Plug valve is a kind of valve with closing part or plunger shaped rotary valve. By rotating 90 degrees, the channel port on the valve plug is connected or separated from the channel port on the valve body to realize opening or closing. The shape of its valve plug can be cylindrical or conical. In a cylindrical plug, the channel is generally rectangular. In the conical plug, the channel is trapezoidal. These shapes make the structure of the plug valves lightweight. It is most suitable for cutting off and connecting medium and shunting use, but sometimes it can also be used for throttling according to applicable properties and erosion resistance of sealing surface.
When installing the plug valves, one shall pay attention to the following four points in order to prevent damage to the plug valves and ensure the full performance of the plug valves.
1. Make sure the valve is open. Heat the pipe first. Transfer as much heat as possible from the pipe to the plug valves. Avoid prolonging the heating time of the plug valves.
2. Use gauze or wire brush to remove the pipe and cutting parts to make the metal surface shine. It is not recommended to use steel wool.
3. First cut the pipe along the vertical direction, trim and remove burrs, and measure the pipe diameter.
4. Apply flux to the outside of the pipe and the inside of the welding cover. The flux must completely cover the welding surface. Please use flux temperately.
According to the structural characteristics and design functions of the plug valves, it can be selected according to the following principles.
1. It is used to distribute medium and change medium flow direction. Its working temperature is not higher than 300 ℃, nominal pressure PN ≤ 1.6MPa and nominal diameter is not greater than 300mm. It is recommended to select multi-channel plug valves.
2. On the equipment and pipelines of food enterprises and pharmaceutical factories such as milk, fruit juice and beer, it is recommended to select tight conical plug valves made of austenitic stainless steel.
3. In the oilfield exploitation, natural gas field exploitation, branch pipe for pipeline transportation, refining and cleaning equipment, the nominal pressure level shall not be greater than class300 and the nominal diameter shall not be greater than 300mm. It is recommended to select oil sealed conical plug valves.
4. In the oilfield exploitation, natural gas field exploitation, branch pipe for pipeline transportation, refining and cleaning equipment, the nominal pressure level is not greater than class7500, the nominal diameter is not greater than 900mm, and the working temperature is not higher than 340 ℃. It is recommended to select oil sealed conical plug valves.
5. In the large-scale chemical industry, in the pipeline and equipment containing corrosive medium, where the opening or closing speed is required to be fast, the PTFE sleeve sealed conical plug valves can be selected for the medium based on nitric acid; For the medium based on acetic acid, Crl8Nil 2M02Ti stainless steel with PTFE sleeve can be selected to seal the conical plug valves.
6. In the pipeline and equipment of gas, natural gas and HVAC system, the nominal diameter shall not be greater than 200nm, and the stuffing conical plug valves shall be selected.