Fire Pump Theory

Fire Pump TheorySugar Land Fire Department

Driver/Operator—Pumper AcademySpring 2003

Positive Displacement Pumps

Have largely been replaced by centrifugal pumps for use as the main fire pump on modern apparatus.Can pump airOperate on the hydraulic law that when pressure is applied to a confined liquid, the same outward pressure is transmitted outward and equally in all directions within the liquidCome in two basic types; piston & rotary

Multicylinder, High Pressure

Are still in use today to provide pressures up to 1,000 psi for high pressure fog lines.Are commonly used in wildland fire fightingRequire a dependable relief valve; if discharge flow is interrupted, pressures quickly build to dangerous levels

Rotary Gear PumpsTotal amount of water than can be pumped dependent on gear pocket size and rotation speedRequire a pressure relief valveAre very susceptible to damage from normal wear and tearAre very susceptible to damage from pumping contaminated water

Rotary Vane PumpsNot as susceptible to damage from normal wear and tear as are rotary gear and piston typesAutomatically adjust: when surface of a vane in contact with casing becomes worn, centrifugal force causes it to extend further, thus automatically maintaining a tight fit.

Changeover– Changeover is the process of switching the transfer valve

on the pump between pressure and volume.– Fire service changeover rule of thumb—leave transfer

valve in the pressure position until it is necessary to supply more than ½ the rated volume capacity of the pump.

– Manufacturer’s changeover recommendation—leave transfer valve in pressure position until it is necessary to flow more than 2/3 the rated volume capacity of the pump

Changeover– Consult operator’s manual for recommended flow rate at

which transfer should occur– Consult the operator’s manual for the maximum net pup

discharge pressure at which the transfer valve can be operated

– Because there may be a slight interruption to fireground operations when changeover occurs, coordinate changeover with attack crews so that line are not shut down at critical times.

Changeover– Try to anticipate the requirements that will be placed on

the pumper as the fire fighting operation progresses, and have the transfer valve in the proper position from the start.

– If there is any question as to the proper operation of the transfer valve, it is better to be in parallel than in series

– Know that there is a built-in safeguard that makes it impossible to accomplish manual transfer while the pump is at high pressure on many two-stage pumps, particularly on older pump models.

Changeover– Use special care when operating the high-pressure

power-activated transfer valves found on newer pumps. – Whenever possible equip the power control on power

activated transfer valves with some sort of manual override to allow the transfer to be operated should the power equipment fail.

Pump WearA very close tolerance must be maintained between the pump casing and the hub of the impeller to prevent water from escaping back into the intakeImpurities in the water supply accelerate pump wear by acting like sandpaper in wearing down metal surfaces.As the gap between the pump casing and impeller hub increase through wear, greater amounts of water escape to the intake

Pump WearTo restore pump capacity and maintain the proper spacing between the pump casing and impeller hub, the driver/operator should replace the wear rings.If the impeller hub is also worn down, it is possible to install smaller wear rings to compensate for the smaller size and maintain clearance.Ensure that some water is running through the pumps at all times to prevent overheating and possible pump damage.

Pump WearCheck the pump temperature by placing a hand on the direct pump intake pipe; if it is warm to the touch, open a discharge or circulator valve.It is best for the driver/operator not to run the pump with the discharges closed for any extended period; if no water is expected to be discharged for an extended period of time, disengage the pump until it is needed.

Pump Mounting & Drive Arrangements

Pump Mounting & Drive Arrangements

Pump Piping & ValvesIntake Piping– Pumpers with a capacity of 500 gpm should be able to

flow at least 250 gpm from the booster tank.– Pumpers with capacities greater than 500 gpm should be

able to flow at least 500 gpm– Many pumpers today are equipped with tank-to-pump

lines as large as 4” in diameter– Mobile water supply units may have multiple small-

diameter tank-to-pump lines.

Pump Piping & Valves– The lines to all modern pumps are equipped with check

valves that make it impossible to fill the tank through the pump by opening the tank-to-pump valve

– To prevent air from being trapped in the pump during priming operations, all intake lines to centrifugal pumps are normally located below the impeller eye, and no part of the piping is above this point.

– The primary intake is large-diameter piping and connections.

Pump Piping & Valves– Large diameter intake piping is round where the hose

connects to it but tapers, as it nears the pump, to a square shape to eliminate the vortex that occurs in round piping.

– Additional large-diameter intake may be piped to the front or rear of the apparatus.

– Front and rear intakes should be considered auxiliary intakes.

