Valve selection issue

In simple terms, for large-diameter valves of DN200 and above, floating ball valves cannot be used; only fixed ball valves are suitable. For more details, see http://bbs.hcbbs.com/thread-117460-1-1.html. For stem gate valves, the valve stem nut is located on the valve cover or bracket, and rotating this nut is used to raise or lower the valve stem in order to open or close the gate. This structure is beneficial for lubricating the valve stem, and it provides a clear indication of the degree of opening and closing; therefore, it is widely used. Dark stem gate valve: The valve stem nut is located inside the valve body and is in direct contact with the medium. Opening and closing the gate plate is achieved by rotating the valve stem. The advantage of this structure is that the height of the gate valve remains constant, thus requiring less installation space; it is suitable for large-diameter gate valves or those where installation space is limited. Such a structure must be equipped with an opening/closing indicator to indicate the degree of opening or closing. The disadvantage of this structure is that the valve stem threads are not only unable to be lubricated, but also are directly exposed to the erosion by the medium, making them prone to damage. Dark stem gate valves are mainly used in applications with low pressure, such as water pipelines, sewage systems, and other municipal engineering projects; the shell material is usually gray cast iron or ductile iron.