Repair allows you to identify and eliminate the following shutoff valve failures:
- Loss of tightness due to leakage of the medium between the seal rings of the flap and the seat, seat and body, spindle and stuffing box packing
- Backfins on the spindle in the stuffing box packing area
- Pinching of the spindle in the packing unit
- Damage to the screw thread of the spindle and nut
- Unregulated flow in the control valve
- Failure of fastening device
- Failure of the control rotate stems
- Failures in the drive operation
- Failure of bellows element in the corresponding valve
At detection of sites and sinks up to 0.5 mm in depth on the sealing surfaces they are ground; the wear up to 0.1 mm in depth is eliminated in the process of mutual movement of the part and lapping-plates or mandrels made of fine-grained cast iron, the surface of which is covered with an abrasive material (sandpaper, corundum or quartz powder, silicon or boron carbide, etc.).
Many lapping works are performed by using pastes. The most common paste is named after the place where it was developed – SOI (State optical Institute). The main component of this paste is chromium oxide. It is applied in a thin layer to the cleaned dry surface of the lapped part.
After their mutual movement with another part or lapping, the paste layer is removed with kerosene and is changed to a new one.
Depending on the composition and nature of the contained abrasives, coarse, medium and fine pastes are distinguished.
The latter usually completes the process of lapping the sealing surfaces of the valve.
During the repair of safety valves, the springs are carefully checked. After disassembly, they are washed in kerosene and are examined. Parts with nicks, risks, and dents must be replaced. In order to detect residual deformation, which should not exist, the springs are compressed three times by a static load.
Safety valves are regulated and tested with air on a special stand. The adjusted valve opens at a given pressure, and closes with a pop when it decreases.
After repair, the rebar is tested for strength and density by pressure test.