Chapter 10- Pump Theory Flashcards
What is the desired rpm for transfer case gear driven primers?
1000 to 1200 rpm.
It is best to activate the primer at idle speed and increase throttle to desired rpm’s to minimize wear on the mechanical clutch pack.
The Master Intake Gauge is also known by what two names?
- Compound Gauge
2. Vacuum Gauge
The Compound Gauge is calibrated for positive and negative pressures. What are these ranges?
Positive: 0 to 600 psi
Negative: 0 to 30 inches Mercury
What is another name for the throttle knob control?
Vernier
What are the three factors that influence a centrifugal pump’s discharge pressure?
- Amount of water being displaced
- Speed at which the impeller is turning
- Pressure of water when it enters the pump from a pressurized source (hydrant, relay)
What is the relationship between volume of water flowed and pressure?
More flow = Less pressure
What is the relationship between the increase in impeller speed and the increase in pressure?
The increase in pressure is approximately the square of the increase in impeller speed. Impeller times 3 = Pressure times 9
In multi-stage centrifugal pumps, each impeller is capable of delivering its rated pressure while flowing what % of rated capacity?
50%
At what pressure does the pump receive its maximum flow rating?
150 psi
Higher pressures result in decreased volume.
When a multi-stage centrifugal pump is in ‘Pressure’, water from the intake is delivered through one impeller at a time. Since only one impeller is delivering water to the discharge, what % of volume capacity is being supplied?
50% to 70% of the volume capacity
In multi-stage centrifugal pumps, the transfer valve should stay in the pressure position until it is necessary to supply what percentage of the rated volume capacity?
50% or more
What happens to the pressure when switching from volume to pressure mode? When switching, what is the recommended max pressure?
The pressure will double when switching from volume to pressure. The max pressure for switching should be 50 psi.
The pressure in the volute is much higher than the intake side of the pump so a very close tolerance must be maintained between the pump casing and the hub of the impeller. What is this distance/difference?
Usually limited to 0.01 inches or less
What is the first indication of pump wear and reduction in the pump’s effectiveness?
Higher rpm’s needed to pump the rated capacity?
What is the best defense against overheating in the pump?
Ensure that some water is moving through the pump at all times.
