A frustrating maintenance task on a control valve
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The last edit to this post was made by zhenlizhijian on 2017-5-8 at 22:08. Tonight, the control room staff said that one of the control valves wasn’t operating at the correct setting; when I went to the site, I… . . It’s him again, the regulating butterfly valve of the vertically mounted cylinder actuator. I did it about 10 days ago. . The medium is warm water at around 30 degrees. The diameter is around 500. Air shut-off valve: fails in the open position, single-acting actuator. This valve tree is part of a technical improvement project. Used for about a month. The current status of the valve is as follows: when tested separately with no water flowing through it, the valve appears to be in good condition. However, when it is put into use, its opening degree is low, and it often fails to reach the desired level of opening. The solution is to close the gas supply shut-off valve, manually remove the gas supply pipe, and use slow tapping or manual striking of the valve body to assist in opening it. Repeat this process several times, and the function will be largely restored. Now the question is: why does this happen? I wonder if it’s a mistake to install a butterfly valve in this location? Is the pressure difference too high? Regarding corrective measures: Would it be cost-effective to replace it with a double-acting positioner if the conditions permit? Adding a spring is rather troublesome, and the results may not necessarily be good. Welcome, brothers, to discuss::lol
It is necessary to determine whether the cylinder pressure meets the design requirements, whether there is any jamming in the butterfly valve, and whether the actuator itself can function properly in the event of a failure
Can we get a close-up of the valve? There’s no need to show the person, and it also needs to be blurred. The key parts aren’t clear to see
With such a large flow capacity, the operation of the butterfly valve is related to the pressure difference; it is significantly affected when moving from an open position to a fully closed position, and vice versa. If the opening degree of this valve is always lower than the actual control value, it might be a problem with the spring force; otherwise, it’s not. This situation can possibly be improved by changing it to a double-acting type. Is the seat of this valve lined with rubber or is it metal?
First, what is the specific differential pressure across it, and what is the diameter? Is your butterfly valve a triple-eccentric one? If the diameter is large and the differential pressure is high, it is recommended to use a triple-eccentric butterfly valve along with a double-acting cylinder.
Is the opening degree often not reaching the required level? What does it mean by not reaching the required level? Please describe it clearly. What’s of concern, just like upstairs, is whether the valve seat is lined with rubber or is made of metal? And what is the water level height in your standpipe? It would be best if you could tell us the model of the cylinder or its diameter. What should the air source pressure be set to? What model is the locator?
With or without a handwheel mechanism? Are there any survey lines?
The simplest method is to modify the double-acting positioner; we have encountered this in our engineering work.
It seems that the spring force of the cylinder is not sufficient. Connecting another output from the valve positioning air supply to the cylinder should resolve the issue, but it’s necessary to verify whether the function of opening when air pressure is lost works properly, or consider using a larger cylinder
Typical valve positioners have two operating modes and two outputs