heat load

How Hot is Too Hot?

When it comes to the oil’s operating temperature – how hot is too hot?

Heating of hydraulic fluid in operations is caused by inefficiencies. Inefficiencies result in losses of input power, which are converted to heat.

A hydraulic system’s heat load is equal to the total power lost (PL) through inefficiencies
and can be expressed as:

PLtotal = PLpump + PLvalves + PLplumbing + PLactuators

If the total input power lost to heat is greater than the heat dissipated, the hydraulic system will eventually overheat.

Hydraulic fluid temperatures above 180F (82C) damage most seal compounds and accelerate degradation of the oil.

So while the operation of any hydraulic system at temperatures above 180F (82C) should be avoided, fluid temperature is too high when viscosity falls below the optimum value for the hydraulic system’s components.

This can occur well below 180F (82C), depending on the fluid’s viscosity grade (weight).

To achieve stable fluid temperature, a hydraulic system’s capacity to dissipate heat must exceed its inherent heat load.

For example, a system with continuous input power of 100 kW and an efficiency of 80% needs to be capable of dissipating a heat load of at least 20 kW.

It’s important to note that an increase in heat load or a reduction in a hydraulic system’s capacity to dissipate heat will alter the balance between heat load and dissipation.

As you’ve probably gathered, there are only two ways to solve overheating problems in hydraulic systems:

1. Decrease heat load; or
2. Increase heat dissipation.

Decreasing heat load is always the preferred option because doing so increases the efficiency of the hydraulic system.


Craig Cook

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