Australian Pipeline Valve - Installation, Operation and Maintenance Manual 19 SIDE ENTRY 2P TRUNNION BALL VALVES API6D STANDARD - FS9000 SERIES The pressure trapped in the body cavity can be vented to the atmosphere while pressure, is maintained in the pipeline, both in the fully open and fully closed positions. This characteristic is used to: 1. Ensure that the seats are providing an effective seal. 2. Drain or flush the body cavity of an in-service ball valve. 8.5.1 Venting Procedure 1. Operate the valve to fully open or fully closed position, whichever is more convenient for you. 2. Turn loose the head of the vent fitting if fitted (22) located at the top of the body, to release cavity pressure. Use extreme caution when venting the body cavity of a pressurised valve. Continue venting until body cavity pressure is atmospheric. It will take some time to depressurise the body cavity. It depends on the size of the fitting, body cavity pressure and field compressibility. If the body cavity keeps venting fluid at a constant flow rate for a very long time, it is a signal of bad sealing of the valve seats. For liquid service only a lower drain valve will immediately indicate a leak. 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. 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. 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 (23) located at the bottom of the body, to bleed liquids trapped in the body cavity. We recommend a drain valve be 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.