Vacuum relief thing-a-ma-jig question

[Bruce Seidner]

What does one call the vacuum relief thing-a-ma-jig that is a weighted flap at the end of a main dust run that opens due to the pressure created when there is insufficient flow due to closed blast gates and you don't want to tax the blower or collect waste in the duct? And where do you obtain one?

I am having a senior moment.

Thanking all of you in advance who take your vitamins and exercise with regularity.

[Bob Wingard]

I think you have that concept backwards ... the job of the blower is to move air ... when the gates are all closed, it speeds up because it is doing less work. Why would you want to put a load on something that isn't doing anything for you in return ???

[glenn bradley]

As Bob states, with the gates all closed the draw on the motor is at its least. I believe the item you are talking about is for a different purpose or being misused(?). Something like a flap gate in hydro systems maybe?

[Bruce Seidner]

Well, being in Knoxville and having esteemed colleagues both close to home in TN and in exotic CA going, "Huh?" is reassuring.

Long story short, I was describing my central dust system to a fellow and was asked what I used for pressure relief. I had never heard of this concern and was admonished that with a 5hp commercial blower and 8" ducting I would surely require air flow at times to protect the blower when the blast gates were closed. I remarked that I had understood the concern of sufficient air flow with insufficient air to chip waste ratios but that stressing a blower spinning with no through put was news to me. I was thinking that the motor would be quite OK having no resistance and requirements placed on it from time to time.

So if I understand Y'all, I am not so daft and this fellow is creating paper tigers.

Thank you.

[Alan Schaffter]

The fellow doesn't have a clue! Worst case is blower with no ducting and open blower inlet- makes the motor work too hard, pull max amps and will pop the breaker in short order. Blower works least with blower inlet or all blast gates closed.

[Bob Wingard]

Strange timing on this one, but, just yesterday, I had most of my dust collector/cyclone down for some repairs. I put a few drops of oil on the upper motor bearing, as it had a slight squeak. The was no cyclone attached ... only the fan wheel hanging from the motor. I hit the remote, and was going to give it a minute to run just to see if the oil did any good. About 10-15 seconds into the run, it just quit ... didn't pop a breaker, so I went back up in the attic to have a look. It was SO overloaded that the internal motor protector popped ... reset it and all is well. Got it almost all back together today, and I think with the few minor changes I've made, it will be better than ever.

[Lon Crosby]

It is a vacuum relief valve. They are commercially available. Here is one description of a home-made one. (http://www.cgallery.com/smf/index.php?topic=198.msg1131#msg1131) A vacuum relief valve protects the tubing, fittings, etc., not the motor. In arm-chair designs, the blower may be able to draw a greater vacuum than the piping can withstand without collapsing. It also occurs in very large systems where a central system serves many machines operatd independently.