Without the proper seal, the failure of a hydraulic cylinder, and thus the entire hydraulic system, is all but guaranteed.

As such, it is critical to make sure that the right seal is selected based on factors such as how the cylinder is expected to operate as the piston is pushed down the cylinder bore.

As a necessary component of fluid sealing in hydraulic cylinders, piston seals, also known as piston rings, are designed to seal in fluid, thus preventing the flow of fluid across the piston. This is made possible when the piston seal secures against the cylinder bore from inside the hydraulic cylinder, meaning that pressure will build up on one side of the piston.

Figure: An O-ring energized piston seal for dynamic applications. Source: Seals-Shop

Yet, because hydraulic cylinder seals are found in everything from machine tools, trucks and off-highway vehicles to injection mold machines, it stands to reason that a seal will sometimes need to conceal pressure from both sides of the piston.

This demonstrates a scenario where the choice between single-acting hydraulic seals versus double-acting hydraulic seals becomes crucial.

Single-acting vs. Double-acting Piston Seals

Single-acting piston seals are designed to keep pressure on one side of the piston without leakage. Because the seal operates in one direction (unidirectional), the pressure is applied on one side only.

Double-acting piston seals, on the other hand, are designed to conceal pressure from both sides, which means that they are designed to be bidirectional.

Selecting between single-acting and double-acting piston seals has everything to do with the intended use of the system and the direction that the system will be operating in. As such, choosing wisely can make all the difference in the life of a cylinder and thus help avoid unwanted machine downtime.

Helping to make that decision easier is Seals-Shop, with a variety of Trelleborg piston seals to fit just about any application. Made from high-quality materials that are durable in most conditions, Trelleborg seals have the answer to just about any question concerning hydraulic, pneumatic and mechanical seals and, as its online shop, Seals-Shop will help find the ideal seal for any application using their convenient Product Finder. Need installation help? Each product description on our shop includes an easy-to-follow diagram detailing the installation steps for each specific seal. Moreover, you can watch some of our installation videos here.

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