By Dave Marlowe, Owner/CEO, DMAR Technical Training and DMAR Business Centers USA
In a previous article, I stated that the most important consideration in the selection of a hydraulic fluid was selecting an oil of the right viscosity. I also explained the difference between viscosity and viscosity index. Now we’ll share insights for the operator and maintenance person responsible to help minimize overheating in your hydraulic system.
Minimize, maintain and prevent system overheating
Maintaining a normal oil temperature in all hydraulic systems is important for successful system operation. Normal operating temperatures for hydraulic systems is 110 to 130° F (unless specified by the equipment manufacturer). If the oil temperature is maintained in the normal range, all the system components will operate efficiently and do what they are designed to do—the pump will create flow; the valves will isolate, direct or regulate flow; the actuator will extend or retract while transferring energy to do work; and seals will prevent internal slippage.
Maintaining normal oil temperature also reduces undesirable chemical compounds such as acids—not to mention sludge build up in the system. Undesirable compounds in the oil from excessive temperatures not only affect the viscosity index and system equipment operation but will cause accelerated wear on the moving parts. This can lead to premature equipment failure. It’s important to note that hydraulic systems are permitted to operate in a temperature range of 130 to 160° F; however, temperatures this high will reduce the lifespan of system components and increase the chances of a system breakdown.
Mobile units seem to run at higher than normal temperatures. Keeping the oil temperature below 160° F is a challenge, as there is no practical way of removing heat. Because mobile units aren’t run like an industrial system, attention to the oil’s additive package, and a preventative maintenance schedule where the oil is changed based on the severity of operation (annually, number of hours of operation, etc.) is a necessity.
It is imperative that the operator monitor oil temperatures when the system is in operation. If the oil temperature rises above normal operating temperature, finding the cause in a timely manner will reduce the odds of system breakdown. Manufacturer service manuals contain a troubleshooting section that list the possible causes. If you don’t have a service manual, carefully examine the following:
- Application—Ensure the system is operating within its limits (the system is not being asked to do more than it was designed for).
- Relief valve—This should be set at the lowest pressure setting that allows actuator operation. (Anytime you have flow across a pressure drop without work being accomplished, there is heat generated).
- Reservoir—Check proper oil level; it should be three times pump capacity. Also confirm that the reservoir is not covered with dirt or oil and all sides, top and bottom are open and free to air currents. The reservoir should be free of external heat sources in direct contact with the reservoir and components (this includes direct sunlight).
- Pump unloading—Make sure that the pressure in the pump line falls to a low value when the actuators are not operating.
- Speed controls—If flow control valves are supplying excessive power to the cylinder but not doing any work, ensure proper actuator speed by reviewing all pressure-compensated flow control valves and manual flow control valves (needle valve).
- Pressure reducing valve—Heat is generated across the metering orifice.
Normal component and system operation require that the oil temperature is maintained in the normal temperature range. If the system temperature runs above normal and you decide to incorporate a heat exchanger, proper heat exchanger size and efforts to prevent the addition of cooling water into the hydraulic system is imperative.
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