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How tight to torque V-bands?


RebekahsZ

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Check with the clamp manufacturer, they should have a chart. Usually on aerospace / milspec grade clamps of this type the torque is required to be stamped on the clamp band.

 

This is a SPECIALTY application, and not your typical "clamp metal together" like generic torque charts are geared towards. I would not be surprised to see fat lower clamping torque requirements than for straight bolting.

Edited by Tony D
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Emailed supplier. They said the v-band clamps are rated to 75 inch-lbs. but they are confident that folks torque them more than that. They say you can crush the flange before the clamp breaks but I doubt that.

 

bubububububullshit! I've broken one of mine already. Likely from over-torquing it.

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Broke the v-band bolt on the 3" clamp for the muffler.  I didn't torque it hard at all.  I think the nut just galled (gauled?) onto the bolt then it took just a little elbow grease to brake the bolt off.  I'm anti-seizing them all now.  And why the heck are these bolts just a little too short to let me keep the nut on?  I have to remove (and drop) the nut everytime I remove the v-band!  A 1/4" longer and I'd just have to loosen it.

post-5903-0-55594000-1362374073_thumb.jpg

Edited by RebekahsZ
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My wisdom is vindicated!

I wanted to say 76 inch-pounds for a 1/4-28 thread as that spec stuck in my head from MC1-A GTC's, A/N PSM-60A GTC/Gensets, etc.... But all those years of having "go by the work cards" had me not consciously remember that specific number.

 

But it was there...

 

Lurking...

 

Those were the problems on the GTC and most Combustor-Cap V-Bands:

1) Threads Strip in nut from over torque

2) Clamp bends from over torque due to someone thinking adding anti seize on the threads and not adequately compensating for "dry vs lubed" friction coefficients and still using un-lubed numbers while lubricating the threads.

 

Example:

Hardened Coupling Bolts torque spec DRY: 68 ft-lbs

Same Hardened Coupling Bolts torque lubed with Coupling Grease: 22ft-lbs

 

Result of trying to get 68 ft-lbs on threads lubed with coupling grease: thread failure inside nut at between approximately 35-42 ft-lbs observed on beam-indicating torque wrench.

 

Use a good beam-indicating wrench pulling these up, you will see the band seat, clamp take-up, and threads yield...

 

I'm always full of good news, ain't I?

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Siliconeintakes.com.  $9.99 for the clamp, $29.99 for a set of two flanges.  I wish the bolts were 1/4" longer so I didn't have to remove the nut to remove the clamp, and the clamp interferes with the bolt a little, so I trimmed the bands a little to get them to work a little better.

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  • 4 weeks later...
  • 1 year later...

The v-bands we use in the Air Force are torqued to 45-55 inch pounds per tech data. A good trick to ensure the clamp is seated all the way and to keep it from rattling, is to tap around the clamp with a rubber mallet before torquing, it "takes the slack out" per say (at least this works for hydraulic pumps). give it a try, install the clamp, torque, then tap it with a hammer and recheck torque. chances are it is at least a little under torque if you don't gorilla torque that is. 

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