VALVES - DISMANTLING AND ASSESSMBLY PROCEDURE

VALVES - DISMANTLING AND ASSESSMBLY PROCEDURE

Dismantling Procedure:

• All valves are designed to permit inspection without removing the body from the pipeline. 

• The section of the pipe shall be shut off to ensure no pressure is trapped in the line, before dismantling the valve for inspection.

• Gate and Globe Valves can be inspected by removing the bonnet assembly. However, the valves shall be kept in fully open or partially open position to relieve pressure in the body cavity before removing the bonnet assembly. 

• Check valves can be inspected by removing the cover.

• In case of Check valve, there is no stem and hence only the cover is to be removed. The disc is hinged inside the body. For ease of illustration only the word bonnet is used below in the dismantling and reassembly procedure. This may be changed to read as cover with respect to Check valves.

• Keep the valve in mid position and remove the handwheel / gear unit / actuator from the top of the valve (Fig. 10).

• Loosen the body-bonnet bolting and remove the studs and nuts

• Lift the bonnet assembly including stem and wedge out of the body (Fig. 11). Care shall be taken not to drop the wedge while lifting out. 

• Mark the matching surfaces of the gate and body seat rings of Gate valves so that they are not interchanged during assembly.

• Remove the bonnet gasket.

• Carry out the required replacement of the parts and reassemble the valve with new parts.

• For gear unit or actuator orientation change, refer Appendix A3.

Assembly Procedure:

• Place the gasket on body correctly. It is recommended to use fresh gasket. Refer Gasket Replacement Procedure.

• Lower the bonnet assembly including the wedge smoothly into the body, keeping the wedge in open position Remember to match the marking done earlier on wedge and body seat rings.

• A blue bearing test will confirm if there is a uniform contact between wedge and body seat rings.

• If required replace the gland packing. Refer Packing Installation Procedure.

• Tighten the gland nuts as per torque given in Table 2.

• Fit the bonnet studs and tighten the nuts as per torque figures shown in Table 1, evenly working at diagonally opposite pairs. Do not over tighten as the gasket may get damaged.

• Assemble the Handwheel / Gear unit.

• Operate the valve from fully closed to fully open position manually and ensure smooth operation.