Burst Airline - at 1am

[Shox Dr]

I was in my workshop, beavering away at 1am this morning when a 1" airline blow. It was only 3 foot from my head, to say I jumped is an understatement

It failed on a double clipped (jubilee type) 1" barbed fitting.

Its in between the ceiling and upper floor, and once the floor covering is down up stairs there will be no access barr cutting a hole in either the floor or ceiling. Something I don't want to do.

I have some doulbe eared P clips, that I was going to use, on this fitting but thought the hose clip would have held. Would the eared P clips be better.

Has anyone got any suggestions as to how I can stop this from happening again.








...That's the washing machine stopped so Im off to hang my underpants out

 

[MattF]

What type/composition of hose? Any reason you can't put the joint somewhere accessible? Barbed fittings are always a source of weakness, IMHO, where pressure is concerned. Much better would be a length of tube with olives soldered/compressed at either end. There's some physical obstruction to hose and clip movement that way, rather than just relying on a few small ridges to press into the hose wall.

 

[Shox Dr]

Yes, I was thinking along the lines of a Compression type fitting such as used on blue alkathene water pipe. The hose is multi braided PVC

 

[FranV8]

I had a Clarke hose blow and delaminate shortly after purchase. I wouldn't use a hose of any sort in an inaccessible place, they do tend to have a life, even the blue nylon ones (they seem to go hard and brittle, or the push fittings start leaking)

How about some threaded pipe, or copper soldered?

 

[Shox Dr]

No not possible, this hose is ducted underground and leads from another workshop, I had a 1/2" bore of the same hose running for 12yrs with never a problem, so I don;t see this as been anymore of one, once I have this fitting sused

 

[tigler]

The hose is multi braided PVC

Bingo, there's the clue !!

 

[Shox Dr]

Bingo, there's the clue !!

My bad The hose didn;t fail it was the hose slipping off the barbed Hosetail

Besides it's rated to 150psi

 

[tigler]

It may be rated at a nominal 150 psi but PVC is highly susceptible to temperature changes. It hardens noticeably at low temp and softens noticeably at high temps. In fact at high temps it de-rates significantly. The larger the bore the worse the effect. I hate the stuff. If it slipped of the serrated tail it may have been slightly oversize for the diameter of the tail. Also, plastic deforms under the clip so the force of the clip does not apply full to the tail. Rubber, being elastic transmits the force of the clip much better.
Personally I would only use rubber for airline, particularly for larger sizes. Best worm drive clips are ABA and should be more than adequate for 10 bar if the sizing of the hose and tail are correct.

 

[Shox Dr]

That's all a bit academic now. I wouldn't use rubber where I couldn't get to it as it perishes. I'm more than satisfied it's up to the job. If I hadn't cut the bloody hose too short I doubt we would be having this conversation.

 

[tigler]

Only poor quality rubber perishes. I have rubber airlines that are now over 20 years old with no sign of degradation.

 

[drivewasher]

When my air pipe did the very same thing I went to Pirtek (for speed bay down) They told be not to use braided pvc AND that jubilee clips on ANY air line was not allowed, as the ends had to be a proper swage/machine crimp affair. OR if I used the 3/4 or 1" rubber compressor hose (the yellw stuff they use on road drills) it had to be the special clamps with 2 nuts and bolts

 

[tigler]

No offence but Pirtek are a bunch of tosswits ! Their main area of business is hydraulic and their knowledge there isn't that impressive either ! That's without mentioning their prices !
There are actually no formal regulations for air hose assemblies but there are recommendations for best practice. If they supplied a swaged air hose assembly they would use hydraulic ferrules, for which there are no assembly specifications when used on anything but hydraulic hose ! There is nothing wrong with using worm drive clips as long as hose, fitting and clip are of correct dimensions. Just make sure the fitting is a tight fit in the hose, if it's loose problems are likely to occur.
Although on 3/4" and above I would crimp using industrial, not hydraulic ferrules for peace of mind. There is a wide variety of clamps for air hose assemblies.
I do agree with them about braided PVC hose though, it is mostly inadvisable for applications like airline. Quality varies so much you can never be certain of what you are using and it's adversely affected by temperature.
The main reason for industrial suppliers avoiding worm drive clips is to prevent users without proper knowledge tampering with or re-assembling hose assemblies.

