"Where seals are created, not just made!"


TECHNICAL INFORMATION


Glossary of Terms

  • Anti-extrusion Ring
  • A ring used to support a softer sealing ring and prevent it from extruding.
  • Back-up Ring
  • Anti-extrusion ring or support ring.
  • Bearing
  • See Wear Ring
  • Bi-directional Seal
  • A seal that prevents leakage from both directions.
  • Cold Flow
  • Continued deformation under stress
  • Composite Material
  • Materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.
  • Compression Set
  • The permanent deformation of a seal after release of a compressive load.
  • Copolymer
  • A copolymer is a polymer derived from two (or more) monomeric species.
  • Creep
  • Creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses.
  • Double acting Seal
  • A seal designed to take pressure from two sides.
  • Dynamic Seal
  • A seal designed to prevent leakage between two moving surfaces.
  • Elasticity
  • The property of a substance that enables it to change its length, volume, or shape in direct response to a force effecting such a change and to recover its original form upon the removal of the force.
  • Elastomer
  • An elastic substance occurring naturally, as natural rubber, or produced synthetically, as butyl rubber or nitrile.
  • Extrusion
  • Distortion or flow of part of a seal into an extrusion gap under pressure.
  • Extrusion Gap
  • The clearance on the low pressure side between two parts, which house the seal.
  • Face Seal
  • A seal that is compressed in a direction parallel to its axis.
  • Flash
  • Extruded material on the partially finished product formed during the molding process.
  • Flex Cracking
  • A surface cracking induced by repeated bending or flexing.
  • Free Height
  • The height of a seal in its free-state.
  • Friction
  • Friction is the force resisting the relative motion of two surfaces in contact.
  • Gasket
  • A rubber, metal, or other material, for packing a piston or placing around a joint to make it seal a fluid or gas.
  • Gland
  • A cavity into which a seal is installed. Component at the working end of a cylinder which contains seals.
  • Hardness
  • The measured resistance of a material to indention, abrasion, deformation, or machining.
  • Housing
  • A rigid component which contains a seal assembly.
  • Hydraulic Seal
  • A hydraulic seal is usually a relatively soft, non-metallic ring captured in a groove or fixed in a combination of rings, forming a seal assembly, to block or separate fluid in reciprocating motion applications.
  • Leakage Rate
  • The rate at which a fluid passes a seal in a given time.
  • Lip Seal
  • An elastomeric seal that prevents leakage in rotary seal applications through the use of one or more contact lips operating on the shaft surface. These seals are commonly called shaft seals, oil seals or rotary lip seals.
  • O-ring
  • A toroidal shaped sealing device usually made from an elastomeric material, may also be made from metal or PTFE.
  • Perfluoroelastomer
  • An elastomer with high temperature and chemical resistances.
  • Permanent Set
  • Permanent deformation of spring or elastomer upon release of load.
  • Permeation
  • The passage of a fluid under pressure through a solid material by diffusion.
  • Polymer
  • A material formed by the joining together of many (poly) units (mer) of one or more monomers.
  • Porosity
  • Quality or state of being porous.
  • PTFE
  • Polytetrafluoroethylene.
  • Rubber
  • See “Elastomer.”
  • Scraper
  • A seal used to keep dirt or other foreign matter out of a hydraulic or pneumatic device.
  • Seal
  • A device designed to prevent the passage of a medium (fluid or solid).
  • Single acting Seal
  • A seal designed to take pressure from only one side.
  • Spring
  • A machine element capable of restoring energy and releasing it.
  • Static Seal
  • A seal between two non moving parts.
  • Tensile Strength
  • Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material.
  • Thermal Expansion
  • Expansion caused by increase in temperature.
  • Uni-directional Seal
  • A seal that prevents leakage from only one direction.
  • Vacuum
  • An enclosed space that is occupied by a gas at less than atmospheric pressure.
  • Vulcanization
  • Refers to a specific curing process of rubber involving high heat and the addition of sulfur or other equivalent curatives.
  • Weepage
  • A minute amount of liquid passing by a seal.
  • Wiper Ring
  • See “Scraper.”
  • Wear Ring
  • Element used to protect moving parts from wear.

Materials Compatibility

If you have any concerns about material being compatible with a particular medium, please look at the pdf below or contact one of the Swan Seals Sales Teams.

 Fluid Compatibility Tables (PDF)

Fitting Tips

 

Rod Seals

Before installing seals the following should be observed:

  • Make sure the rod has a lead in chamfer, if not, use an installation tool.
  • Chamfer or round sharp edges.
  • Cover screw threads.
  • Carefully clean all parts making sure any machining debris are removed.
  • Grease or oil housings for seals and rods to aid installation.
  • Do not use sharp tools to fit seals.

Installation into a split housing.

Installation into a split housing is relatively simple. The shape of the seal corresponds to the housing it is to be fitted in. The seal should not be allowed to twist when fitted.

When fitting the rod into the housing, the seal will need to be sized. If the rod has a long enough chamfer it will probably be suitable for this. If not, a sizing sleeve should be used.

Installation into a closed housing

For seals manufactured from polyurethane, nitrile or similar elastomer a fitting tool is recommended.

Where a fitting tool is not available or suitable the seal should formed into a kidney shape. The seal should have no sharp bends.

Insert the seal into the groove, then apply pressure to the kidney shape as indicated by the arrow in Fig.2.

When the seal is in the housing, reshape by hand. Finally, resize the seal using either the rod itself, provided it has a sufficiently long chamfer, or a mandrel manufactured from a polymer material with good sliding properties. It should have a chamfer of 10-15° over 30mm.

Piston Seals

Before installing seals the following should be observed:

  • Make sure the cylinder has a lead in chamfer, if not, use an installation sleeve.
  • Chamfer or round sharp edges.
  • Cover screw threads.
  • Carefully clean all parts making sure any machining debris are removed.
  • Grease or oil housings for seals and rods to aid installation.
  • Do not use sharp tools to fit seals.

Installation into a split housing.

Installation into a split housing is relatively simple. The shape of the seal corresponds to the housing it is to be fitted in. The seal should not be allowed to twist when fitted.

When fitting the rod into the housing, the seal will need to be sized. If the cylinder has a long enough chamfer it will probably be suitable for this. If not, a sizing sleeve should be used.

Installation into a closed housing.

Installation of polyurethane and nitrile rubber seals are relatively straight forward. These will generally stretch over the piston and slot into the groove with no further adjustment required.

The installation of PTFE seals though will require the use of installation aids.

PTFE seals can be installed easier if the are heated up in oil or water to between 80°C to 100°C Do not use tools with sharp edges to stretch the seals.

For the series production installation of PTFE piston seals, the use of installation tools are recommended. These parts should be manufactured from a polymer material with good sliding properties.

Seal Failure Causes

Please find link below for information relating to possible causes of seal failures.

Seal Failure Causes