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Old 01-22-2010, 06:25 PM   #1
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How to block air duct


I have an air pipe which is hooked up to a pump. It is plugged and the
pump is doing nothing useful but still runs. This is all in a big building,
where I have no control over the pump or piping but the management
does not mind if I do something with the useless end of pipe in my room.
The problem is the pipe is potentially useful so I do not want to simply
hack it off. But plugging the end produces vibrational noise due to the
pump. So I want to plug this pipe for good and I am looking for the
cheapest and easiest way to do it.
The pipe is 10" diameter and 20 feet long (maybe a bit longer). So the first
thought was to go to a custom foam maker and buy a 10" diameter
cylinder of 20' length and stuff the sucker. But that's $400 not counting
shipping. And I am not even sure the online place I found would fulfill that
order. So is there anything easier and cheaper I can do? Is there 50X
expanding foam which is non-stick? Any other ideas? I just want to
completely mute the pipe.

Thanks in advance.

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Old 01-23-2010, 10:01 AM   #2
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How to block air duct


Just a WAG without seeing it but I would think the vibration from the pump is being transfered through the hangers of that pipe to the structure. If that's the case then shimming a vibration dampener between the pipe and the hangers would be the solution. Foam pipe insulation cut into strips and placed between the pipe and hangers would be the cheapest and easiest to try first.

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Old 01-23-2010, 02:35 PM   #3
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How to block air duct


Thanks for the comment. I guess I should add that this is in a research lab and so I am not looking to reduce sound. Like I said, I am looking to completely mute the pipe. If I put my finger on the pipe I can feel the vibrations so that will be unacceptable whether or not the hangers resonate as well. I have plenty of prior experience with pipe vibration isolation and all of it suggests that external approaches (dampeners at mount points, replacing hangers with spring suspensions and such) do not provide research-grade solutions.
The way I see it, I need to prevent any air from going into the length of pipe in the lab.
What I have so far are several ideas:
1. One way would be to put an expansion plug into the pipe before it enters the room. This will not eliminate pipe vibrations completely but it should then be possible to wrap the pipe from the outside with vibration dampening material. The issue is how to install the plug. Someone would have to crawl in 10" diameter space and push the plug in front of them then tighten the screws. OSHA may frown.
2. Fill it tightly with foam from the inside to block off air and dampen pipe vibrations. The foam can in theory be pushed in from the open end but it is unclear what we would do if the leading end catches on something. Cost and foam availability is also an issue.
3. Use expanding foam. The problem is finding non-stick foam which is soft and flexible when cured so the plug could be removed if need be.
4. Give up and hack off the pipe.

Any other options or ways to improve on existing options?
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