Working principle and structural principle of plastic diaphragm valve!

Plastic diaphragm valve is a stop valve that uses a diaphragm as an opening and closing part to close the flow channel, cut off the fluid, and separate the inner cavity of the valve body from the inner cavity of the valve cover. It is a special type of cut-off valve. Its opening and closing part is a diaphragm made of soft material, which separates the inner cavity of the valve body from the inner cavity of the valve cover and the driving components. It is now widely used in various fields. Plastic diaphragm valve materials include FRPP, UPVC, CVPC, PVDF, and PPH.

The plastic diaphragm valve is equipped with a flexible diaphragm or combined diaphragm in the valve body and valve cover, and its closing member is a compression device connected to the diaphragm. The valve seat can be in the form of a weir or the wall of a straight flow channel. The advantage of the diaphragm valve is that its operating mechanism is separated from the medium passage, which not only ensures the purity of the working medium, but also prevents the possibility of the medium in the pipeline impacting the working parts of the operating mechanism. In addition, any form of separate sealing at the valve stem is not required unless used as a safety feature in controlling hazardous media.

In plastic diaphragm valves, since the working medium only contacts the diaphragm and the valve body, both of which can be made of a variety of different materials, the valve can ideally control a variety of working media, especially suitable for chemically corrosive or suspended particles. medium.

The operating temperature of plastic diaphragm valves is usually limited by the materials used in the diaphragm and valve body lining. Its operating temperature range is approximately -40 to 130°C. The diaphragm valve has a simple structure and consists of only three main components: valve body, diaphragm and valve head assembly. The valve is easy to quickly disassemble and repair, and diaphragm replacement can be completed on site and in a short time.

Plastic diaphragm valve is a special form of cut-off valve. Its opening and closing part is a diaphragm made of soft material, which separates the inner cavity of the valve body from the inner cavity of the valve cover. Due to the limitations of the valve body lining process and diaphragm manufacturing process, the manufacturing process of larger valve body lining and larger diaphragm is difficult, so diaphragm valves are not suitable for larger pipe diameters and are generally used in pipes ≤DN200 or less. On the way. Due to the limitations of the diaphragm material, diaphragm valves are suitable for low pressure and low temperature situations. Generally do not exceed 1130℃. Because plastic diaphragm valves have good anti-corrosion properties, they are generally used in devices and pipelines with corrosive media. Since the operating temperature of the diaphragm valve, the applicable medium is limited by the lining material of the diaphragm valve body and the material of the diaphragm.

1. The diaphragm valve uses a corrosion-resistant lined valve body and a corrosion-resistant diaphragm instead of the valve core assembly, and uses the movement of the diaphragm to regulate. The valve body material of the diaphragm valve is cast iron, cast steel, or cast stainless steel, and is lined with various corrosion-resistant or wear-resistant materials, diaphragm materials rubber and polytetrafluoroethylene. The lining diaphragm has strong corrosion resistance and is suitable for regulating highly corrosive media such as strong acid and strong alkali.

2. The diaphragm valve has a simple structure, small fluid resistance, and larger flow capacity than other types of valves of the same specification. It has no leakage and can be used to regulate media with high viscosity and suspended particles. The diaphragm isolates the medium from the upper cavity of the valve stem, so the medium will not leak without packing. However, due to the limitations of the diaphragm and lining materials, the pressure resistance and temperature resistance are poor, and it is generally only suitable for nominal pressures of 1.6MPa and below 150°C.

3. The flow characteristic of the diaphragm valve is close to the quick-opening characteristic. It is approximately linear before 60% of the stroke, and the flow rate does not change much after 60%. Pneumatic diaphragm valves can also be equipped with feedback signals, limiters, positioners and other devices to meet the needs of automatic control, program control or flow adjustment. The feedback signal of the pneumatic diaphragm valve adopts contactless sensing technology. This product uses a membrane-type propelling cylinder instead of a piston cylinder, which eliminates the disadvantage that the piston ring is easily damaged, causing leakage and causing the valve to be unable to open and close. When the air source fails, the handwheel can still be operated to open and close the valve.

4. The sealing principle of the diaphragm valve is to rely on the downward movement of the operating mechanism to press down the diaphragm or diaphragm assembly to closely fit with the channel of the weir-type lining valve body or the straight-through lining valve body to achieve sealing. The sealing specific pressure is determined by the downward pressure of the closing member. Since the valve body can be lined with various soft materials, such as rubber or polytetrafluoroethylene, and the diaphragm is also made of soft materials, such as rubber or synthetic rubber-lined polytetrafluoroethylene, it can be achieved with a smaller sealing force. Completely sealed.

5. The diaphragm valve has only three main components: valve body, diaphragm and valve cover assembly. The diaphragm separates the lower valve body cavity from the upper valve cover cavity, so that the valve stem, valve stem nut, valve disc, pneumatic control mechanism, electric control mechanism and other parts located above the diaphragm are not in contact with the medium, and no medium is produced External leakage eliminates the need for the sealing structure of the stuffing box.

6. Diaphragm valves can be divided into six types according to their structural forms: house type, direct flow type, cut-off type, straight-through type, gate type and right-angle type; the connection form is usually flange connection; according to the driving method, it can be divided into manual, electric and pneumatic There are three types, among which pneumatic drive is divided into three types: normally open type, normally closed type and reciprocating type.