Introduction to Pressure Compensated Pumps

Objectives

  • Explain the advantage of a pump with a pressure compensator
  • List two common types of pressure compensated pumps
  • Describe the function of the compensator
  • Differentiate between on-stroke and off-stroke pump states

What Is It?

When people say that a pump is pressure compensated, what on earth are they even talking about?

A pressure compensated pump is a pump that can reduce its output displacement (flow) when the system pressure rises to a specified pressure setting.

Variable Displacement,
Pressure Compensated
Vane Pump
Variable Displacement,
Pressure Compensated
Piston Pump
There are two types of pumps capable of pressure compensating: a variable displacement, pressure compensated vane pump and a variable displacement, pressure compensated piston pump.

But Why?

Why would we want to add this extra complication to our hydraulic systems?
Having a hydraulic pump which reduces its output to near zero when the system pressure reaches maximum saves the system from pointlessly forcing oil over a relief valve.

This translates into real world energy savings!
Let's examine both a non-compensating pump and a compensating pump so we can better understand the difference!

Using a Non-Compensating Pump

This system uses a simple gear pump.

A gear pump is a positive and fixed displacement pump, and it has no pressure controls built in. For this reason, the hydraulic system must contain a relief valve to limit the maximum system pressure.

Relief Valve
Pressure
Max
Displacement
Max
Power Usage

Whenever a system is at maximum pressure, and the pump is a fixed displacement model, like a gear pump, then the system is at maximum displacement as well.

The combination of these two maximums also means that the power requirement from the prime mover (diesel engine or electric motor) is at maximum as well.

A prime mover at maximum power is consuming maximum energy (fuel or electricity). Much of this energy is being used for nothing other than a conversion to heat.

You could compare this to operating a truck at maximum throttle while it is parked against a solid wall of rock. You'll burn a lot of fuel but you won't be doing any useful work!

This is clearly not a good idea.

Sending large volumes of flow over the spring-loaded relief valve is extremely inefficient.

If you are using the relief valve for a prolonged amount of time, you are wasting a lot of energy to produce only heat.

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We hope you enjoyed Introduction to Pressure Compensated Pumps

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