Whistling Dixie

airfieldman, the big vac trucks I’ve used on the job do that at high vac suction levels. I sort of wonder if the dia. and perhaps a spiral combined with length are creating resistance and starving the shop vac for air. I could be wrong but I believe that the whistle is caused by the rotation turbulence at high velocity. Is there any way to provide additional inlet opening, like a tee or wye, at or near the vac that you could adjust to optimize airflow, suction, and whistle? No guarantees to stop the whistle, just a passing thought. Any way, it was just a thought so good luck and how bout some ear plugs if you don’t resole the issue. Tone deafness is very real and common in my trade, not a lot of fun.

That makes a lot of sense. As I covered the nozzle, the whistle stopped (obviously…). And as I slowly removed my hand, there was a point where the whistling started…not immediately upon resumption of any suction, but a break point if you will.

The problem that hightlighted was that the suction generated caused greater pressure than the bucket could accomodate. Will have to re-due the bucket with a tin version.

-- Measure with a micrometer, mark with a crayon, cut it with a chainsaw.

airfieldman, Your plastic bucket should have been fine as long as the inlet nozzle remains somewhat clear for air passage to feed the vacs cubic feet per minute of air. I think what is going on is sort of the reverse of the linked description. But it is just a guess.

http://www.americanwhistle.com/how.html

That is an interesting theory. Hadn’t looked at it quite that way before. Thanks. I am starting to believe it has to do with the reduction of volume allowed when switching from the wider, 2.5” to the 1.25” tubes. The resulting sound is similar to those noise makers that were everywhere during the last summer olympics. Can’t remember what they were called…

-- Measure with a micrometer, mark with a crayon, cut it with a chainsaw.

Is there any way to provide additional inlet opening, like a tee or wye, at or near the vac that you could adjust to optimize airflow, suction, and whistle?

Your problem reminds me of my furnace. The cold air return duct has a 1/4” hole drilled in it. When I asked the HVAC repair man what the hole was for, he explained that it was an old trick installers used to use to eliminate any whistle. It seems to work because my furnace does not whistle. I think casual1carpenter has the right idea. You need to provide another inlet near the vacuum. Whether you drill a hole in you hose or add a wye…

I’ve had this happen to when I bought sump pump hose to use for the shopvac. Everything I’ve read says its the high velocity of the air going through the corrigated hose. I’m looking at replacing that hose with either a larger diameter which will slow down the air speed, or finding hose with a smooth interior. Smooth walled hose would be best, but I haven’t found a cheap source.

AH-HA! I found an answer finally! It’s explained real well on this webpage. But to boil it down, it’s because the ribs are TOO symetrical. So changing the spacing on them (via heat) occasionally fixes that problem!

-- Measure with a micrometer, mark with a crayon, cut it with a chainsaw.