Adjusting valve is widely used in desulphurization plant, petroleum and chemical industries. It can work accurately and play an important role to ensure the normal operation of process equipment and safety production. Therefore, it is very important to strengthen the pneumatic adjusting valve maintenance.

1. Key Checking Site

Check valve body wall: in the occasion of the high pressure difference and strong corrosion, we must focus on examination of pressure and corrosion conditions because the valve body wall is attached and corroded by the media to avoid accident.

Check valve spool: the valve spool is rotating parts which are used to adjust the valve. It is more seriously corroded, so we should carefully check whether each part of the spool is corroded or worn, especially in the case of high pressure difference, valve wear become even more serious.

Check the valve seat: because the media penetrates during the work, the valve seat is corroded and becomes loosed;

Check Seal Packing: should pay attention to whether it is damaged;

Check whether the executive body is normal and cracked.

2. Maintenance of Pneumatic Adjusting Valve

When the adjusting valve is made by graphite, we should add lubricant in the filling about every 5 months to ensure the good use of the adjusting valve. If the filling pressure cap is found to be very low and loosed, we should add the filling. In the case of PTFE and graphite filling sclerosis, we should change it timely; we should pay attention to the regulation during the check, and we should check the whether the output of locator and adjustor is accurate; we should always check the gas supply for the adjusting valve and keep the maintenance and the integrity of all parts.

We should pay attention to the operation of adjusting valve, inspect whether the locator output is accurate; we should always check the gas supply of adjusting valve, keep the maintenance and integrity of all components of adjusting valve.

3. Common Faults and Causes

(A) The adjusting valve does not work. The reasons are as follows:
1. Have gas source but no signal.
① Adjustor fault ② Signal pipe leaks ③ Locator leaks
2. No gas source and signal.
① Gas source is not open; ② Gas source tube is blocked or filter and reducing valve are blocked.
3. Locator has gas source but no output. Locator holes are blocked.
4. Locator No gas source.
① Filter plug ② Valve fault ③ Pipeline leak or blockage
5. Have signal but no action.
① Stuck valve spool ② The spool falling off ③ Stuck valve seat; ④ Executive body fault
(B) Adjusting valve movement is unstable. Faults phenomenon and the reasons are as follows:
1. Signal pressure and adjustor signal are instable.
2. Air pressure is instable. Reducing valve is in fault and the pressure isn’t adjusted well.
3. Air pressure and the signal pressure are stable, but the action of adjusting valve is still not stable. ① Locator is worn off and can’t be shut closed, so it will produce the output shock particularly when gas consumption is big; ② Output tube is leak; ③ The twister of the executive body is too small

(C) Adjusting valve vibrates. Faults phenomenon and the reasons are as follows:
1. Vibration of adjusting valve under any opening degree ① The fault of valve spool and seat ② Holder is instable;
2. Vibration of adjusting valve near the fully closed position ① Adjustment valve is big but it is often used in small openings; ② Single-medium flow and the valve seat are in the opposite direction.

(Iv) Slow movement of the adjusting valve. The reasons are as follows:
1. Slow movement in a single direction of the stem.
① Damage and leak of the pneumatic executive body
② The leakage of the "O" type seal in the executive body.
2. Slow when the stem moves back and forth.
① Graphite packing lubricant drying;
② have plug in the valve body;
③ add too tightly packed, friction increases;

(E) Adjusting valve leakage. The reasons are as follows:
1. The leak volume is big when the valve is fully closed.
① The spool is worn and internal leakage is serious;
② Valve is’ not adjusted well and is too loose to shut.
2. The valve isn’t fully closed.