Question

What hydraulic fluid viscosity and temperature was used in preparing the performance data shown on this information sheet? Give specific examples of what changes would occur in the data if the viscosity and/or temperature was varied.

Answer 1

Viscosity is a basic property of hydraulic fluids. The permissible viscosity range of complete systems needs to be determined takingaccount of the permissible viscosity of all components and it is to be observed for each individual component.

The viscosity at operating temperature determines the response characteristics of closed control loops, stability and damping of system, the efficiency factor and the degree of wear.

The optimum operating viscosity range of each component should be kept within the permissible temperature range. This usually requires either cooling or heating, or both. The permissible viscosity range and the necessary cleanliness level can be found in the product data sheet for the component concerned.

If the viscosity of a hydraulic fluid used is above the permitted operating viscosity, this will result in increased hydraulic-mechanical losses. In return, there will be lower internal leakage losses. If the pressure level is lower, lubrication gaps may not be filled up, which can lead to increased wear. For hydraulic pumps, the permitted suction pressure may not be reached, which may lead to cavitation damage.

If the viscosity of a hydraulic fluid is below the permitted operating viscosity, increased leakage, wear, susceptibility to contamination and a shorter component life cycle will result.