Hose Barb Fitting Specifications - Do they exist? 3

[JavaMoose]

Are there any US specification for dimensions/tolerance for barb fittings used with hose? Specifically, we have had problems with our manufacturer making barb fittings that are far too loose when used with standard ID hose (PVC, spiral reinforced).

For example, hose is 50.8mm ID and the barb fitting we received was 50.8mm OD (at the widest part of the barb) - of course, this makes for a loose fit. However, their engineer insists this is the SMS specifications and is correct. Just trying to find documentation on this, if it exists.

The issue of them polishing, unevenly, the part - bringing the OD down to 50.5mm is a whole different animal to tackle...one step at a time.

 

[JavaMoose]

Hmm, I just realized, I probably should have posted this in the machining forum. Well, I don't want to double-post and it seems like either spot would fit.

Mods, If I'm wrong, please move the post to the appropriate spot.

 

[MintJulep]

Maybe

SAE J2552_200903 : Push-On Hose and Mating Hose Fittings

or

SAE J846_200904 : Coding Systems for Identification of Fluid Conductors and Connectors

 

[dgallup]

It's going to depend on if you expect the hose to hold by itself or are using a clamp or ferrule to hold the hose. Also what type of fluid & pressure. We always specify the barb completely for the products we buy. In our case we have enough interference that we have to use a press to install the hose and we use a ferrule. But we can't have any leaks for safety reasons.

 

[JavaMoose]

dgallup,
We do use a clamp, but it seemed like we needed excessive pressure to get a leak-free seal. Our process fluid is sea-water or well brine-water, pressures range from .35 barg to 3.5 barg.

I think maybe you hit the nail on the head, we messed up by not providing the specifications for the barb. We also use commercially available cam&groove fittings and the barb fitting on those have an OD of 52.8mm. We have to heat the hose to get it on the barb and even without a clamp, they have been leak free up to 1.3 barg. We'll specify that OD from now on with our manufacturer.

I still, if it exists, would like to find some kind of specification that would give some direction on these types of connections.

Mint - I'm getting a copy of SAE J2552_200903 - from the description that sounds like it might be what I'm looking for...

 

[dgallup]

This might be useful, although they have more of a formed bead than a barb.

SAE J1697 RECOMMENDED PRACTICES FOR DESIGN AND EVALUATION OF PASSENGER AND LIGHT TRUCK COOLANT HOSE CLAMPED JOINTS

"Interference—Interference of the inside diameter of the hose to the sealing surface (shank) of the fitting is one
of the most important criteria in designing a sealed system. There is a direct relationship between hose to
fitting interference and push-on force. As the interference increases so will the push-on force. The relationship
between interference and push-on will also change with hose material, reinforcement type and construction.
Minimum design requirements should always have a line to line fit between inner diameter of the hose and the
shank of the fitting. Clearance fits of any magnitude can lead to joint leaks. More interference has been
proven to provide better sealing than less interference or a clearance fit. The greater the interference (provided
the joint can still be assembled), the better probability of the sealed joint."

There is also SAE J1231 Formed Tube Ends for Hose Connections and Hose Fittings Again, these are more beads than barbs.

 

[DesignerGuy16]

Look for some Oetiker one ear hose clamps. Dirt cheap, easy to install and will seal when the hose it slightly larger.

We had a similar situation and they fixed it up nicely. Likely is more of a hose thermal expansion problem than the fittings themselves. We changed hose vendors after the initial problem and there was definetly a difference.

James Spisich
Design Engineer, CSWP

 

[DesignerGuy16]

PS, if you want to see some dimensioned drawings, look up Thogus. They've got pdf's of all of their fittings.

James Spisich
Design Engineer, CSWP

 

[racookpe1978]

Good point. In a general note, thermal expansion of the hose would cause a perceived (and very real!) loosening of the barbed joint. That would cause a leak under service temperatures, but might not be noticed not when installed.

But a change in fluid conditions (a flush perhaps with a cleaning fluid or thinner) could also chemically affect the hose and weaken the barbed joint over time. Your clamp will help seal the hose under both conditions - but the clamp is an extra part, more assembly time to put it on and tighten up, and a change in the catalog and parts lists. Those might be more expensive than the clamp itself.