Check Valve Inside Unit Automated Block Valve

[maddocks]

Interesting question came up in a hazop. We have a number of recip compressors on site and each is equipped with an automated outlet unit block valve that closes on compressor shutdown. There is also a check valve between the compressor outlet and the block valve. A plant ESD is going to vent all gas in the plant but there will be a small pocket of gas trapped between the check valve and the unit block valve.

Any suggestion on how to handle this? My gut reaction is just to bolt the check valve directly to the unit block valve and the actual pocket of trapped gas will be extremely small. Seems crazy to have to install yet another blowdown for a micro amount of trapped gas.

 

[TD2K]

Do you have a sketch of the system? It would be interesting to see where the blowdown is coming off at versus your various valves.