In brief
A hydraulic power unit is a compact assembly of tank, pump, drive motor and valves that supplies a machine with pressurised hydraulic oil.
Contents
What is Hydraulic power unit?
The hydraulic power unit is the energy source of a hydraulic system. An electric motor drives the pump, which draws oil from the tank and delivers it into the system under pressure. Valves control direction, pressure and flow before the oil reaches cylinders or motors and then flows back into the tank after filtering.
In addition to the pump and motor, a unit usually includes a pressure relief valve, suction, pressure or return filters, a cooler, level and temperature indicators, a breather filter and a pressure gauge or pressure sensor. Depending on the application, accumulators, heating and a control block are added. Key parameters are tank volume, flow rate, operating pressure, motor power and oil type. Units are built as standard assemblies for low power ratings or as custom-designed systems, for example for presses and rolling stands.
Many failures are caused by contaminated or overheated oil. Clogged filters, defective coolers and air in the system damage the pump and valves. Oil analysis and temperature monitoring are therefore key maintenance measures. Because many units are configured individually, the replacement of individual components depends heavily on complete documentation. If the circuit diagram or bill of materials is missing, components must be recorded on site from their nameplates.
In practice: maintenance and procurement
Spare parts require the hydraulic circuit diagram, bill of materials and the nameplates of the pump, motor and valves. Filter elements, seals and breather filters should be kept in stock as maintenance materials with their exact designations.
Synonyms and abbreviations: HPU · hydraulic power pack · hydraulic station · hydraulic unit · power pack
Frequently asked questions
What does a hydraulic power unit consist of?
The basic components are the tank, pump, electric motor with coupling and bell housing, and a pressure relief valve. These are complemented by filters, a cooler, level and temperature indicators, a breather filter and a pressure gauge. Larger units have control blocks with directional valves, accumulators, heating and sensors for monitoring.
Why does the oil in the hydraulic power unit get too hot?
Heat is generated wherever pressure is reduced without doing work, for example across throttles or a pressure relief valve that responds constantly. Other causes are a dirty or undersized cooler, a low oil level or internal leakage in the pump and cylinders. Oil that is too hot ages faster and damages seals.
What information is needed for hydraulic power unit spare parts?
The most important documents are the hydraulic circuit diagram and the bill of materials. Nameplate data is needed for each component: for the pump, the design, displacement and shaft end; for the motor, power, speed and frame size; for valves, nominal size and actuation. For filters, the filter rating, design and element designation count.
How often does the oil in the hydraulic power unit need changing?
Fixed intervals from the operating manual are a starting point. More meaningful is regular oil analysis for contamination, water content and ageing. Clean systems operated at low temperatures allow longer service lives than hot or heavily loaded ones. Filter elements should also be renewed when changing the oil.