Before introduce you about O-ring seal work principle, we have to know what O-ring is, and as seal industry, there are so many terminology to cater to O-ring seal things. Well, let us read the definition below and know what o ring seal is firstly?
What is O ring seal?
- ring, also known as packing or toric joint, is a kind of ring-shaped mechanical washer; it is an elastic body ring with circular cross-section, which is designed to be fixed in the groove, compress when assembling two or more parts, and form a seal at the interface. O-rings can be used in static or dynamic applications where there is relative motion between the part and the O-ring. Dynamic examples include rotating the pump shaft and the hydraulic cylinder piston. The static application of O-ring can include fluid or gas sealing application, in which: the O-ring is compressed and leads to zero clearance; the material of O-ring is sulfurized solid, which makes it impermeable to fluid or gas, and the O-ring material can resist the degradation of fluid or gas. O-rings are one of the most commonly used seals in mechanical design because they are cheap, easy to manufacture, reliable and easy to install. They have been tested to seal up to 5000 psi (35 MPa) and the maximum recommended pressure for pressure O-rings depends on seal hardness and gland clearance. O rings are available in various metric and English standard sizes. Dimensions are specified by the inner diameter and cross-section diameter (thickness). In the United States, the most common standard inch size meets the SAE AS568c specification (e.g., AS568-214). ISO 3601-1:2012 contains the world’s most commonly used standard sizes, including inches and metric. There are also standard sizes known as BS sizes in the UK, usually ranging from BS001 to BS932. Other sizes are also available.
Work principle of O-ring
The O-ring is probably the most common hydrodynamic seal. They are multi billion dollar products made by manufacturers around the world, and they prevent leakage from anything from pumps and valves to cylinders and connectors. Compact, economical components handle both static and dynamic operation in pneumatic and hydraulic applications. These simple seals consist of a ring (technically a ring) with an annular cross-section. They are usually made of elastomers such as nitrile rubber, chloroprene rubber or silicone rubber, but they are also made of plastics such as polytetrafluoroethylene, metals and other materials. Sizes range from a few inches to a few meters in diameter.
The O-ring is sealed by mechanical deformation, creating a barrier between two closely matched surfaces for a potential leak path of the fluid. The O-ring is usually installed in a groove that is machined or molded on one of the surfaces to be sealed. Their rubber like properties enable them to compensate for dimensional changes in mating parts. When the size is appropriate, the clearance between the surfaces is less than the outer diameter of the O-ring. As a result, when the two surfaces come into contact to form a gland, they compress the O-ring and deform the circular section. This radial extrusion of the seal produces a force that ensures that the surface is in contact with the inner and outer walls of the gland.
With little or no pressure, the natural elasticity of the elastomer compound provides a seal and prevents the passage of fluid. Increased extrusion (e.g. use of larger diameter O-rings in grooves of the same size) increases deformation and sealing force. But this will lead to problems in high pressure dynamic applications.
Apply fluid pressure to push the O-ring to the groove wall on the low-pressure side to increase the sealing force. The interference between the seal and the mating surface makes the O-ring continue to operate without leakage. At higher pressure, the O-ring will form a “d” shape, and the contact area between the elastomer and the gland surface may be twice as large as that under the initial zero pressure condition. Due to the elasticity of the elastomer, the pressure is released to restore the O-ring to its original shape, ready for the next pressure cycle. It also allows a properly designed O-ring to seal in both directions.