Eight major faults and treatment methods for on-site installation of regulating valves
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The common problems at the on-site of the regulating valve are that they are not dead, can't open, have large backlash, large leakage, vibration, oscillation, etc. The treatment of them is:
1. The valve has small stability and poor stability: the site first checks whether the flow direction is reversed, or the valve selection is too large. The solution is to open the installation and reduce the size of the valve core.
2. Large leakage: first check whether the sealing surface is damaged, whether the valve seat connecting thread is loose, and whether the pressure difference when the valve is closed is greater than the output force of the actuator. The solution is to replace the sealing surface, tighten the valve seat, and replace the actuator with high output force.
3. Sharp vibration: When the frequency of the selected valve is the same as the system frequency, a sharp vibration will occur, which is about 1% probability. The solution is to replace the valve with a different structure.
4. Oscillation phenomenon: It is caused by the valve being operated at a small opening or the flow direction being closed. The solution is to avoid small opening work and change the open work.
5, the valve core is not dead: the solution to the gas-closed valve is to increase the air source pressure or loosen the spring pre-tightening force (ie reduce the pressure outside the membrane starting point). The solution to the air valve is to increase the spring preload. At the same time increase the steam source pressure.
6, the push rod action is slow or no action: check whether the diaphragm, rolling diaphragm, gasket is aging, rupture, causing air leakage.
7. The difference is large: whether the push rod is bent, whether the packing gland is pressed too tightly, especially the graphite packing, or whether the valve core guiding surface is injured. The solution is to change the valve stem, change the packing, increase the guiding gap, and change the powerful actuator.
8. The full stroke of the valve is not enough: loosen the stem connecting nut. Rotate the stem outward or inward so that the full stroke deviation does not exceed the allowable value and tighten the nut.
However, after some of the above-mentioned common problems on the spot, we have to make corresponding measures. The basis of the Zui is the inspection and maintenance of the control valve. So what are the key areas for inspection and maintenance?
1. Check that the diaphragm, "O" ring and other gaskets are cracked or aged.
2. Sealing packing. It should be noted that the PTFE filler, sealing lubricant is aging, the mating surface is damaged, and should be replaced if necessary.
3. Inspection and maintenance of accessories to ensure that the accessories and other valves operate normally.
4. The inner wall of the valve. For regulating valves used in high pressure and corrosive media, the inner wall of the valve and the diaphragm are often subjected to impact and corrosion of the medium. The pressure and corrosion resistance should be checked.
5, valve seat. The fixed seat is threaded, and the inner surface is susceptible to corrosion and the valve seat is moved. This part should be inspected. Valves operating under high pressure differentials should also be inspected for seal erosion and cavitation.
6, the valve core. Due to the scouring and corrosion of the medium, it is serious. During the inspection, it is necessary to carefully check whether the valve core is corroded or worn. Especially in the case of high pressure difference, the valve core is more worn due to cavitation.