Oil Viscosity

Viscosity of Hydraulic oil
Often in hydraulic systems the type of oil can be the last thing to consider in the overall design.
ISO 32 mineral oil is the most common Hydraulic oil and I often advise my clients to use this grade of oil because of its availability and compatibility with most pumps, valves and hydraulic components.
The viscosity can be extremely important and I will give a few examples of situations that I have encountered where the oil has been a key factor to resolving problems.
1) We designed a system for an animal park. Large sliding hydraulic doors enclosed Rhinoceros and it was our job to ensure that the doors closed quickly but with minimum force so not to injure the animal. Everything worked to plan but our client complained that on some occasions the electric motor would cut out. We discovered that the motor only cut out on cold days when the oil was at its thickest. The pack worked off 240v 30amp supply and we had no way of increasing the supply. The simple solution was to change the oil from iso 46 to 32. Our customer never had another failure and was very pleased with the simple remedy.
2) An aluminium casting machine uses hydraulic rams to tilt the machine and allow molten metal to fill the mould. When solidified the machine is tilted back to open the die and remove the casting. We had already increased the speed by using a Regen circuit but our customer wanted even more speed. We noticed that there was a difference in speed from morning to afternoon when things began to slow down. By monitoring the temperature we knew this was due to the change in oil viscosity. We recommended he replace the iSO32 for 46 and saved 8 seconds in the total cycle time.
3) In a saw mills proportional valves were used to set adjustable fence. The customer complained that the hydraulics needed to run for at least one hour before the system cut accurately. We changed the oil to thinner grade and immediately improved the accuracy without the need to waste time to bring the oil up to temperature.
The viscosity of hydraulic oil can be very important and often a great problem solver without having to modify expensive hardware.
Always best to check with pump manufacturer to be sure that the pump or motor will not be damaged by a change in oil viscosity.
A great problem solver to keep up your sleeve!
Very best
Bob Jackson
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