What is the difference between a Fixed Hydraulic Pump and a Variable Hydraulic Pump?
April 25, 2020
Hydra-Tech Pumps uses a variety of different hydraulic pumps on their hydraulic power units – the choice of pump is typically determined by the customers’ needs. Hydraulic pumps that we use are either fixed displacement or variable displacement. So what is the difference between the two?
Fixed Displacement Pumps. Gear, vane and some piston hydraulic pumps deliver the same displacement per revolution and cannot be adjusted. Adjustability with a fixed displacement pump is done only with engine RPM. If you were to match a Hydra-Tech Pumps power unit to a pump or tool where the maximum potential flow and pressure of the HPU will not exceed the maximum hydraulic flow and pressure the pump or tool is able to use, there would be no need to adjust the hydraulic flow and pressure that the hydraulic pump on the power unit delivers.
Variable Displacement Pumps. Variable displacement piston hydraulic pumps can be adjusted to provide a range of flows and pressures (all determined / limited by the horsepower of the engine or motor that is driving it). If you were purchasing a hydraulic power unit to run multiple pumps (or other hydraulic tools) with a range of hydraulic requirements, having a variable displacement piston pump on your HPU is essential. A typical 74 horsepower diesel engine HPU with a variable displacement pump would be set up at Hydra-Tech Pumps for 30 GPM @ 2900 PSI. There are a number of Hydra-Tech pumps that will run at this flow and pressure, but if you had a pump or hydraulic tool that had a max flow and pressure of, for example, 20 GPM @ 2700 PSI, you could make adjustments to the piston pump to “reset” your HPU to run this piece of equipment. Keep in mind that this change would require a flow meter and some hand tools and is not something that is done by simply turning a knob or adjusting a setting in a control panel – this adjustment is actually altering the geometry of the displacement chamber which in turn affects the flow and pressure that the pump delivers.