Plug valves are rotary valves.are closure or plunger shapedthe plug valve relies on the rotation90After a certain degree, the passage port on the valve plug communicates with or separates from the passage port on the valve body to realize opening or closing.The shape of its valve plug can be cylindrical or conical. In cylindrical plugs, the passages are generally rectangular; in tapered plugs, the passages are trapezoidal. These shapes make the structure of the plug valve light. It is more suitable for cutting off and connecting media and shunting, but it can also be used for throttling sometimes depending on the properties of the application and the erosion resistance of the sealing surface.
The pressure test method of the plug valve:
① Plug valveWhen carrying out the strength test, the medium is introduced from one end, the rest of the passages are closed, and the plug is rotated to each working position of full opening in turn for the test. If no leakage is found in the valve body, it is qualified.
② During the tightness test, the straight-through cock should keep the pressure in the cavity equal to the passage pressure, turn the plug to the closed position, check from the other end, and then turn the plug180°Repeat the above test; for three-way or four-way plug valves, keep the pressure in the cavity equal to that at one end of the channel, turn the plugs to the closed position in turn, introduce the pressure from the right-angle end, and check from the other end at the same time.
Before the plug valve test, it is allowed to coat a layer of non-acid thin lubricating oil on the sealing surface, and it is qualified if no leakage and enlarged water droplets are found within the specified time.The test time of the plug valve can be shorter, generally according to the nominal diameterl~3min.
The plug valve for gas should be1．25Doubling the working pressure for air tightness test.
Selection of plug valves and structural characteristics of plug valves:
(1) The fluid of the plug valve passes through directly, the resistance is small, and the opening and closing are convenient and rapid.
(2) Plug valves are mainly used in pipelines to cut off, upgrade and change the direction of medium flow. It is easy to adapt to the multi-channel structure, so that one valve can obtain two, three, or even four different flow channels, which can simplify the design of the piping system, reduce the number of valves and some connecting accessories required in the equipment.
(3) The plug valve is a valve part that was adopted earlier in history.Quick opening and closing due to simple structure(stopper rotation1/4Qcircle can complete the opening and closing action), easy to operate and small fluid resistance, it is still widely used today. At present, it is mainly used in the case of low pressure, small caliber and low medium temperature.
(4) According to the structural characteristics of the plug valve and the functions that can be achieved in the design, it can be selected according to the following principles.
①It is used to distribute the medium and change the flow direction of the medium, and its working temperature is not higher than300°C, nominal pressurePN≤1.6MPathe nominal diameter is not greater than300mmit is recommended to use a multi-channel plug valve.
②Austenitic stainless steel tight-set conical plug valves are recommended for equipment and pipelines in food companies such as milk, juice, beer, and pharmaceutical factories.
③In oil field exploitation, natural gas field exploitation, branch pipes of pipeline transportation, refining and cleaning equipment, the nominal pressure level is not greater thanClass300the nominal diameter is not greater than300mmit is recommended to choose an oil-sealed conical plug valve.
④In oil field exploitation, natural gas exploitation, branch pipes of pipeline transportation, refining and cleaning equipment, the nominal pressure level is not greater thanClass7500the nominal diameter is not greater than900mmthe working temperature is not higher than340℃, it is recommended to choose an oil-sealed conical plug valve.
⑤In the large-scale chemical industry, in the pipelines and equipment containing corrosive media, where the opening or closing speed is required to be fast, the PTFE sleeve-sealed conical plug valve can be selected for the nitric acid-based medium; Acetic acid-based media, optionalCrl8Nil 2M02TiStainless steel inlaid PTFE sleeve seal conical plug valve.
⑥In gas, natural gas, HVAC system pipelines and equipment, the nominal diameter is not greater than200nmIt is advisable to choose a stuffed conical plug valve.
All of the above content is about the structural characteristics and pressure test methods of the plug valve shared with you today. Let’s collect it and read it slowly~