A gasket is a flat piece of material (such as rubber) or a component (such as an O-ring) that is placed at the intersection between two or more surfaces. Gaskets create a static seal between the surfaces, preventing leakage from, or into, the joined objects when subjected to compression or vacuum pressure.
Custom gaskets are typically cut from sheet materials. They can be manufactured from several materials, including rubber, cork, paper, metal, copper, and foam. Gaskets are very common components used in the manufacture of boats, planes, cars, trains, electrical equipment, pumps, and many other structures.
As well as their primary sealing function, gaskets can be used for additional purposes, including anti-vibration, packaging, and noise reduction. Their diverse properties make them suitable for a broad range of applications, and many industries use them—from the Food Processing, Construction, and Automotive industries, to the Pharmaceutical, Water, Petrochemical, Oil and Gas sectors.
When selecting a gasket type for any type of installation, it is necessary to consider whether the material it’s manufactured from possesses the features and characteristics you want to take advantage of – for example, its capability to withstand environments such as mining or deep sea diving, or its resistance to chemicals, alkaline acids, gases, extreme temperatures, fluctuations in temperature, electromagnetic forces, electrical forces, or pressure. A faulty or leaking gasket can have serious financial and safety implications, which is why it’s essential to select the correct material according to the needs of the application.
Plumbing repair, maintenance, and installation jobs require the use of ring gaskets to create tight seals against water seepage.
Low-pressure fluid applications, including regulators and pumps, require cam-and-groove gaskets to seal couplings tightly.
Food, beverage, pharmaceutical, and biotech industries use sanitary gaskets in their piping systems.
A head gasket is a critical component in motor vehicle engines, as it prevents water, oil, coolant, fuel and exhaust gases from mixing with each other. The gasket acts as a seal between the cylinder heads and the engine block, and is essential for keeping your engine’s temperatures within safe parameters. Overheating and excess pressure in the engine bay can cause the head gasket to blow!
For a gasket to seal against leaks effectively, there must be adequate compression present. The aim of the compression is to generate a pressure-tight barrier that will protect the contents inside the seal.
Gaskets also protect moving parts of an application by separating them, to prevent them from rubbing against hard surfaces and creating friction.
There are three things to remember when attempting to achieve an effective seal with a gasket.
1. First, sufficient force must be available to seat the gasket.
2. Adequate force must also be in place to ensure there is sufficient residual stress on the gasket under operating conditions.
3. The gasket material must be able to handle the pressures against it and the temperature range to which it is exposed.
A compression gasket is a gasket that is specifically designed to seal a joint between two mating surfaces, to ensure that no leakage occurs. Compression gaskets are most often used within pipeline systems.
Compressing the gasket material causes it to flow into any gaps and spaces between the sealing areas and this causes a bond to be formed, to prevent the escape of the contained media (fluids, gas, etc). When sufficient load is applied to oppose the hydrostatic force created by the system’s internal pressure, the seal remains intact.
An inner compression ring can be incorporated into the gasket, to allow for higher flange compression while preventing gasket failure. The effects of a compression ring are minimal, however, so they are only usually used when the standard design is prone to failing. An outer guiding ring can also be used as a minor compression inhibitor, allowing for easier installation of the gasket.
An O-ring is actually a type of gasket. While gaskets can be made with a simpler, flat flange, an O-ring requires a groove or channel in the flanges. The channel around an O-ring is used to prevent blowouts when pressures are very high. O-rings are usually found in hydraulic seals, fuel systems, oil seals, and pipe joints.
Gaskets can either be manufactured to standard specifications, or supplied in bespoke shapes and sizes to suit the particular needs of a specific application. The most commonly used materials for gaskets include polymers, gasket sheet materials such as synthetic, silicone and engineering rubbers, and plastics such as Acetal and PTFE.
The best gasket material will always be the one that’s best suited to the specific application it’s being used for. A material that performs exceptionally well in one may be disastrous in another.
It is essential to select a material that won’t degrade prematurely, to prevent serious ramifications such as leakage of reactants, voltage loss, weakness of mechanical structures, deterioration of fuel cell performance, short circuits, or a decrease in compression pressure.
Whatever the project, the following factors should be considered carefully when selecting gasket and filler materials.
Temperature: Temperatures can adversely affect a gasket’s mechanical, chemical, and physical characteristics.
Pressure: The internal piping pressure could destroy a gasket manufactured from unsuitable materials.
Media: Gasket materials must be resistant to corrosive attacks from the media.
Joint design: The force holding the surfaces together must be sufficient to resist the hydrostatic pressure of the entire system, to prevent potential separation of the flanges.