 

[Drains]

No offence but Pirtek are a bunch of tosswits ! .

Ain't that the truth. I'd be inclined to agree with them up to a point though - I would imagine (i'm making this up, if you couldn't tell) that in a work/employment situation, jubilee clips are not the right thing to use and that swaged/ screwed/ compression connections are in fact correct. In your own garage/shed/workshop/sitting room/toilet/cupboard under the stairs/baby's bedroom, though (it's amazing where people work) , you can do what the hell you like!

 

[Shox Dr]

I thought, it was illegal to use air lines with anything than swaged ends in a "work" environment. ISTR that air lines over a given size had to have safety lines to stop connections from lashing out if they fail. As Drains says what you do at home is your business

 

[snowcat]

I assume braided PVC doesn't shatter? as I know PVC shouldn't be used., I use Nylon when making or servicing trailers with brass safety compressions, these have an insert that the olive grips onto, everything past the EMRV then goes onto push fits.

Cant beat galv in the workshop with some short whips..

 

[Robotstar5]

We had a spate of 1" air lines blowing off barbed fittings at work even though they were double clipped found out the installers had used the wrong size hose/fittings!.
Replaced the hose with the correct size and used double eared crimp clips, no problems since.

 

[tigler]

I thought, it was illegal to use air lines with anything than swaged ends in a "work" environment. ISTR that air lines over a given size had to have safety lines to stop connections from lashing out if they fail. As Drains says what you do at home is your business

As I said above, there are no formal regs but there is industry accepted best practice.

I assume braided PVC doesn't shatter? as I know PVC shouldn't be used., I use Nylon when making or servicing trailers with brass safety compressions, these have an insert that the olive grips onto, everything past the EMRV then goes onto push fits.

Cant beat galv in the workshop with some short whips..

Braided PVC does become very inflexible at low temps, even just freezing point but it wouldn't shatter until at extreme low temp. It will split if bent at about -15 though.

We had a spate of 1" air lines blowing off barbed fittings at work even though they were double clipped found out the installers had used the wrong size hose/fittings!.
Replaced the hose with the correct size and used double eared crimp clips, no problems since.

That is the main problem, incompatible dimensions. There is still a problem with mixing imperial and metric, so you can end up with an undersize fitting in an oversize hose with the clip being used in an attempt to compress the hose onto the fitting. Also, many fittings are badly tolerance controlled.
We used to put all fittings through QC as a matter of course and when making assemblies we would plug gauge the hose before assembly and de-grease the bore too.

The main issue to remember is that the end load or force trying to eject the fitting from the hose increases exponentially with bore size. So more care and consideration is needed on the larger bore sizes.

One application we supplied assemblies for would always stress me out though. Those for superheated steam !! 250 PSI and 250 Deg C !!
It filled me with dread to consider the consequences of a fitting blowing out of one of those ! The fitting and clamp was specific to the application, 4 bolt clamp that locked into a groove on the fitting.
Fortunately we never had a failure !

 

[gavuk]

Shox did you use a screwdriver,jubilee driver or something else to tighten the clips up?..at work we use a lot of pvc braided hoses,not normally on air but on water/fluid .
I carry a jubilee driver in my tool roll all the time but i often use a 1/4" ratchet and 7mm socket,rarely if ever a screwdriver ......can't say we have too many failures,even with the pipes connected to barrel nipples instead of barbs

 

[Norm]

...That's the washing machine stopped so Im off to hang my underpants out

made you jump then what you doin workin at 1 in the morning

 

[Shox Dr]

Gavuk; They were normal hose clips, tightened up with a socket.

Norm; A mate had brought me a petrol tank to mod' I wanted to get it cut out and fitted to the bike. Besides I had nothing better to do.