Both in static as well as dynamic fluid power applications, back-up rings are ultimately employed to help stop O-ring migration by limiting the extrusion of O-rings into the gap during pressure cycles.
A back-up ring is, in the end, a stiff ring that secures a sealing or plastic connector in the proper position. Back-up rings are most frequently used in conjunction with O-rings, but they are also utilized as reciprocating shafts seals and with lip seals.
What are Back-up Rings?
Back-up rings are typically associated with the use of O-Rings. However, they are also utilized with different types of piston seals, T-seals, and infrequently U-Seals. The back-up ring’s main function is to minimize the extrusion space between the metal surfaces of the two cylinder components so that the seal can function under higher pressures without damaging itself by extruding.
In most applications, the flat-sided back-up ring also works effectively to prevent the softer seal substance from pressing into the extrusion gap. Neither style has a definite performance edge. Also, there are many different types of materials for back-up rings.
The back-up ring’s performance is largely influenced by the component from which it is built. Use a material that is both tough enough to withstand extrusion and elastic enough to have enough memory to make installation simple. For example, the back-up ring should expand during installation but then return to its previous size and form.
According to the principle behind the concave style, as the pressure regulator changes the shape of the O-Ring against the back-up ring, it is deflected far from the extrusion gap by the curve of the back-up ring.
O-Ring back-up rings come in two different forms. One design has two flat sides, while the other has one concave side and two flat sides that support the metal surface.
The different shapes of a back-up ring are as follows:
- Scarf Cut Back-up Ring
The scarf cut back-up ring or the single turn back-up ring is split at one point in its body. Owing to this split it can be made up of very hard materials that can withstand high pressures. It is because of this spit that it is able to perform better than the solid back-up ring when it comes to filling extrusion gaps under pressure. It is widely utilized in modern hydraulic systems. However, the split in the middle can cause tears in the O-ring leading to wear and tear which might cause unwanted sealant issues.
- Solid Back-up Ring
These rings are easy to install and differ from the scarf cut variety in terms of not having a split in them. Due to the ease of installation, they are helpful while working with pistons as well as rods. They are usually made up of flexible material and can be stretched into position to fit into piston glands. However, if they are built of the right material they can be pressed into solid rod glands.
- Spiral Wound Back-up Ring
Due to the expense and availability, modern systems hardly ever use this kind of Back-up ring. Although it isn’t frequently used, the Spiral Wound Back-up ring is occasionally needed for particular tasks. Spiral Wound back-up rings come in a wide range of variations depending on the different devices.
- Contoured Back-up Rings
Applications that require simultaneously static and dynamic solutions use contoured back-up rings. When not tightly managed, these rings are useful. These rings’ contoured faces enable a smooth fit with the o-diameter. When possible, installing two back-up rings is always advantageous.
What are O-rings?
A circular elastic loop known as an O-ring serves as a seal in both static along with dynamic operations. Their primary function is to act as a seal between different types of constructions, including pipes, tubes, pistons, and cylinders. O-rings are extremely flexible and come in a variety of materials based on how they will get utilized. They stop the leaking of liquids or gasses when positioned between two surfaces.
An O-ring is employed as a static seal that stays in place to control pressure or create a vacuum. O-rings apply pressure on the inside of a tube or pipe to create a seal. They are self-energizing and can move in a rotating or reciprocating fashion.
O-rings are produced and manufactured by extrusion as well as injection, compressing, and transfer molding. Elastomers are shaped during the extrusion stage of the process in preparation for molding.
Different types of O-rings include:
- Polytetrafluoroethylene (PTFE)
O-rings made of polytetrafluoroethylene, sometimes known as PTFE O-rings, are a common choice. They are prized for their resistance to the majority of chemicals, acids, lubricants, and steam and have a naturally white tint. They can work in temperatures ranging from -100 to 500 degrees Fahrenheit. Although they are sturdy and resistant to abrasion, they are difficult to compress, which results in less reliable sealing.
