How to maintain a faulty pneumatic control valve?

a) The regulating valve does not operate. The fault symptoms and causes are as follows:

1.No signal, no air supply. The air source is not opened, due to the water content of the air source freezing in winter, resulting in the blockage of the air duct or the blockage of the filter and pressure reducing valve, and the failure of the compressor; Leakage of air main.

2.There is an air supply, no signal. Regulator failure, signal tube leakage; Positioner bellows leakage; Damage to the adjusting omentum diaphragm.

3.The locator has no air supply. clogged filters; Faulty pressure reducing valve leaking or clogged pipes.

4.The positioner has an air supply and no output. The throttle hole of the positioner is blocked.

5.There is a signal, but there is no action. The valve core falls off, and the valve core is stuck with the society or with the valve seat; bent or broken stems; Frozen or coke dirt from the seat, spool, and spool; The actuator spring rusts due to long-term use.

2) The action of the control valve is unstable. The fault symptoms and causes are as follows:

1.The compressed air pressure is unstable. The compressor capacity is too small; Failure of the pressure reducing valve.

2.The signal pressure is unstable. The time constant (t=rc) of the control system is inappropriate; The regulator output is unstable.

3.The air supply pressure is stable, and the signal pressure is also stable, but the operation of the control valve is still unstable. The ball valve of the amplifier in the positioner is not tightly closed by dirt wear, and the air consumption is particularly increased, and the output will be generated**; The nozzle baffle of the amplifier in the positioner is not parallel, and the baffle cannot cover the nozzle; air leakage from output pipes and lines; The rigidity of the actuator is too small; The friction resistance of the stem is large during the movement, and there is a blockage phenomenon with the contact part.

c) Vibration of the regulating valve. The fault symptoms and causes are as follows:

1.The control valve vibrates at any opening. unstable support; There is a vibration source nearby; The spool and bushing are heavily worn.

2.The control valve vibrates when it is close to the fully closed position. The control valve is selected to be large, and it is often used under a small opening; The medium flow direction of the single-seat valve is opposite to the closing direction.

4) The action of the regulating valve is sluggish. The phenomenon of sluggishness and its causes are as follows:

1.The stem is sluggish only when acting in one direction. Diaphragm damage and leakage in pneumatic film actuator; Leakage of type "O" seal in the actuator.

2.The valve stem is sluggish when it reciprocates. There is sticky blockage in the valve body; PTFE filler deteriorates and hardens or graphite-asbestos filler lubricating oil drying; If the filler is added too tightly, the friction resistance increases; High frictional resistance due to the non-straight stem; Pneumatic control valves without positioners can also lead to sluggish action.

5) The leakage of the regulating valve increases. The reasons for the leak are as follows:

1.When the valve is fully closed, there is a large amount of leakage. The valve core is worn, the internal leakage is serious, and the valve is not adjusted and closed tightly.

2.The valve does not reach the fully closed position. The pressure difference of the medium is too large, the rigidity of the actuator is small, and the valve is not tightly closed; There is a foreign object in the valve; Bushing sintering.

6) The adjustable range of flow becomes smaller. The main reason is that the spool is corroded and smallened, resulting in an adjustable minimum flow rate.

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 are the top ten domestic first-line valve brand manufacturers in 2022-2023, but for reference only: Suzhou Neway Valve Co., Ltd., Shanghai Guanlong Valve Machinery, Shanghai Qizhong Valve Manufacturing, 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.

Summary. We'll be happy to answer this question for you.

There are many reasons why the pneumatic butterfly valve is not closed tightly, and it can be adjusted according to the specific situation, such as impurities on the sealing surface of the valve, the valve can be adjusted and then closed, and repeated operation can be eliminated; Secondly, it may be that the stem thread is rusty, it is recommended to adjust the valve switch more, or it is not possible, only to overhaul or replace the sealing surface; Finally, adjust the opening and closing flexibility of the valve, and it is best to add lubricating oil in an appropriate amount. Hope it helps.

