Level IV is the commonly used leakage level. It is suitable for regulating valves with additional special sealed balanced metal metal seats and unbalanced single seat regulating valves. The test medium is 50~I25T (10~52 "C) air or water, and the test pressure is 45~60psi (0.3~0, 4MPa), which is lower than the maximum working pressure. During the test, the outlet end of the valve is directly connected to the gas or to the device for measuring the loss of the low-pressure head, and the actuator is adjusted to the maximum closing thrust state. The maximum allowable leakage of Level IV is 0.0l of the rated flow of the valve (Note ① The rated flow of the valve is the maximum flow that the valve can pass when the flow condition from the valve opening to the maximum rated stroke is exactly the same as that specified in the test procedure. ② This does not mean that the G value when the valve is closed is 0.0l of the maximum C value of the valve). As with Level VI, this level is not allowed to be extrapolated to the actual working condition of the valve. Grade IV only provides the original measured data of valve closing ability under low pressure difference and room temperature.

4. Protective facilities of drain valve:
There are two kinds of traps beside the trap: bypass pipe and no bypass pipe. The trap with condensate recovery and condensate non recovery payment, drainage capacity and other special requirements can be installed in parallel.