What is pressure compensation?

So what is pressure compensation?
For any flow of fluid through a pipe there must be a pressure drop with greater pressure at the source of flow (pump) and lessoning the further you go downstream. This is due to the frictional losses in pipe, fittings, valves, filters etc and we call this Pressure Drop or Delta P and often signified using the symbol (ΔP). If there is no difference in pressure then there will be no flow.
If the pressure difference (ΔP) is constant then the flow and hence the speed of the actuator will also be constant but if the flow or load changes there will also be a change in the pressure drop and consequently change in speed of the actuator.
With some applications, constant speed of a ram or motor can be very important, take an application like a hydraulic passenger lift. It is important that the speed with only one passenger is the same as when the lift is full of people. Without compensating for the pressure difference the speed would change. With more people in the lift the downward speed would increase and with just one person might be unacceptably slow.
So we need a valve that will automatically close down and reduce flow when the load is greater and open when the load is less or a pump that will increase flow or decrease flow to maintain a constant Delta P.
With a speed control valve make sure it is a pressure compensated type and sized correctly for the flow. To maintain Delta P with the pump use a load sensing option. Variable piston and vane pumps only have this option available. A load sensing pump will automatically adjust the flow to the required load and maintain the correct speed. Another benefit with this type of arrangement is power saving and less heat generation.
Bob Jackson (The Hydraulic man)
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