# 30ga Metal Ductwork Test



## Bill5866 (Sep 3, 2015)

New to this forum and thought I would post some testing I have done with 30ga ductwork. Long story short I bought 30ga instead of 26ga as that what I thought was being used not doing proper research. Then after doing research many said it would collapse, however a few said they used it. A couple eluded to using plywood rings to make it work. Being a hose dragger for 15+ years I didn't want to install this and have it collapse. So I decided to do testing first. My DC is a 3hp Jet 1900. Specs say 1900 CFM, 5629 FPM, 12.5 static pressure @ 8". My test set up was three 5' sections with a wye on the end so I could incorporate my vacuum relief. The relief valve did not work. There were blast gates at the end and before the wye. I used flex hose to connect to the DC. I made three 6" plywood rings and placed them around the pipe center of the joints. 
My testing sequence was A) plywood rings, open gate open vacuum, B) plywood rings closed gate, open vacuum, C) plywood rings closed gate, closed vacuum. Then repeat without the rings. The results were with the plywood rings there was no failure. When I tested without rings and the vacuum open and gate closed the pipe collapsed. Not totally, but significantly. It didn't collapse completely as there was some vacuum relief and it did bounce back when the DC gate was open. The first photo is the test set up. All the photos are with the DC running. The second tries to show the pipe distortion. The picture shows 1/2 of my wood ring to give an idea of the distortion.
















I then expanded the test using 5 horizontal and 1 vertical duct, no vacuum relief. In this test I slammed the gate shut to simulate a sudden blockage. The horizontal pipe again collapsed without the rings, but no permanent set. However to my surprise the vertical duct did take a set. 
















I replaced the vertical and added plywood rings and repeated without damage. Also during the testing the orientation of the seam showed importance. When the seams were inline the duct collapsed easily. When I rotated the seams 90 degrees the pipe didn't collapse when shutting the gate normally. 

I am not recommending the use of 30ga, but just providing information. I have installed the 30ga with plywood rings and I have not seen any problems. I will post the installation later. Sorry for sideways pictures but can not figure out how to change.


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## Oneal-Woodworking (Apr 14, 2013)

By plywood rings - Do you mean the plywood rings holding the pipe up?

Also, Is that 4" pipe?

Just curious - Thanks for sharing your test results. :yes:


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## Bill5866 (Sep 3, 2015)

By plywood rings I took a 8" square piece of plywood and cut a 6" hole in it. The duct is all 6".


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## Oneal-Woodworking (Apr 14, 2013)

Bill5866 said:


> By plywood rings I took a 8" square piece of plywood and cut a 6" hole in it. The duct is all 6".


 
I follow now. :yes:

Appreciate you posting your results. Stuff like this is what helps me learn... :thumbsup:


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