- Viton
O-rings can also be made of the synthetic fluoropolymer rubber known as Viton, which is utilized in demanding, demanding, and stressful environments. They are the preferred option for situations where an O-ring must withstand high temperatures and harsh atmospheric conditions that may include the presence of oxygen, mineral oil, different fuels, hydraulic oils, chemicals, and solvents. Even at high temperatures, Viton O-rings continue to operate superbly.
- Silicone
Quartz is used to extract the element silicon, which is used to make silicone. By coupling it with organic components like methyl, phenyl, or vinyl, it is created. The silicone material’s characteristics are determined by the inclusion of these other components.
Oils, chemicals, temperature, ozone, corona, and acids have no effect on silicone. Low temperatures are known to not affect its elasticity. The typical operating range of silicone is -60° to 225° C, with highly formulated versions able to tolerate temperatures as low as -100° to 300° C.
- Ethylene Propylene (EPDM or EPM)
Ethylene and propylene are combined to form the terpolymer EPDM, which is then vulcanized using a monomer like diolefin. It is flexible at low temperatures and has resilience to ozone, UV, and weathering.
Because of its resistance to weak acids, alkalis, and some solvents in addition to its electrical insulating qualities, EPDM is utilized for O-rings. For applications requiring the sealing of hydraulic fluids with phosphate ester bases and braking fluids with glycol bases, it is available in a variety of colors. Additional uses for EPDM include situations with hot liquid up to 150° C.
- Nitrile butadiene rubber (NBR)
NBR is also referred to as Buna-N or acrylonitrile butadiene. It is a butadiene and acrylonitrile-based synthetic rubber copolymer. The amount of the different chemicals from which NBR is made has an impact on its mechanical qualities and wear resistance. Its resilience to the impacts of oil or fuels increases with the amount of nitrile present. It comes in a wide range of hues and is utilized in situations where diluted acids, alkalis, and sodium salts are present.
Why are O-rings Used?
O-rings are among the most affordable and dependable ways to create a robust seal because of their innate tendency to revert to their original form whenever the cross section is put under strain.
A channel that would otherwise enable a liquid or a gas to exit is blocked using O-rings. The O-ring is stamped between two surfaces after being inserted into a channel to clasp them there. The O-ring becomes stuck when it is squeezed, blocking the passageway for the liquid or gas that you are attempting to seal in place.
The O-ring is pushed against the opposing wall of the groove when the system is put under pressure, maintaining a flawless seal even at extremely high or low pressure. When the pressure is released, the O-rings’ constituent elastomers—which are inherently springy and eager to assume their original shapes—spring back to their initial positions, maintaining the seal and making them ready for the subsequent cycle.
Difference Between Back-up Rings and O-rings
Back-up rings work in tandem with O-rings to avoid extrusion gaps at extremely high pressures. Since they are made up of sturdier material, they help in maintaining the elastomeric seal in place. Their essential feature is to assist the O-ring in its functioning.
Back-up rings are made up of firmer material but they are still flexible enough to fill up the extrusion gap. They help to maintain the efficiency of O-rings since they tend to extrude into the clearance of mating surfaces when exposed to high temperature and pressure. Even though O-rings have been tested to properly seal at a pressure of 5000 psi or more, temperature and pressure trends are on the higher side in present fluid systems and will probably continue to rise, placing more and more emphasis on the importance of back-up rings.
Conclusion
O rings and back-up rings are essential components of machinery across countless industries as they help to create efficient seals that do not allow the flow of liquids and gases. While O-rings carry out this function, back-up rings assist them in this process. There can be several types of o-rings and back–up rings made up of a wide variety of materials, depending on the industry in which they need to be utilized.
Regardless of the project, whether it is a little PTFE product for electronics or a huge gasket for the oil and gas industry, Dechengwang, a PTFE O-ring manufacturer has the knowledge and a wealth of talent to deliver a high-quality, precise service.
They also have knowledge of other custom Teflon parts such as bellows, ball valve seats, insulators, etc. In addition, they are capable of clean PTFE molding, basic forms, and near-net forms to conserve raw materials and basic shapes. Contact Dechengwang for more information on the subject.
