Drain Vent Check of API 6D ball valve

Drain, vent, and sealant valves

Drain and vent block valves may be provided. When provided, the drain and block valves shall have a rated pressure not less than the valve on which they are installed and be suitable for blow-down operation. Block and check valves fitted to sealant injection lines shall be rated for the greater of piping valve rated pressure and the injection pressure defined in 5.10. Seat leakage shall be monitored from each seat via the valve body cavity vent or drain connection. Leakage detected as originating from behind set rings or around resilient closure materials  shall be cause for rejection.