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Taking the pressure off

When, where, and why to use a buffer seal

A recent SKF-led investigation studied the interaction between buffer and rod seals and their combined effect on overall sealing performance. Solutions of optimized sealing capabilities with a focus on friction, intermediate pressure & external leakage were placed onto an in-house rod seal package test rig to enable a comprehensive and fair analysis of the full range of products.

What exactly is a buffer seal?

As the name suggests, buffer seals are used to safeguard the main rod seal within a complete rod sealing system. They act as a primary seal and combine different functions: handling system pressure, absorbing system pressure spikes, allowing oil to pass the seal lip to lubricate the rod seal and wiper, and venting intermediate pressure traps which can occur between the buffer and rod seal.

Buffer seals are typically used as part of heavy-duty rod sealing systems

How they work

Various buffer seal designs are available for use in rod sealing systems in hydraulic cylinders – and for several medium- to heavy-duty industrial applications. Generally, they use one of two basic design principles: Either they are designed for high seal ability or to lower the friction of the whole rod sealing system.

High seal ability buffer seals will handle entire system pressure and any potential pressure spikes. Therefore, the rod seal will not be pressurized and damaged. High seal ability also means that only a very thin lubrication film can pass the buffer seal which could cause poor lubrication of the rod seal, resulting in stick-slip, increased friction, and higher sealing edge temperatures which will shorten the lifetime of the whole rod seal package.

Friction optimized buffer seals allow a thicker lubrication film to pass through the seal lip, so that the rod seal remains well lubricated in operation. Depending on the operating conditions it allows a certain amount of pressure to build up between the rod and buffer seal (intermediate pressure). On the one hand, the design of such a buffer seal needs to be optimized to avoid system pressure passing the seal – and on the other hand, vent intermediate pressure back to the system. If the selected buffer seal, rod seal, and wiper are interacting correctly, the overall friction level could be reduced significantly, and the service lifetime of the whole rod sealing system will be increased.

Which seal is right for you?

Approaching the seal selection process demands extensive knowledge of the application and the operating environment that the seal will have to deal with. A rod seal package with a friction-optimized buffer seal should be used in OEM components which will result in a longer service lifetime of the hydraulic cylinder right from beginning. Whereas high seal ability buffer seals can be more suitable in the aftermarket – where dynamic sealing surfaces are no longer in an optimal condition –to provide a proper working rod sealing system.

The table below will assist you when choosing the right buffer seal:

*New products currently in validation phase

Whereas selection of the buffer seal type is important, the rod seal and the wiper need to be selected accordingly. It is imperative to select the right seal combination to gain the best working rod seal package for the related application.

SKF and Industrial Seals Expert understand the complexities involving sealing system selection – especially in rod sealing arrangements where application criteria are stringent and there are many differing components to source.

If any detailed information is requested, please contact your local SKF Seals Expert, or leave a comment below and we will be sure to reply!

Read the full technical article in EVOLUTION