5 Best Ways to Design a Hydraulic System that Runs Cool

Very simply….. the best way to have a cool running hydraulic system is to design it to draw the least amount of energy as possible to perform the work required. In other words, make it as efficient as possible.

Here are the 5 Best Ways to Keep Your Hydraulic System Cool in no particular order

  1. Minimize system pressure when possible during idle periods: Often during machine cycles there is a hydraulic dwell (idle) period where parts are loading or the process may be heating or cooling. During this period of time high pressure pump flow is turned into heat as it spills over the relief valve. If a pressure compensated pump is utilized, the pump’s leakage through the case drain creates heat which is greater at higher pressures than lower pressure, often a compensator dump valve can be utilized to lower pump pressure .
  2. Slow Electric Motor Speeds to Match Flow Demand: The advent of variable speed drives and inverter duty electric motors provides a great way to “slow your hydraulic system down”  during non-peak use periods especially while using fixed displacement pumps. Torque- speed curves of the drive/motor combination must be studied due to the fact that torque will drop off at lower speeds when using inverters.
  3. Make Sure Relief Valves are Set Properly:.A common cause of heat generation in closed center circuits is the setting of relief valves below, or too close to, the pressure setting of the variable-displacement pump’s pressure compensator. This prevents system pressure from reaching the setting of the pressure compensator. Instead of pump displacement reducing to zero, the pump continues to produce flow, which passes over the relief valve, generating heat. To prevent this problem in closed center circuits, the pressure setting of the relief valve(s) should be 250 PSI above the pressure setting of the pump’s pressure compensator.
  4. Utilize a cooling loop that runs 100% of the time: Sometimes return line flow does not provide enough oil volume to pass through a heat exchanger. By designing in a secondary low pressure fixed displacement pump that runs 100% of the time through a heat exchanger,  heat removal can be guaranteed during both high usage and idle periods.
  5. Minimize pressure drops in the hydraulic system: When high pressure oil becomes low pressure oil it means energy has been expended. That energy either turns into work (in a perfectly efficient hydraulic system which is impossible), or heat. The goal is more energy to work and less energy to heat. All hydraulic systems produce heat, the hydraulic oil and surface areas the oil resides in (reservoir) and is transferred though (hose & tubing) helps dissipate the heat. Minimizing the paths in a hydraulic system where no work is being done and  high oil pressure drops to low oil pressure is key to coolness. Flow control valves, relief valves, case drains on pumps/motors are often the biggest pressure drop sources. Best practices to minimize heat related to pressure drop include: Minimizing the time that high pressure oil is dumping over a relief valve, especially in system dwell times. Flow can often be dumped or proportional relief valves can be set to a minimum. In the case of pressure compensated pumps, pressure can often be lowered with a remote valve from the compensator to reduce deadhead horsepower, and thus heat.