A manual body bleed valve is included on the APV as standard. This bleed valve installed in the relief system is opened after the APV valve is closed. Seal effectiveness can be immediately evaluated, after allowing a few seconds for stabilisation of cavity volume due to entrained air or gas. The bleed valve must be closed before the APV valve is opened. An isolation valve installed in the upstream throat tap is also included. It must be left open to permit relief system to relieve pressure upstream. The isolation valve will be used only for maintenance and troubleshooting which will be explained later. Valve is to be CLOSED ON FOR REPAIR. If closed during normal operation the automatic portion of the relief system (relief/check valve) will be defeated. (The outlet of the relief valve would close when closing the isolation valve). Valve Operation In the fully open position, the resilient seals are positioned out of the flow path and protected within the body of the valve itself. As the valve is cycled from the fully open to closed position, the plug begins a 90 degree rotation. During the entire rotation of the plug the resilient seals located on both slips are retracted away from the body. This ensures that there is no rubbing or scraping action on these resilient seals during rotation of the plug from the open to the closed position. Australian Pipeline Valve - Installation, Operation and Maintenance Manual 15 EXPANDING SEAL PLUG VALVE DOUBLE BLOCK & BLEED API6D - TWIN SERIES