The pumps on all newer pumpers manufactured today are
capable of delivering their highest capacity at 150 psi net
pump pressure. Once the pump is producing 150 psi, an
increase in RPMs/throttle/pressure will actually decrease
the flow of water. If this happens, look for additional water
supply.
Being a good pump operator means knowing what
questions to ask yourself as you are stepping off the
engine. What is the first question you should be asking your
self? The answer is "What is my flow rate?" You cannot
determine friction loss until you know this. To figure this out,
look at the nozzle being used and then you can figure out
your flow rate.
If you are looking to determine your total engine pressure,
remember the following master formula, which you will
need to know regardless of which friction loss method you
choose to use:
TEP=NP+FL+DL+/- EL
TEP=Total Engine Pressure NP=Nozzle Pressure
FL=Friction Loss DL= Device Loss EL= Elevation Loss/Gain
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HYDRAULICS BOOKS
In order to determine how many more hoselines you can
supply while one hose line is in operation, use the
following formula. Remember to always record your static
pressure before opening any lines.
% drop = (SP-RP)/SP
Take that percentage and apply it below:
0-10% pressure drop
3 equal lines/flows
11-15% pressure drop
2 equal lines/flows
16-25% pressure drop
1 equal line/flow
Pressure Governor / Flow Meter Points To
Remember
  • DO NOT fall victim to the belief that you can hit
    the preset button and walk away. The preset of
    about 130 psi is the incorrect pressure for ALL of
    our attack lines.
  • Make sure that you are in PSI mode when attack
    lines are in use, or you will not have the protection
    of the governor for pressure spikes.
  • If on hydrant pressure alone, you will NOT have
    pressure surge protection, regardless of what
    mode the governor is in.
  • When making the transition from tank to hydrant,
    you need to switch to RPM mode and throttle
    down, the manufacturer does not feel the
    governor can react quickly enough to hydrant
    surges to offer the optimal protection
  • If you are using the flow meter to determine the
    proper operating pressure, be mindful of what the
    operating pressure should be in case of kinks,
    burst hoselines, and water supply problems
NET PUMP PRESSURE

Net pump pressure is a concept that is
vital for pump operators to understand.  
Net pump pressure (NPP) is the
difference between pump discharge
pressure and inlet pressure. It is telling
you the actual pressure the pump itself
is delivering. For example, if your
discharge pressure is 140 psi, and your
inlet pressure is 80 psi, then your net
pump pressure is 60 psi, 140-80. So why
is that number important ? Remember
your pump discharges its maximum
output at 150 psi. That maximum output
is 1,500 gpm. So if your NPP is 60 psi,
you still have 90 psi left of pressure for
the pump to develop. Many people think
that if your pump discharge pressure
reads 150 psi, that no matter what, you
have reached the maximum output of the
pump, and you have not.