– Pumps with a capacity of 1,500 gpm or greater may require more than one large intake connection

Pump Piping & Valves– Additional intake lines, usually gated, are provided for use

in relay operations or anytime water is being received through small-diameter supply lines.

– Most small-diameter intake openings are threaded for 2 ½ hose couplings

– If 2 ½ pipe contains 90 degrees bends or T-fittings, friction loss may limit flow to 250 gpm

– 3” pipe is capable of flowing as much as 450 gpm if care is given to the fittings.

Pump Piping & Valves– Must be enough 2 ½ or larger discharge outlets to flow

rated capacity of pump– Apparatus with a rated pump capacity of 750 gpm or

greater must be equipped with at least two 2 ½” discharges

– Apparatus with a rated pump capacity less than 750 gpm are required to have only one 2 ½” discharge

– Discharges larger than 2 ½” may not be located directly on the pump operator’s panel.

Pump Piping & Valves– Apparatus may be equipped with 1 ½, 1 ¾, and 2”

discharges– Discharges 2” and smaller must be supplied by at least a

2” piping– To prevent movement, the discharge locking ball valve

should be kept locked when the discharge is open.– All valves are designed to be easily operated at pressures

up to 250 psi.

Pump Piping & ValvesTank Fill Lines– Should be located on discharge side of pump– Allows tank to be filled without making any additional

connections– Provides a means of replenishing the water carried in the

tank– Requires a tank fill line with a diameter of at least 1” on

apparatus with water tanks less than 1,000gals per NFPA 1901

Pump Piping & Valves– Requires a tank fill line with a diameter of at least 2” on

apparatus with water tanks 1000gals or larger Per NFPA 1901

– Can be used to circulate water through pump to prevent overheating when no lines are flowing

Pump CoolingTank Fill LineCirculator ValveBooster line cooling valveWaster/dump line

Valves Push/pull Handle (T-handle)

Allows easy operation of valve under pressureAllows driver/operator to set precise pressure values when adjusting individual linesCan be mounted in a position remote from pump panel.Can usually be locked in any position with a 90 degree twist of the handleMust be pulled straight out to prevent binding the shaftUsed to actuate ball valves

Valves Quarter-Turn Handle

Has simple mechanical linkage mounted directly on valve stemOpens and closes valve with 90 degree movement of handleMay be locked by raising or lowering the handle, but newer versions lock automatically when handle is released or when handle is rotated clockwiseUsed to actuate ball valves and butterfly valves

Valves Toggle Switch

Found on newer apparatusVisually display a readout of how far the valve is openedIndicated through panel markings which direction to operate the switch to open and close the valveUsed to actuate ball valves

Valves Handwheel—most commonly used to actuate

gate valves

Pump Drain and Bleeder Valves

Drain Valves– Provides a way for driver/operator to relieve pressure from hoseline

after discharge valve and nozzle have been closed– Useful when hose has not been bled off and is a great distance from

apparatus– Allows for draining and disconnecting unused lines even when the

pump is still in service– Allows for all water to be removed from the system in freezing

climates– When connected to master drain valve, pump and piping can be

drained in one operation.

Pump Drain and Bleeder Valves

Bleeder valve on gated intake– Allows air to be removed from system before it enters fire

pump– Makes it possible to change over to the supply line without

interrupting fire streams: 1. Wait until all air is evacuated form line and bleeder valve is

discharging a steady stream of water 2. Close the drain valve 3. Open the intake valve 4. Close the tank-to-pump valve

Automatic Pressure Control Devices

Discharge pressure relief valve—relieves excess pressure within the pump discharge

Automatic Pressure Control Devices

Intake pressure relief valve—prevents damage to pump and discharge hoselines when valves/nozzles are closed too quickly

– Integral pressure relief valve—part of pump intake manifold; relieves pressure on intake side of pump

– Screw-on pressure relief valve—add-on device screwed onto pump intake connection; relieves pressure on intake side of pump

Pump Panel Instrumentation

NFPA 1901 requires:– Master pump intake pressure indicating device– Master pump discharge pressure indicating device– Weatherproof tachometer– Pumping engine coolant temperature indicator– Pumping engine oil pressure indicator– Pump overheat indicator– Voltmeter– Pump pressure controls

Pump Panel Instrumentation

– Pumping engine throttle– Primer control– Water tank to pump valve– Tank fill valve– Water tank level indicator

Pumping Engine Throttle Text book page 238

Figure 10.78Figure 10.79

Primer Control Textbook page 239

Figure 10.80