VALVE GRINDING
Flat seats and tight sealing valves with new generation of valve grinding machines
Valve grinding technology has come a long way over the years . We have gone from large , cumbersome machines that could be used in the field only with great difficulty , to small lightweight equipment that produces excellent results despite its compact size . The goal is still the same – a perfectly flat valve seat and a tight seal .
By Björn Carlsson , R & D Manager , LarsLap International
Power is transferred via shafts to several individual grinding heads from a central gear hub in a modern valve grinding
machine
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tight seal is necessary for process valves to function properly . Leaking valves are annoying , compromise the performance of the process plant and can , in the worst case , be a hazard to health and safety and to the environment . Leakage of product and process medium also represents money that disappears down the drain . Most valves in the process industry are hard sealing , metal to metal . To provide an effective seal , the surfaces need to be perfectly flat , finished to a high standard and , in many cases , polished to a mirror finish . But over time , the sealing surface finish gets worn . In addition , particles might get caught between the disc and the valve seat , scratching the seat surface as the valve closes . There are many ways in which the valve seat can become damaged and stop performing . If this happens to a critical valve , you may have an emergency situation where the valve needs to be repaired or replaced without delay to prevent costly downtime . But perhaps the most common scenario is that the valve is repaired during planned shutdown of the plant and the work is scheduled in advance . Preventing failure is far more economical than dealing with emergency repair or replacement .
Workshop or in-situ repairs
Valves can either be removed from the pipeline and overhauled in the workshop or repaired insitu . The latter is almost always more efficient . The exception is if the valve is to undergo a major rebuild , for instance if a new seat needs welding into place . In-situ maintenance is performed directly on the valve within the piping system , eliminating the need to re-install the valve . The valve grinding equipment used in such situations needs to be portable , easy to use and be able to get into the small spaces inside the valve body . It must be easy to attach to the pipework and able to produce a flat surface regardless of the angle of the machine relative to the pipeline . Plus , it must produce an excellent result .
The valve grinding machine needs to be easy to attach securely to the flange or pipeline and be able to produce an excellent result regardless of its angle to the valve seat
60 Valve World June 2024 www . valve-world . net