4" #1500 Ball valve is with seats that are pushed by springs against the ball. In the middle of ball valve, there is 1/2" hole drilled to ball cavity in which we connected drain ball valve 1/2"#1500.
With closed 4" ball valve was pressurized it from one side with 100 bar of natural gas.
With 1/2" drain ball valve connected to ball cavity we checked seat leakage by opening the valve and no leak was detected - which means metal seat is tight on that side, Using 3/4" bypass line around 4" ball valve we pressurized same ball valve from the other side on the same pressure - and still no leakage.
1/2" Drain valve was closed and 4" ball valve opened/closed - 3-4 times, letting gas go inside the valve and valve cavity. We tried to open 1/2" drain ball valve again to release the pressure from valve cavity, but after just small opening it was leaking and not stopping
for 5-6 mins.We closed back the 1/2" valve and tried to release the pressure after the 4" ball valve on 1" relief pipe down the line to atmosphere but the pressure remained 100 bar - like the ball valve is open
1/2" Drain valve was closed and 4" ball valve opened/closed - 3-4 times, letting gas go inside the valve and valve cavity.We tried to open 1/2" drain ball valve again to release the pressure from valve cavity, but after just small opening it was leaking and not stoppingfor 5-6 mins.

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