Hello, I have seen your question and am sorting out the answer, please wait a while and I'm glad to answer this question for you. There are many reasons why the pneumatic butterfly valve is not closed tightly, and it can be adjusted according to the specific situation, such as impurities on the sealing surface of the valve, the valve can be adjusted and then closed, and repeated operation can be eliminated; Secondly, it may be that the stem thread is rusty, it is recommended to adjust the valve switch more, or it is not possible, only to overhaul or replace the sealing surface; Finally, adjust the opening and closing flexibility of the valve, and it is best to add lubricating oil in an appropriate amount. Hope it helps.

The adjustment of the pneumatic control valve can be carried out according to the specific control requirements and the change of the medium flow, and the following methods are generally adopted:

1.Manual adjustment method: manually switch the pneumatic control valve, and adjust the opening of the valve by observing the value of the flow gauge or pressure gauge to meet the control requirements. Although the adjustment accuracy is low, it is suitable for some simple occasions.

2.Electronic adjustment method: The electronic regulator controls the opening of the pneumatic control valve valve and adjusts the flow rate of the medium through the electrical signal transmitted from the circuit. The electronic regulator can be continuously and automatically adjusted according to different media flow changes.

3.Automatic variable stool frequency adjustment method: The automatic frequency conversion regulator realizes the adjustment function by adjusting the actuator of the pneumatic control valve, and usually uses the PID adjustment algorithm to accurately adjust the valve.

It should be noted that when adjusting the pneumatic control valve, it is necessary to choose the appropriate adjustment method according to the actual situation, and at the same time understand the laws and elements of control, so as to avoid the impact on the production process. When installing and debugging the pneumatic control valve, it should also be operated in accordance with the requirements, and the parameters and control scheme of the valve should not be changed at will.

Adjustment method of automobile pneumatic valve: 1. The pneumatic valve switch type is generally a pneumatic ball valve and a pneumatic center butterfly valve, and the adjustment type is generally a pneumatic control valve, the switch valve is angular stroke, and the regulating valve is linear stroke; 2. The on-off valve is switched through the cylinder, and the adjustment Huihe valve is realized by the pneumatic membrane head; 3. At the same time, the on-off valve can also achieve adjustment performance by adding a positioner on the cylinder, but the adjustment performance is not as accurate as the linear control valve.

Hello, the adjustment of the pro-pneumatic control valve is divided into the following steps:1Adjust the zero position:

The pneumatic control valve is closed, then the piston of the actuator is moved to the valve's closed position (the so-called "zero position") by manual operation or other means, and the valve position indicator (if any) is adjusted to match the zero position. At this point, the control gauge reading should be zero. 2.

Adjust the adjustment range: Under the condition of keeping the actuator in the zero position, the setting value is gradually increased or decreased by adjusting the adjustment knob or button on the control instrument, so that the actuator moves along the adjustment curve. Observe changes in the valve position indicator and make sure the valve opens or closes accordingly as the set value changes.

3.Calibration stroke: In the process of adjusting the adjustment range, if the actual stroke of the valve is found to be inconsistent with the set value, the stroke calibration can be carried out.

This is done by first adjusting the actuator to the desired maximum stroke position and then aligning the actuator maximum stroke position with the corresponding position on the control instrument via the stroke calibration option on the control instrument. 4.Debug:

Once the adjustment is complete, a system test and inspection is carried out to check that the valve is working as intended. According to the specific application scenario, you can adjust the control parameters, such as adjusting the proportional bandwidth and integration time, to obtain better control results. It should be noted that the adjustment of pneumatic control valve requires professional skills and experience, if you do not understand the relevant knowledge, it is recommended to consult professionals or refer to relevant literature for operation.

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Common faults and treatment methods of pneumatic control valves.

The control valve does not operate.

First, confirm whether the pressure of the air source is normal and find the fault of the air source. If the air source pressure is normal, then judge whether the amplifier of positioner or electric converter has output; If there is no output, the amplifier throttle hole is blocked, or moisture from the compressed air accumulates at the amplifier ball valve. Use a small thin steel wire to dredge the constant throttle hole to remove dirt or clean the air source.

