#1 What is meant by the sealing gap?
The sealing gap is the distance between two surfaces that are sealed by means of an O-ring.
After an O-ring has been pressed, there is still a small gap between the two surfaces to be sealed. This gap is called the sealing gap.
The aim of a seal is to seal this sealing gap securely and for the long term so that no medium can make it from one side of the sealing gap to the other.
In principle, it is important that the sealing gap is kept as small as possible. This is because the O-ring can be pressed into the sealing gap and damaged, especially under pressure. This damage is called “extrusion” or “gap extrusion” and means nothing other than that parts of the O-ring are sheared off.
The O-ring may have been damaged to such an extent that it is leaking and needs to be replaced.
#2 How can gap extrusion be avoided?
1 In principle, the higher the pressure in the system, the higher the Shore hardness of the O-ring should be selected.
2. a small sealing gap is always positive and supports the longevity of the O-ring seal.
3. the use of a support ring can prevent slippage in the direction of the sealing gap.
4 When designing, care should be taken to ensure that the groove clearance after pressing the O-ring is approx. 20%, especially in pressure applications.
#3 The 3 rules of thumb for the design of O-rings under pressure
Rule 1: Pressure from the inside = O-ring should be in contact with the outer diameter of the groove.
Rule 2: Pressure from outside = O-ring should be in contact with the inside diameter of the groove.
Rule 3: Keep the sealing gap small at high pressure and use support rings.