Can a control valve equipped with a single-acting pneumatic piston actuator achieve position holding?
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In the design, the following issues arose: 1. The client requested pneumatic on-off valves, with the requirement that the valve should be in the FL state in case of either a gas supply failure or a power supply failure. How can this be achieved? 2. During design, the designer selected a pneumatic piston-type concentric angle travel control valve in order to ensure that FL can be activated in the event of a valve failure. Is this feasible? Everyone is welcome to participate actively in the discussion.
The first option is relatively easy to implement; after all, it just involves adding a check valve. With so many brands and models available these days, it’s likely possible to achieve this using a check valve together with a solenoid valve. There are probably also integrated solutions available Depending on the size of the cylinder, its leakage rate, and the requirements regarding service life, options such as gas tanks or cylinders can also be installed. The second actuator: a cylinder actuator, combined with a holding valve and solenoid valve, can be used for securing things without causing any interference. It’s also important to pay attention to the leakage rate as well as the security requirements, especially in the case of gas cylinders.
1. Add a check valve. 2. Use a double-acting actuator; both of these can maintain position. However, if your valve is an interlocked valve, it is not allowed to maintain its position in the event of a power loss or air loss!
OP, could you explain what is meant by “the valve is required to be in the FL state in case of a power failure”? What does this power failure refer to? Is the solenoid valve powered down? (Valve wire broken?)
Can a hold-down valve be used alone on a single-acting diaphragm valve? Without cylinders or anything like that
The power supply being cut off means that the power supply for the solenoid valve has been disconnected.
For the first type of on/off valve, a pneumatic double-acting ball valve can be chosen; it can be equipped with a solenoid valve to achieve this function. In the event of a failure in the air supply or the solenoid valve, the valve can still maintain its position. For the second type, you mentioned a control valve, but an angular-motion cylinder was chosen. This is because such valves have a regulating function – for example, pneumatic control ball valves. Control valves operate with linear motion, so it doesn’t make sense to use an angular-motion cylinder in that case. If it’s a control ball valve, then a double-acting cylinder can be used directly; the positioner receives 4-20mA signals to control the valve’s opening degree. In the event of a problem with the air supply, the cylinder cannot provide the necessary power, and since there is no spring inside a double-acting cylinder, it cannot return to its original position. In this situation, the valve will remain in its current position. If a pneumatic valve is required to maintain its position in the event of air loss, a double-acting cylinder must be used; whereas if it needs to return to its original position in such a situation, a single-acting cylinder is required.
Is what the poster is asking for something like this: a pneumatic on/off valve, such that when the power supply to the solenoid is cut off, the valve moves to a certain position, for example, closed?； Is it also required that when the power supply to the solenoid valve is cut off, the valve should be in the FL state?
1. Install a air lock valve in series at the cylinder end. 2. Replace the double-acting cylinder, and change the solenoid valve to a 2-position 5-way type.