The clearance between the valve seat and the valve body groove is the basic condition to ensure the normal operation of the pneumatic ball valve. When selecting the clearance, it is necessary to consider that the uniform mid length of the precompressed valve seat should be within the total elastic deformation range. For this reason, the formula:; Average valve seat diameter;; Allowable stress of cross section of valve seat within elastic deformation range, for PTFE valve seat,; Elastic modulus of valve seat material, for PTFE valve seat,.

Brief discussion on the application of corrugated compensator in diversion type and hybrid hydropower stations diversion type hydropower stations are hydropower stations that use diversion channels (such as open channels, tunnels, penstocks, etc.) to concentrate river flow and head for power generation. Diversion type hydropower stations are mostly built on rivers with steep slopes and large falls. Their main structural characteristics are that the upstream water intake is far away from the downstream powerhouse, and the middle water diversion channel often passes through different geological layers.
Hybrid hydropower station is a kind of hydropower station which consists of dam and diversion channel to form the generating head. This kind of hydropower station usually has the advantages and engineering characteristics of dam type and diversion type hydropower stations.
The corrugated compensator used in the penstock of diversion type or hybrid hydropower station is mainly used to compensate the displacement of the penstock caused by temperature and geological changes. Its characteristics mainly include:
1. The internal pressure of downstream steel pipes is generally high (up to 12.0MPa).
2. When it is used for open air pipe section, it is mainly axial displacement, but cyclic displacement is frequent.
3. When it is used in the tunnel, the ordinary radial displacement is large (± 50~100mm and above), but the number of cycles of operation is very small.
The corrugated compensator used in the penstock of the headrace tunnel has no condition and possibility of stopping and changing after installation. Therefore, the application of this kind of corrugated compensator should also be cautious.