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Positive Displacement Pumps
positive displacement pumps has largely been replaced by the centrifugal pumps ,but are still used as priming devices to get water into centrifugal pumps during drafting operations
There are two basic types of positive displacement pumps:
Piston and rotary
piston pumps contain a piston that moves up and down or back and fourth inside a cylinder.
the forward stroke causes water to be discharged and the return stroke causes the pump to fill with water again
most rotary type pumps in use today are either of the rotary gear or rotary vane
consist of two gears that rotate in a tightly meshed pattern inside a water tight case
this is one of the most common types of pumps used to prime centrifigul pumps
modern fire apparatus utilize the centrifugal pump as their major pump.
the centrifugal pump is classified as a nonpositive displacement pump because it does not pump a definite amount of water with each revolution
centrifugal pump consist of two parts:
Two basic types of centrifugal pumps used by the fire service:
single - stage
two - stage
Pumping in the parallel position
Pumping in the Series position
when switching from pressure to volume:
maximum pressure will not exceed 50 psi.
Power Take Off ( PTO )
the pump is driven by a drive shaft that is connected to the power take off on the chassis transmission
There are two basic concepts for pressure relief valves:
those that relief excess pressure on the discharge side of the pump
those that relief excess pressure on the intake side of the pump
regulated on centrifugal pumps by a mechanical or electric governor
the main feature of a pressure governor is that it regulates the power output to match pump discharge requirements
primers fall into three categories:
- positive displacement
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