Bolt load: Leaks will occur if the bolt load is excessive, or if the gasket material isn’t strong enough.
Surface finish: The seal won’t be successful if the gasket material isn’t appropriate for the surface finish.
Rubber gaskets can seal against both liquids and gases to connect two surfaces together. Because of its manipulative properties, rubber is a perfect material for plugging gaps and irregularities in tight spaces.
Rubber gaskets can be manufactured from many types of rubber compounds, including neoprene, nitrile, silicon, Viton, polyurethane, EPDM, and butyl. Most rubber gaskets are water-resistant, and they can also be blended with other materials — for instance, rubber blended with cork is often used for low-pressure applications.
A sheet gasket is simply a gasket shape punched out of a sheet of material. This method of gasket manufacturing is commonly used when large volumes of gaskets are required, as it is fast and inexpensive. The gaskets are cut to size by purpose-built machines, and can be made either with or without bolt holes. Size, thickness and materials can be customised to suit a specific application, or they can be supplied as standard.
Gaskets produced in this way are usually made from carbon, mineral or synthetic rubbers such as EPDM, neoprene, nitrile, and SBR. These materials have unique and versatile properties which are suitable for a wide range of uses, including noise reduction, anti-vibration, supporting mounts, and sealing. Acids, corrosive chemicals, steam or mild caustics are usually involved in applications using sheet gaskets.
Solid material gaskets are made from metals which are cheap to produce, but which cannot be punched out of sheets. The quality control of these gaskets is much more rigorous than that of the sheet gasket, and these gaskets can withstand much higher temperatures and pressures. However, because solid metals are used in the manufacture of these gaskets, there is sometimes a risk of process contamination or oxidation.
In order for solid metal to become flush with the head, it must be heavily compressed. The metal used should also be softer than the flange to prevent warping, which could affect the sealing effectiveness of other gaskets in the system.
A gasket which is made to fit between two sections of flared pipe is known as a flange gasket. Flange gaskets come in a wide variety of sizes and inner/outer diameters.
Flange gaskets can be classified into four categories: Sheet Gaskets; Corrugated Metal Gaskets; Ring Gaskets; and Spiral Wound Gaskets. Here is a link to our guide with tips on fitting a flange gasket.
Spiral-wound gaskets comprise outer and inner metallic (often stainless steel) rings, as well as softer filler materials in the centre — this is usually flexible graphite PTFE, which is spiral-wound into a V shape with stainless steel tape to achieve alternating layers of metal and filler for precise density control. The filler material acts as the sealing element, while the metal provides structural support. Internal pressure applied to the faces of the V forces the gasket to seal against the flanges.
Spiral-wound gaskets can be manufactured in a variety of shapes, such as oblong, rectangular, oval, pear and diamond. They are durable and reliable, as well as being easy to install and remove. They’re often used in high pressure pipelines, as they allow lower clamping forces and the ability to compress at a higher stress than solid gaskets, which means they offer a superior performance. Adding a steel ring to the inside of a spiral wound gasket helps to further improve its pressure rating.
Kammprofile (or Camprofile) gaskets are both flexible and reliable, which is why they are often used in older seals. With their flexible covering and solid corrugated core, Kammprofiles can withstand high levels of compression, and can make an extremely tight seal. They are long-lasting gaskets due to their strong metal core but, for this reason, they can be too expensive for many applications.
In the same category as Kammprofile and Spiralwound gaskets, Fishbone gaskets are flange seals that are machine manufactured from similar materials, but with a more durable and consistently reliable design. These gaskets do not unwind in storage or in the plant as Spiralwound gaskets sometimes do, and their rounded edges prevent flange damage. The added “Stop Step” helps prevent the gaskets from being over-compressed and crushed by hot torque techniques, and the gasket’s bones remain ductile as they adjust to thermal cycling and system pressure spikes. Overall, the Fishbone gasket significantly outperforms all other gaskets in this category.
This type of gasket comprises two components: a solid (usually metallic) carrier ring, and two sealing elements made from compressible materials such as PTFE, vermiculite, or expanded graphite. The sealing elements are installed within two opposing channels — one on either side of the carrier ring.
Constant seating stress gaskets take flange rotation and deflection under bolt preload into account. The profile of the carrier ring can be adjusted according to the flange size and the pressure class, to enable radial uniformity of seating stress across the entire sealing area. This effectively makes the gasket immune to common failures found in other gasket types, such as creep relaxation or high system vibration.
A soft cut gasket refers to a gasket that can easily shrink, even when the bolt load is low. Soft cut gaskets can be found in applications such as compressors, heat exchangers, and pipe flanges.