If all of the above is normal, there is a signal but no action, the actuator is faulty or the stem is bent, or the spool is stuck. In this case, the valve must be removed for further inspection.

The regulating valve is jammed.

If the reciprocating stroke of the valve stem is sluggish, there may be viscous substances in the valve body, coking blockage or packing pressure is too tight, or PTFE packing is aging, and the valve stem is bent and scratched. Most of the control valve jamming faults appear in the early stage of the newly put into operation system and overhaul, due to the blockage caused by welding slag and rust in the pipeline at the throttle and guide parts, so that the medium flow is not smooth, or the packing is too tight in the maintenance of the control valve, resulting in the increase of friction, resulting in the phenomenon of small signal not acting and large signal action being excessive.

In such a situation, the secondary line or regulating valve can be quickly opened and closed, so that the stolen goods can be washed away by the medium from the secondary line or regulating valve. In addition, the stem can be clamped with a pipe wrench, and under the condition of external signal pressure, the valve stem can be rotated forward and backward to let the valve core flash through the jam. If the problem cannot be solved, the problem can be solved by increasing the air source pressure and increasing the driving power by moving up and down several times.

If it still can't be operated, it is necessary to dismantle the control valve, of course, this work requires strong professional skills, and must be completed with the assistance of professional and technical personnel, otherwise the consequences will be more serious.

Valve leakageThe leakage of the control valve generally includes the leakage caused by the leakage of the control valve, the leakage of the packing and the deformation of the valve core and valve seat, which are analyzed separately below.

1) Valve leakage.

The length of the valve stem is not suitable, the valve stem of the air opening valve is too long, and the upward (or downward) distance of the valve stem is not enough, resulting in a gap between the valve core and the valve seat, which can not be fully contacted, resulting in loose and internal leakage. Similarly, if the stem of the gas shut-off valve is too short, it can also lead to a gap between the valve core and the valve seat, which cannot be fully contacted, resulting in poor closing and internal leakage. Workaround:

The stem of the control valve should be shortened (or extended) so that the control valve is of the appropriate length so that it no longer leaks.

Symptom Check Item Resolution.

The pneumatic valve cannot be operated.

1.Whether the solenoid valve is normal, whether the coil is burned out, whether the solenoid valve core is stuck by the stolen goods, replace the solenoid valve, replace the coil, and clear the stolen goods.

2.Check whether the actuator is working normally, such as cylinder piston blowing, air leakage between the cylinder block and the end cover or the rotating shaft, etc., disassemble the actuator to check whether the seal has been damaged, and whether the surface of the cylinder bore has been damaged.

Replace broken seals, cylinders or pistons.

3.The impurities in the valve will be stuck in the ball core, and the impurities will be clear, and the damaged valve parts will be replaced4The handle of the manually operated actuator is in the manual position.

Pull the handle into the pneumatic automatic position.

5.Twisted or flattened tubing Correct or replace tubing.

6.The medium or ambient temperature is too low, causing the pipeline to freeze.

Even if the condensate is clear, add water removal equipment.

The pneumatic valve moves slowly and crawls.

1.The compressed air pressure is insufficient.

Increase the pressure of the air supply, and set up a gas storage tank on the way to reduce the pressure fluctuation.

2.The flow rate is insufficient or there are other devices with large air consumption at the same time, add gas storage tanks and air compressors to reduce pressure fluctuations.

3.Pneumatic actuator torque is too small Increase actuator specifications.

4.The valve load is too large, and the valve spool or other valve parts are too tightly assembled and unreasonable.

Re-refitting and adjusting the valve torque.

5.Cylinder friction fluctuates greatly and lubricates appropriately.

Other faults. 1.The valve action starts to beat, and the load is too large to increase the actuator specification 2The valve jumps at the end of the action, the action is too fast, and the inertia energy is too large to add a speed regulating valve or an external buffer.

There is no signal for the return signal.

Signal power lines, short circuits, open circuits.

1.Repair power lines.

2.Readjust the cam to the correct position.

3.Replace the micro switch.

Pneumatic valves are valves driven by compressed air, which can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, slurries, oils, liquid metals and radioactive media.