When sourcing sealing products, you may often come across this question: Should I use an O-ring or a gasket? Both of them are used to prevent leaks, but they are different from each other. Understanding the difference between them can help you choose the more suitable sealing product.
What Is an O-Ring?
An O-ring is a circular sealing component. It looks like a circle if you see it from the front. O-rings are generally made of silicone, rubber, or other flexible materials.
When purchasing seals, O-rings are often classified by inner diameter, cross-sectional diameter, and material type. Although the O-rings look simple, they are widely used in industrial supply chains and the manufacturing sector.
What Is a Gasket?
A gasket is usually flat. Unlike an O-ring, it can be made in many different sizes and shapes. You can order gaskets according to drawings, dimensions, thickness, and material requirements. Gaskets can be made in simple or complex shapes according to your needs. It is often used for sealing as well.
What’s the Difference Between an O-Ring and a Gasket and How to Choose?
Structural Difference Between O-ring and Gasket
The most obvious difference between O-rings and gaskets is their structure.
The O-rings’ structure is very simple. They’re a completely closed circle, and if you put one on a table, it always keeps its circular shape.
When sourcing, O-rings have two dimensions: the inner diameter and the thickness of the ring itself. Their structure is always a fixed circle, so there’s not much difference between different orders. This makes it easy for you to match the right model in the catalogs or supplier lists.
Gaskets, however, have a different structure. They generally do not have a fixed shape, and they are often flat when they are used.
What’s more, an O-ring is more compact and takes up less space. Its contact area is concentrated relatively. While a gasket usually needs to cover a larger contact surface, so its overall size is often much bigger than an O-ring.
When you are sourcing O-rings, you may mainly talk about the inner diameter and cross-sectional diameter of them. However, when you are sourcing gaskets, you often need to choose their length, width, thickness, hole sizes, and overall shape.
Difference in Sealing Mechanism Between O-ring and Gasket
Sealing is the most important application of O-rings and gaskets, but they are different in their sealing mechanism.
O-rings will be placed in a pre-designed groove, and then the two parts will be pressed together. When the two parts are pressed, the O-ring will be squeezed from all sides, changing shape slightly and filling the gaps in the groove.
Because of this sealing mechanism, groove dimensions and compression amounts are very important points that need to be repeatedly checked in O-ring design.
Gaskets work differently. They don’t need to sit in a groove but are pressed between two flat surfaces. When the parts are tightened, the gasket is flattened and spreads out, filling in the gap between the two surfaces.
So, although both O-rings and gaskets are used to prevent leaks, they work in very different ways. An O-ring is squeezed in a tight space, while a gasket is pressed between two flat surfaces.
When purchasing O-rings or gaskets, this difference in sealing mechanism is very important, and you’d better think about it carefully. Groove design and compression space are important points for O-rings, and if you choose gaskets, you should pay more attention to the contact area, thickness, and their positioning between the two surfaces.
If the sealing area is inside a closed groove and the compression is controllable, an O-ring is usually a better choice. If the sealing area is pressed between two flat surfaces, a gasket would be more suitable for you.
Performance Differences Between O-ring and Gasket
O-rings and gaskets are also different in their performance.
First, O-rings and gaskets have different pressure performance. O-rings are often placed in small grooves, and when the system pressure increases, they will be pressed tighter. This can make the sealing contact more stable. Therefore, the O-rings have better pressure resistance.
As it is mentioned above, gaskets are pressed between two flat surfaces to seal the area. So if the force is not distributed evenly, different areas will be compressed differently, and the final sealing effect can be different according to the assembly.
The temperature resistance of O-rings and gaskets usually depends on their material. However, in practical application, they’re still different. Gaskets have a larger, flat structure, so uneven heating across the surface can cause different areas to change. While O-rings are small and are often restricted in grooves.
Moreover, O-rings and gaskets are different in long-term use as well. O-rings may gradually lose their elasticity after long-term compression. Gaskets may have localized deformation because of uneven contact surfaces or uneven force after being used for a long time.
If the sealing product needs to work under high pressure and the sealing space is small, the O-ring will be more suitable for you. If the sealing place has a large contact area and may be uneven in heating, a gasket may be more suitable.
Differences in Application Between O-ring and Gasket
O-rings are often used inside equipment where small seals are needed, and these areas often have movement or pressure changes. In pumps, O-rings can be found at internal sealing places to control liquids. In hydraulic cylinders, they’re used in internal parts like pistons that will move back and forward.
In valves, O-rings are installed in internal grooves to control the flow of media in the system. For medical devices, O-rings are often used in small connectors to make sure that gas or liquid will not leak. These sealing applications are all used inside the equipment, not on the external equipment.
Gaskets, however, are more often found where two larger parts need to be assembled. In engines, they are usually placed between the cylinder head and the metal casing. In piping systems, gaskets are used at flange connections, sandwiched between two pipes and tightened with bolts.
And in compressors, the gaskets are often placed between two large metal surfaces and are fixed with screws for sealing. In HVAC systems, gaskets are used for duct connections to prevent air leakage between panels. In industrial equipment, they’re also generally used to seal between outer casing plates.
In food processing equipment, both O-rings and gaskets can be used. O-rings are usually in the valves or small connectors, while gaskets are used at tank lids or large sealing cover connections. Also, they can be used in water treatment systems where O-rings are used in internal control structures, and gaskets work at pipe flange connections.
If you need the sealing product to be used inside a pump, valve, or small connector, the O-ring is a better choice. If your design involves flanges, covers, or large structural connections, gaskets are more common.
Price Difference Between O-ring and Gasket
O-rings often have a lower cost because they are standard round shapes, and they can be easily made in many different sizes. While gaskets tend to be more expensive because they are often flat, customized according to different requirements, and sometimes use different materials.
Therefore, when sourcing, O-rings are a cheaper and more consistent choice for you, while gaskets may cost more if you need special designs.
FAQ
Are There Products on the Market That Combine O-rings and Gaskets?
Yes. A typical example is the encapsulated O-ring. It has a flexible O-ring core inside, with an outer layer made of PTFE or FEP. It combines the elasticity of an O-ring with the chemical resistance of a gasket, and it’s commonly used in highly corrosive environments.
Can O-rings and Gaskets Be Used Interchangeably?
Usually, they can’t be used interchangeably because they are designed for different sealing structures. In most cases, the shape of an O-ring or a gasket is decided in the design phase of the product.
Are the Materials for O-rings and Gaskets the Same?
Sometimes they can be the same. Both of them can be made of silicone, EPDM, NBR, or FKM. Silicone O-rings and silicone gaskets are quite common, but you can choose other kinds of materials according to your needs as well.
How to Choose the Size of an O-Ring?
Generally, O-rings have a standard size, but the actual selection still depends on the groove design. Many engineering problems are not because of the wrong size, but because the groove depth and compression ratio do not match.
Are They Easy to Damage During Installation?
O-rings are more likely to get damaged during installation because when they’re rolled into a groove, they can get cut or twisted by sharp threads, burrs, or edges. Gaskets are laid flat, and they are just pressed down during installation, so they are not easily damaged during installation.
Final Thoughts
O-rings and gaskets are used for different kinds of sealing products, and they are suitable for different fields and working environments. If you’re not sure which one to choose, feel free to contact us, and we can offer you professional advice.
