are suitablefor use:

(1) Polyvinyl chloride (PVC). PVC pipe isavailable in diameters 4-inch through 12-inch, and withscrew, push-on, or solvent weld joints.

(2) Polyethylene (PE). PE pipe may be usedin diameters 11/2-inch through 48-inch. Pipe jointsconsist of mechanical, flanged, or heat fusion type.

(3) Polypropylene (PP). Pipe diametersavailable with polypropylene pipe are 1/2-inch through4-inch. All pipe will be joined by heat fusion methods.Screwed and flanged joint pipe will not be usedunderground. Manufacturer's recommendations will beused in design of plastic pipe, in addition to theHandbook of PVC Pipe-Design and Constructionpublished by the Uni-Bell Plastic Pipe Association.

g. Fiberglass. Fiberglass pipe provides a goodalternative for use in large diameter force mains. High

structural integrity, low pipe friction coefficient, and ahigh resistance to internal/external corrosion and to hightemperature wastes, are important properties offiberglass pipe. The following types of fiberglass pipemay be used:

(1) Reinforced thermosetting resin pipe(RTRP). RTRP pipe may be installed in diameters of6inch through 144-inch. Jointing systems for RTRP pipeinclude bell and spigot, flanged, or special mechanicaltype couplings. Elastomeric gaskets are used to provideflexible joints.

(2) Reinforced plastic mortar pipe (RPMP).Pipe diameters available for RPMP pipe range from 8-

inch to 144-inch. Pipe joints are made with groovedcouplings or bell and spigot joints utilizing rubbergaskets. Design of fiberglass force mains will follow themanufacturer's recommendations.

h. Interior piping. Pump suction and dischargepiping inside the station will normally be ductible iron orsteel. However, other pipe materials covered in thisparagraph are not precluded from use. Pipe, fittings and

joints serving as force mains will be selected towithstand the maximum internal operating pressures,including transient surges, as determined in chapter 5.The project specifications will indicate the appropriatepressure class and rating for each pipe application.

6-2. Valves and appurtenances. The use of valvesin wastewater pumping can be divided into the followingcategories:

a. Isolation or shutoff valves. Where the need toisolate pumps or part of the piping system occurs,manually operated shutoff valves will be used. Gatevalves or butterfly valves generally serve as shutoffvalves, however ball valves or plug valves may also beused. Shutoff valves are required on the suction anddischarge sides of all pumps.

b. Surge control valves. To protect pumps andpiping from surges caused by pump shutdown or powefailure, gravity operated swing check or ball checkvalves, or automatically operated cone, plug, ball obutterfly valves will be installed in the pump dischargeline. The operation of surge control valves is discussedin paragraph 5-5.

c. Blowoff valves. A valve outlet installed at thelow point in a force main, and arranged to drain or flushthe pipeline, is termed a blowoff. Normally, blowoffs wilbe required only on long depressed sections of forcemain, or where an accumulation of solids is likely tooccur. Blowoff connections will be installed in manholesor valve structures, and will be protected againsfreezing. A means of discharging to a suitable locationmaterials flushed from the system will be provided. Thepipe size of the outlet connection should coincide withthe size of the force main.

d. Air valves. Air valves will be installed at highpoints in force mains for the purpose of admitting and

releasing air. When the pipeline is taken out of servicefor draining, flushing and filling operations, a manuallyoperated valve will be adequate. However, where aipockets or pressures less than atmospheric are likely tooccur with the pipeline in service and under pressureautomatic air release and/or air vacuum valves will beused. Manual valves can also be used with the pipelineunder pressure by leaving the valve partially openAutomatic valves are not recommended due tomaintenance problems, and should be used only whereabsolutely required. Automatic valves will be of a typespecially designed for sewage, and will be provided withbackflushing connections. All valves will be installed in

a manhole or valve structure with adequate drainageand protection against freezing.

