Why not use rubber joints with hose clamps?

[26281090]

I am looking for rubber expansion joints with straight sleeves to use with hose clamps at 6-10 BAR working pressure. The first reactions are not to do this, but why? Can anyone explain me why I should not do this? When they are tested on burst (3-4 x working pressure) it should be Ok, or not?

 

[Latexman]

What's inside the pipe? Is the rubber essentially chemically inert to it? What are the hazards when (not if) it bursts or gets damaged? Is the fluid going to harm anyone standing nearby? These are the type of questions that must pass the "red face test" before it is implemented

Good luck,
Latexman

 

[26281090]

Latexman, thanks for your reply. I understand that all these factors are of great importance. However, my real question is, if these joints are successfully tested why should it be less safe than using a flanged joint which has the same burst pressure?

 

[C2it]

Do you have any imposed displacments to absorb or maybe you just want a cheap joint ?

Passing a burst test reflects just one facet of operation. The joint may be subjected to torsion, pressure extension, vibration, misalignment, shock, none of which are covered by a test. A flanged joint has far more inherent safety.

 

[btrueblood]

What C2it said, with some more information: Rubber is produced (mixed) in batches, and then molded and cured on a part-by-part basis. The curing (crosslinking) develops most of the strength of the rubber, so you can't accurately predict the strength of the part until you've molded it.

All of the uncertainties of mixing, molding, curing affect each parts' mechanical properties (tensile strength, fatigue life), thus rubber parts typically have much greater statistical variation in these properties.

Finally, most rubbers degrade by a variety of mechanisms over time. Rubbers are quite visco-elastic, and can creep under load, or relax. Chemical, oxidation, UV, and thermal degradation mechanisms can also come into play.

All that said, I've used similar parts, and seen them used, and they do work when the above variables are accounted for. One thing your coupler installation in your photo does not seem to account for is the tendency of a bellows-type joint to expand under pressure, unless there are pipe restraints elsewhere (out of frame) to react that load.

 

[DLite30]

Check this out for your flexible couplings:

http://www.metraflex.com/flex_rubber.php#flex

 

[pennpiper]

Assuming that your commodity inside the line is water at a low temperature and Pressure I would not have a real problem with what you show in the picture. However, what are the threaded rods on each side of the line?

 

[Artisi]

Would assume that the threaed rods you can see are part of a restraining device so the joint isn't subject to seperation forces.

 

[Latexman]

Could it also be providing electrical continuity?

Good luck,
Latexman

 

[26281090]

Sorry for late reaction, i had a few days of vacation

@btrueblood
Thanks for additional info. Regarding the tendency of a bellows-type joint to expand under pressure; we are now testing a newly developed sleeve joint with bellow that does not want to expand/contract under pressure. First results look promising, even at high pressures.

@DLiteE30
I checked the Metraflex joints but they are only 75psi...

@Pennpiper and Artisi
The rods are there for security as this is a test set-up to test this joint before actually using it.

 

[unclesyd]

We use quite a few of the type rubber joint you are referring to mainly on cooling tower water up to 125 psig. You must remember that this type joint has undetermined finite life for most applications. We use both the sleeve type and flange type
The only other application has been on 150 psig plant air.

Look at the top three brochures on the site posted below.

http://www.mason-industries.com/mercer/html/ProdIndx.htm

 

[26281090]

Thanks. One more question: I am looking at a situation where the piping is axially aligned, guided and properly anchored. However, the required working pressure is more than 150 psig. What would be the main reason not to use a sleeve type? Is it the required working pressure only?

As mentioned above, we are now testing a sleeve type that does not expand/contract under pressure and therefore can handle high pressures (600 psig tested without pull-off or burst at this moment). Are there other things we should consider?

 

[C2it]

26281090 .... ref your second para.

So how does this sleeve joint work ?

Are you saying it has no end thrust ? Is it somehow pressure compensating or is there some restraint axially ?