Why do my valves keep breaking down?

The valve is the control component in the pipeline fluid conveying system, used to change the channel section and the direction of the medium flow, with diversion, cut-off, throttling, check, diversion and other functions. Valve in the use of the process, there will be a variety of failures, especially safety valve. As the ultimate protection device of the pressure vessel, a small failure can cause serious consequences! So why do valves keep failing? Is it really because of quality?
Generally speaking, the valve failure is related to the number of parts that make up the valve; Secondly, it is closely related to the design, manufacture, installation, working state, operation and maintenance of valves. If every link of the work is done, valve failure will be greatly reduced!
1. Common valve failures and treatment methods
1. Valve body leaks
Reasons:
(1) The valve body has sand holes or cracks; ② The valve body cracks in the repair welding.
Deal with:
① Grind suspected cracks and etch with 4% nitric acid solution. If there is a crack, it can be shown; ② Repair cracks.
2. The valve stem and its matching thread are damaged or the valve stem head is broken, and the valve stem is bent
Reasons:
① Improper operation, too much switching force, limit device failure, over torque protection failure;
(2) too loose or too tight;
Too much operation, too long service life.
Deal with:
(1) Improve the operation, do not exert too much force; Check the limit device and over torque protection device;
② Proper selection of materials, assembly tolerance should meet the requirements;
③ Replace the spare parts.
3. The surface of the valve cover connector leaks
Reasons:
① bolt tightening force is insufficient or eccentric;
The gasket does not meet the requirements or the gasket is damaged;
③ There are defects in the joint surface.
Deal with:
① Re-tighten the bolts or make the clearance of the door cover flange consistent;
② Replace the gasket;
③ Remove and repair the sealing surface of the door cover.
4. Internal leakage of valve
Reasons:
① the closure is not strict;
② joint surface injury;
(3) The gap between the valve core and the valve stem is too large, resulting in sagging or poor contact with the valve core;
④ Poor sealing material or spool stuck.
Deal with:
① Improve the operation, restart or shut down;
(2) Remove the valve and polish the sealing surface of the spool and seat again;
Adjust the gap between the valve core and the valve stem or replace the valve plate;
(4) Remove the valve to eliminate the phenomenon of stuck;
⑤ Replace or weld the sealing ring.
5. The valve core is separated from the valve stem, resulting in switch failure
Reasons:
① Improper repair;
(2) Corrosion at the connection between valve core and valve stem;
③ The switching force is too large, causing damage to the connection between the spool and the valve stem;
④ The spool check washer is loose and the connection part is worn.
Deal with:
(1) Pay attention to check when maintaining;
② Replace the door rod made of corrosion-resistant material;
③ Do not force the switch during operation, or continue to open the valve after it is not fully opened;
④ Check and replace the damaged spare parts.
6. The spool and seat are cracked
Reasons:
① Poor surfacing quality of joint surface;
The temperature difference between the two sides of the valve is large.
Deal with:
Cracks should be repaired and welded, heat treated as required, and polished and ground.
7. Valve stem does not lift normally or the switch does not move
Reasons:
(1) In cold state, it is closed too tightly after heat, or closed too tightly after full opening;
② The packing is too tight;
③ Valve stem clearance is too small to expand;
(4) The valve stem is too tight with screws and nuts, or the threaded parts are damaged;
(5) packing gland pressure deviation;
⑥ The door rod is bent;
⑦ medium temperature is too high, poor lubrication, valve stem serious rust.
Deal with:
(1) After the valve body is heated, open as slowly as possible or close gently when it is fully opened;
(2) Gently loosen the packing gland, and then try to open;
③ Increase the valve stem clearance appropriately;
(4) Replace the valve stem, screws and nuts;
⑤ readjust packing gland bolts;
⑥ Straighten or replace the door rod;
⑦ Gate rod adopts pure graphite powder as lubricant.
8. Packaging leaks
Reasons:
① The filling material is incorrect;
(2) no compression or deviation of packing gland;
③ The filling method is incorrect;
(4) Valve stem surface damage
Deal with:
① Correct selection of filler;
(2) Check and adjust the packing gland to prevent pressure deviation;
(3) Fill in the correct;
④ Repair or replace the valve stem.