In order to reduce the leakage point, sometimes before the factory will be welded to death.DRAIN position must be in the lower position of the valve body, is generally able to reach the lowest point.
VENT generally use a check valve (resembling a screw, spring preload), also directly using the plugA two-way sealing type ball valve for example, in order to detect the leakage of the pressure after the end, also for pressing the cavity is convenient, usually in the body cavity external to the up position to open a checking leak, which is VENT.
VENT position usually refers to the valve on the leak detection valve, relief valve, but not the same as the use of DRAIN, which is used for sewage.
