Silicone Rubber Plunger Seals
Silicone Plunger Seals or Silicone Plunger Rings are used in pneumatic and hydraulic cylinders for fluid sealing. Some Silicone Plunger Seal profiles are designed with similar inside and outside sealing geometry. Therefore, they can also be used as piston seals.
Silicone Plunger Seals are specially engineered for fluid power applications, these compounds provide exceptional resistance to wear and outstanding extrusion properties. Compatible with virtually all media, they demonstrate great performance at extremes of temperature.
Silicone Plunger Seals are internal to the cylinder head and seal against the cylinder bore, preventing fluid from flowing across the cylinder head. This allows pressure build up on one side of the piston, making the cylinder extend or retract. Silicone Plunger Seals are typically classified into single-acting (pressure acting on one side only) and double-acting (pressure acting on both sides) seals. Silicone Plunger Seal cross section is Y profile, which is designed for sealing, rotating and pressure work.
Silicone Plunger Seals are mainly made by silicone rubber compression mold tooling or LSR injection molding ( LIM ) with middle mold plates. Silicone Piston Seals are better in sealing, life span and working pressure limit without retain ring compared with other rubber plungers seal, which are mainly made of NBR or PU rubber. Notes:
1. Silicone Plunger Seal’s margin & edge should not have silicone rubber flashing ( burrs ) because it will rotate when device is working. For sealing function, silicone piston seal is demanding in design and dimension tolerance, especially for seal edge.
2. Middle mold plates are chamfer processed by cutting tool, which will wear out with processing. Therefore the cutting tool needs to be changed frequently.
Silicone Plunger Ring is used in reciprocating seal devices, which has a longer life span than Silicone Rubber O ring.
Working pressure: < 25 MPa
Working temperature: -40~+120℃
Medium: hydraulic oil, water, air
Silicone Plunger Gasket working speed ranges vary from material to material:
NBR: 0.01~0.6 m/s
FKM: 0.05~0.3 m/s
PU rubber: 0.01~1 m/s Silicone Plunger Seal made of PU rubber is better in sealing, life span and working pressure limit without retain ring.
Silicone Plunger Seal properties:
Excellent sealing
Less friction and smooth movement
Good pressure resistance and wide applicable pressure range
Simple structure and low cost
Easy installation Silicone Plunger Seal & Y Profile Ring Sealing Principles
Relying on the open lip, Y ring attaches coupling surface in a linear contact, producing “peak” contact stress under medium pressure, the higher pressure, the greater contact pressure. When coupling parts do relative motion at working speed, a layer sealing liquid membrane forms between sealing lips and sliding coupling surface, thus producing sealing effect. After sealing lip worn, it has the automatic compensation ability caused by medium pressure.
Piston Seal & Y ring with side lip for shaft. After each reciprocating motion, a little liquid (work medium) remains between main lip and side lip. With increasing reciprocating motion, the remaining liquid will filled with the room between main lip and side lip, finally forming a special “siege area”.
While the main lip is in the state of work, its pressure is higher than working pressure in small chamber due to the incompressibility of liquid in “siege area”. At the moment, the contact stress between side lip and coupling surface is also stronger than the contact stress between main lip and coupling surface. Therefore shaft extension forces the liquid in “siege area” back to small chamber, forming the reliable sealing condition, which improves Y ring sealing performance. The higher pressure in “siege area”, the greater contact stress from side lip on coupling surface and the sealing will be better. Y Ring Applications Lip mouth must be towards the side with higher pressure during installing Y ring. Only in this way, can Y ring produce sealing effect.
Fit clearance between sliding coupling parts must be controlled in order to prevent Y ring root from being squeezed into the intermittence of sealing coupling surface under high pressure because of material plastic deformation .
As for Y ring, whose working pressure is more than 16 MPa, for ensuring Y ring’s life
span, circlip must be installed in seal ring’s root to prevent the root from being squeezed into fit clearance.
In order to keep the moving stability and avoid overturn & distortion during reciprocating motion, supporting ring can be installed to Y ring lip.
Lip Seal & Y ring with supporting ring
1. one-way compression 2. two-way compression
There are small diversion holes distributing uniformly on supporting ring, which is good for pressure medium affecting on sealing lip sides through small holes，distracting two lips and keeping the right dynamic posture of Y ring to ensure the good dealing.
As for wide Y ring, the width of its cross section is twice or above as long as the height. This kind of seal ring can’t turn over or twist in groove, so we can choose not to install supporting ring. 
