Dust System Gizmo

[Robert Waddell]

I saw a shop made gizmo on the WW Channel the other day that opens incase all the blast gates get closed to prevent light gauge metal duct work from collapsing. It was on the WW at Home show. I wish I could remember what it is called but ole timers keeps me from remembering such. Anyway, I may have need for such an item in the very near future. If anyone has made one of these I would be interested in seeing pic's, any info on making it, and how to go about adjusting it initially without damaging the duct work.
Thanks in advance.
Rob

[Norman Hitt]

I've not seen what you are describing, but I guess one way you could make one would be to make a flappervalve type blast gate that would be held shut with an electro magnet that would be controlled by a negative pressure switch that could be set to open when a given negative pressure/vacuum was reached, which would kill power to the electro magnet and allow the flapper to swing open from the suction of the DC. You would, however need to also provide some way to keep the electromagnet from re-energizing as soon as the airflow became positive until it was manually reset, or the thing would be turning off and on with the fluctuating of the pressure from positive to negative and back as the flapper gate opened and closed. There might be other more simpler ways to accomplish it, but it might be cheaper and easier to just use a thicker guage duct.;) :D

[Mike Weaver]

I've seen this too - I can't recall if it was on Bill Pentz's site (www.billpentz.com), but I recall that it consisted of nothing more than adding an "extra" port, with a damper in it (like a chimney flue damper) with enough weight on the lower half to keep it closed under normal circumstances. If all the other gates are closed, the suction could overcome the weight of the damper, thereby allowing air to enter the system.

Anyway, check Bill's site - I think i may have been there.

-Mike

[Tom Jones III]

You might give it a try before you go to any trouble or expense. I found with my super light ducting that the strength of the joints make it far stronger than necessary. My Dust Gorilla never collapses the ducting when all gates are closed.

[Art Mulder]

I know a fellow on the Canadian Woodworking forum who did something like this... No need for fancy electromagnets and switches. He just put a flapper on the end of the line, and hooked up a spring that would normally keep it closed. A bit of experimentation with springs and using the system and he's got something that works pretty good, from his reports.

[Bill Pentz]

I know a fellow on the Canadian Woodworking forum who did something like this... No need for fancy electromagnets and switches. He just put a flapper on the end of the line, and hooked up a spring that would normally keep it closed. A bit of experimentation with springs and using the system and he's got something that works pretty good, from his reports.

I'm with Art on this one, but instead of a spring, just use a rod with a weight you can move in and out. The weight needs adjusted in and out until the door stays closed when any other gate is open and should open when all others are closed. On my ducting page I share what a commercial unit looks like and its real name, hyperbaric dampener. I used one with my airfoil because if the pressure gets too high the blades stall creating chatter. This ensures there is always enough air to keep it from stalling.

bill

[Ken Garlock]

Our HVAC system has 3 zones. Each zone has a motorized damper that is controlled by the computer that is controlled by the thermostats. Recently we had a one motorized dampers 'go casters up'. If its zone was demanding A/C, it would not open. The designers of the HVAC system provided a loop-back from the distribution plenum back to the cold air return. In that loop-back is a hyperbaric damper to prevent air movement in the loop-back except when the zone damper doesn't open; thus not puttng a heavy load on the variable speed blower. I thought it was rather clever, but to the HVAC man it was probably ancient history.

In an early issue of Woodworking At Home magazine, Dick Sing, that does the turning section, did a shop tour and at the far end of his DC piping he had an almost H damper, his was spring loaded, but the principal was there....

[Robert Waddell]

Art and Ken are describing what I saw. Bill's weight idea may be easier to do than getting the right spring with the correct amount of tension. Thanks for your input guys.