Flow and pressure have different roles
A hydraulic pump converts mechanical drive energy into hydraulic energy. In a positive-displacement pump, displacement and shaft speed determine the available flow, allowing for internal losses. Operating pressure develops according to the load and the resistance encountered by that flow in the circuit. A low-pressure problem therefore does not, by itself, prove that the pump has failed.
What determines circuit pressure
A hydraulic cylinder or motor requires a pressure difference to overcome its load. Pressure losses through the components carrying the oil add to that demand. Relevant factors include actuator load; pipe bore, length and internal roughness; elbows, bends and reducers; and resistance through filters, directional valves and other valves. A pressure reading also depends on where the measurement is taken and which machine function is operating.
Pump capability and pressure limitation
The fact that load determines the required pressure does not mean that a pump can operate at any pressure. Every pump has permitted pressure, speed, fluid and temperature limits. The relief valve and other protective devices must keep the system within its design conditions. Pump selection needs to relate the application’s required flow and operating pressure to the available drive power.
What to check when pressure is too low
Before replacing a pump, assess the complete circuit using the machine’s diagnostic procedure. A valve diverting oil to the reservoir, or internal leakage in a directional valve, cylinder or another component, can prevent the required pressure from being reached. Internal pump wear can also reduce effective flow, but it must be confirmed by testing rather than a pressure reading alone. Compare flow and pressure under defined operating conditions and check the authorised valve settings.
Select the replacement for the actual fault
Do not try to compensate for a fault by raising pressure without identifying its cause. Establish the pump reference, drive speed, expected flow and machine operating conditions before choosing a replacement. A qualified technician can distinguish insufficient flow, internal leakage and incorrect adjustment. See the hydraulic pump range and provide Hidraoil with the application details to check the selection.
