Alternative to push-on fittings for air lines?

dead_nuts · Oct 9, 2018

My 2011 machine has all push-on fittings and they continuously leak. Short term fix is to cut the line and re-insert, but they pull the hoses so tight that you can only do that once or twice. Plastic hose and push-on fittings is the cheapest you can buy and also the cheapest to install -which is probably why they use them.

I already had to replace the fittings on the grease tube after just one month, it was constantly spewing grease all over the components in the air panel. Terrible design choice. I used a barbed fitting with a hose clamp as a quick fix but need a better permanent fix.

I think the only solution is to get rid of all of the push-on fittings. What is the best solution? Compression? Hard lines?

Milland · Oct 9, 2018

Any high pressure, high "friction" use (as for grease) should be a more robust fitting than a press-in, so I think changing those out is sensible, but for regular pneumatic use a press fitting should work for ages.

Are the tubes the right size for the fittings? Do they have scratch marks along them, making it hard to get a good seal?

You can try wiping a thin coat of silicone o-ring lube on the OD of the hose where it mates with the o-ring seal. It shouldn't stop the "grippers" from holding onto the hose, and should help maintain an air seal.

You could go to compression fittings, but may need a hard sleeve to support plastic hose and prevent collapse. Hard lines can work for static applications, but be sure they're well supported so they can't vibrate and fatigue.

Larry Dickman · Oct 9, 2018

Geez, what are you doing to the poor things? We've never had one leak, ever. Haas Mazak or otherwise. I suppose if you really wanted to make it bullet proof you could go with some AS1300 ring locked o-ring fittings and braided hose.

D.D.Machine · Oct 9, 2018

I wounder if you got some bad pipe or something ? My 2014 and 2015 mills have had ZERO air hose problems. Even my old 2000 SL10 does not leak at all .. I did have a few air leaks on my doosan but it was they cut the air hose to short. You might try getting some new hose from Mc Master and swap it out ... I had to re-hose my autosaw but that was 40 year old hose and it got hard as a rock and busted all the time ,, but I reused the air fittings.

SeymourDumore · Oct 9, 2018

Yes, there are some truly crappy hoses out there, mostly the material that sucks.
Otherwise a good quality hose and a good fitting should last for very long time.

I have an EDM Drill that started pissing air and oil after a year or so, but when I got pissed off enough and replaced all fittings and hoses
from McMaster, it is now and has been for 10+ years leak-free.

haastec · Oct 10, 2018

dead_nuts said:
My 2011 machine has all push-on fittings and they continuously leak. Short term fix is to cut the line and re-insert, but they pull the hoses so tight that you can only do that once or twice. Plastic hose and push-on fittings is the cheapest you can buy and also the cheapest to install -which is probably why they use them.

I already had to replace the fittings on the grease tube after just one month, it was constantly spewing grease all over the components in the air panel. Terrible design choice. I used a barbed fitting with a hose clamp as a quick fix but need a better permanent fix.

I think the only solution is to get rid of all of the push-on fittings. What is the best solution? Compression? Hard lines?

For air lines, the push in fittings have been great in my experience, however, I have seen some machines where the push in fittings for the grease lube lines leaked grease. I just replace the push in fittings with better quality ones, usually an all metal type, and have not had any problems since. If you don't like the push in fittings at all, I would probably opt for compression style.

Good luck!

dead_nuts · Oct 10, 2018

We never touch them, they are hidden inside the panel box. Only time I open it is when I hear the sound of an air leak.

The problem with push-on fittings is that the plastic tubing expands and contracts which eventually leads to a gap that causes it to leak.

I will buy some compression fittings that have a internal support for the tube so that it clamps the tube internally AND externally. Push-on and regular OD only compression fittings only grip the OD and loosen over time because of the high expansion rate of plastic tube.

fmari --MariTool- · Oct 10, 2018

I am a huge advocate for leaving the compressor on 24/7. I've witnessed to many regulators or fittings leaking from just turning the air back on from a weekend. The entire air system runs better and more reliable when always pressurized.

Never had any issues with push-on fittings. Once in a blue moon a tiny leak, just remove tube and cut off 3/8" and reinsert.

SIM · Oct 10, 2018

Mine don't leak...but I have had problems getting them apart.
That leaves me with fitting that leak or the grippers stop gripping altogether. I now keep a few sizes in my desk draw so if and when I need to pull a line...I can also replace that fitting.

gusmadison · Oct 10, 2018

Lots of good suggestions already, but I'll throw in my experience as well. Been making equipment using pneumatic lines for a long time. I've found over the years that there is only one brand of push to connect fittings I have full confidence in. They are manufactured by Legris. Available through McMaster, Fastenal, your bearing house, etc.

I agree with those saying you often need to snip off some poly line when reinserting, due to possible scratches on the O.D.
Even though it undeniably works 99% of the time for people without, I still think you need to apply due diligence in tube prep. Square cut, light chamfer on O.D. with their little hand tool, and make sure the tubing has recovered to 'round' after cutting it before you jam it back into the fitting.

Same caution when releasing the line as well. You need to take something and apply near full radial contact to the release ring, not just two points your fingers touch on the sides.

Your mileage may vary, I'm admittedly anal about such details (comes with old age?)

dead_nuts · Oct 11, 2018

I think our situation is different from most. We only make our own products and use the machine for 2 days every 2 weeks because there are many other processes that don't involve CNC machining. So most of the time the tubing is aging with no pressure. When the tube is cold it contracts, and if it ages while contracted it will harden in the contracted state, which can lead to leaks.

A shop that operated 24/7 with hot pressurized air inside the tube will be less likely to have leaks when the tubes age.

machineit2 · Oct 12, 2018

It sounds like bad tubing to me. I would replace with new quality tubing.

Pathogen · Oct 12, 2018

I had mix and match in 1/4" where someone installed metric sized tubing. Worked fine for a year and started leaking. Found it by measuring the tubing.

rons · Oct 12, 2018

dead_nuts said:
I think the only solution is to get rid of all of the push-on fittings. What is the best solution? Compression? Hard lines?

What brand are they? Have you heard about the SMC brand fittings? SMC also sells polyurethane tubing. I use their products and never had a problem. I do not trust push-on fittings in general and stay with compression.

I assume that your current fittings are NPT on one side and push-on on the other side. Like this:

North American (Inch) | SMC Corporation of America

If you have a good name brand (not made in China) then you next better choice would be compression.

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