Coupling plain bare end tubing for pneumatic conveying 2

[hollerg]

I am updating piping specifications, and haven't been able to confirm the pressure rating for compression couplings. So far a VERY frustrating search.

Morris Coupling, INC, sells these two prototypical configurations

these "lower pressure" couplings use 3 to 6 bolts to clamp the rubber sleeve to the tubing.

and this split style is used for "higher pressure".

Although Morris Coupling Inc, sales stated 15 psig some vacuum (~ 7 psi vac), they would not put the pressure limitation in writing. Similarly HP Products does not publish limits, but verbally reports 15 psig / FV. Two other manufacturers said similar things.

(a)Is there a standards organization that covers these plan bare end compression couplings?

(b)Are there other bare end tubing/piping couplings that have like UL standards proof testing, or that meet some recognized standard, similar to the ASME piping code?

(C)Is there a consensus or published manual on how to apply them, e.g., when to deviate from the first coupling and use the second &/or know how many bolts to specify on the coupling? etc.

 

[jadedfire32]

Curious if you got anywhere with this, I am experiencing the same frustrations. Particularly trying to figure out what the maximum pull out force is that these couplings can withstand and how you are supposed to pick between the number of bolts since the companies offer absolutely no information or ratings associated with them.

 

[bimr]

It is somewhat obvious that the suppliers are trying to keep their products from being ASME code rated. Typically, if the pressure is more than 15 psi, then the product should be stamped for the ASME code.

Suggest you limit the pressure to less than 15 psi. Also, specify system responsibility for the supplier of the conveying system. This probably should not be in a piping specification, it is part of an engineered equipment package.

 

[donf]

Take a look at Victaulic Roustabout type couplings.

donf

 

[Duwe6]

Morris cplg's work well at low pressures. Victaulic couplings work well at 100-200 psi. I would probably start with Morris-type if the pressure was <30 psig.

 

[LittleInch]

These things are not "compression couplings" as is normally understood by plumbers and instrument techs where a ring of metal is squashed into the tube and deforms to provide both sealing and axial strength.

These things are just mechanical versions of wrapping gaffer tape / duck tape around a connection and are about as good in terms of pressure and axial strength.

I had a similar lack of data when trying to find mechanical couplings I could use on fibre glass pipe and just had to give up. The vendors are just not willing to provide data as they don't have enough control over the fitting, the surface preparation, the actual force on the coupling etc etc.

I don't believe there are any standards as they are designed for very low pressures (<15psi), smallish pipe sizes and shouldn't be used for anything where you need axial strength.

For a piping spec I would not use them and either specify screwed joints / couplings or weld it or use screwed couplings.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

". . . .as they don't have enough control over the fitting, the surface preparation, the actual force on the coupling etc etc."

Exactly. A light coating of 'dust' [from soil, dirt] on shiny stainless is amazingly slick. So a Morris cplg on galvanized steel, or squeaky clean stainless, would hold a lot of internal pressure. And on dusty stainless it would fail at a much lower pressure.