Modern industrial production process, the degree of automation is getting higher and higher, while the control valve as an automatic control system in the executive body, in the stable production, optimal control and so has an important role. With the long period of equipment, high load operation, the control valve jamming, corrosion, vibration, leakage and other issues continue to occur, resulting in shortened service life of the valve, reduce the reliability of the work, seriously affecting the safe and stable operation of the production plant. Therefore, it is very important to find and solve the fault timely and accurately in routine maintenance. Some common faults and their solutions are listed.
First, adjust the valve leakage
01
Valve leakage, stem length discomfort.
Valve leakage reasons: air valve, the valve stem is too long and the valve stem is too short, the valve stem up (or down) the distance is not enough, resulting in a gap between the valve core and valve seat, can not be fully exposed, leading to the closure Not strict and internal leakage.
Solution: Should shorten (or extend) the valve stem so that the length of the stem so that it no longer internal leakage.
02
Packing leaked. The reasons for the leakage of packing: (1) packing stuffing letter and stem close contact, but this contact is not very uniform, some parts of loose contact, some parts of the contact tight, and even some parts of the contact is not. (2) there is a relative movement between the stem and packing, with the impact of high temperature and high pressure and permeability of the media, resulting in leakage of packing. (3) filler gradually reduce the contact pressure, the filler itself and other reasons, the media will leak out from the gap. To solve the problem: (1) In order to facilitate the filling stuffing, chamfering at the top of the stuffing box, placed at the bottom of the stuffing box erosion resistant gap smaller metal guard ring to prevent packing media erosion. (2) The stuffing box and the filler contact surface should be smooth, reducing the packing wear. (3) The selection of flexible graphite as a filler, which has good air tightness, small friction, small deformation, no change in friction after re-fastening characteristics.
03
Regulating valve spool, core deformation leaks. Spool valve seat leak is mainly due to the control valve manufacturing process casting or casting defects can lead to enhanced corrosion, and corrosion medium through the fluid medium scouring, it will have on the valve core, seat material erosion and Impact, resulting in spool, valve seat deformation (or wear) is not complete, there is a gap, a leak. Solution: spool, seat selection of corrosion-resistant material. Occurrence of wear deformation is not serious, can be fine sandpaper grinding, eliminate traces, improve finish. If the deformation is serious, can only replace the spool, seat.
Second, the valve positioner failure
Locator nozzle baffle is the use of technology, the general failure often occur the following:
1) Components affected by temperature, vibration, etc., causing the mediation valve fluctuations.
2) The nozzle is blocked by foreign matter, the positioner can not work normally.
3) The spring's spring constant changes, causing the regulator to control the non-linearity.
4) electrical interface seal is not good, rain will locate the coil of the short circuit or open circuit.
Solution: fix the locator firmly; the electrical interface is sealed well; improve the quality of the purifying wind, and regularly drain the sewage.
Third, the control valve malfunction
01
No action valve.
Causes: lack of air pressure; actuator failure; no control valve output signal; valve foreign body; high temperature parts of the valve stuck.
Solution: Check the air supply, restore the pressure; check the actuator spring elasticity and whether the spring fracture and whether the diaphragm is damaged (pneumatic valve); check the signal; disassemble the valve, check and repair.
02
Insufficient valve travel
Reason: Locator is not calibrated, stroke adjustment is inappropriate; actuator spring rating is too small; foreign body valve.
Solutions: Resolve the positioner; adjust the spring; remove the valve removed foreign material.
03
Slow valve movement
Causes: packing is too tight or aging deterioration of packing; stem is not straight, not aligned, resulting in large friction; gas pressure is small.
Solution: to restore the supply pressure; replacement packing or valve stem and other components.
Control valve maintenance and care is a highly specialized, involving a wide range of technical work. To do this work, we not only need solid theoretical foundation, but also have rich practical experience, adopt scientific methods, improve the level of maintenance, reduce equipment failure rate and ensure the safety, stability, length, fullness and excellent operation of production facilities , Thereby improving production efficiency and economic benefits.
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