1 top threaded STEM cut-off valve: thread of the cut-off valve stem
Outside of the valve body. The advantage is that the stem is not subject to medium erosion and is easy to lubricate, which is generally used.
2 lower threaded stem cut-off valve: the cut-off valve stem thread in the valve body. This structural stem thread is directly contacted with the medium, is susceptible to erosion and cannot be lubricated. This type of structure is used for small-caliber and temperature-low places.
Domestic production cut-off valve manufacturers more, the connection size is also mostly not unified. Mainly divided into the following major categories: to jb/t2203-1999 "cut-off valve structure length" is the main general class. At present, most of the domestic cut-off valve manufacturers are designed and manufactured according to this standard. But this standard is not perfect, the specification is not complete, the single gate cut-off valve maximum nominal diameter is DN1200, the Double gate globe valve biggest nominal path DN1500. According to the manufacturer's cut-off valve specifications and the information, the current angle-type cut-off valve nominal diameter of the smallest DN15, z-type pass-through valve nominal path to reach DN2000. By textual research, the connection size of each manufacturer is not uniform. In order to have a unified standard, users in the selection and installation of the same specifications can be interchangeable, recommended that China General Machinery Institute of jb/t2203-1999 "cut-off valve structure length" to be revised. Recommended design institutes and users according to the standard selection, cut-off valve manufacturers in accordance with the standards designed and manufactured.