What causes excessive temperature rise in a hydraulic system?

Analysis of the causes of the temperature increase:

1. The oil tank has too small a capacity, resulting in insufficient heat‑dissipation surface area; no oil cooler is installed, or if one is present, its capacity is inadequate.

2. In a fixed-displacement pump system where the pump capacity is selected based on the fast‑forward speed, most of the excess flow is diverted back to the reservoir through the relief valve under high pressure during operation, resulting in heat generation.

3. In the system, a malfunction in the unloading circuit—or the absence of such a circuit—can prevent the pump from relieving pressure when it stops operating. As a result, the entire pump flow is diverted through the relief valve under high pressure, leading to overflow losses and heat generation that cause a temperature rise.

4. The system piping is too narrow, excessively long, and contains too many bends, resulting in significant local pressure losses as well as substantial frictional pressure losses along the pipeline.

5. Insufficient component precision and poor assembly quality can both lead to significant mechanical friction losses in relative motion.

6. If the clearance between mating parts is too small, or if wear during operation causes the clearance to become excessively large, internal and external leakage will increase significantly, leading to substantial volumetric losses. For example, this can reduce the pump’s volumetric efficiency and cause a rapid temperature rise.

7. The pressure setting of the hydraulic system is significantly higher than what is actually required. In some cases, this is due to overly tight seals or damage to sealing components, which leads to increased leakage and necessitates a higher pressure setting for the system to function properly.

8. High ambient temperature and operating conditions cause the oil temperature to rise.

9. If the selected hydraulic fluid has an inappropriate viscosity, high viscosity leads to greater viscous resistance, while too low a viscosity results in increased leakage; both scenarios can cause overheating and elevated operating temperatures.