Low pressure sealing

The use of polyurethane U-rings in cylinders operating at pressures up to 400bar is common practice in the hydraulics industry. Seals such as these provide long life and excellent sealing capabilities which were hardly achievable by using rubber and rubber fabric rod seals.

In some special applications where operating pressures are generally lower, (up to a maximum of 250bar), it is more difficult to obtain the low friction and high sealing efficiency which are often required using polyurethane alone.

PTFE is regularly used as a material for the manufacture of piston seals because of its good low friction properties, but it does have some deficiencies as a sealing material. PTFE has a non elastomeric nature and is readily damaged by scoring on assembly or during service.

Now, by combining the properties of PTFE with the sealing properties of polyurethane, Hallite Seals has created a new seal concept. The seal was created by using an existing design and incorporating a PTFE slip ring into the heel of the seat. The trick was to ensure that the only part of the polyurethane seal that came into contact with the rod was the primary sealing lip. This lets the PTFE act as a slip ring and ensures that `sticking’ does not take place.

The design is particularly suited to single acting cylinder applications with low return forces. Using the design in these low pressure cases, the effects of friction were reduced without compromising the seal.

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