In the modern industrial production process, the automation degree is more and more high, and the regulating valve as the executing mechanism in the automatic control system plays an important role in stabilizing production and optimizing control. With the long period and high load operation of the device, the problems such as jam, corrosion, vibration and internal leakage of the control valve occur constantly, which lead to shorten the service life of the regulating valve, reduce the working reliability and seriously affect the safe and smooth operation of the production device.
Therefore, it is very important to find and solve the faults in the daily maintenance, and enumerate some common fault phenomena and treatment methods.
I. Control VALVE LEAKAGE
Valve leakage, stem length is not suitable.
Valve leakage Reason: gas valve, stem too long and valve stem is too short, stem upward (or downward) distance is not enough, resulting in the spool and valve seat gap between, not fully contact, resulting in tight and internal leakage.
Solution: The valve stem should be shortened (or extended) to fit the stem length so that it is no longer leaking.
02 Filler leaks. Packing leakage reasons: (1) Filler loaded into the filler letter and stem close contact, but this contact is not very uniform, some parts of the contact with loose, some parts of the tight contact, and even some parts of the contact. (2) There is a relative movement between the stem and the filler, with the influence of high temperature and high pressure and strong permeability of the media, which leads to the leakage of filler. (3) Filler contact pressure gradually decay, fillers themselves and other reasons, the media will leak out from the gap. Solution: (1) in order to facilitate filling, at the top of the filler letter chamfer, at the bottom of the packing letter to place a small corrosion-resistant metal protection ring, to prevent the filler media scouring. (2) Packing letter and filler contact surface to smooth, reduce filler wear.
(3) using flexible graphite as filler, it has the characteristics of good gas tightness, small friction, small deformation, and no change of friction after fastening.
03 Control valve spool, core seat deformation leakage. Valve spool, valve seat leakage is mainly due to the control valve production process of casting or casting defects can lead to the strengthening of corrosion, and the corrosive medium through, the fluid medium scouring, will produce to the spool, the valve seat material erosion and the impact, causes the valve core, the seat deformation (or wears) does not support, has the clearance, has the leakage. Solution: Valve Core, Valve seat selection of corrosion-resistant materials. Wear deformation is not serious, can be fine sandpaper grinding, eliminate traces, improve smoothness.
If the deformation is serious, can only replace the spool, valve seat.
Second, valve locator failure
The positioner is the technical principle of the nozzle baffle, usually the following faults occur:
1 parts by temperature, vibration and other effects, resulting in the adjustment valve fluctuations.
2 nozzle is blocked by foreign bodies, the locator can not work properly.
3 the elasticity coefficient of spring changes, which causes the control nonlinearity of the mediation valve.
4 The electrical interface seal is not good, the rain will be the locator coil short circuit or circuit breaker.
Solution: Fix the locator, seal the electrical interface Well, improve the quality of purifying air, and drain the sewage regularly.
Third, the control valve action failure
The control valve has no action.
Causes: Lack of gas source pressure, actuator failure, control valve no output signal, the valve has foreign bodies, high-temperature parts of the valve inside die.
Solution: Check the gas source, restore the pressure, check the actuator spring and the spring or not broken and the diaphragm has no damage (pneumatic valve);
Insufficient stroke of valve
Cause: The locator is not calibrated, the trip adjustment is improper; The actuator spring rating is too small; there is foreign matter in the valve.
Solution: Reposition the locator, adjust the spring, and remove the foreign body from the valve.
Slow Valve Movement
Causes: The packing is too tight or the filler metamorphic aging, the stem is not straight, not in the middle, resulting in large friction, the gas source pressure is small.
Solution: Restore the supply of wind pressure, replacement repair packing or stem parts. Control valve maintenance and maintenance is a strong professional, involving a wide range of technical work. To do this work, not only need a solid theoretical basis, but also have a wealth of practical experience, to adopt scientific methods to improve maintenance level, reduce equipment failure rate, to ensure that the production equipment Ann, stability, long, full, excellent operation, thereby improving production efficiency and economic benefits.