Does The Reservoir Temperature Make The Seals Leak?
August 14 IN Oil Scrubber

Due to the distance from the reservoir to the seals, the reservoir temperature is not likely to cause the seals to leak directly.  However the oil condition, which is directly impacted by the reservoir temperature, can cause the seals to leak.

A hydraulic seal that hardens or becomes brittle is more likely the result of friction between the seal and piston rod due to an insufficient oil film.  Degraded oil can have an altered viscosity, bulk modulus and viscosity index resulting in adhesion between the piston rod and the seals.

Asperities are microscopic peaks on the surface of two meeting parts and represent the true area of contact.  An oil film is required to separate the opposing asperities or a cold weld will develop between the two surfaces.  In an elevator, this is experienced as a hard break away when leaving the floor or vibrations as the car slows down.  The longer the time between car runs, the stronger the cold welds can be.

Degraded or dirty oil does not provide a sufficient oil film to separate the two surfaces resulting in elastic and plastic deformations of the asperities.  These deformations reduce the surface finish of the piston rod resulting in even greater adhesion. The friction that is generated between the two smooth surfaces can generate enough heat to over cure the seals over time making them brittle.

New seals in old equipment typically do not last as long as new seals in new equipment, because the piston surface finish has been burnished by the previous seals. If the surface finish is below 12ra, shortened seal life can be expected due to an insufficient oil film.

If the piston has been burnished, it can be sanded in the field to re-establish the surface finish above 12ra resulting in an increase in seal life.

Urethane seals are very smooth and do not contain natural asperities, therefore they may require a friction modifier to prevent burnishing.  Fabric reinforced neoprene seals have natural asperities and good lubricity and do not typically require a friction modifier.