February 11, 2025
First, the regulating valve does not operate
Reason 1: no air source or air source pressure is too small
Measures: should first check whether the air source (instrument air) is smooth, whether the pressure of the air source to meet the requirements of the use of the valve.
Reason 2: there is a gas source, no output signal gas pressure
Measures:
1. For mechanical controller or positioner, should be more mechanical pressure controller or positioner.
2. For the mechanical controller of the control valve, check the control valve installation pipeline medium signal acquisition pipeline valve is fully open or leakage is serious, if there is anomaly should be dealt with in a timely manner.
Reason 3: The output signal gas pressure is normal, still no action.
Measures:
1. Check whether the diaphragm of the pneumatic diaphragm actuator has serious leakage, if there is leakage, the diaphragm and related seals should be replaced in time.
2. If check the diaphragm is intact without air leakage, it should be the main valve spool and bushing, valve seat stuck, should be disassembled to check the main valve, clean up debris.
3. Valve stem bending deformation is serious, should be disassembled to check the main valve, according to the inspection of replacement processing.
4. Signal gas source pipeline has leakage, check and deal with the leakage point.
5. Signal amplifier failure or improper adjustment, the main gas source does not enter the diaphragm cavity through the amplifier, should be adjusted or replaced amplifier.
Second, the regulating valve work to produce regulation shock, control instability
Reason 1: the gas source pressure changes or filter, pressure reducing valve is not working properly.
Measures:
1. Check the operating status of the compressed air system.
2. Check and replace the filter or pressure reducing valve.
Reason 2: The air source pressure is stable, but the signal pressure is unstable.
Measures:
1. If it is still unstable after replacing the intelligent positioner, the PID parameters should be rectified.
2. For mechanical controller or positioner, the mechanical controller or positioner should be replaced and the controller should be adjusted.
3. If it is still unstable after replacing the mechanical controller or positioner, the signal gas amplifier should be checked and replaced and tuned.
Reason 3: The gas source and signal pressure are stable, but the work of the regulating valve is still unstable.
Measures:
1. Check the air tightness of the pneumatic diaphragm actuator. Carefully check whether there is slight air leakage of the drive actuator seal, if there is air leakage, it should be disassembled to replace the seal; disassemble the diaphragm to check whether there is slight air leakage caused by scratches and punctures, if there is air leakage, it should replace the diaphragm.
2. Check carefully whether there is a gap between the positioner and the main valve connection part, the positioner and the main valve should be replaced or fastened again with the relevant connecting parts.
3. Use soapy water to double-check whether there is any slight air leakage in the signal gas pipeline, once found, it should be dealt with in time.
4. Signal gas source amplifier adjustment is unreasonable, adjust the signal gas source amplifier balance screw.
5. Regulating valve movement mechanism (including the main valve and pneumatic diaphragm actuator) resistance is too large, the main valve should be disassembled, check and replace the abnormal components, including the valve spool, valve seat, valve stem, valve stem sealing and drive actuator.
6. Check whether the pressure balance spring in the pneumatic diaphragm actuator is damaged, detect whether the spring has been fatigued and deformed, if there is an abnormality, the pressure balance spring should be replaced.
Third, the slow action of the regulating valve
Reason 1: Sticky material in the valve body is blocked.
Measures: disassemble the main valve body, clean up the viscous material in the valve body.
Reason 2: Stem packing deterioration and hardening or graphite, asbestos packing lubricant drying.
Measures: Disassemble the main valve body and replace the stem packing.
Reason 3: The packing is too tight, the friction resistance increases.
Measures:
1. After loosening the stem packing compression nut, reciprocate the action of the main valve for many times, and adjust the stem packing compression nut to the appropriate torque.
2. If measure 1 has no effect, replace the stem packing and adjust the stem packing compression nut to the proper torque.
Reason 4: The valve stem is not straight, resulting in high friction resistance.
Measure: Disassemble the main valve and replace the valve stem.
Reason 5: Pneumatic diaphragm actuator diaphragm or signal gas pipeline has a slight air leakage.
Measures: replace the pneumatic diaphragm actuator diaphragm, deal with the signal gas pipeline leakage.
Fourth, the regulating valve action is normal, abnormal process control parameters
Reason 1: control valve spool off.
Measures: disassemble and check the main valve body of the control valve, according to the inspection to restore the spool off.
Reason 2: The spool of the control valve and the valve stem connecting parts of the relative displacement, but not disengaged.
Measures: disassemble and check the main body of the regulating valve, and restore the position of the spool according to the inspection.
Cause 3: Control valve stem fracture.
Measures: Disassemble and check the main valve body and replace the valve stem.
Cause 4: Control valve spool blocked with dirt.
Measures: disassemble and check the main body of the control valve, clean up the dirt in the spool.
Reason 5: the controlled media system other control parameters are not appropriate, such as media flow, pressure is not within the design requirements.
Measures: adjust the system control parameters within the design requirements.
Fifth, the maintenance should focus on what parts of the inspection
1, the inner wall of the valve body: in the high pressure difference and corrosive media occasions, the inner wall of the valve body, diaphragm valve diaphragm is often subject to media impact and corrosion, must focus on checking the pressure and corrosion resistance.
2, spool: spool is one of the movable parts of the control valve, by the media erosion is more serious, maintenance should carefully check whether the spool ministries are corroded, worn. Especially in the case of high pressure difference, the wear and tear of the spool due to cavitation caused by cavitation is more serious damage to the spool should be replaced to check the sealing packing: check the packing asbestos rope is dry, such as the use of PTFE packing, should pay attention to checking whether the aging and the surface of its cooperation is damaged.
3、Valve seat: Because of the medium infiltration during the work, the inner surface of the thread used for fixing the valve seat is easy to be corroded and make the valve seat loose.
4、Diaphragm and O-ring: wear parts, check whether aging.
5, packing: when the regulating valve using graphite or asbestos as packing, about three months should be added to the packing lubricant to ensure that the regulating valve action is flexible. If the packing cap is found to be low, the packing should be supplemented; if the PTFE dry packing is found to be hardened, it should be replaced in time.
6, gas source: the regulator is equipped with a positioner regulator should always check the gas source to ensure that the quality of the gas source, free of water and other debris.
