Australian Pipeline Valve - Installation, Operation and Maintenance Manual 21 API6D THROUGH CONDUIT EXPANDING GATE VALVE - AP400-405 SERIES f- Once venting is complete, CLOSE fitting (‘B’ below) tightly, then operate the valve to the OPEN position and OPEN valve ‘A’ to allow the thermal relief system to operate as designed. 8.5.2 Draining procedure The purpose of draining the body cavity is to bleed out all the liquid collected in the body cavity. Even in gas service, some condensate, compressor oil and other residues may get trapped in the body cavity after a while. We recommend to drain the body cavity once a year. To drain the body cavity, proceed as follows: 1. Operate the valve to the fully open or fully closed position, whichever is more convenient for you. 2. Turn loose the head of the drain fitting (18) located at the bottom of the body, to bleed liquids trapped in the body cavity. We recommend a special drain valve specified for this task. It will take some time to bleed the body cavity. It depends on the size of the fitting, pressure in the body cavity and compressibility of the fluid. Drain the liquids into a suitable bucket to avoid releasing them to the environment. Keep your working area clean. The cavity can be exposed to line or cavity pressure, wear protective eye wear. B A C DIAGRAM 1 Thermal relief system with bonnet vent If there are hydrates in gas service, the drain fitting may freeze during high- pressure draining. Work slowly and ensure that the pressure trapped in the body cavity has been completely released, by opening and closing the drain fitting several times.