5.8　Valves and Unloaders

5.8.1　Valves shall be in accordance with 6.9.1 of API Std 618-2007.

5.8.2　Unloaders shall be in accordance with 6.9.2.2 through 6.9.2.7 of API Std 618-2007.

5.8.3　Valve disk/plate shall be capable of corrosion prevention from the compressed gas.Valve plates/disks should be polyether ether ketone（PEEK）or alternate high temperature polytetrafluoroethylene.Valve material shall have proven performance in similar environment.

5.8.4　For process gas applications，pneumatically operated valve depressors，plug，or port type unloaders shall be provided based on the purchaser's application and vendor's manufacture experience.

5.8.5　Unloaders should be pneumatically operated valve depressors type.Unloader cylinders and shafts shall be stainless steel.Unloader pistons shall be stainless steel or aluminum.

5.8.6　When non-metallic valve plates or disks are furnished，sufficient considerations are necessary for suction valve depressors with respect to unloaded，partially loaded or variable operating conditions，which may cause higher operating temperatures.

5.8.7　The pneumatical air of the actuators shall be sized 0.05MPa（G）less than the specified minimum site load pressure.Unloaders shall be shop tested for proper actuation.