What are the causes of leakage of pneumatic diaphragm control valves?

There are many types of leakage in pneumatic diaphragm control valves:

Leakage between the upper and lower covers of the diaphragm: it may be that the fastening bolts of the upper and lower covers are not all effectively fastened, which can be solved by fastening bolts; If the leakage is caused by a crack in the diaphragm, the diaphragm can only be replaced.

The leakage at the diaphragm lower cover and the push rod of the air-closed membrane control valve is caused by the aging of the O-ring seal, which can be solved by replacing the O-ring; If the pusher is leaked due to the non-slip caused by corrosion, the pusher can be polished when the situation is not serious, and the pusher must be replaced when the corrosion is serious.

The leakage between the valve stem and the valve body is that the sealing packing of the valve stem does not play a sealing role, and the gland bolt of the sealing packing can be adjusted to re-compress the sealing packing; If adjusting the gland bolt does not work, the sealing packing can only be replaced.

If the valve core leaks, the distance between the valve stem and the push rod can be adjusted to make the distance between the valve stem and the push rod longer, even if the valve stem can enter the valve body more deeply, so that the valve core is in contact with the sealing surface of the valve seat; If the medium controlled by the valve has strong corrosiveness, causing the corrosion of the valve core and causing leakage, when the corrosion situation is not serious, the surface of the valve core can be sprayed and then grinded, and the contact surface between the valve seat and the valve core can also be repaired in this way, if the corrosion situation is more serious, the entire valve can only be replaced.

Here are some of the well-known brands recognized in the valve industry, which are widely recognized and have a high reputation. While rankings may vary depending on time and market conditions, the following brands are generally considered to be among the top brands in the valve industry:

The following influential first-line brands of water system valves and industrial valves can be used as a reference, but for reference only: Suzhou Neway Valve, Shanghai Guanlong Valve, Shanghai Qizhong Valve, Sanhua, Su Yan, Shentong, Su Valve, Nanfang, Jiang.

First, the word Yao. The above manufacturers are only estimates and references, and the specific situation may vary or fluctuate at any time due to changes in a series of factors such as changes in the market, the size of the competition pattern, and the stability of product quality. As an indispensable key device in industrial production and civil facilities, the quality and reputation of the valve brand directly affect the satisfaction and trust of users.

These brands are known in the valve industry for their innovative technology, high-quality products and reliability. It is important to note that the market and industry are evolving rapidly, and different rankings may vary depending on time and region. For the most up-to-date ranking information, it is recommended to refer to industry reports, professional organizations or market research data for more detailed and accurate information.

(1) There is a lot of moisture in the air source. Because the positioner works on the principle of mechanical force balance, i.e. nozzle baffle technology Due to the small nozzle hole, it is easy to be blocked by dust or unclean air sources. The air source is compressed air, which contains water vapor, oil, dust, etc., which is easy to cause the blockage of the nozzle and amplifier, so that the positioner cannot work normally.

2) The zero drift of the valve positioner is large. Because the valve positioner adopts the principle of force balance, the elastic coefficient of the spring changes in the harsh field, resulting in the zero drift of the valve positioner, resulting in a large change in the zero position, making the amplifier output unstable, resulting in a decrease in the adjustment quality or inability to adjust.

3) The feedback lever is loose. Because the valve positioner is a mechanical force balance type, it has many moving parts, which is easily affected by temperature vibration, resulting in the loosening of the feedback rod.

There are no relevant regulations on the total gas supply, but the valve has gas requirements, and the pressure configuration of the gas source is suitable for the valve requirements.

In order to ensure the pneumatic components, it is generally better to use dry and clean compressed air nitrogen source than compressed air, because the nitrogen obtained by pressure swing adsorption or cryogenic is clean and dry.

Yes, if you have any questions, please contact us, we produce pneumatic valves

Both compressed air and nitrogen sources are available, generally from 4 to 10 bar.

a.Two-position valve: mainly used to close or turn on the medium;

b.Control valve: mainly used in the control system. When selecting a valve, it is necessary to determine the flow characteristics of the regulating valve;

c.Diverter valves: used for dispensing or mixing media;

d.Shut-off valve: Usually refers to a valve with a leakage rate of less than 1 in 100,000. This type of valve should generally be installed horizontally in the pipeline. 1 Classification by pressure.

1) Vacuum valve: the working pressure is lower than the standard atmospheric pressure;

2) Low pressure valve: nominal pressure pn;

3) Medium pressure valve:;

4) High pressure valve: usually PN22, PN32;

5) Ultra high pressure valve: PN IOOMPA.

2 Classified by medium operating temperature.

1) High temperature valve: T>450;

2) Medium temperature valve: 220 t 450;

3) Normal temperature valve: 40 t 220; Cryogenic valve: 200 t 40. This classification method is divided according to principle, function and structure, and is currently the most commonly used classification method at home and abroad. It is generally divided into nine categories:

1) Single-seat control valve;

2) Double-seat control valve;

3) sleeve control valve;

4) Angle control valve;

5) Three-way control valve;

6) Diaphragm valve;

7) Butterfly valve; 8) Ball valve;

9) Eccentric rotary valve. The first six are linear strokes, and the last three are angular strokes.

These nine products are also the most basic products, also known as normal products, base products, or standard products. All kinds of special products and special products are improved and varied on the basis of these nine types of products. (1) Soft-seal shut-off valve;

2) Hard seal shut-off valve;

3) Wear-resistant regulating valve;

4) Corrosion-resistant control valve;

5) Full PTFE corrosion-resistant control valve.

6) Full corrosion-resistant alloy control valve;

7) Emergency action shut-off or venting valve;

8) Anti-clogging control valve;

9) Corrosion-resistant and anti-blocking shut-off valve;

10) Insulation jacket valve;

11) Large pressure drop shut-off valve;

12) Small flow control valve;

13) Large-diameter control valve;

14) Large adjustable ratio control valve;

15) Low S energy-saving control valve;

16) Low noise valve;

17) Compact control valve;

18) Lined (rubber, PTFE, ceramic) control valves;

19) Special ball valve for water treatment;

20) Caustic soda special valve;

21) Ammonium phosphate valve;

22) chlorine gas regulating valve;

23) Bellows seal valve ......The flow capacity CV value (flow coefficient) is one of the main parameters of the control valve selection, the flow capacity of the control valve is defined as: when the control valve is fully opened, the pressure difference between the two ends of the valve is, and the fluid density is 1g cm3, the flow rate of the flow diameter control valve per hour is called the flow capacity, also known as the flow coefficient, expressed in CV, the unit is T H, and the CV value of the liquid is calculated according to the following formula.

According to the flow capacity CV value of the table, the nominal diameter DN of the control valve can be determined.

Flow characteristics of the control valve The flow characteristics of the control valve are the relationship between the relative flow rate of the medium flowing through the control valve and its opening under the condition that the pressure difference between the two ends of the valve remains constant. There are three types of flow characteristics of control valves: linear, equal percentage and parabolic. The significance of the three note characteristics is as follows: