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Keep air, dirt, and moisture out of reservoirs

A hydraulic system’s reservoir may pose the greatest challenge for keeping dirt and moisture out of a system. That’s because fluid level constantly rises and falls as a machine cycles.

out of reservoirs

Fluid leaving the reservoir is replaced by ambient air from the surrounding environment, and this air is usually contaminated with dirt and humidity. Consequently, if air is not filtered and dried before entering the reservoir, the contaminants will be drawn into the system. A sealed or pressurized reservoir could be used, but these recourses add substantial cost and complexity to the system and introduce their own challenges.

As a solution, Pronal, Leers, France, invented a volume compensator, an inflatable bladder made of heavy synthetic fiber coated and vulcanized inside and out with an oil-resistant elastomer. The separator fits inside the reservoir and inflates as the dropping fluid level creates a vacuum, expanding to occupy any voids. When fluid returns to the reservoir, pressure pushes the air out to deflate the compensator.

volume compensator
Pronal’s volume compensator keeps ambient air from coming in direct contact with hydraulic fluid in a reservoir, eliminating the potential of contamination from dirt and water.

If the top of the reservoir is cluttered with valves and other components, the separator can be placed outside the reservoir and connected with tubing. The compensator can also be configured to enable the reservoir to work submerged under water.

For more information, call +33 (0)3 20 99 75 00 or visit