Common faults and repair of valves

1、 Valve body leakage:

Reason: 1 There are sand holes or cracks in the valve body; 2. The valve body cracks during repair welding

Treatment: 1 Polish the suspected crack and etch it with 4% nitric acid solution. If there is a crack, it can be shown; 2. Repair the cracks.

2、 The valve rod and its matching screw thread are damaged, or the valve rod head is broken, and the valve rod is bent:

Reason: 1 Improper operation, excessive switch force, limit device failure, over torque protection does not act.; 2. The thread fit is too loose or tight; 3. Too many operations and too long service life

Treatment: 1 Improve the operation and do not use too much force; Check the limit device and the over torque protection device; 2. Select appropriate materials and the assembly tolerance meets the requirements; 3. Replace spare parts

3、 Valve cover joint surface leakage

Reason: 1 The tightening force of bolts is insufficient or eccentric; 2. The gasket does not meet the requirements or the gasket is damaged; 3. The joint surface is defective

Treatment: 1 Re tighten the bolts or make the gap between the flanges of the door cover consistent; 2. Replace the gasket; 3. Disassemble and repair the sealing surface of the door cover

4、 Valve internal leakage:

Reason: 1 Lax closure; 2. Joint surface damage; 3. The clearance between the valve core and the valve rod is too large, causing the valve core to sag or poor contact; 4. The sealing material is poor or the valve element is jammed.

Treatment: 1 Improve operation, restart or close; 2. Disassemble the valve and regrind the sealing surface of the valve core and valve seat; 3. Adjust the clearance between the valve core and the valve rod or replace the valve disc; 4. Disassemble the valve to eliminate jamming; 5. Replace or weld the sealing ring again

5、 The valve core is separated from the valve rod, causing switch failure:

Reason: 1 Improper repair; 2. The joint of valve core and valve rod is corroded; 3. The switch is forced too hard, causing damage to the joint between the valve core and the valve rod; 4. The valve core retaining gasket is loose and the connecting part is worn

Treatment: 1 Pay attention to inspection during maintenance; 2. Replace the door rod made of corrosion-resistant materials; 3. Do not force the switch or continue to open the valve after it is fully opened; 4. Check and replace damaged spare parts

6、 Cracks on valve core and valve seat:

Reason: 1 Poor surfacing quality of joint surface; 2. The temperature difference on both sides of the valve is large

Treatment: repair welding shall be carried out at the crack, heat treatment shall be carried out according to the regulations, polishing and grinding shall be carried out.

7、 The valve rod does not lift or the switch does not move:

Reason: 1 Closed too tightly in cold state, swelled to death after heating, or too tightly after full opening; 2. The packing is pressed too tightly; 3. The valve rod clearance is too small and expands; 4. The valve rod is too tightly matched with the screw nut, or the matching screw thread is damaged; 5. Packing gland pressure deviation; 6. The door rod is bent; 7. The medium temperature is too high, the lubrication is poor, and the valve rod is seriously rusted

Treatment: 1 After heating the valve body, try to open it slowly or close it slightly when it is fully opened and tightened; 2. Slightly loosen the packing gland and then try to open it; 3. Properly increase the valve stem clearance; 4. Replace the valve rod and screw nut; 5. Readjust the packing gland bolts; 6. Straighten the door rod or replace it; 7. Pure graphite powder is used as lubricant for the door rod

8、 Packing leakage:

Reason: 1 The filler material is wrong; 2. The packing gland is not compressed or biased; 3. The method of adding filler is wrong; 4. Valve rod surface damage

Treatment: 1 Correct selection of fillers; 2. Check and adjust the packing gland to prevent pressure deviation; 3. Add filler according to the correct method; 4. Repair or replace the valve rod