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