The double-jacketed gasket combines metallic materials with fillers pumped in between the shell and piece. The metal tube has an additional piece which is made to fit inside of the “C”-shaped ends, making the tube thickest at the meeting points when the gasket is compressed. This is necessary so that the gasket can bear the sealing burden. As this is such a simple gasket, it can be manufactured from almost any material that can be made into a sheet.
The Klinger Sentry Reverse Integrity Gasket allows leak testing on individual flanged joints in newly erected or amended pipelines, without the need to pressurise the entire system. This allows for a much faster testing process and reduces plant downtime. Manufactured from soft sealing PTFE material, the Klinger sentry gasket also offers maximum chemical resistance.
RTJ gaskets (also referred to as annular seals) are solid rings of metal manufactured in a variety of differently shaped cross sections (such as round, oval, or octagonal). They are typically used in offshore oil drilling, gas pipelines and valves. Designed to withstand extremely high pressure and temperatures, the RTJ seal has a large surface pressure between the groove and the sealing surface, because of its small load area.
With a pressure class of up to 300, this type of reinforced gasket is metal-coated on both sides of the core and covered with a pliable sealant. Its soft core guarantees excellent sealing properties.
Non-metallic gaskets are stamped or cut from base materials such as rubber, cork, foam, sponge, and vulcanised fibre. Although ideal for low pressure applications, some non-metallic gaskets – such as those manufactured from some types of Klingersil (CNAF) material – are specifically designed to withstand huge amounts of heat and steam pressure.
Non-metallic gaskets are relatively cheap to manufacture (a few pence per piece), yet they are strong enough to form a seal between, and protect the longevity of, two mating metal surfaces. This means that it’s usually cheaper to replace the gasket than part of the machine or structure.
For example, most door handles have a nylon/nylatron/PTFE washer (gasket) behind the handle and the housing. This is for two reasons: 1) it helps with the friction and allows the door handle to be pulled up and down without resistance; 2) it protects the metal handle scraping against the metal housing. Without the gasket, the handle would develop a groove over time. Similarly, old types of shower screens have gaskets between the glass and the metal hinge. This is to create a water tight seal, as well as to protect the glass from bruising when the bolts are tightened up on installation.
Full-face non-metallic gaskets are typically held between flat-face mating flanges, whereas flat-ring gaskets which do not cover the full face are used with raised-faced flanges.
Gylon is a brand name, and it describes a specific type of gasket made from a superior PTFE material. It’s available in a broad range of grades and sizes for specific applications and industries. Manufactured using a proprietary thermal bonding and mixing process, this homogenous material offers unique and impressive physical properties that cannot be achieved with conventional manufacturing methods. Gylon’s chemical resistance abilities are excellent, and it also has a very broad operational temperature range.
Gylon addresses the problems of creep relaxation and cold flow, fluctuation, fugitive emissions, and the process and media loss usually associated with other types of gasket materials such as inexpensive PTFE sheeting. Its high-tensile properties offer consistently superior, high-performance fluid sealing qualities, making this type of gasket ideal for use within pipeline protection products.
Throughout most of the twentieth century, gaskets for many applications – such as engines and high-pressure steam systems – were commonly manufactured from asbestos. These gaskets were known as CAF (compressed asbestos fibre) gaskets.
In the 1970s, scientists discovered a link between asbestos exposure and serious diseases such as mesothelioma, lung cancer, ovarian cancer, and laryngeal cancer. They found that when asbestos is cut or disturbed it releases toxic microscopic fibres into the air that can become lodged in a person’s lungs, causing cellular damage in the long term.
Subsequently, manufacturers were instructed to phase out the use of asbestos in gasket products, and replace it with other materials. We now know these gaskets as CNAF (compressed non-asbestos fibre) gaskets.
When taking apart old engines or industrial machinery, some workers may still be at risk of exposure to asbestos toxins. Parts sealed with asbestos gaskets could include pipes, pumps, compressors, valves, boilers, engine cylinder heads, heat exchangers and condensers.
Here at RH Nuttall, we have over 100 years’ experience as a leading UK gasket maker. We stock most gasket sheet materials in a wide range of standard patterns, and we also have the facilities to manufacture custom parts quickly and easily. Whether you need rubber gaskets, foam gaskets, neoprene gaskets, or gaskets made from PTFE sheeting, we can help.
If you would like more information about our gasket manufacturing process, or you need help to select the best gasket for your needs, please contact a member of our experienced customer service team. We always do our utmost to assist our customers; your complete satisfaction is our end goal.
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