MECHANICAL REQUIREMENTS
The quality of the seal alone is not enough to guarantee a satisfactory hold. Many conditions play their part, among them
- the roughness of the seats,
- their concentricity
- the coupling clearance.
It is vital, therefore, to verify that at least these three components match the requirements as listed below, prior to installation.
Here are some insights on the subject.
Roughness
In the case of static hold tests with Helium gas, it is always preferable to have a surface roughness of not more than 0.3 Ra for temperatures up to -46 ° C and 0.2 Ra for lower temperatures.
| Temperature | Surface finish |
| +200°C/ 0°C | 0,6 Ra |
| -1°C/ -46°C | 0,4 Ra |
| -47°C/ -100°C | 0,3 Ra |
| -101°C/ -196°C | 0,2 Ra |
For dynamic hold tests carried out with helium gas, it is always preferable to have a surface roughness of not more than 0.2 Ra for temperatures up to -46 ° C and 0.1 Ra for lower temperatures.
| Temperature | Surface finish |
| +200°C/ 0°C | 0,4 Ra |
| -1°C/ -46°C | 0,3 Ra |
| -47°C/ -100°C | 0,3 Ra |
| -101°C/ -196°C | 0,2 Ra |
CONCENTRICITY
The diameter concentricity for radial grooves should match those in the table. For axial grooves, the same height tolerance applies.
| Temperature | |
| +200°C/ 0°C | +/- 0,05 mm |
| -1°C/ -46°C | +/- 0,03 mm |
| -46°C/ -196°C | +/- 0,01 mm |
COUPLING CLEARANCE
To avoid sealing problems in the planning stage it is good practice to aim for reduced coupling clearance, and for high pressures situations it is essential to reduce them to allow space for the placement of a Back-Up: e.g. 0.20 mm (diameter) for seals without Back-Up and 0.30 mm (diameter) for those with BackUp is considered suffi cient in almost all cases.
For pressures above 600 bar and temperatures over 180° C, we recommend contacting our technical department.
