March 2017

The Role of Fiber Gaskets

While there are many new elastomeric sealing materials, it’s often prudent to follow the mantra, “What comes out of the joint goes back into the joint.” Especially in older processing and heating equipment that is often a fiber gasket. Many different materials can be used to provide the fibers, so the properties and applications of these gaskets vary enormously.

Back to Asbestos Gaskets

In 1899 an Austrian called Richard Klinger discovered a way of making effective soft gaskets by compressing asbestos fibers into sheet form. These sealed under low loads and resisted steam, oil, water and high temperatures and pressures. That made them ideal for use in boilers, heat exchangers and heating and hot water systems as well as oil refining and other process industries.

By the 1980’s the health hazards of asbestos were well-known and gasket manufacturers were substituting other materials with similar properties. Sticking with fibrous material in a binder meant they could use the existing manufacturing processes, one reason why fiber gaskets remain commonplace today.

Modern Fiber Gaskets

The main types of fiber gasket material are:

  • Cellulose
  • Cellulose with rubber
  • Cellulose with insulating fiber
  • Cellulose with synthetic fiber
  • Cellulose with vulcanized fiber
  • Vegetable fiber (Detroiter)

These are all available in a range of sheet thicknesses and die-cut readily. They are considered “soft” gaskets, meaning they are suitable for applications with relatively low clamping forces, such as Class 150 and 300 flanges.

Fiber Gasket Properties

Gasket properties are determined by both fiber and binder material. For example:

  • Vegetable fiber (Detroiter) gaskets – upper temperature limit of around 250°F (121°C), good resistance to oil, gasoline, water and steam. Generally inexpensive.
  • Cellulose fiber with rubber – upper temperature limit around 350°F (177°C), good resistance to oil, gasoline, water and steam.
  • Aramid fiber in NBR binder – upper limit on temperature can be up to 825°F (440°C), suitable for a wide range of industrial applications.

Fiber Gasket Identification

If you’ve removed a fiber gasket and aren’t sure what type it is, bring it in. Our materials experts should be able to help.

Brewery Gaskets? We’ll Drink to That!

Most gaskets are used to seal fluids or for environmental protection. Every so often though we are asked for a gasket for a less common application. One interesting example is the silicone or EPDM gaskets used around manways in brewery tanks.

Equipment Cleaning

Brewing depends on fermentation, a natural process involving lots of enzymes and chemistry. If the equipment is less than perfectly clean bacteria may contaminate what will become beer.

To avoid this, breweries clean and sterilize rigorously. Every mash tun and fermentation tank, plus the pipework in between, is treated with steam, caustic cleaning solutions, or both. Larger tanks often need someone to go inside to do the cleaning, which is why they’re usually constructed with a “manway”.

Manway Gaskets

A “manway” is an entrance point big enough for a man to enter through. Usually circular or oval, if located at the bottom of the tank, they need to withstand the pressure and temperature of the liquid inside. Some are just cover plates bolted to a flange, but in brewery equipment, it’s far more common to have a hinged door that clamps shut.

Regardless of design, every manway needs a gasket to stop it leaking. Those used in breweries must tolerate cleaning chemicals and steam as well as process heat. To avoid the need for high clamping forces, they should be soft, and ideally will resist taking a compression set. They also have to be food-grade to avoid imparting any kind of taint or contamination.

Suitable Gasket Materials

For manways in brewery tanks food-grade silicone and EPDM gaskets are the most common choice. Both are elastomers, so while they are elastic and deform under even quite light loads, they do not compress. Silicone gaskets have the higher temperature limit, typically 400°F (204°C), and are resistant to fungal attack, but have poor tolerance to steam.

EPDM gaskets have a lower upper-temperature limit, (250°F – 121°C) but are resistant to steam, ozone, acids, and alkalis. For this reason, these are the type of gasket used in many brewery tank manways.