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Design of an oil cooler

In hydraulic systems that are in continuous operation or have only a small tank available, it is necessary to cool the oil. An oil cooler can basically be designed when designing a hydraulic system or after commissioning a hydraulic system. If a hydraulic system is already in operation and it is determined that the hydraulic oil is getting too hot, it is easier to design the cooler because all relevant temperature and time measurements can be made without making assumptions. It becomes much more problematic if temperatures and heating time of the hydraulic oil are not yet known. Either assumptions are made or a simplified design taking into account system pressure and oil flow rate is used. These two variables are usually known.

Simplified interpretation

In the simplified design, the necessary cooler capacity is determined as follows:


PK = required radiator listing [kW]

PM = required motor power for the pump [kW].

Q = Pump capacity [l/min]

p = system pressure [bar]

η = Efficiency of hydraulic system

Hydraulic systems with fixed displacement pumps have an efficiency of approx. 70 - 75% => η = 0.70 - 0.75.

Hydraulic systems with variable displacement pumps have an efficiency of approx. 75 - 80% => η = 0.75 - 0.80.


Hydraulic system with fixed displacement pump: η = 0.70

Pump delivery rate: Q = 80 L/min

Operating pressure: p = 280bar

Required cooler capacity in kW

Thus, the cooler can be determined on the basis of the calculated cooler capacity and taking into account the oil flow.


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