Tolerance Stack Up

In any sealing application, the tolerances of ALL the parts in contact with the O-ring must be considered in order to create an effective seal. The combination of these tolerances is the tolerance stack-up.

Illustration 5.5 shows a situation where the O-ring cross section tolerance is ±0.003", the groove diameter tolerance is ±0.002", and the bore diameter tolerance is ±0.001". In this example the metal and O-ring dimensions can vary up to 0.012". If the nominal O-ring size is 0.030", it is easy to see that the tolerance stack-up is nearly half the size of the O-ring. This can result in too much or too little compression which can cause the O-ring to fail.