An O-Ring seal is a means for closing off a passageway preventing an unwanted escape or loss of fluid. The seal consists of an O-Ring installed in a gland and is exactly that - a circular run in which the elastomeric material has a section that is virtually circle. The gland is the cavity (usually within metal) into which the O-Ring is placed. The combination of these two elements comprises an O-Ring seal.
O-Rings are used in two general design applications: static (non-moving) and dynamic 9 moving). Static application stay range from vacuum to over 60,000 ps for sealing flanges and O-Ring grooves. O-Ring seals with lobed cross sections were designed for both static and dynamic applications. The four and six lobed configurations resist spiral failure and also extrusion failure in application with large clearance between parts. Of the some 20 different types of O-Ring seals available, the common round cross section O-Ring type is the most versatile. The conventional type of O-Ring may e used in almost any application if the plan to contain he deal is designed correctly and the right size and material is chosen.
All fluid-tint seals are characterized by the Adsense of any passage by high fluid might escape. Detail differences exist in the manner by which zero clearance is obtained - welding, brazing, soldering, ground or lapped fits or the yielding or softer material wholly or partially confined between two harder and stiffer members of the structure. The O-Ring seal falls in the latter class. The rubber seal should e considered as an incompressible, viscous fluid having a very high surface tension. now, whether by mechanics pressure from the surrounding structure or whether by pressure transmitted through hydraulic fluid, this extremely viscous fluid (the elastomeric O-Ring) is forced to flow in the gland to produce zero clearance or a positive block to the flow of the less viscous fluid being sealed. The rubber absorbs the stack-up of tolerances of the unit and its memory maintains a sealed condition.
How do you achieve optimum performance of an O-Ring?
Surface Finish
All metal surfaces over which the O-Ring moves should be held to a maximum finish of 16 RMS, although the groove finish can have a maximum of 32 RMS. There should be no nicks, burrs, or scratches.
Metals
All metals over which an O-Ring moves should have a hard surface such as steel, nickel-plated, or chrome-plated. Special attention should be given if you select soft metals such as aluminum, brass, or bronze.
Excessive Metal Clearance
Clearances should be held to the recommended maximum diametrical tolerance. Consideration must be given the breathing of cylinder in your calculations - which is the possibility of the cylinder bore to expand or balloon out as its cente.
Concentricity
It is important to hold eccentricity within the recommended practice and to design for sufficient bearing area to take care of see loads or off centre loading.
Squeeze (preload)
For good sealing, the minimum diametrical squeeze should be observed. Where pressures are low and friction is critical, the amount of squeeze can be decreased but caution should be exercised.
Cleanliness
All systems should be kept clean and free form dirt, grit, chips, and any foreign materials. Any type of abrasive material will cut the O-Ring. When replacing a failed O-Ring, look for tiny metal chips embedded into the O-Ring, which could mean a pump concern.
Lubrication
When used in pneumatic systems, O-Rings should be lubricated. If permitted to run dry, then they will face abrasion and twisting.
Groove Design
Proper design is a most essential factor in the successful operation of O-Rings. The rectangular shaped groove is recommended except for special applications.
