(3) In Figure 1, the bottom connecting pipe which plays the role of drainage is connected with the plug by thread. When the temperature rises, it is difficult to ensure the sealing of the threaded part, so it is decided to cancel the plug. In Figure 2, the plug connected with the bottom connecting pipe is replaced with a bench drain plug, and the connecting end is sealed with a winding gasket to ensure the sealing reliability of the bottom end.

The valves have a wide range of uses, types and classification methods. In general, there are two categories: * automatic valves: valves that act by themselves depending on the capacity of the medium (liquid, gas) itself. Such as check valve, safety valve, regulating valve, drain valve, pressure reducing valve, etc. The second type of actuated valve: manually operated, pneumatically operated, hydraulically operated and pneumatically operated valves. Such as gate valve, globe valve, throttle valve, butterfly valve, ball valve, plug valve, etc.