What are typical O Ring applications?
O Rings can be used in static and dynamic applications as long as there is comparative move between the media and the O Ring. Dynamic applications contain hydraulic cylinder pistons and rotating pump shafts.
1. Reciprocating Dynamic Seals
Dynamic reciprocating O Ring applications include a hydraulic and pneumatic piston or rod seals. Smaller diameter O Rings, therefore, work well for short stroke applications. Thicker cross-sectional O rings are demanded by longer stroke applications. In dynamic sealing applications there are a lot of damage modes, which are explained in another blog post – ‘Why do O Rings Fail’, however they are not a problem for static O Rings.
To increase and prolong lifespan and efficiency of the seal the surface finish of the hardware is extremely important. The perfect hardware surface micro-finish is between 10 – 20 micro-inches furthermore anything below 5 micro-inches will cause adequate surface lubrication to be rubbed away by the end of the stroke. A surface finish that is too abrasive will rub the surface of an O Ring, however, the surface that is too sleek will disallow the O ring to be properly lubricated by a fluid film.
2. Rotary Seals
O Rings have demonstrated to be dependable rotary seals subject to the adequate conditions. The following values need to be met for the appropriate O ring: adequate durometer, specific hardware configuration, and feet-per-minute values. For a long-lasting rotary O Ring, a 55-shaft hardness is usually demanded. There are however a number of distinguished O Ring compounds created for rotary applications.
3. Static Axial Seals
The first thing to investigate when designing grooves for static axial seals is whether the stress is oncoming from outward or inward. Pressure coming from outward – the outside groove diameter is main and the width of the groove is the primary thing to consider for the inside diameter. Pressure coming from inward – the inside diameter is primary. This way you can make sure that the O Ring moves the smallest amount of distance to seal the extrusion gap. Due to an increased swell of the seal the grooves are larger in liquid applications. The smaller groove can be used when there are no foreseen swelling problems.
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