Gasket parameters – Part II – Gasket factors Gb, a, Gs
Due to the increasing importance given to environmental protection and with the adoption of norms regulating leakage, starts the research to replace the ”m” and ”y” parameters. These two parameters do not take into account the leak rate and are difficult to reproduce for asbestos-free materials.
In this respect, new testing methods have been designed: the ROOT Test (Room Temperature Tightness Test); and a new parameter – tightness parameter Tp – in order to connect the internal pressure to the tightness level. Testing is performed at ambient temperature using Helium and has two parts: the first refers to the assembly conditions, and the second to the gasket stresses in service.
Representing on the ordinate axis the logarithm of the loading and unloading gasket stress and on the abscissa the logarithm of Tp, we obtain a graph with the three gasket factors: Gb, a, Gs.
Gb – gasket pressure required to achieve Tp = 1 on the assembly (log Tp=0)
a – slope of gasket seating curve
The combined values of Gb and a, describe the seating characteristic of the gasket and its ability to ensure tightness from the initial sealing.
Gs – intercept of the unloading lines with the line Tp =1. Gs is a theoretical point, representing the gasket ability to ensure tightness after pressurization and during operation.
In connection with these now gasket factors, a new calculation method has been developed – Apendix BFJ – the method is not mandatory.
This graphic stage of the procedure is inconsistent with the practical results. The hypothesis of an intersection with the axis Tp = 1 of all unloading possibilites, analyzing the experimental data, was found to be wrong. Therefore, the three gasket factors Gb, a, Gs are not trustworthy and the calculation method Apendix BFJ remains only an alternative to traditional calculation methods.