In modern industrial production processes, the degree of automation is increasing, and as the executing mechanism in automatic control systems, regulating valves play an important role in stabilizing production, optimizing control, and other aspects. With the long-term and high load operation of the device, problems such as blockage, corrosion, vibration, and internal leakage of the regulating valve continue to occur, resulting in a shortened service life and reduced work reliability of the regulating valve, seriously affecting the safe and stable operation of the production device. Therefore, it is very important to timely and accurately search for and solve faults in daily maintenance. Some common fault phenomena and their solutions are listed.

1、 Leakage inside the regulating valve

01

Valve leakage and improper length of valve stem.

The reason for valve leakage: When the valve is opened, the valve stem is too long and the valve stem is too short. The distance between the valve stem and the valve seat is not enough, resulting in a gap between the valve core and the valve seat, which cannot fully contact and leads to poor sealing and internal leakage.

Solution: The regulating valve stem should be shortened (or extended) to make the stem length appropriate, so that it no longer leaks internally.

02

Packing leakage. Reasons for packing leakage: (1) After packing is placed in the packing box, it comes into close contact with the valve stem, but this contact is not very uniform. Some parts of the contact are loose, some parts are tight, and even some parts are not in contact. (2) There is relative motion between the valve stem and the packing, which causes packing leakage due to the influence of high temperature, high pressure, and highly permeable media. (3) The contact pressure of the packing gradually decreases, and due to reasons such as the packing itself, the medium will leak outward from the gap. Solution: (1) To facilitate the packing, chamfer the top of the packing box and place a metal protective ring with a small gap that is resistant to erosion at the bottom of the packing box to prevent the packing from being washed away by the medium. (2) The contact surface between the packing box and the packing should be smooth to reduce packing wear. (3) Choosing flexible graphite as a filler has the characteristics of good airtightness, low friction, minimal deformation, and no change in friction after re tightening.

03

The valve core and seat of the regulating valve are deformed and leaking. The main reason for leakage of valve cores and seats is due to the strengthening of corrosion caused by casting or casting defects in the production process of regulating valves. The passage of corrosive media and the flushing of fluid media will cause erosion and impact on the valve core and seat materials, resulting in deformation (or wear) of the valve core and seat, mismatch, gaps, and leakage. Solution: Use corrosion-resistant materials for the valve core and seat. For those with minor wear and deformation, fine sandpaper can be used to grind them, eliminate traces, and improve the smoothness. If the deformation is severe, only the valve core and seat can be replaced.

2、 Valve locator malfunction

The locator adopts the principle of nozzle baffle technology, and the following faults often occur:

1) The components are affected by temperature, vibration, etc., causing fluctuations in the regulating valve.

2) The nozzle is blocked by foreign objects, and the locator cannot work properly.

3) The elastic coefficient of the spring changes, causing nonlinearity in the control of the regulating valve.

4) Poor sealing of electrical interfaces can cause rainwater to short-circuit or break the locator coil.

Solution: Secure the locator firmly; The electrical interface is well sealed; Improve the quality of purified air and regularly discharge water and sewage.

3、 Malfunction in the operation of the regulating valve

01

The regulating valve is not functioning.

Cause: Insufficient gas source pressure; Execution mechanism malfunction; The regulating valve has no output signal; There are foreign objects inside the valve; The valve components in the high-temperature area are stuck.

Solution: Check the gas source and restore pressure; Check the spring elasticity of the actuator, whether the spring is broken, and whether the diaphragm is damaged (pneumatic valve); Check the signal; Disassemble the valve for inspection and repair.

02

Insufficient valve travel

Cause: The locator is not calibrated and the travel adjustment is improper; The rated value of the actuator spring is too small; There are foreign objects inside the valve.

Shanghai Tingyang Valve Automatic Control Valve

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