Common faults of control valve

1. When the control valve is fully closed, there is a gap between the valve core and the valve seat, resulting in a large flow of medium, and the controlled parameters are difficult to be stable.

1>, improper adjustment of valve stroke or long time spool valve wear and corrosion in regulating valve adjustment. Generally, the valve rod is adjusted downward to reduce the gap, so as to reduce the leakage.

2> The corrosion around the valve core is serious, and the valve core is scratched by welding slag, rust, slag, etc. The valve core should be taken out for grinding, and the serious one should be replaced with a new one.

3> The valve seat is seriously corroded by the medium, or the welding slag, rust, slag and other scratches in the medium produce scars, and the seal between the valve seat and the valve body is damaged. The valve seat should be taken out for grinding, and the sealing gasket should be replaced. If it is serious, the valve should be replaced with a new one.

4> The valve is blocked by welding slag, rust, slag and other impurities, so that the control valve cannot be fully closed. The control valve shall be disassembled for cleaning, and the valve core and seat shall be observed for scratch and wear.

5> The sealing gasket between the sleeve valve core and the valve seat is damaged, and the sealing ring of the butterfly valve is damaged, which makes the flow clearance larger when the control valve is fully closed.

2. Control valve packing failure. The friction between the stem and the packing makes it difficult for the small signal of the control valve to act, and the large signal bouncing vibration causes the fluctuation of the regulating valve in the regulation process, and the parameters are difficult to be stabilized. When the friction is large, the regulating valve will move in one direction or even not move. In daily maintenance, lubricating oil or grease should be added regularly. If the packing is seriously aged and leaked, the packing should be replaced.

1> The high temperature and high pressure of the regulated medium make the packing of the regulating valve expand and age, and increase the friction force on the valve stem;

2> If the medium is high viscosity medium, it will adhere to the valve stem and increase the friction. At the same time, the leakage medium will be cooled and solidified to increase the friction;

3> When dealing with the packing leakage, the packing pressure plate is too tight, which increases the friction force of the valve stem;

4> The pipeline before and after the installation of the control valve is not concentric, so that the control valve has stress and is attached to the valve stem, which increases the friction between the valve stem and the packing.

3. The valve stem and the connecting piece are loose or fall off. Due to the vibration on site or the loose fastening nut of the connecting piece, the valve stem is too low and the connecting part of the connecting piece is too few. During the operation, the valve stem and the push rod of the actuator are not synchronized or fall off, which affects the action of the control valve and even fails.

4. The valve seat is jammed or blocked by foreign matters. Impurities in the pipeline enter into the valve seat, damage the valve core and valve seat, affect the action of the control valve, and increase the leakage. In the regulation of acid gas and gas gas, impurities in the gas gradually precipitate at the throttle of the control valve to block the control valve. In the regulation of water cut-off valve, due to the low pressure and slow flow rate of medium, impurities in the medium gradually precipitate and block the regulating valve or the pipes before and after the regulating valve, which makes the regulating valve lose its function.

5. The diaphragm head of the control valve is faulty. The corrugated film of the control valve is deteriorated after long-time use, the elasticity becomes smaller, the airtightness becomes worse, and even cracks and air leakage are serious. The compression spring is aging, the elastic coefficient changes, and even breaks. The results show that the displacement of the rod output from the diaphragm head of the control valve changes and the thrust becomes smaller, which leads to the poor quality of the control valve and the failure of full opening and full closing, or even the loss of the control function.