Amongst the various valve maintenance best practices to follow, grinding and lapping is high on the priority list as the procedure achieves a dense, flat surface. This effectively seals the valve seat surface in the valve body and on wedge/gate/globe/slide, to completely seal the valve’s metal-to-metal seat area.
An Essential Procedure
Valve reconditioning can be carried out in-situ, with the valve still fitted to the pipeline system, or in the workshop. In-situ valve lapping and repair tends to be more efficient, as it eliminates the need to remove the valve from the system. The only time workshop maintenance is more efficient is when a major valve rebuild is required.
In-situ valve maintenance requires that the bonnet is removed, and that sufficient space is available around and inside the valve body. To make the best use of the available space, ensure that the equipment you buy is light-weight, able to fit in tight spaces, as well as easy to attach. Your time onsite should be spent grinding the valve, not mounting the valve grinder.
Grinding equipment for use in the workshop needs to be easy to operate and adjust, versatile for use on several applications, and be able to extend capabilities with additional accessories for specialized applications.
Preparing for the Procedure
The following step-by-step procedure describes how to prepare the valve, as well as the basic steps to take in valve grinding and lapping:
1. Cover the area under and around the valve with plastic sheeting to prevent loss of parts and to contain dirt and grease.
2. Begin dismantling by removing any lagging. Clean the outside of the valve. Remove any rust and paint from nuts and bolts. Lubricate the bolts with penetration oil. Try to avoid any damage to the fasteners – even just one damaged nut will add an inordinate amount of downtime and cost.
3. Dismantle the interior parts of the valve. Clean, check and mark to ensure correct refitting. Clean the inside of the valve body, removing rust and any residual liquid. Check gaskets for cracks, corrosion, and defects.
4. Start the grinding by machining any large defects on the surface of the valve seat. Grind defects with portable valve grinders, using appropriate abrasives based on seat material and condition.
5. Remove grinding dust from the valve.
6. Leak-test the valve, ensuring it meets current standards.
7. Reassemble and refit the valve to its original position. Make sure the actuator still works.
8. Finally, write a report on the performed procedure.
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