Hydraulic seals and pneumatic seals are designed as per the cylinder working pressure, cylinder speed, operating temperature, working medium and application.
Hydraulic seals are generally relatively soft, non-metallic rings captured in groove or fixed in a combination of rings, forming a seal assembly, to block or separate fluid in reciprocating motion applications. Hydraulic seals are vital in machinery. Their use is critical in providing a way for fluid power to be converted to linear motion. Not only must the hydraulic seals prevent leakage of fluid from the Cylinder, but hydraulic seals must also withstand high pressures, extreme temperatures and transverse forces within the cylinder. In such applications, the function of Hydraulic Seals goes far beyond preventing fluid leakage.
Hydraulic seals can be made from a variety of materials such as polyurethane, rubber or PTFE. The type of material is determined by the specific operating conditions or limits due to fluid type, pressure, fluid chemical compatibility or temperature.
A static hydraulic seal is located in a groove and sees no movement - only sealing within its confined space, acting like gasket.
A type of dynamic hydraulic seal called a rod seal is exposed to movement on its inner diameter along the shaft or rod of a hydraulic cylinder. A type of dynamic hydraulic seal called a piston seal is exposed to movement on its outer diameter along the tube or bore of a hydraulic cylinder.
A hydraulic seal is used to contain fluids and maintain the hydraulic pressure (piston seal, rod seal, back-up ring), to stop the inlet of impurities and to preserve the lubricating film on the rod (wiper seal) and to resist any deformation under a radial load by guiding the piston and rod (wear ring and guide strip).
DEF Seals has a complete range of hydraulic seals and we can also assist you in creating custom-made seals for linear and static hydraulic applications.
The DEF rotary cap seal GNS is a bi-directional seal for use in pneumatic and low to medium duty rotary or oscillating applications. The rotary piston seal is a two piece design comprised of a standard size o-ring energizing a wear resistant PTFE cap. The rotary piston seal offers long wear and low friction without stick-slip. This PTFE outer diameter is designed with a special interference wiht the o-ring to eliminate spinning between the o-ring and seal. Special grooves are designed into the PTFE inner diameter to provide lubrication and create a labyrinth effect for reduced leakage. The seal is commonly used in swivel joints, hose reels and machine applications.


Mobile machinery
Injection presses
Machine tools
Standard cylinders
Injection moulding machines
Optimal sealing in static and dynamic applications
Low friction coefficient; no stick-slip effect
Excellent abrasion and extrusion resistance
Wide temperature range and excellent chemical resistance.



