A Brief Analysis of Heating in Hydraulic Systems

When the oil in the hydraulic system gets hot and has a high temperature, it can cause problems such as inflexible operation, discontinuous work, weak performance and reduced working pressure. The following is a simple analysis and discussion on the causes of heat generation in hydraulic systems, the resulting hazards and preventive measures.

I. Causes of Oil Heating

(1) The fuel tank volume is too small, the heat dissipation area is insufficient, no oil cooling device is installed, or although there is a cooling device, its capacity is too small.

(2) In a quantitative pump oil supply system where the oil pump capacity is selected based on the fast-forward speed, during operation, a large portion of the excess flow will overflow back from the relief valve under high pressure, causing heat generation.

(3) When the unloading circuit in the system malfunctions or is not set up, the oil pump cannot unload when it stops working. The entire flow rate of the pump overflows under high pressure, causing overflow loss and heat generation, which leads to the heating of the oil.

(4) The system pipelines are too thin and long, with excessive bends, resulting in significant local pressure loss and pressure loss along the way.

(5) Insufficient component precision and poor assembly quality result in significant mechanical friction losses during relative motion.

(6) The fit clearance of the mating parts is too small, or it becomes too large due to wear during use, resulting in large internal and external leakage and significant volumetric loss. For instance, the volumetric efficiency of the pump decreases and it heats up quickly.

(7) The working pressure of the hydraulic system is adjusted higher than the actual requirement. Sometimes, it is due to overly tight sealing, or damage to the sealing parts and increased leakage that the pressure has to be raised to work.

(8) High climate and working environment temperatures cause the oil temperature to rise.

(9) Improper selection of oil viscosity: If the viscosity is too high, the viscous resistance will be large; if it is too low, the leakage will increase. Both situations can cause the oil to heat up.

Ii. Hazards of Excessively High Temperatures

(1) It causes thermal deformation of the machinery. The moving parts with different thermal expansion coefficients in the hydraulic components get stuck due to the reduced fit clearance, resulting in malfunction of the action, affecting the transmission accuracy of the hydraulic system, and causing the working quality of the components to deteriorate.

(2) It will reduce the viscosity of the oil, increase leakage, and significantly lower the volumetric efficiency of the pump and the overall efficiency of the system. Due to the decrease in oil viscosity, the oil film on moving parts such as spool valves becomes thinner and is cut through, increasing frictional resistance and leading to accelerated wear.

(3) It causes deformation of rubber sealing parts, accelerates aging and failure, reduces sealing performance and service life, and leads to leakage.

(4) Accelerate the oxidation and deterioration of the oil, and precipitate asphalt substances, reducing the service life of the hydraulic oil. The precipitated substances clog the damping small holes and slit-type valve ports, causing the pressure valve to get stuck and fail to operate, the metal pipeline to elongate and bend, and even break, etc.

(5) It reduces the air separation pressure of the oil, causing the dissolved air in the oil to escape and generate cavitation, which in turn reduces the working performance of the hydraulic system.

Iii. Prevention and control measures

(1) According to different load requirements, frequently check and adjust the pressure of the relief valve to make it just right.

(2) Select hydraulic oil reasonably, especially the viscosity of the oil. Where conditions permit, try to use a lower viscosity to reduce viscosity friction loss.

(3) Improving the lubrication conditions of moving parts can reduce friction losses, which is conducive to lowering the working load and reducing heat generation.

(4) Enhance the assembly quality and self-precision of hydraulic components and systems, strictly control the fit clearance of mating parts and improve lubrication conditions. By using sealing materials with low friction coefficients and improving the sealing structure, the starting force of the hydraulic cylinder is reduced as much as possible to minimize the heat generated by mechanical friction losses.

(5) Add necessary cooling devices.