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What Is an Hydraulic Oil Cooler?

By Paul Scott
Updated May 17, 2024
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An hydraulic oil cooler is a device designed to prevent oil used in hydraulic systems from overheating. This is a critical function in hydraulic systems, as overheating of the oil can lead to a drop in system efficiency and excessive wear of the system components in general due to reduced oil viscosity. In most cases, the coolers allow the oil to shed accumulated thermal energy into a secondary medium, typically water or air, by passing the hot oil through a series of thin tubes exposed to a constant flow of low temperature cooling medium. The cooling medium absorbs heat from the oil and carries it away from the cooler, where it is typically shed into the atmosphere. Common hydraulic oil cooler designs include radiator, shell and tube, or plate and frame types.

Hydraulic systems utilize the power of pressurized oil to perform work such as the actuation of valves, machine parts, or lifting equipment. The oil is pressurized by pumping it into the actuator chamber, where the internal pressure grows until it overcomes the inertial force of the actuator mechanism, moving it and supplying the working motion in the process. One of the unavoidable results of this type of system is an accumulation of thermal energy, or heat, in the oil as a result of friction and compression. A certain amount of heat build-up in the hydraulic oil is acceptable, but, should it escalate beyond the operational specifications of the oil, a drop in efficiency is inevitable.

One side effect of temperature increases in oil is a loss of viscosity, or thickness. Hydraulic systems are designed to function effectively with an oil of specific viscosity and, should the oil become too thin, will begin to work less efficiently as the oil continues to thin out. Mechanical damage to the system is also possible as seals begin to degrade and the moving parts receive less lubrication from the thin oil. To prevent the unconstrained heating of the oil, most high-performance hydraulic systems include a hydraulic oil cooler, a device placed in line with the system to allow heat to dissipate from the oil.

Most hydraulic oil cooler types work on a conductive transfer principle that sees heat in one medium conducted to another for removal and disposal. This is generally achieved by passing the oil through a series of thin pipes exposed to direct contact by the cooling medium. As the cooling medium is kept at a lower temperature than the oil, heat in the oil flows into the cooling medium upon exposure. The cooling medium and the hydraulic oil constantly move through the cooler ensuring that thermal saturation and equilibrium is never attained, so the heat transfer process remains ongoing. The heat absorbed by the coolant is then shed, typically into the atmosphere, away from the hydraulic system.

There are several hydraulic oil cooler types in general use, most of which utilize a flow of air or water as a coolant medium. Air coolers resemble an automobile radiator and employ a powerful fan to force air across the pipe coils carrying the hot oil. Water-based oil coolers are typically shell and tube types, where the oil-carrying pipes are enclosed in a sealed shell through which cold water is circulated. Other hydraulic oil cooler types include plate and frame coolers and brazed plate coolers.

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