What is an o-ring?
An o-ring is doughnut-shaped object, generally made from an elastomer. It is usually installed in a cavity and then pressed against. The combination between the hard cavity and the soft o-ring results in a completely leak free system. O-rings are used at every connection of the air conditioning system creating a sealed system. The seals can withstand variable or constant pressures,high and low temperatures,preventing the venting of the refrigerant into the atmosphere.
Why do o-rings fail?
The only way to properly install an o-ring is by deforming it. Male and female fittings or other ac component connections must be compressed to a point where the clearance between the gland and the o-ring is zero not allowing the refrigerant gas to escape.
The most common causes of an o-ring failure are:
Incompatibility between the o-ring material and the fluid it is to seal.
The wrong o-ring size.
Improper o-ring installation.
Gland or cavity deformation.
O-ring dry installation or using the wrong type of lubrication
O-ring failure analysis.
Compression set failure:
This type of failure produces flat surfaces on the sides of the o-ring that were compressed. Compression set failure has its roots in the material used for the fabrication of o-rings with low compression set resistance and limited heat resistance.Excessive o-ring swelling in the cavity can occur due to refrigerant or oil incompatibility or too much squeeze in the groove or cavity.
After the replacement or repair of any ac component the replacement of o-rings are a must. It’s never a good idea to reuse o-rings. High quality, low compression set material is the best way to minimize this type of failure, along with choosing the right o-ring size according to cavity dimensions.
Explosive decompression o-ring failure:
Random ruptures, crater-like pores and small slits, which have originated within the body of the o-ring. These are signs indicating gases permeating the o-ring material and then rapid changes of compression and decompression taking place with micro-explosions occurring during decompression stage.
Heat hardening and oxidation o-ring failure:
A flattened area will appear on the dynamic surface of the o-ring. Sometimes cracked, hardened and pitted areas can be seen throughout the entire body of the o-ring. This failure is caused by higher than recommended temperatures for the material.
Spiral o-ring damage:
The surface of the o-ring appears to have been twisted, or to have rolled in its groove. It stays in this position when freed. This type of failure is caused if the wrong o-ring size is chosen causing excessive clearance in its cavity or during an improper installation. Choosing the right o-ring size and properly lubricate the o-ring is a good way to minimize this type of damage. It is always a good idea to check the ac component where the o-ring will be installed for roundness.
Excessive o-ring swell:
Identified by obvious dimension of the body of the o-ring. Reduced physical properties, which causes improper fit. Heat and friction accelerates seal failure. Due to chemical incompatibility the material absorbs ac system fluids causing swelling of the o-ring.
Materials used for o-rings.
Material usage will depend upon the environment the o-ring is to be used in.Various fluids,gases temperatures,and other environmental properties will affect the material.
O-RING SEAL MATERIAL
|SEAL MATERIAL NAME||COLOR||TEMPERATURE LIMITS|
|Nitrile Rubber (NBR)||Black||-22 to 210 °F|
|Highly saturated nitrile rubber||Black||-13 to 302 °F|
|Fluoroelastomer (Viton®)||Brown, black or green||-4 to 392 °F|
|EPDM rubber (EPD)||Black||-49 to 300 °F|
|Silicone rubber (SIL)||Blue, white or orange||-75 to 392 °F|
|Virgin PTFE ( Teflon,Virgin Teflon||White||-328 to 500 °F|
|Neoprene®||Black||-65 to 250 °F|
|Perfluorolastomer (PFR)||Black with brown hue or white||-20 to 570 °F|
|Fluorosilicone||Blue||-80 to 350 °F|
|Aflas® (AFL)||Black||-20 to 400 °F|
|Armor-o-rings ™||Black with opaque shell||-99 to 401 °F|
O-ring tools & installation
The use of the proper tools for O-ring installations are critical to avoid any damage to the o-ring surface.The use of sharp-edged tools, passing the o-rings over sharp threads,lack of lubrication and use of poor quality o-ring materials are the main causes of o-ring damage and possible air conditioning leaks.It is recommended the use of picks for removal & installation of the o-rings.Always lubricate the o-ring with the right type of oil and cover sharp threads before passing the o-ring over. Choosing the right size of o-rings for every application in the air conditioning system is crucial.
O-ring storage & handling
The best practical way to store o-rings is inside a sealed polyurethane bag and then placed in a closed box or container which light cannot penetrate. O-rings should be kept cool below 86 F. Excessive humidity will deteriorate some seal element material as well as cause corrosive damage to metal cases and spring. O-rings should be kept away from direct or reflected sunlight and electrical equipment that may generate ozone.