Designing a Hydraulic Power Unit or Aggregate
A hydraulic power unit supplies the flow and pressure for the whole system. Reservoir size, pump type, motor power, cooling and filtration must fit together, otherwise the oil overheats or the pump cavitates. This guide walks step by step through designing a reliable power unit.
View power unitsHow big must the reservoir be?
The reservoir stores oil, separates air and dirt and sheds heat through its surface. As a rule of thumb use a volume of 3 to 5 times the pump flow per minute, so the oil has enough dwell time to settle. For high heat load or continuous duty, go to the upper end or add a cooler. A baffle between suction and return side prevents short-circuit flow and foaming.
Which pump and motor fit?
The pump sets flow and pressure level, the electric motor the available power. The required drive power follows roughly from pressure and flow: 20 l/min at 210 bar needs around 7 to 8 kW including efficiency. Gear pumps are robust and cheap, vane pumps run quietly, axial piston pumps reach high pressure and can be variable.
- Calculate drive power from maximum pressure and flow, and add a reserve for efficiency.
- Match pump speed to the motor, usually 1450 rpm on 4-pole motors.
- For varying demand, check a variable pump or pressure control to save energy and heat.
How do I keep the oil temperature under control?
Oil works best between 40 and 60 °C. Above 70 °C it ages fast, viscosity drops and the lubricating film tears. If the reservoir surface is not enough, an air or water-oil cooler holds a stable temperature. A thermostat switches the cooler in only on demand and keeps the oil in the ideal window.
What filtration and oil care does the unit need?
Most hydraulic failures trace back to contaminated oil. The cleanliness class per ISO 4406 must match the most sensitive component: servo valves demand very clean oil, simple directional valves tolerate more. A return filter with the right rating and a breather filter on the reservoir keep the class stable over time.
Frequently asked questions
How do I calculate the motor power for my power unit?
Multiply maximum pressure by flow and divide by efficiency. Roughly, 20 l/min at 210 bar needs around 7 to 8 kW. Add a reserve so the motor does not overheat under full load.
Why does my hydraulic oil get too hot?
Usually the reservoir is too small, the cooler undersized or a valve is in constant relief. Check reservoir volume, cooling capacity and whether oil constantly bleeds over the relief valve and generates heat.
Which oil viscosity should I choose?
ISO VG 46 is the common mid-range value for industrial systems at normal temperatures. Choose VG 32 in cold surroundings, VG 68 for high temperature or heavy load. Always follow the approval of pump and valves.
Design the right hydraulic power unit
Our hydraulics specialists help with reservoir size, pump, motor and cooling for your system.
Vetted design
Recommendations from field values and maker data.
Correct reservoir size
Volume matched to pump flow and heat load.
Stable temperature
Cooling and oil temperature clearly explained.
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