How to adjust the flow rate of your pump.

There may be times when you want to regulate the flow rate or delivery pressure from a pump. For example, you may want to use a flexible to hose to fill your car's tank, and plan on using a pump and shutoff nozzle to do this.

When you close the nozzle on the end of the hose, the pressure in the hose will rise to whatever the pump can create. If you have a powerful pump, the chances are high that you will blow the hose off its spigot, and biodiesel will spray all over the place.

Here is a simple way to limit the pressure the pump can create. It is useful in such applications where you may want to close the outlet valve completely, or partially, while the pump is still running. This is particularly important if you are using a powerful centrifugal pump, or any positive displacement pump.

The 'Pressure Adjust' valve allows some of the pump's outlet to return to the inlet, which reduces outlet pressure, when fully or partially open.

The 'Flow rate Adjust' valve can be used to shut off flow completely. The two valves will interact with each other to some extent, and flow rate and pressure will tend to vary if you change the operating conditions, such as head height, fluid viscosity etc, but it is a simple system, with many uses.

How to throttle the flow of a pump

Other applications where it may be useful to reduce a pump's delivery pressure include...

  • Pumping through a fuel filter, which may eventually become blocked
  • Pumping into a resin tower, which may not be able to handle the pump's pressure
  • Pumping through a hose which may burst or become uncoupled under pressure
  • Pumping into a spray head

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Graham Laming