Pipelines are the nerves of process industries. They carry liquids and gases all over and crisscrossing entire plant. To allow or stop the fluids flowing through these pipelines, in numerous valves are employed. Among these valves, Gate valves are quite common and are used for isolation purpose. In this episode we shall discuss an issue that we all come across on gate valves.
In a heat exchanger, water was the coolant. This exchanger was used for cooling acid in the Chlorine compressor circuit. In all there were five compressors and every compressor had an exchanger in their circuit. Four compressors were used to run while one compressor used to be the stand-by. The stand-by would-be put-on operation when any running one needs to be stopped for some maintenance purpose.
On one such occasion, when the stand-by was being started, the acid cooler in the loop was being included by opening its respective water and acid valves. While so, the water inlet valve got stuck. The operator tried to force open that valve using an extra-long valve key. That’s it; the valve spindle alone moved leaving the stuck valve wedge between its seats. The T- slot in the wedge broke and gave way.
The defective valve could be replaced, if only total water circulation was stooped, which meant total shutting down the plant. How to manage the situation? How to open the defective valve by some means and avoid the shutdown? How to push the wedge off its seats?
Since the wedge could not be pulled by its spindle, how about pushing it from the bottom. Sounds great, but how?
It was 3” cast iron valve.
Planned to drill a hole at the bottom below the wedge and push it.
Normal electric hand drilling machine was not the best choice for this operation. By chance if water leaks profusely, during the drilling operation, a severe electric shock was feared.
Battery operated hand drilling machines were not popular those days also were limited by their capacity to drill beyond ½” holes.
Fortunately, service airline was available nearby. So, using a heavy-duty pneumatic drilling machine was opted.
Full threaded, 6” X 5/8” UNF bolt was selected for this purpose.
After two pilot drills, a hole of 37/64” tap drill was made finally.
Fortunately, there was no continuous water dripping, after a brief drip from the pocket therein.
Later it was threaded using 5/8” UNF taps. Enough threads were availed to accept 5/8” bolt to jack the wedge.
A fully threaded, 6” X 5/8” UNF bolt with suitable fiber washer backed by a steel washer and a lock nut was screwed in.
Slowly the bolt applied a study push on the wedge till it yielded and started to move. Pushed the wedge all the way till it touched the spindle firmly. Thus, the passage through the valve was made free for the water flow.
The lock nut was tightened firmly till loading the fiber washer to take care of water seepage if any.
Then the outlet valve was opened to establish the flow through the cooer. Thus, the cooler and the compressor was turned to operation.
Great relief as a costlier shutdown was averted.
This uncommon repair can be tried with enough precautions. I would not suggest this procedure for any other services other than water, oil, or similar docile fluid services. Surely, not recommended for corrosive fluids or inflammable liquids or for gases (including Air).
At times, some such solutions, call it as hacks or lateral thinking, with calculated risks could help to manage a vulnerable condition.
15 сен 2024
