Spriral Duct Couplings

[ascj]

I have a few older Trane Vav's that need new Plunger Valves. The boxes have spiral pipe on the primary side. I have no way of moving the boxes forward, so I'm going to have to cut the primary ducts.

I'm looking for the best option to reconnect the primary ducts. There are some that were do already and they just used fiberglass flex duct with metal bands. Just doesn't look like the best way of doing it.

Is there such a thing as a band coupling for spiral?

[Nam515]

when i hung spiral, we used many couplings for long runs. i belive the company that made them was called McQuay, but im sure you have a distro closer to you. in a pinch ive also cut a 4" piece of flat stock the size x pi + 1", screwed it to the inside of the hanging spiral, crimped other side and slipped the next piece on

[Tech Rob]

It doesn't have to be a work of art if it's going to be sealed and insulated. I'd take a sawzall to that pipe and then cut a band of sheet metal to fit around the outside like Nam said. If you can't move the VAV forward and you can't move the primary air duct backwards, you're going to have a @#$%& of a time trying to get a normal spiral pipe coupling in there.

I'm curious why you have to disconnect the duct, though. I've repaired hundreds of these things and haven't had to disconnect the primary air ductwork from one yet. If the aluminum casting for the air valve is cracked, you may just need a new VAV. If you just have to replace the backplate, motor, capacitor, and micro-switches, get your tin snips out and cut the hole as big as you need!

[ascj]

when i hung spiral, we used many couplings for long runs. i belive the company that made them was called McQuay, but im sure you have a distro closer to you. in a pinch ive also cut a 4" piece of flat stock the size x pi + 1", screwed it to the inside of the hanging spiral, crimped other side and slipped the next piece on

I have never crimped spiral duct......seems awful thick. Then I need to rely on mastic to seal it. I'm looking for minimal down time on the 1.8-2.0"wc primary ducts.

I was really hoping for a band coupling with rubber gasket that could go around the duct. Don't know if it exists?

[ascj]

I'm curious why you have to disconnect the duct, though. I've repaired hundreds of these things and haven't had to disconnect the primary air ductwork from one yet. If the aluminum casting for the air valve is cracked, you may just need a new VAV. If you just have to replace the backplate, motor, capacitor, and micro-switches, get your tin snips out and cut the hole as big as you need!

So you just left the aluminum casting, and rebuilt it the components?

The aluminum casting is ok. Something is stripped out on them.....I can hear it. The problem is these are cooling only boxes, so I can't see the valve without cutting something.

Would you suggest just ordering a entire replacement.....then cutting a access panel in the bottom of the box and rebuilding it?

I just thought it would be easier to replace the whole valve and try to find a coupling for the spiral primary.

[Tech Rob]

The only problems I have seen with the castings themselves is that on very old ones that are subjected to dirty and/or moist air, the threads for the rods that support the backplate assy. can crack. If they crack, there is no cost-effective permanent repair that I have found other than replacing the entire VAV.

There is a small plastic bearing in the center of the air valve that supports the shaft. I have seen them crack from age and bind the shaft up, causing the motor to strip the gears out and make noises. I've also seen the triacs on the UCM fail and cause the motor to make noises. A bad microswitch can cause the valve to try and overdrive one way or the other. More grinding noise.

As long as you are very careful and patient in the way you remove the rods from the casting (sometimes you don't even have to remove them at all), it'll be ok. You can replace everything in there and all of the parts are still available. The casting is not.

[ascj]

Thanks for the advise.

I did finally find what I was looking for.........
http://www.ductmate.com/product.aspx?id=8

[Tech Rob]

Any time. That spiral coupling you posted the link to looks pretty neat. I think I may have seen something like that before from Lindab also. If the coupling is going on a pipe that'll need to be opened up again and again, it's a definite time saver.

I am curious about what you find inside that VAV. Let us know when you get it fixed.

[wogpa67]

Just thinking outloud but what about using a canvas connection. Tape one side , mastic the far side and wrap it.

[ascj]

I got quotes back from Trane. They told me the only thing available was the complete back plate assembly. He rattled off the list of what is consisted of, but the one thing he said it didn't include was the motor. It's got me a little worried.

I might just order one and see what happens, before I try to tackle the others 5 that have problems.