Fire Pump Theory Flashcards
What is a Piston Pump?
A positive-displacement pump using one or more reciprocating pistons to force water from the pump chambers.
Where are Piston Pumps used?
Although the positive displacement has been replaces by the centrifugal pump as the main pumping unit on the fire apparatus, positive displacement pumps continue to serve a vital role on modern apparatus because of their ability to pump air and foam. In this capacity, they are used as priming devices to get water into the centrifugal pump during drafting operations. By removing air trapped in the centrifugal pump, water is forced into the pump my atmospheric pressure.
What are the different types of pumps used in the fire department?
1) Piston Pump
2) Rotary Pump
3) Rotary Vane Pump
4) Centrifugal Pump
What is a Centrifugal Pump?
Pump with one or more impellers that rotate and utilize centrifugal force to move the water. Most modern fire pumps are of this type.
What are the three main factors influencing a centrifugal fire pump’s discharge pressure?
- Amount of water being discharged
- Speed at which the impeller is turning.
doubling the speed will result in 4 times the pressure - Pressure of water when it enters the pump from a pressurized source (hydrant, relay, etc.)
Unable to get a reading on the pressure gauge when the pump is put in service. Symptom: Green light is on, no MPH reading registers on the speendometer.
1) Vehicle clutch is not engaged
2) Road transmission is not in position for pump operation. Transmission selector is in wrong position.
Unable to get a reading on the pressure gauge when the pump is put in service. Speedometer reading is for pump operation. All indications are correct and the rpm reading is as specified.
1) There is no water in pump. Check water supply, Primer may need to be operated to eliminate air in the main pump.
2) Gauge is defective. Pressure may be there but not reading on the master pressure gauge. Open a gate valve to a capped discharge and look for pressure reading on individual gauge.
Pump will not develop sufficient pressure. The rpm reading is normal when compared with the UL plate. Symptoms 1-5
1) Two-stage pump: pump transfer valve is in the wrong position, The transfer valve should be in series anytime more then 200 psi is needed.
2) Swing check valve may be leaking if pump is in the series position
3) Transfer valve is not completed its travel and is only partially operated. May need to manually override controls.
4) Automatic transmission not staying in pumping gear lockup and is downshifting as load increases,.
5) Wear on the clearance rings inside the pump causing excessive slippage.
Pump will not develop sufficient pressure. The rpm reading is normal when compared with the UL plate. Symptoms 6-8
6)Relief valve is operating and the indicator light is on. Relief valve pressure adjustment is set too low.
7) The indicator light shows that the relief valve is closed. May be stuck open or not properly seated.
8)Engine rpm cannot be raised to the value required by the UL plate.
Flow requirements may be exceeding the capacity of the pump. Series is (50% capacity at 250psi, and 70% at 200psi of net pump pressure)
Throttle linkage may be stuck. May be able to override using the accelerator.
Severe engine overheating can reduce the power available to drive the pump. Check engine temp, adjust auxiliary cooling valve. Check level of the coolant
The pump is unable to supply its rated capacity and the intake gauge registers or has a positive pressure indicated.
1) Blockage in the waterways of the pump. An object lodged inside the impeller can reduce the capacity. Back-flush the pump by connecting a supply line to the highest discharge outlet and opening the large intake fittings.
2) Wear in the pump, usually the clearance rings or relief valve
The pump is unable to supply its rated capacity and the intake compound gauge is registering a high vacuum and the discharge pressure gauge is fluctuating (cavitation.)
1) Blockage of the strainer at the intake fitting of the pump. Disconnect the intake line and clean any accumulated debris from the strainer.
2) Inadequate water supply or supply lines. Connect an additional supply line to the intake pump. Reduce the amount of discharge lines being supplied. Lower the discharge pressure to reduce the amount of water flowing through the lines.
The pump is overheating while in operation. Discovered by overheating warning light or physical observation
1) Inadequate flow through the pump while operating under pressure. Open booster cooling valve or circulator valve to Tank. Open the tank fill valve if it is connect to the discharge side of the pump. Use booster line to maintain a minimum flow of water while pumping.
2) Excessive throttle on relief valve-equipped pumps, Reduce engine rpm
When operating from draft, what are the common reasons the pump will not prime and you are unable to get water into the pump through the hard suction hose. No vacuum reading is registered on the intake compound gauge?
1 Drain valve left open.
2 Intake valves left open or caps not airtight
3 booster line cooler valve or circulator left in OPEN
4 Intake relief valve may be leaking.
5 Suction hose connections are not airtight
6 Pump packing is too loose and leaking air
7 Not operating the primer long enough to get rid of air
8 Tank to Pump valve not sealing with an empty tank
9 Engine rpm is too low
10 No oil in the reservoir for the priming pump.
