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S.F. Components GmbH

Piston seals of PTFE

The classic type KD double-acting piston seal has a proven track record as a low-friction component for application in hydraulic cylinders and has been successfully employed over many years.

Its compact design with an O-ring of NBR as the preload element provides for an optimum sealing system in most hydraulic applications. The broad spectrum of material combinations available for the sealing element and selection of the appropriate material for the preload element ensure almost unlimited suitability in a wide range of different applications.

The piston seal has a rectangular profile with the edges on the dynamic side slightly bevelled. Stress-relief notches are provided on both faces of the seal to enable fast response to load changes while at the same time preventing backpressure build-up.

A special stepped profile, type KE, is available for hydraulic cylinders pressurised on one side only. The otherwise identical properties of the PTFE combinations likewise ensure high functional reliability throughout the entire service range of this seal.


  • Outstanding friction behaviour
  • No stick-slip effect, even at low velocities
  • High wear resistance, long service life
  • Very good thermal and chemical resistance
  • Individual size ranges possible
  • Simple groove design
  • Two-part design suitable for fitting to single-piece pistons


Application ranges

Velocity:reciprocating up to 15 m/s
Temperature:- 60° C to + 200° C
depending on material combination and O-ring material
Pressure:up to 80 MPa (800 bar)
Groove root:Ra 1,8 µm / Rt 10 µm
Groove flanks:Ra 3,0 µm / Rt 16 µm
Contact area:Ra 0,4 µm / Rt 4,2 µm


The type KD piston seal can be installed without problem in continuous grooves.

To facilitate mounting, it may be advisable to warm the seal in oil at a temperature of approx. 80°C prior to fitting. After fitting the preload and sealing elements, the PTFE piston seal must be sized. This can be done by using the insertion bevel on the cylinder barrel, which should have an angle of between 15° and 20° and a length of 2 mm to 8 mm depending on the as-designed sealing height. Likewise, a separate sizing sleeve can be used. It must always be ensured that sharp edges are removed by rounding or bevelling. Thread tips should be covered. Before fitting, ensure that all machining residues such as swarf, chips, dirt and other foreign particles have been removed.

The surface quality of the mating faces being sealed is of decisive importance for the functional reliability and service life of the seal.

It is important to ensure that there are no ridges, scratches or recesses, nor any concentric or spiral machining marks on the surface.

The parameters usually applied for surface description such as Ra, Rz, Rt and Rmax are defined in DIN 4762 and DIN 4768.

In order to properly assess surface quality for sealing applications, the material ratio (bearing curve tp) should also be taken into account.

This profile shape parameter is influenced by the machining process applied. The material ratio (Mr) should lie between 50 and 70% as determined at a slice depth of approx. 0.25 x Rz based on a reference percentage of approx. 5%.


All information and values stated concerning our product portfolio are based on the knowledge optained through a long experience of manufacturing and application.
These figures are for indicative purposes only and may vary (exceed or deceed) according to the particular circumstances. Unknown factors in the applications and practice can considerably change the conditions and reduce and change statements, which may cause the above information to be invalid.
No liability can be accepted for any mistakes or omissions, error and subject to change without prior notice.


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Piston Sealings

KD double acting


KE single acting



KDAQ double acting


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