Designed to stop leakage when fluids are transferred, o-rings may be in place along rotating shafts, sleeves, placed in flange grooves, valve bonnets, or any threaded or bolted connection. O-rings are an important accessory in every industrial and residential purpose. The concept is extremely simple at first look. However sizing o-rings to the correct size, and the housing that accommodates them with the right interference fit, or groove depth will determine the pressure capability of the o-ring. The use of back-up rings will also extent the extrusion resistance strength of the o-ring.
Not all o-rings are created equally. To understand this you really have to go back to the way o-rings are made. With the exception of the more exotic o-rings such as FEP encapsulated o-rings, PTFE O-rings and Flexible Graphite o-rings, most o-rings are molded from rubber. Any rubber manufacturer will confirm that molded rubbers are made of "compounds" which essentially means it is a blend of materials. It's a fact that although a rubber part (not just o-rings) may contain over 50% of a given type of rubber, be that Buna-N, SBR, Neoprene, Viton, etc, it also contains other filler materials which in some cases are to enhance the functionality of the given compound. It's also true that some rubber compounders will utilize inexpensive fillers like clay, to help lower the cost. O-rings that have cheap fillers will often show premature cracking when in service.
The critical variables that the supplier must be made aware of to insure the correct compound is selected include:
- Temperature Range required
- Applications (Static or Dynamic)
- Media being sealed
- Pressure being sealed, continuous and excursion pressures
- Size (Cross Section) Inside Dimension, and Outside Dimension
- Speed - if the seal is dynamic.
Based on the above variables American Seal & Packing can advise what compound will provide the highest probability of a successful, long term seal. In many applications there are multiple compounds that will seal equally well, which allows the customer to select the compound that will help the OEM customer provide a product with the lowest cost point.
An efficient o-ring is a significant accessory for every mechanical assembly and provided the seal used in connecting areas in a pump, valve, engine, compressor, heat exchanger, oil filter, strainer, or millions of other industrial applications.. It ensures that the fluid while flowing from one part to another doesn't leak into other areas of the assembly or completely out of the assembly disrupting the process.
O-Rings Industrial Application
O-rings are predominantly used in places where different parts of a mechanism meet and where chances of leakage is high. In technical terms, the meeting point is usually referred to as the mating surfaces and any gap found in this region is identified as the clearance gap. When O-rings are used, they will block these clearance gaps strongly and will ensure not even a single drop of the fluid passes through it in static applications.
While there are other methods to block this area including welding, soldering or brazing, those methods would not allow for easy dis-assembly unit. The concept of using a soft material between two hard elements has been proven to be more efficient and reliable not to mention making a seal possible in a dynamic application where one of the contact services has motion. A common method involves two different parts – the O-ring and the gland. A machined groove will be found in the gland to which the ring is attached and the mating surface will be sealed.
By default, most O-rings are shaped like a doughnut and are made using different materials. However there are Lobe style o-rings and rectangular cross sectional o-rings which each have there advantages in specific o-ring type applications.
Most commonly used raw materials are synthetic rubber combined with steel or plastic for the connection areas. As they are made of flexible rubber material, these accessories are highly versatile and has the capacity to deform themselves so as to suit any shape found in the cavity that is near the clearance gap. They are usually over sized because the rings are primarily being used to lock surfaces and prevent leakage.
Smaller ones may lead to improper sealing and will let the fluid leak out. Over sized design ensures a tight fit and it also increases the longevity of the rubber to retain its shape for years to come. Dimensions that define a ring include its inner diameter, cross section diameter along with the hardness of the material that is used to design it. Radial and axial are the two major types of o rings available in the market. Molecular aspects of the O-ring will always be made to force itself to regain its original shape even though they are always squeezed into tiny cavity at mechanism joints. Constant pressure will be exerted by the rubber ring to retain its memory shape. Specifying the right rubber compound is critical in that if an elastomer is compressed in a joint and exposed at or near it's temperature limitation, it will take a set and loose it's recovery.