Diaphragm Valve

Diaphragm valve is a shut-off 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. The diaphragm is usually made of rubber, plastic and other elastic, corrosion-resistant, and non-permeable materials. The valve body is mostly made of plastic, glass fiber reinforced plastic, ceramic or metal rubber-lined materials. Simple structure, good sealing and anti-corrosion performance, and low fluid resistance. It is used for media with low pressure, low temperature, strong corrosiveness and suspended matter. According to the structure, there are roof type, cut-off type, gate type and so on. According to the driving mode, it is divided into manual, pneumatic and electric.
 
The structure of the diaphragm valve is quite different from the general valve. It is a new type of valve and a special form of cut-off valve. Its opening and closing part is a diaphragm made of soft material. The inner cavity of the cover and the driving part are separated and are now widely used in various fields. Commonly used diaphragm valves include rubber-lined diaphragm valves, fluorine-lined diaphragm valves, unlined diaphragm valves, and plastic diaphragm valves.
Diaphragm valve is equipped with a flexible diaphragm or combined diaphragm in the valve body and valve cover, and its closing part is a compression device connected with the diaphragm. The valve seat can be weir-shaped, or it can be a pipe wall that passes through the 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 from impacting the working parts of the operating mechanism. In addition, there is no need to use any form of separate seal at the valve stem, unless it is used as a safety facility in the control of hazardous media. In the diaphragm valve, since the working medium is only in contact with the diaphragm and the valve body, both of which can use 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 working temperature of the diaphragm valve is usually limited by the materials used in the diaphragm and the valve body lining, and its working temperature range is about -50～175℃. The diaphragm valve has a simple structure, consisting of only three main parts: the valve body, the diaphragm and the valve head assembly. The valve is easy to quickly disassemble and repair, and the replacement of the diaphragm can be completed on site and in a short time.
 
Working principle and composition:
The diaphragm valve uses a corrosion-resistant lining body and a corrosion-resistant diaphragm instead of the valve core assembly, and the movement of the diaphragm is used for adjustment. The valve body of the diaphragm valve is made of 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 the adjustment of strong corrosive media such as strong acid and strong alkali.
The diaphragm valve has a simple structure, low fluid resistance, and a larger flow capacity than other types of valves of the same specification; it has no leakage and can be used for the adjustment of high viscosity and suspended particulate media. The diaphragm isolates the medium from the upper cavity of the valve stem, so there is no packing medium and no leakage. However, due to the limitation of the diaphragm and lining materials, the pressure resistance and temperature resistance are poor, and it is generally only suitable for the nominal pressure of 1.6MPa and below 150°C.
The flow characteristic of the diaphragm valve is close to the quick opening characteristic, which is approximately linear before 60% of the stroke, and the flow rate after 60% does not change much. Pneumatic diaphragm valves can also be equipped with feedback signals, limiters and positioners to meet the needs of automatic control, program control or flow adjustment. The feedback signal of the pneumatic diaphragm valve adopts non-contact sensing technology. The product adopts a membrane type propulsion cylinder instead of a piston cylinder, eliminating the disadvantage of easy damage to the piston ring, causing leakage and unable to push the valve to open and close. When the air source fails, the handwheel can still be operated to open and close the valve.
 
The sealing principle of the diaphragm valve is to rely on the downward movement of the operating mechanism to press down the diaphragm or the diaphragm assembly and the channel of the weir-type lining valve body or the straight-through lining valve body to achieve a seal. The specific pressure of the seal is achieved by the downward pressure of the closing member. Since 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 rubber or synthetic rubber lined polytetrafluoroethylene, so it can be achieved with a smaller sealing force Completely sealed.
 
Diaphragm valves have only three main components: body, diaphragm and bonnet 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, valve stem nut, valve clack, pneumatic control mechanism, electric control mechanism and other parts located above the diaphragm do not come into contact with the medium, and no medium is generated. External leakage saves the sealing structure of the stuffing box.
 
Where the diaphragm valve is applicable
Diaphragm valve is a special form of shut-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 limitation of the valve body lining process and the diaphragm manufacturing process, the larger valve body lining and the larger diaphragm manufacturing process are difficult. Therefore, the diaphragm valve is not suitable for larger pipe diameters, and is generally used for pipes below DN200. On the way.
Due to the limitation of diaphragm material, diaphragm valve is suitable for low pressure and low temperature occasions. Generally do not exceed 180°C. Because the diaphragm valve has good anti-corrosion performance, it is generally used in corrosive media devices and pipelines. Because the operating temperature of the diaphragm valve is limited by the applicable medium of the diaphragm valve body lining material and diaphragm material.
 
Features:
(1) The fluid resistance is small.
(2) It can be used for the medium containing hard suspended solids; since the medium only contacts the valve body and diaphragm, there is no need for stuffing box, there is no problem of stuffing box leakage, and there is no possibility of corrosion to the valve stem.
(3) Suitable for corrosive, viscous, and slurry media.
(4) Cannot be used in high pressure occasions.
 
Installation and maintenance:
①Before installing the diaphragm valve, carefully check whether the operating conditions of the pipeline are consistent with the scope of use specified by this valve, and clean the inner cavity to prevent dirt from jamming or damaging the sealing parts.
②Do not apply grease or oil on the surface of the rubber lining and the rubber diaphragm to prevent the rubber from swelling and affecting the service life of the diaphragm valve.
③The hand wheel or transmission mechanism is not allowed to be used for lifting, and collision is strictly prohibited.
④ When manually operating the diaphragm valve, do not use auxiliary levers to prevent excessive torque from damaging the drive components or sealing parts.
⑤Diaphragm valves should be stored in a dry and ventilated room, stacking is strictly prohibited, both ends of the stock diaphragm valve must be sealed, and the opening and closing parts should be in a slightly open state.