Faulty pneumatic control valve. . .
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Our factory has a single-seat valve for compressed air with a DN50 size. The pressure after the pressure relief filter valve is 0.4 MPa; the positioner is a Yaskawa AVP100, brand new and just purchased. Gas on valve, with check valve. After installation, the self-tuning function worked normally; the valve position was set at 25%, and the pressure gauges on both sides of the positioner fluctuated, with the valve position also showing some fluctuations. 75% is the same; there is no shaking only when it is fully open. I checked the cylinders and there are no leaks. I set the locator to manual mode; using a filter pressure reducing valve to control it works just fine. I really can’t find any issues. I was wondering if there are any other situations that could cause this problem, according to the experts here
It has been replaced; no problem. I also removed the hold-down valve. I still can’t figure out the reason
It is caused by an imbalance between the feedback rod and the output pressure; it is recommended to try adjusting the position of the locator
There is a 90% chance that the amplifier needs to be adjusted (it has many names; you’ll have to find them yourself)
It is recommended to check whether the pressures before and after are within the specified range by referring to the usage conditions outlined in the manual; it would be best to send a picture of the valve when discussing such issues, as this facilitates the discussion. The type of valve you’re referring to seems to be called a pneumatic self-regulating valve? “What does “depressurized filtration” refer to? “Is a \"positioner\" the same as a locator? Once again, it is advised to compare the instructions with the actual conditions on site; in case of any discrepancies, contact the equipment department of your organization and consult the manufacturer.
Try increasing the pressure of the pressure reducing valve; it seems that the change in pressure before and after the valve is caused by changes in the valve’s position. It appears to be due to insufficient gas phase pressure, so give it a try by raising the pressure
Try a different locator. If there is a damping screw on the positioner output, adjust it and see.
Valve surge? Manual is easy to use, but automatic isn’t? The retaining valve was removed, a pressure reducing valve was installed, and a new locator was used – is that right? If mechanical issues such as overly tight packing, a loose locator, or a loose feedback rod can be ruled out, it’s very likely that the problem lies with the locator itself. The analysis is as follows: 1. Water in the instrument air may cause the diaphragm in the amplifier part of the locator to stick together; the locator needs to be taken apart, along with the plastic cover on the left side. There’s a metal component there, in cylindrical shape; taking that out and drying it out inside should resolve the issue. 2. The absence of the retaining spring for the positioner feedback rod can also cause similar issues. 3. When the pressure relief valve was installed, the collar part wasn’t fitted properly, and tape blocked some of the holes in the air supply tube. 4. A low-quality filter pressure regulator can also cause such issues; in that case, you can increase the pressure setting of the filter pressure regulator slightly. For example, if the pressure is 0.4 after the regulator, try setting it to around 0.5. 5. Perform self-tuning a few more times; the zero point and full stroke settings must not change after self-tuning. I also have a few questions as follows: 1. How did you set it manually? For the Azubel positioner, when it’s set to manual mode, it’s in full-pass mode; then the valve position is adjusted using a pressure reducing valve. Is that how you operate it? If that’s the case, it doesn’t tell us anything; it only indicates that there is no jamming in the mechanical structure… 2. Has the pressure relief valve been replaced with a new one and tested? If the instrument air is not pure, the failure rate of pressure relief valves is actually quite high. Is it certain that it’s not the issue of older valves being used, but rather that these are brand new valves?
1. Indeed, when it’s set to manual mode, full flow is achieved; by adjusting the pressure through the pressure relief valve, there are no issues with the pressure gauges located before and after any valve positioner. But it seems that this doesn’t tell us anything meaningful. 2. The pressure relief valve has been replaced with a new one, and the instrument air is nitrogen. The filler gland screws are also loose; they aren’t very tight. Vibration is low at high valve positions, while the problem is severe at low valve positions. Currently, the front pressure gauge on the locator is fluctuating, while the rear end is fine.
Try another pressure regulator, or disassemble this one to see if something is blocking the air holes inside. Then check the valve positioner... Feel free to disassemble it; if it gets damaged, it can still be repaired at the factory……