Stop valve, also known as shut-off valve, is a forced sealing valve. Therefore, when the Dalian marine valve is closed, pressure must be applied to the valve disc to force the sealing surface not to leak. When the medium enters the valve from the lower part of the valve disc, the resistance to be overcome by the operating force is the friction between the valve stem and the packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve stem is larger, otherwise the failure of the valve stem bending will occur.

There are three connection methods: flange connection, screw connection and welding connection. After the self sealing valve appears, the medium flow direction of the stop valve enters the valve cavity from above the valve disc. At this time, under the medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve rod can be reduced accordingly. At the same time, under the action of medium, this type of valve is also relatively tight. The "three chemical supplies" of valves in China once stipulated that the flow direction of stop valves should be from top to bottom. When the stop valve is opened, the opening height of the valve disc is 25% ~ 30% of the nominal diameter The flow has reached a large value, indicating that the valve has reached the full open position. Therefore, the full open position of the stop valve shall be determined by the stroke of the valve disc.

The opening and closing part of the stop valve is a plug-shaped valve disc. The sealing surface is flat or sea cone. The valve disc moves linearly along the center line of the valve seat. The movement form of the valve stem (common name: concealed rod) and the lifting rotating rod type can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media.

Therefore, this type of shut-off valve is very suitable for cutting off or regulating and throttling. Because the valve stem opening or closing stroke of this type of valve is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat opening is proportional to the stroke of the valve disc, it is very suitable for regulating the flow.