Hydraulic power units

Required flow and pressure of the actuators, duty cycle, number of control circuits, supply voltage and installation space. Motor power follows from flow and pressure: power (kW) is roughly flow (L/min) times pressure (bar) divided by 600, then divided by efficiency. The installation environment and ambient temperature decide whether a cooler is needed.

A common rule for industrial power units is a tank of about 3 to 5 times the pump flow per minute, giving the oil time to release air, settle contamination and shed heat. Intermittent mini power packs can use smaller tanks. The tank must also hold enough reserve for all cylinders fully extended.

Oil heats when energy is wasted across the relief valve while a fixed displacement pump idles, or across throttle valves with large pressure drops. A tank that is too small or a dirty cooler also raises temperature. Mineral oil is best kept below about 60 degrees C for long seal and fluid life.

12 or 24 V DC mini power packs suit lift tables, dock levellers and specialist vehicles with intermittent duty and a battery supply. AC units suit continuously running plant machines such as presses and shears. DC motors in mini packs usually have limited continuous run time, so check the duty cycle.

Place the unit in a ventilated area away from heat sources and dust, with room to change filters, top up oil and service the motor. The floor must be level and solid, and anti vibration mounts can reduce noise transmission. Locating it close to the actuators shortens the lines and cuts pressure and heat losses.

Flush the pipework with clean oil before connecting the actuators, to remove swarf and installation debris. Check motor rotation with a brief jog, set the relief valve low and raise it gradually to the design pressure. Watch oil level, temperature, noise and leaks during the first hours of running.

A cooler is needed when heat generated by system losses exceeds what the reservoir can dissipate naturally. Air blast coolers suit sites without cooling water, while water coolers are more effective in hot workshops. Working oil temperature is best kept around 40 to 60 degrees C to preserve viscosity and seal life.

Daily checks cover oil level, temperature and unusual noise. Periodically watch the filter indicators, clean the cooler fins, check the breather filter, tighten leaking connections and take oil samples for analysis. Logging pressure and temperature helps reveal degradation trends before a failure.