Installation of pneumatic diaphragm actuators
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The pneumatic diaphragm actuator and the valve body are installed together at the time of manufacture, but once a problem occurs and the actuator separates from the valve body, how should they be reconnected to ensure proper operation of the actuator and good sealing of the valve? Here’s my way of thinking: For example, if the operating range of the spring is 0.02~0.1 MPa, 1) the air-operated valve is supplied with a working pressure of 0.1 MPa via a regulator; when the valve handle is pressed all the way down, the valve closes completely, with the valve stem connected to the push rod of the pneumatic diaphragm mechanism. 2. The pneumatic control valve is set to an operating pressure of 0.02 MPa via a regulator; the valve closes completely when the handle is pressed all the way down, with the valve stem connected to the push rod of the pneumatic diaphragm mechanism. Please advise if this is correct
Remove the valve and test its opening and closing functions; record a set of data when it is opened to its maximum position, and record another set of data when it is completely closed, then compare them.
Can’t it just be valve positioning? Isn’t there an auto-tuning procedure? Just install it and let it run by itself
I don’t know why, but I can no longer see the content of the post I made; it seems to have been modified by the moderators, and I have no idea why And it’s impossible to understand now too! Why should the moderator make changes? My post, in simple terms, is about how to connect a pneumatic diaphragm actuator to a valve stem, that is, the assembly process; the key points are ensuring the proper travel of the valve and its proper sealing. Note: It is not about installing the locator, but rather the tasks to be carried out before installing it. This job must be quite important; otherwise, it will be difficult to adjust the locator once it’s installed later. Those who say to just install a valve positioner and let it self-tune have definitely never done this before.
Firstly, there are significant differences in the ways in which different pneumatic diaphragm actuators (with direct or reverse action) are connected to various valves (with linear or rotary motion, in normal or reversed orientation, etc.). Here, we will use the most common type of device: a normally operating single-seat valve with a direct-acting pneumatic diaphragm actuator, as an example: 1. Connect the diaphragm actuator to the single-seat valve using brackets, and also connect it to the air supply source； 2. Adjust the stroke by referring to the stroke scale; that is, the adjusting element of the spring seat can be used to change the spring stroke, and by controlling the air supply and exhaust air supply to the actuator’s diaphragm chamber, it is possible to monitor the movement stroke of the actuator’s push rod ； 3. Connect the actuator push rod to the single-seat valve stem (it may be connected using nuts or clamps) ； 4. By adjusting the pressure of the air supply to the actuator’s diaphragm chamber, it is possible to prevent the valve core from making contact with the valve seat; by adjusting the position of the push rod and the valve stem, as well as changing the air pressure, the valve core can be positioned so that it presses precisely against the valve seat when the valve indicator is in the closed position. This requires repeated adjustments, and the force used for this compression can be adjusted accordingly depending on the required closing pressure ； 5. Check again whether the itinerary has changed; if so, make the appropriate adjustments by following step 2 ； Check again whether the valve closing travel indicator has changed; if it has, proceed to step 4 and make further adjustments until both the valve travel and closing force meet the requirements ； 6. Install the valve positioner and perform calibration at various positions throughout the full stroke.