Hydraulic Reservoir Sizing and Tank Design

How big should the hydraulic reservoir be?

The rule of thumb for stationary systems is a tank volume of 3 to 5 times the pump flow per minute. A pump at 40 l/min therefore needs 120 to 200 litres. The large volume gives the oil dwell time so air bubbles rise and heat sheds through the tank walls. On mobile or space-critical units smaller ratios are possible, but then with active cooling.

How do I settle the oil and separate suction from return?

A baffle plate between return and suction forces the oil onto a longer path. That lets air bubbles rise and dirt settle before the oil is drawn in again. Return and suction lines end below the minimum oil level so no oil free-falls and foams. A gap of 50 to 100 mm between the two ends prevents short-circuit flow.

• End the return line below oil level and cut it at an angle to reduce air entrainment.
• Size the suction strainer with ample reserve so no cavitation risk arises.
• Set the baffle to about two thirds of the oil height so oil must flow over and under it.
• Provide a sloped floor and drain plug at the lowest point for condensate and sediment.

Which breather, filters and sensors belong on the tank?

A breather filter balances the level change as cylinders extend and retract, keeping dust and moisture out. A sight glass and temperature gauge belong in clearly visible spots. Return-line or offline filters secure the target cleanliness. A level switch warns of low oil before the pump draws air.

Frequently asked questions