Gasket Design Guide

Guide to basic Gasket Design

Basic information concern gasket design can be found in this section. The information here is offered as a general guide only, please check the details of your application and material specifications carefully.

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The gasket is only one component of a sealing system. The other components are the mating surfaces, the clamping method, the internal and external environments. First we need to consider the general function of a gasket:

Prime Function

To allow two surfaces to be adequately mated and sealed.
Provide easy separation of the mated parts at service intervals.
Prevent escape or ingress of fluids (gas or liquid) even at extreme pressures and temperatures.

Major Requirement

Impermeable: Must not allow leakage through the material, even under pressure.

Resilience and Strength: Must conform and mould itself into all irregularities on flange surfaces whilst having sufficient tensile strength to resist blow-out under operating conditions.

Recovery: Must seal when tightened down (and often crushed) but recover to maintain a seal when the flanges move under mechanical, temperature or pressure forces.

Creepage: Must not creep, spread or extrude under conditions of high bolt pressure or high contained fluid pressure – even at high temperatures.

Chemicals: Must not be attacked or weakened by a wide range of fluids even when exposed for extended periods at high temperatures.

Temperature: Must remain resilient for long periods of time at low or high temperatures.

Contamination: Must not contaminate the sealed fluids – especially important in the pharmaceutical and food industries.

Gasket Design Guide

Step 1: Material Selection

Evaluate the application, the likely temperatures, pressures, and any chemicals.

For dust sealing with low bolt loading consider a foam rubber.
Lids and sumps can be sealed with cork.
At low temperatures and pressures select a rubber suitable for the environment.
Uses above 100 centigrade but at low pressures could be accommodated by a specialist rubber.
For aggresive chemicals below about 240 centigrade PTFE can often help.
Various non-asbestos jointings are available for conditions up to 450 centigrade and 160 bar.
Consider graphite for steam with a variable process cycle and mica for extreme temperatures.

Step 2: The Flange and the Gasket

Once the material is chosen the flange and bolting need to be designed to ensure the following:

The gasket is compressed evenly over the whole surface area. Thin flanges or excessive distance between bolt holes can result in some portions of the gasket being crushed whilst other areas are not sufficiently loaded to prevent leakage or blow-out.

The flange and gasket will appear thus;

bolt1

Vary the width of narrow flanges. If the bolts are widely spaced and the flange width is constant then excessive loading will occur on the limited material around the bolts.

For example;

bolt2a

 

This design will even the loading;

bolt4

 

Note: Sheet metal flanges can be stiffened by forming a lip. Soft materials can be protected by using compression stop (could be a washer).

Additional requirements for dynamic sealing (Typically “O” rings and other shaft seals).

Fitting: Often must flex or compress during assembly of parts and then maintain a seal with no means of assistance to provide post assembly pressure.

Friction: Must not burn or wear when in contact with rotating or sliding components.

Sealing: Always a compromise. Most dynamic seals must leak to function. It is the leaking fluid which provides the buffer between the moving parts and acts as a lubricant.