Considerations for Mounting Slip Rings to Hydraulic Swivels

Posted on Tuesday, July 19, 2016 in UEA Blog

It is a well-known fact that oil and water do not mix.  This fact has been dramatically demonstrated by the devastating environmental effects of crude oil spills and pipeline ruptures which have occurred over the past few years.   Neither water nor oil mixes well with electrical slip ring assemblies either, but they are often encountered within the typical operating environment for UEA slip rings on a wide variety of mobile construction equipment.

The presence of oil or water within a slip ring enclosure can lead to everything from slight discoloring of one or two components to complete failure of the slip ring assembly.  Complete destruction of the slip ring is not necessary to produce slip ring failure in the mind of the customer. Any failure to conduct a signal through the slip ring fails to produce the desired or necessary result.   The contaminating oil is frequently a result of a leaking hydraulic component. Moisture or water contamination is often a result of rain, snow melt, condensation or high-pressure cleaning.

Logic would suggest the slip ring assembly be located in a place away from oil and water as much as possible, along with sealing the slip ring enclosure as tightly as possible.  Unfortunately, machine design and space constraints often limit the slip ring to a mounting location below a hydraulic swivel assembly rather than to the preferred location above the hydraulic component.

Positioning the slip ring below the hydraulic swivel means the center leads or harness from the slip ring must pass up through a center hole in the hydraulic swivel.   Unless the center hole of the hydraulic swivel can be sealed at the top of the swivel, using either a liquid-tight style connector or flexible conduit around the center leads, any rain, oil, etc. can pass down through the hydraulic swivel and directly into the slip ring unless the leads are sealed where they exit the slip ring through a flanged mounting tube.  Sealing at this point is often provided by potting or, where space is available, a liquid-tight connector.

To avoid a potential column of water or oil in the center hole of the hydraulic swivel, spacers are often added between the bottom of the hydraulic swivel and the mounting flange of the center tube of the slip ring to allow drainage of the center hole.

Another important factor­, whether mounted above or below the hydraulic swivel, is to provide adequate drainage from the bottom of the slip ring.  The slip ring can survive oil or moisture in the environment but does not often survive if submerged, as can happen if moisture is allowed to accumulate or fill the enclosure.  The sophistication of the drain required will depend upon the operating environment and the possibility that the slip ring will be sprayed from below with either road spray or high pressure cleaning spray.  Allowing the slip ring to have air exchange or 'breath' through the drain also helps to prevent condensation from forming inside the enclosure.

Put simply, for slip rings in an outdoor industrial environment and independent of the mounting orientation, the assembly needs to be sealed as well as possible from the top and drained at the bottom.  UEA has many years of experience in working within these outdoor environments and welcomes your questions concerning your specific application. For more information about UEA slip rings and hydraulic swivels visit

Brent Jensen
Engineering Manager