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Pressure class PN 40 is an imaginary limit within which flat die-cut seals can be used relatively safely. From PN 40, it is recommended to use metal seals (eg spirally wound, comb seals, etc.).
The size of the seal is given by the standard, eg: ČSN EN 1514-1. This standard was created at a time when tightness calculations were not known. The asbestos seals used could be "blown to the blood" and subsequently sealed due to absorbency. After the asbestos ban, the sealing materials changed, but their dimensions and installation procedures remained .
If you want to calculate a flange joint of a lower pressure class for tightness according to EN 1591-1, you will find that the calculation may not be based.
If you use a gasket that is over the entire sealing surface of the flange, the calculation will show that the bolts or flanges are not strong enough. You are not able to achieve sufficient specific pressure on the seal without tightening the screw or bending the flange during installation .
You can seal such a joint only at the cost of a tightened screw or bent flange.
To ensure that the flange connection is designed correctly, a leak test must be performed and the seal size optimized.
It pays to optimize the seal size, for example, for pipelines. Based on the tightness class for which the joint was calculated, you can declare the maximum amount of emission leaks from the entire route.
We will be happy to help you with calculations of tightening torques and optimization of seal dimensions. In case of questions, do not hesitate to contact us directly or via our contact form at www.tesneni.cz.