SERIES / PUMPING IN PRESSURE
The first mode we will look at is our pump running in series. We also call this "pumping in pressure."
When our two-stage pump runs in series, we have routed water in such a way that the two impellers have been set up in a "series," or are "stacked." The goal here is to maximize our engines' pressure capacity/output.
As water enters the intake side of our pump, it is routed (via the transfer valve and two flapper valves that close) from one impeller into the eye of the second impeller. As velocity is imparted to the water by our first impeller, it is discharged and routed directly into the second impeller (this is that stacking effect we mentioned above). The second impeller does its job to increase the incoming pressure even further (via imparted velocity that is then contained by the pump casing). It is now ready to be discharged to the fire ground.
As a FORCE MULTIPLIER, Series allows us to take the already pressurized water source (the municipal water system via hydrant) and add TWO levels of pressure increase to the total discharged volume. This is how we achieve our goal of maximizing pressure capacity, which is directly tied to how fast we can move water through our pumps, hose, and nozzles... which is one of the two key elements of hydraulics/pumping.
A Simple Scenario...
These numbers are entirely fictitious but serve as round numbers that can help us better understand this PRESSURE/SERIES concept:
We have a 50psi hydrant feeding our Engine via a 5" supply hose.
If impeller #1 produces 500 GPM @ 100 psi, it will take the incoming hydrant pressure and increase it to 150psi.
Than impeller #2 will increases the original 500 GPM another 100 psi...
Combined, our dual stage pump is able to produce 500 GPM @ 250 psi (50+100+100=250psi)d generates additional pressure as it leaves the second stage of our pump resulting in greater discharge pressures than if we ran in parallel. Whereas the stages of our pump were working independently in parallel, now our stages are working in a series… one feeding the next.
ADDITIONAL RESOURCE:
In the following Episode from The Urban Pump Series, we cover Dual Stage Pumps and in more depth this concept of pumping in Volume/Pressure:
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PUMP SCHOOL W/ RICK BREWER
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