6-3. Installationa. Structural design. Structural design of force

mains will be in accordance with the requirements setforth for sewers in chapter 5 of TM 5-811/AFM 88-11Vol. 1.

b. Thrust restraint. Force mains will be restrainedto resist thrusts that develop at bends, tees, wyeconnections and plugs in the pipe. The magnitude osuch forces can be calculated with the use of formulasfound in standard hydraulics textbooks. Required

methods of restraint will consist of tie rods and clampsor concrete thrust blocks, and will be designed inaccordance with Section VI of the CIPRA Handbook ofDuctile Iron Pipe, Cast Iron Pipe.

c. Depth of cover. Force mains will be installedwith sufficient depth to prevent freezing, and to protectthe pipe from structural damage. A minimum

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CHAPTER 7PUMP STATION COMPONENTS

7-1. Construction requirementsa. Station configuration. The space requirements

of pumps, piping and equipment, along with the storagevolume required in the wet well, will be carefullydetermined so that the proper size, shape andconfiguration of the pumping station can be selected.The size and shape of the station will often be dictatedby equipment other than pumps, such as bar screens,comminutors, grit collectors, etc. Rectangular or squarestructures normally have more usable interior spacethan circular ones, and will be employed wheneverpossible in the design of medium to large sized pumpingfacil ities. However, where the below ground portion ofthe station must be made deep to accommodateincoming sewers, and where foundation conditions arepoor, circular caisson type structures will be required iflateral earth pressures are excessively high. Factoryassembled or package type stations will generally becircular in design, and will be anchored to base slabswhere warranted by subsurface conditions. Pumpstations located in cold regions or in seismic zones willrequire special design considerations.

b. Designing for operation and maintenance. Thedesign of medium to large sized, conventional typepumping facilities will include adequate floor openings,doorways, or access hatches for the installation,removal, and replacement of the largest items ofequipment. Interior dimensions in the dry well willprovide a minimum clearance of 4 feet between

adjacent pump casings, and a minimum of 3 feet fromeach outboard pump to the closest wall. Other majoritems of equipment will be provided similar spacing. A7-foot minimum clearance between floor and overheadpiping will be maintained where practicable. Smallerpackage type stations will be furnished with necessaryaccess openings for removal of pumps and equipment,however interior dimensions and clearances willgenerally be less than for field erected stations. Wetwells for medium to large sized stations will be dividedinto two or more compartments to facilitate cleaning andrepairs. Wet wells for all stations will have no length,width or diameter smaller than 4 feet. Eye bolts or

trolley beams will be provided in smaller stations, andoverhead bridge cranes in large stations, for hoistingand removing equipment from mountings. Stairs will beprovided in medium to large sized stations so thatpersonnel may inspect and maintain equipment.Smaller stations, except those utilizing submersiblepumps, will require the use of vertical safety ladders. Asuitable means will be provided to service and maintainall equipment. A floor drainage system will be providedin the dry well, and throughout the superstructure, for

collection of wash down, seepage, and stuffing boxleakage. These wastes will be piped or conveyed to the

wet well, either by gravity or by sump pump. Openingsto the wet well and dry well through the main floor of thestation will be above the maximum flood level, or wilotherwise be protected from flooding.

c. Materials of construction. Large to mediumsized, conventional type stations will ordinarily beconstructed of reinforced concrete. The above groundportion of the building may be of masonry, wood ormetal panel construction. The requirements oDepartment of Defense (DOD) Construction CriteriaManual 4270.1-M will be followed in designing for fireresistive structures. Small package type stations wilgenerally be manufactured of steel or fiberglass, withseparate wet wells constructed of precast concrete ofiberglass manhole sections. Where steel structures areused, cathodic protection or appropriate corrosioncontrol measures will be provided for the undergroundsteel shell in conformance with TM 5-811-4 or AFM 88-45. Alternatively, steel structures may be protected by aconcrete or gunite coating where proof can be furnishedby the manufacturer of satisfactory design life. Alstructures will be designed to withstand flotation.

