How to Choose a Sealing Gasket

Sealing gaskets, also commonly referred to as sealing washers or seals, help prevent leakage at a pipe or component joint. To achieve a successful seal, the gasket must be flexible enough to conform to both mating surfaces while resisting extrusion, creep, and blowout. Clamping forces act on the gasket surface, squeezing the gasket and forcing it to conform to the flange flaws, resulting in a seal.

Sealing gaskets are made from a variety of materials that enable them to retain their functional integrity in specific environments. Operational environments may include extreme temperature fluctuations, continuous exposure to corrosive materials, or exposure to abrasive materials. There are specific sealing gaskets for each unique application.

Choosing a gasket type

To choose the right gasket for an application, the elimination of materials is the first step. The more extreme the use case, the more specific the choice will be. Below is an overview of the materials used in sealing gaskets and their unique properties.

• PVC
• PTFE
• Polyamide (Nylon)
• Copper
• Aluminum
• Vulcanized Rubber

PVC

PVC is a cost-effective and durable material that has excellent shock absorption and vibration properties. Due to a pressure range of -0.95 to 16 bar (-13.77 to 232 PSI) this softer, malleable material has extensive potential including vacuum applications. Below are the key characteristics of the PVC sealing gasket:

Pros

• Tough, resilient, and abrasion-resistant
• Compressible and flexible
• Superior UV stability
• Excellent shock absorption and vibration properties

Cons

• Limited temperature range -30°C to +60°C (-22 to 140°F)
• PVC should not be used with esters, aromatic compounds, chlorinated hydrocarbons, and some concentrated inorganic acids.

PTFE

Polytetrafluoroethylene (PTFE), also referred to as Teflon, is mainly known for its resistance to heat and non-stick properties. When using PTFE as your material of choice for a gasket it must be noted that once tightened, the joint should be retightened after 24-hours. A characteristic of PTFE is that it flows under pressure.

Pros

• Can be used in a wide temperature range of -200°C to +250°C (-328 to 482 °F), even at temperatures above this range, up to 300°C (572 °F), there are no appreciable decompositions.
• The pressure resilience of PTFE is dependent on temperature, yet the material maintains a certain amount of compression even near absolute zero of -273.15°C (−459,67 °F).
• Excellent seal integrity
• PTFE has excellent chemical resistance to almost all chemicals and solvents.
• Exceptionally low friction and anti-stick properties
• Non-toxic and non-flammable

Cons

• PTFE has a Shore hardness between D50 and D60. This hardness makes it more difficult to seal. Therefore, PTFE is not recommended if temperatures or pressures do not require it
• Fluorinated hydrocarbons do cause reversible swelling.
• Highly fluorinated oils have a dissolving effect at temperatures over 300°C (572 °F).

Polyamide (Nylon)

Polyamide, more commonly referred to as Nylon, stands out for its resistance to wear, excellent damping capacity, and a low creep tendency. Besides this, Nylon has high compressive/tensile strength, good shock-absorbing properties, and impact resistance is a good electrical insulator and can be used in vacuum applications.

Pros

• Operating pressure is -0.95 to 16 bar (-13.77 to 232 PSI) so suitable for vacuum
• Resistant to hydrocarbons and lubricating agents
• Dimensional stability

Cons

• Lower melting point than PTFE
• Although Polyamide can operate in low temperatures of -40°C (-40 °F), it should not be used in temperatures higher than +80°C (176 °F)

Copper

Copper is commonly used for electrical conductivity and heat-absorbing properties. Copper seal gaskets are widely used in high performance motorsports industries due to their high heat tolerance while being malleable under pressure offering increased sealing qualities.

Pros

• With a melting point of 1085 °C (1985 °F) copper has an extremely high heat tolerance
• Malleable under pressure offering a high seal quality
• Reusable if undamaged

Cons

• Copper should not be used in highly acidic environments

Aluminum

Aluminum has unique properties that make it one of the world''s most widely used metals. This material has a ductile property, which means it can be formed into intricate shapes without damaging or deteriorating. In the right forms, aluminum can withstand tremendous forces and is incredibly durable. Aluminum naturally forms a thin surface layer of aluminum oxide on contact with oxygen through oxidation, creating a physical barrier against corrosion or further oxidation in many environments, including contact with other metals.

Pros

• Good corrosion resistance to organic acids except for nitric acids
• Temperature stable at -100°C to +200°C (-148 to 392 °F)
• Oxidation resistant
• Minimal thermal response.

Cons

• Not every type of aluminum Aluminum is prone to react with other metals, something to consider when using aluminum gaskets.

Vulcanized fiber

Vulcanized fibers are natural fibers that have been heat-treated to form a hard rubber. It is among the oldest plastics ever developed and is used in a wide variety of applications, including washers and gaskets. There are very few downsides to using vulcanized fibers, they have an incredible range of resistance for pressure, chemicals, penetration by solvents and oils, and have high integrity.

Pros

• Environmentally friendlier to produce than other materials
• Supremely versatile
• Resists heavy pressure
• Compressible
• High resistance to penetration by most organic solvents, oils, and petroleum derivatives
• Provides high levels of electrical, chemical, and mechanical integrity over a wide range of temperatures

Cons

• Resistance is bound to the type of fiber the gasket is made of, the size, and the thickness.

Choosing the right gasket size

The size of the gasket, as well as its ability to endure degradation and damage, all play a role in how well it can prevent gasses or fluids from escaping. Because the two surfaces aren't precisely flush or straight, there will be gaps through which gas or water can escape. Gaskets fill in the spaces by compressing between the two surfaces, effectively blocking any leakage path.

Selecting a size is not an exercise of visual guessing. Rather, it’s the discipline of considering both the union surfaces, the flow aperture, and the joint type. Consider using a caliper to measure the exact requirements.