There are two common seat sealing structures for turnnion mounted ball valves.
1. DBB double block and bleed valve
Valves with two seat seal pairs may provide pressure sealing across the valve in their closed position by means of venting/venting the body cavity between the two seat surfaces.
2. DIB double isolation and bleed valve
Valves with two seat seal pairs, each of which provides a single source pressure seal in the closed position by venting/evacuating the valve body cavity between the two seat seal pairs .

Valve pressure test method
1. Double shut-off and relief valve DBB
The valve is in a half-open state, and the experimental medium is completely injected into the valve and the valve cavity. Then close the valve and open the valve body relief valve to allow excess test fluid to escape from the valve cavity test port. Pressure should be applied from both ends of the valve at the same time, and the tightness of the valve seat should be monitored by the overflow at the valve cavity test interface.

2. DIB valves are divided into DIB-1 and DIB-2.
(1) Double isolation and relief valve DIB-1 (two-way double seat)
Each seat should be tested in both directions. Remove the cavity relief valve if installed. Keep the valve in a half-open state, and the valve and the valve cavity should be filled with the test medium until the test liquid overflows through the test interface of the valve cavity. To test for seat leakage in the direction of the cavity, the valve should be closed. The test pressure should be applied to each end of the valve one by one in order to test the leakage upstream of each valve seat separately. Leakage should be monitored for seat tightness by overflow at the cavity test interface. After that, each seat is tested as a downstream seat. Both ends of the valve are opened so that the valve cavity is filled with the test medium. Then pressurize, while observing the leakage of each valve seat at both ends of the valve.

(2) Double isolation and relief valve DIB-2 (single seat one-way, one-way double seat)
Two-way seats shall be tested in both directions. Remove the cavity relief valve if installed. Keep the valve in a half-open state, and the valve and the valve cavity should be filled with the test medium until the test liquid overflows through the test interface of the valve cavity. To test for seat leakage in the direction of the cavity, the valve should be closed. The test pressure should be applied to each end of the valve one by one in order to test the leakage upstream of each valve seat separately. Leakage should be monitored for seat tightness by overflow at the cavity test interface. For the two-way sealed seat test of the valve cavity test, the test pressure is applied to the valve cavity and then to the upstream end. Leak detection is performed on the downstream end of the valve.