1) Upper threaded stem stop valve: The thread of the shutoff valve stem is outside the valve body. The advantage is that the valve stem is not eroded by the medium and is easy to lubricate, and such a structure is relatively common.
2) Lower threaded stem stop valve: The thread of the shutoff valve stem is inside the valve body. This type of stem thread is in direct contact with the media and is susceptible to erosion and lubrication. This structure is used in places with small diameters and low temperatures.
There are many manufacturers of shut-off valves in China, and the connection sizes are mostly not uniform. Mainly divided into the following major categories:
JB/T2203-1999 "cut-off valve structure length" is the general category. At present, most domestic shut-off valve manufacturers are designed and produced according to this standard. However, this standard is not perfect, the specifications are not complete, the maximum nominal diameter of the single gate stop valve is DN1200, and the maximum nominal diameter of the double gate stop valve is DN1500. According to the specifications of the shut-off valve produced by the manufacturer and the information obtained, the nominal diameter of the angle-type globe valve is DN15, and the nominal diameter of the Z-type straight-through globe valve is DN2000. According to research, the connection sizes of various manufacturers are not uniform. In order to have a uniform standard, the user can exchange the same specifications during the selection and installation. It is recommended that China General Machinery Research Institute revise JB/T2203-1999 "Structure Length of Globe Valve". It is recommended that the design institute and users choose according to the standard, and the manufacturer of the globe valve is designed and manufactured according to the standard.