Pit Document Flashcards
From the Cab, How can you tell if you are in pump?
- Hear and Feel the pump engage
- The “Pump Engaged” and “OK to pump” lights are on
- Speedometer registers 10-15mph
- With slight acceleration the apparatus will not move
At the Pump, how can you tell you are in pump?
- The light on the pressure governor turns on
- The second from the left Pump panel light turns on
- The flashing red light near the driver’s side rear passenger step light turns off
- The pressure governor can be switched to pressure
- As engine speed increases there is a corresponding increase in pressure with a primed pump
If the air actuator in the cab fails how do you engage the pump?
If the air actuator in the cab fails, the pump can be shifted manually. Assuming that the transmission is in neutral, the parking brake has been set.
- The in-cab pump shift control is in the “Pump” position
- Push the manual shift control rod on the pump panel in for pump position.
- The “ pump engaged” light should come on.
- Shift the truck transmission into pumping gear and the “ok to pump” light should come on.
Explain how a centrifugal pump works?
A centrifugal pump does not use positive displacement action to force water from the pump; rather it depends on the velocity of the water produced by centrifugal force to provide the necessary pump discharge pressure for effective operation
Explain the path a drop of water would take through the centrifugal pump?
A drop of water enters a centrifugal pump through the eye of the impeller. Water then comes in contact with the vanes of the impeller and is thrown by centrifugal force to the outside of the impeller. Water then travels through a gradually increasing cross-sectional area known as the volute. The gradually increasing size of the waterway reduces the velocity of the water, thus enabling the pressure to build up as the drop exits the discharge of the pump.
Explain the principles of the pressure governor?
The pressure governor system consists of a computer, pressure transducer, control panel, throttle actuator, and a rpm counter. The computer (DDEC II Electric Control Module) is located on the engine, and a pressure transducer on the discharge side of the fire pump. The transducer senses pump discharge pressure and sends a signal to the ECM. The ECM will control the pressure by regulating the engine RPM.
What is the governed speed for a Pierce Quantum
2175 rpm
Explain the principles of a pressure relief valve?
When the components of the relief valve are activated by
turning on the four-way valve, water from the discharge side of the pump passes through the strainer and fills the pressure chamber. The chamber is held closed by the adjustable spring loaded pilot valve. With excess pressure on the discharge side of the pump, it will overcome the spring-loaded pilot valve causing
it to open. Water from the pressure chamber, that was helping to hold the main relief valve closed, is diverted through the dump line back to the intake side of the
pump. This causes the main relief valve to open and bypass water from the discharge to the intake side of the pump relieving the excess pressure.
What are the main components of the pressure relief valve?
The main components of the pressure relief valve consist of a: four-way valve, a strainer, a spring-loaded pilot valve, a pressure chamber, a dump line, and the main relief valve.
Define cavitation
Cavitation is basically pumping more water out the pump than you have coming in. For instance, operating a pump at excessive speed, too high of an intake lift, restricting the intake, or any other factor that causes the pressure on the liquid to fall below it’s vapor pressure causes cavitation. When this condition exists, the liquid vapor released in low- pressure regions of the pump forms bubbles. The bubbles are carried into the high -pressure sections of the impeller, where they collapse with considerable force. This may cause pitting near the impeller vane tips.
Signs of cavitation
- A sudden pressure or capacity loss.
- An increase in pump speed without corresponding increase in volume or pressure.
- Excessive pump vibration.
- Rattling sound resembling gravel going through the pump.
How can you overcome cavitation?
You can overcome cavitation by:
- Reducing engine speed
- Decreasing the gpm’s flowing
- Finding an additional water source.
Describe the cavitation protection feature on the 2009 Pierce Quanton pressure governor system.
The cavitation protection feature protects the pump from a water supply that has been reduced or interrupted by advancing the engine speed until the set pressure is attained or the maximum engine speed is reached.
If discharge pressure drops below 45 PSI the governor will go into “Low-Water –Cycle” and the engine will be set to 1100 RPM. The Display will begin to flash “Low Water”. If the pressure does not rise above 45 PSI in 7 seconds or drops below 15 PSI, the Governor will set the RPM to idle and drop out of pressure mode.
What is residual pressure?
Residual pressure is that part of the total available pressure not used to overcome friction loss or gravity while forcing water through pipe- fittings, fire hose, and
adapters. Residual means a remainder or that which is left.
Define net pump pressure?
Net pump pressure is the total work done by the pump to get the water into, through, and out of the pump, hose and nozzles. It is the sum of pump pressure, suction, and lift losses.
How do you convert inches of mercury on the compound gauge to psi?
To convert inches of mercury to psi, multiply the reading on the suction gauge by .434. For field calculations you can multiply by .5 (or divide by 2).
What is the compound gauge?
The compound gauge is the gauge on the pump panel that registers pressures above atmospheric in psi or below atmospheric in inches of mercury on the intake side of the pump.
How does the compound gauge work?
The gauge consists of two closed coiled tubes called Bourdon tubes. As the pressure increases the tubes will tend to uncoil, while a reduced pressure will cause the tubes to coil more tightly. This motion is transferred to a
gear mechanism connected to the indicating needle at the pump panel. The gauge is usually calibrated from 0-600 psi positive pressure and 0-30 inches of mercury
in negative pressure
What fluid is in the gauges of the pump panel and why?
The fluid in the gauges is a mineral oil and it is used to minimize vibration of the needle, lubricate and protect the parts within the gauge and prevent lens condensation. The product name is Interlube.
When would you change from pressure to volume?
2/3rds (1000 gpm) or more of the capacity of the pump.
At what pressure can the transfer valve be electronically operated?
250 psi
How can the transfer valve be operated if the electronic switch fails?
Turning the wrench in a counterclockwise rotation transfers the valve into the pressure mode. Turning the wrench in a clockwise rotation transfers the valve into the volume mode. It is approximately 15 rotations in either direction and should never be operated over 75psi.
What is the function of the intake screens?
The intake screens serve two functions. First, they block debris from entering the pump. Second, the die-cast screens are made of zinc to counteract electrolysis. They inhibit corrosion of crucial pump components by becoming corroded sacrificially.
At the pump panel, what gauges reflect engine functions?
Engine RPM Oil Pressure Water Temperature Voltage Meter Fuel Gauge
