plastic diaphragm valve structure principle
Plastic diaphragm valve is a special type of block valve. Its opening and closing piece is a diaphragm made of soft material, which separates the inner cavity of valve body from that of valve cover. Due to the limitation of valve body lining process and diaphragm manufacturing process, it is difficult to make larger valve body lining and larger diaphragm. Therefore, diaphragm valve should not be used for larger pipe diameter, and it is generally used in pipelines less than or equal to DN200. Due to the limitation of diaphragm material, diaphragm valve is suitable for low pressure and low temperature. Generally, it should not exceed 1130 ℃. Because of the good anticorrosion performance of the plastic diaphragm valve, it is usually used in the device and pipeline of corrosive medium. Due to the service temperature of diaphragm valve, the applicable medium is limited by the lining material of diaphragm valve body and diaphragm material.
1. The valve core assembly is replaced by a corrosion-resistant lined valve body and a corrosion-resistant diaphragm, which uses the movement of the diaphragm to play a regulating role. The valve body material of diaphragm valve is cast iron, cast steel or cast stainless steel, and lined with various corrosion-resistant or wear-resistant materials, diaphragm material rubber and polytetrafluoroethylene. The lining diaphragm has strong corrosion resistance and is suitable for adjustment of strong corrosive media such as strong acid and alkali.
2. The structure of diaphragm valve is simple, the fluid resistance is small, the flow capacity is larger than other types of valves of the same specification; no leakage, it can be used for the adjustment of high viscosity and suspended particles medium. The diaphragm separates the medium from the upper chamber of the valve stem, so the medium without packing will not leak out. However, due to the limitation of diaphragm and lining materials, the pressure resistance and temperature resistance are poor, which are generally only applicable to 1.6Mpa nominal pressure and below 150 ℃.
3. The flow characteristic of the diaphragm valve is close to the quick opening characteristic, which is approximately linear before 60% stroke, and the flow rate changes little after 60%. Pneumatic diaphragm valve can also be equipped with feedback signal, limiter and positioner to meet the needs of automatic control, program control or flow regulation. The feedback signal of pneumatic diaphragm valve adopts contactless sensing technology. The product uses membrane type propulsion cylinder instead of piston cylinder, which eliminates the defects of piston ring easily damaged, resulting in leakage and unable to push the valve to open and close. When the air source fails, the hand wheel can be operated to open and close the valve.
4. The sealing principle of diaphragm valve is to press the diaphragm or diaphragm assembly to be close to the channel of weir type lining valve body or straight through lining valve body by the downward movement of operating mechanism, so as to achieve sealing. The sealing specific pressure depends on the downward pressure of the closing part. Because the valve body can be lined with various soft materials, such as rubber or polytetrafluoroethylene, etc.; the diaphragm is also made of soft materials, such as polytetrafluoroethylene lined with rubber or synthetic rubber, so it can be completely sealed with less sealing force.
5. Diaphragm valve only has three main parts: valve body, diaphragm and valve cover assembly. The diaphragm separates the inner cavity of the lower valve body from the inner cavity of the upper valve cover, so that the valve stem, stem nut, valve disc, pneumatic control mechanism, electric control mechanism and other parts above the diaphragm do not contact with the medium, and the medium leakage will not occur, so the sealing structure of the stuffing box is omitted.
6. Diaphragm valve according to the structure can be divided into: house type, DC type, cut-off type, straight through type, gate type and right angle type; the connection form is usually flange connection; according to the driving mode, it can be divided into manual, electric and pneumatic three kinds, of which pneumatic drive is divided into normally open, normally closed and reciprocating.