Distinguishing reservoir volume, usable oil and cylinder oil requirement

Reservoir size and usable oil quantity

Nominal reservoir capacity does not automatically describe the fully usable quantity. For PB43, for example, the manufacturer specifies 4.8 l usable oil for a 5.7 l reservoir and 8.7 l usable oil for a 9.5 l reservoir.

These values are specific to the respective versions. The ratio must not be applied generally to other pump series or reservoirs.

The cylinder determines the requirement

A cylinder’s oil requirement depends on effective area and the stroke travelled. The manufacturer lists these quantities in selection information and model tables. With several consumers, the intended simultaneous movement must be considered.

Double-acting cylinders can have different oil volumes for extension and retraction. Planning therefore requires knowing which side is being considered and how the complete hydraulic circuit is arranged.

Volume is not flow rate

Litres or cubic centimetres describe a quantity. Litres per minute or cubic centimetres per pump stroke describe how quickly, or in what increments, oil is delivered. These figures answer different questions.

An enquiry therefore benefits from both the usable oil supply and the flow rate at the intended working pressure. A large reservoir does not, by itself, make a pump faster.

Important for your enquiry

• Is the stated value reservoir capacity or usable oil quantity?
• Which cylinders move simultaneously and through what stroke?
• What flow rate is needed at what working pressure?

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