Torque Specs for Hose Clamps

[Traveler 45C]

I know these were posted here some time ago. I failed to print them out for myself then and now I find myself needing the info and can’t find it in the archives. Care to re-post please?

Thanks.

 

[Nonchalant1]

I think it was discussed, but never actually specified, and of course, it makes a big difference what kind of clamp you're torquing. Do a search for "T-bolt" and you'll find some specs MikeP996 had for regular clamps by size when I asked about T-bolt clamps.

For regular perf type clamps, you can get a feel for how tight they are just before the perf band starts to distort and bends out of line with the rest of the clamp. That's the max. If you see the perf end bending sideways after the worm gear, stop.

For a turbo clamp (like a big beefy perf clamp with multiple washers on the clamping screw) you can go tighter until you see the tension washer stack squeezing together. The stack of washers compresses like a spring and keeps even pressure on the clamp even as it gets hot or cold. Stop tiightening it when the stack is compressing and it doesn't yet feel like it's really getting as tight as a standard perf clamp.

For a T-bolt clamp (by far the best kind but hard to get the right size range) it's almost impossible to tell, because you can put an incredible amount of very even pressure around the hose. I just watch the hose material and if it is compressed by the clamp, feels tight, and the hose won't turn on the barb with hand pressure, that's enough. You can crank it up so tight it'll start to cut into the hose or crush the barb. T-Bolt clamps are the only thing you should have on your shaft logs and shaft packing glands.

They make T-bolt clamps with springs on the T-bolt (like the washer stack on a turbo clamp) and those you just tighten until the spring is about 1/3 compressed, but it kind of defeats the purpose of a having very powerful clamp.

Clear as mud....huh? Sorry that's the best I can do. Maybe the hot rod builder guys and machine shop guys on the forum can add to this. For standard hose clamps, mostly "my hands just know"....but that's hard to explain on the web.

Doug Shuman

 

[REBrueckner]

As Doug suggests, tightness "feel" is subjective and tough to convey. Usually the torque from a medium sized screwdriver turned pretty hard by one hand works ok on conventional clamps. But if you use a ratchet, use a light touch as torque is multiplied by a factor of ten or so. The best approach in absence of specs is to tighten to a reasonable pressure....then check for leaks.

Don't overtighten to the point where the hose is being crushed or cut. It's easy to go back and tighten another half turn if required later to stop a drip. When using conventional hose clamps, a slight further tightening is often required after half a dozen or so heat and cool cycles of hoses. Also, hoses compress and tighten more easily hot than cold.

 

[first230sl]

Interesting. A few months ago I had all the engine hoses replaced with silicone and t-bolt clamps. I find, though, that a number of them were leaking. They were already pretty tight, but I tightened the leaking ones more. I was surprised how tight I had to make some of them to make the leak stop and was worried I was over-tightening.

No prob so far though. They seem to take the torque in stride.

Take care - Murray

 

[Trojan]

I think Doug sized it up real well. Most hose clamps have a do not exceed X amount of torque. Very seldom published. Each application has its own tightness rule. You should start by looking at the compression under the clamp. Then how much twisting exertion (torque) you are applying. You should always re tighten the application after the item your clamping has warmed up. Do not over tighten to the point where the clamp is cutting into the surface or the item is starting to crush. Surprisingly most people over tighten the clamps. If it is a real critical application 2 clamps should be used. The width of the clamp is also important. The harder the material the narrower-er the clamp should be, within reason. The application should dictate the size, type of clamp and TIGHTNESS. Not torque. In some applications you can not reach the torque listed before the clamps break. Torque does not secure the application compression does. Use your eyes and feel. If you can twist the joint it's loose?




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