d. Personnel safety. Guards will be placed on andaround all equipment where operators may come incontact with moving parts. Railings will be requiredaround all floor openings, and along platforms orwalkways, where there is a danger that personnel may

fall. Warning signs will be placed at all hazardouslocations. Rubber mats will be provided in front of alelectrical equipment where the potential exists foelectrical shock. Adequate lighting and ventilation wilbe provided as required in paragraphs 7-2 and 7-3. Inattended stations where the possibility exists for toxicexplosive, or otherwise hazardous atmospheres, propedesign for personnel safety will be in conformance withchapter 19 of TM 5-814-3/AFM 88-11, Vol. 3. Designfor fire protection will be in accordance with DODManual 4270.1-M and TM 5-812-1. Wastewatepumping stations will be classified as light hazardindustrial type occupancies.

7-2. Heating and ventilationa. Heating. All pumping stations subject to

possible freezing will be supplied with automaticallycontrolled heaters in the equipment areas. For

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tubes, venturi meters, magnetic and ultrasonic flowmeters.

7-7. Paints and protective coatings. The use ofpaints and protective coatings at wastewater pumpingstations will be in accordance with Water PollutionControl Federation (WPCF) Manual of Practice No. 17.A thorough investigation will be made in the design ofprotective coating systems. Paint materials selected willbe appropriate for the types of surfaces being protected,both submerged and nonsubmerged. Coating systemswill be designed to resist corrosion from the wastesbeing handled, and from gases and vapors present,taking into consideration the expected temperature and

humidity variations within the station. Coating systemswill consist of adequate surface preparation, and theapplication of prime and finish coats using compatiblematerials as recommended by the coatingsmanufacturer. All pumps and equipment will receiveprotective coatings in conformance with themanufacturer's recommendations. All ferrous materialsincluding galvanized surfaces will be protectedParticular care will be taken to protect welds and threadsat connections. Package type stations will be shipped tothe construction site with factory applied paints andcoatings sufficient for the required service.

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BIBLIOGRAPHY

Brater, E. F. and King, H. W., Handbook of Hydraulics, 6th ed., McGraw-Hill, New York, 1976.Hicks, T. G. and Edwards, T. W., Pump Application Engineering, McGraw-Hill, New York, 1971.Joint Committee of the Water Pollution Control Federation and the American Society of Civil Engineers, Wastewate

Treatment Plant Design, WPCF Manual of Practice No. 8, Washington, D.C., 1977.Joint Committee of the Water Pollution Control Federation and the American Society of Civil Engineers, Design andConstruction of Sanitary and Storm Sewers, 2nd ed., WPCF Manual of Practice No. 9, Washington, D.C., 1970.

Metcalf & Eddy, Inc., Wastewater Engineering: Collection and Pumping of Wastewater, McGraw-Hill, New York, 1981.Morris, H. M. and Wiggert, J. M., Applied Hydraulics in Engineering, 2nd ed., Ronald Press, New York, 1972.Water Pollution Control Federation, Design of Wastewater and Stormwater Pumping Stations, WPCF Manual of Practice

No. FD4, Washington, D.C., 1981.

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The proponent agency of this publication is the Office of the Chiefof Engineers, United States Army. Users are invited to sendcomments and suggested improvements on DA Form 2028(Recommended Changes to Publications and Blank Forms) direct

to HQDA (DAEN-ECE-G), WASH D.C. 20314-1000.

By Order of the Secretaries of the Army and the Air Force:

JOHN A. WICKHAM, JR.General, United States Army

Official: Chief of Staff

DONALD J. DELANDROBrigadier General, United States Army

The Adjutant General

CHARLES A. GABRIEL, General USAFOfficial: Chief of Staff

JAMES H. DELANEY, Colonel, USAFDirector of Administration

Distribution:Army: To be distributed in accordance with DA Form 1234B, requirements for TM 54800 Series: Engineering

and Design for Real Property Facilities.Air Force: F

*U.S. GOVERNMENT PRINTING OFFICE: 19-61U11001M/401-M


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