What to do if the double-acting pneumatic diaphragm valve has a high failure rate? I need expert advice!
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Our factory currently has a batch of pneumatic double-acting diaphragm valves in use in the water treatment workshop of a power plant; these valves remain in the closed position when there is no air supply, but internal leakage occurs frequently. The pressure gauge on the pressure reducing valve shows 6 kilograms of pressure, while the pressure in the pipes is usually around 5 kilograms. Is it possible that the air leakage at the inlet is causing the diaphragm to be pushed open by the pressure of the fluid in the pipeline? Is it necessary to add a locking valve to the air supply pipe? Or is it a problem with the solenoid valve? Now I want to switch to a single-acting diaphragm valve, using a spring to keep the valve in the closed position and prevent leakage; is this better than a double-acting diaphragm valve? Which expert can please explain the advantages and disadvantages of single-acting and double-acting types when used in actual applications? (The larger valve shown in the image above is of the double-acting pneumatic diaphragm valve type.)
Additionally, smaller-diameter ones will leak internally, while the larger DN200 diameter ones do not
This post was last edited by CHANGBAISHI on 2019-6-8 at 16:17. After seeing the appearance of this valve, haha, it’s just a copy, just like mine. It’s like this when you’re looking for a cheap deal. The full name of this valve should be “pneumatic diaphragm control valve”. Its working principle indeed involves the air pressure on one side and the spring force on the other side to control the opening degree of the control valve. The position of the manual screw wheel at the upper end of this valve should be set to the automatic position so that it is not restricted when in automatic mode. Otherwise, it’s the internal spring that’s damaged. It is recommended to conduct a disassembly inspection; by disassembling it, its internal structure can be understood, and this is the actuator section. By disassembling the lower valve body, it is possible to check whether the valve port is damaged or has any dents. It is best not to make any changes unless design flaws are confirmed. If rectification is indeed necessary, the relevant procedures outlined in the regulations must be followed. For example, a request for technical modifications to a certain piece of equipment must be submitted to the Equipment Department, and approval must be obtained at each level before such modifications can be carried out; it is absolutely not permissible to act on one’s own.
The inner membrane and air bags are in good condition. It is preliminarily assumed that insufficient air supply or a leak at the air source connection is to blame for the air pressure being lower than that in the pipeline, which causes the valve to stay in an open state instead of its normal closed position. It’s a bit confusing, so I’m thinking of using a spring to ensure stable operation of the valve
Moreover, this double-acting diaphragm valve has no springs; its operation is controlled by air
Well, this valve control might have a solenoid valve, or something else. First, it is necessary to set the limit of this handwheel correctly; in other words, to ensure that when it is in the fully closed position, the handwheel is in a position without any restrictions. Or if there is a leak in the air supply system, it should be checked as well. If it is controlled by a solenoid valve, problems can occur if the solenoid valve leaks air or does not operate properly.
Hehe, there are still multiple possibilities; the problem hasn’t been found yet. Insufficient pressure can be determined directly with the help of instruments for reference. If it’s anything else, it needs to be checked. You can’t report something without a valid reason; once they discover an issue, you’ll be in trouble. One must act with reason and caution.
There must be specific design considerations behind the use of double-acting diaphragm valves in the design; otherwise, single-acting diaphragm valves should be used instead. It is recommended to first examine the requirements of the process flow, and any changes will also need to be confirmed by the process team. Looking at the photos as well, to be honest, the diaphragm valves are likely of domestic manufacture; they have a high probability of failing. Our company uses Fisher valves for all its critical control valves – it’s necessary to invest in quality equipment from a long-term perspective. Even if it is changed to a single-acting type, it is still necessary to ensure that there are no leaks in the air supply
In terms of stability, single-acting is definitely superior to double-acting. However, it is necessary to consider whether the spring force, in a single-acting scenario, meets the pressure required for shutdown. If the conditions are met, overall, a single-acting type is still better
In the closed state, try to close it again using the handwheel to see if it can be fully closed. If it cannot be closed even with the handwheel, then there may be damage to the seal; in such a case, even attempting to replace the seal will be ineffective!