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A back-up ring is a rigid ring that holds an
The back-up ring is matched to the steel pipe flange specification and is placed behind the HDPE flange adapter - an end piece on the HDPE pipe that looks much like a steel flange at the end of the HDPE pipe. As the flange adapter does not have much structural strength, the back-up ring supports and compresses the HDPE flange adapter against the steel flange and creates an effective connection between the two piping materials.
"Rubber Contoured Back-Up Ring Size Chart"Technical Note PP 811-TN PE Flange Connections
Seal rings {{engineering-stub
elastomeric
An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
seal
Seal may refer to any of the following:
Common uses
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impr ...
or plastic (such as Polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
) connection to its designed shape and in its correct place. Back up rings are commonly used with O-rings
An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more par ...
, lip seals, and as reciprocating shaft seals. They are also used for piping connections joining two different materials - typically one flexible and one rigid.
Seals
When sealing the piston inside apneumatic cylinder
Pneumatic cylinders (sometimes known as air cylinders) are mechanical devices which use the power of compressed gas to produce a force in a reciprocating linear motion.
Like hydraulic cylinders, something forces a piston to move in the desire ...
, a soft and flexible material is required to prevent leakage, but those same properties may leave the seal material vulnerable to being pulled out of its seat and then pinched or torn in the narrow space between piston and cylinder wall. If the joint cannot be redesigned, or a more resistant elastomer used, then the solution may be direct reinforcement with a stiffer material - in the form of a hard inner ring in this case. A second function can be to hold the elastomer in place while a machine is being assembled, as geometry may prevent the seal from being directly checked after assembly.
Rubber Contoured Back-Up Ring Size Chart
Contoured back-ups are routinely produced in a 90durometer
The Shore durometer is a device for measuring the hardness of a material, typically of polymers.
Higher numbers on the scale indicate a greater resistance to indentation and thus harder materials. Lower numbers indicate less resistance and soft ...
nitrile
In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix ''cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...
. This provides sufficient elasticity to permit stretching over the major diameter of a piston and then snapping back into the gland
In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).
Structure
De ...
groove cut into the piston. 90 durometer has sufficient hardness to resist extrusion of the softer elastomeric O-ring performing the actual sealing function against the high pressure liquid or gas.
* 000 Series O-rings 0.070" ±0.003" - .045" Thick
* 100 Series O-rings 0.103" ±0.003" - .045" Thick
* 200 Series O-rings 0.139" ±0.004" - .040" Thick
* 300 Series O-rings 0.210" ±0.005" - .060" Thick
* 400 Series O-rings 0.275" ±0.006" - .096" Thick
Pipe Connections
Back-up rings are used in Polyethylene (PE) pipe connections, such as HDPE pipes, where they are connected to steel pipe or pipe fittings.
The back-up ring is matched to the steel pipe flange specification and is placed behind the HDPE flange adapter - an end piece on the HDPE pipe that looks much like a steel flange at the end of the HDPE pipe. As the flange adapter does not have much structural strength, the back-up ring supports and compresses the HDPE flange adapter against the steel flange and creates an effective connection between the two piping materials.
References
External links
Seal rings {{engineering-stub