Saturday AM maintenance ...

[Swingman]

Been putting up with a slow leak in the air compressor and simply haven't had time to address it. With the last project that is not in planning stages out the door, this morning was a good time to stop procrastinating:

is about five years old and arguably too new to have pinhole leaks in the tank, but still had to basically bathe in soapy water (after replacing the drain c*ck which was suspect, but didn't stop the problem) until I found two more brass connection leaks.

The hardest to pinpoint was at the input _plug_ at the far right ... tiny, tiny bubbles, almost imperceptible were the giveaway.

Some pipe dope and been holding steady for three hours, for the first time in a year ... wish me luck.

[Leon]

>>> Unit is about five years old and arguably too new to have pinhole leaks

My now 18 year old compressor developed a high pitched chirping sound, cast iron dual cylinders, and filled much slower than normal. This came about about 7 years ago. I had "blow-by". The head gasket between the intake and exhaust ports had a crack. New gasket fixed the problem.

[G. Ross]

>> Unit is about five years old and arguably too new to have pinhole leaks

When I had a slow leak in my distribution system (black iron) my brother introduced me to the hand soap which comes out as a foam when you press the pump handle on top. This stuff works great and stays where you put it without running everywhere. Found the leak in a female connector.

[dpb]

...

Just tested my brazing job on the small airless tank I had posted about a while back--still have a small spot or two... :(

For some reason I've been unable to figure out the brazing stuck very nicely on one side of the patch (used a piece of 1/8" flat stock to cover the stretch where the failure line was apparent) but can not seem to get it to do so consistently on the other. I'm not an expert but never had this kind of inconsistency on a single job so I'm at a loss of what the issue is.

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[Swingman]

You're a better man than me when it comes to brazing tanks ... I totally lack the gene, or something.

At one time I was a master at forge welding/brazing what we called "Louisiana Grabbers" on the toes of handmade racehorse shoes, but that's about the extent of it, and those days are long over. ;)

[Swingman]

My favorite hand soap, AAMOF, we have it in every bath and in the kitchen. Never thought of using it for air/gas leaks ... good tip. Thanks!

[dpb]

...

Ground to shiny surfaces on all faces before starting...heat shouldn't be problem; rod flows but then on cooling is occasional minute fracture line along one surface edge. Meanwhile, same technique to best as can replicate worked perfectly on other edge.

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[dpb]

Well, I'm not sure I'm better than anybody at this point... :) (or :(, maybe is more like it)

It's small and figured not much to lose--it's toward the bottom side of a horizontal tank so if it does fail it'll not be going anywhere except towards the floor so it's not like I've got something that could go sailing across the shop...

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[Dave]

Depends if you open the drain c*ck and purge collected condensation on a regular basis. I know you would, but many people don't.

[dpb]

Me neither, but don't know where it could have come from...if were disparate pieces that acted differently I'd see it at lot more readily...

[dpb]

On 10/13/2012 7:03 PM, Mike Marlow wrote: ...

Don't think so (on the latter) -- it's a small tank that is open to air and hasn't had anything in it for a month.

As for A), yes, I bridged the hole areas w/ a piece of strap ground to match tank curvature pretty closely.

[clare]

Perhaps your patch is too thick, and it cools at a different rate than the base metal. The first edge worked good - the patch was unconstrained. Now the second edge is moving around all over the place as it heats and cools. Nice to have 2 different brazing metals - one melting hotter than the other. Braze the one side with the "hot" rod, then heat the whole thing - base and patch, to just under the plastic temperature of the hot rod, which will hopefully be high enough to melt the "cool" rod to braze the other 3 sides - while not melting the first joint. Then let the whole thing cool slowly and evenly - with no cracks.

The other way requires having the job set up so gravity hold the patch in place. Have the patch formed to a close fit. "sweat" a coating of braze onto the base metal, and while still hot, drop the heated patch in place, and keep heating untill the braze flows out the edge of the patch and wets the edges of the patch. You might want to flow a bit more braze into the edges of the patch to be sure it is fully sealed - then let cool slowly and evenly - no cracks or pinholes.

[basilisk]

One possibility comes to mind, the patch material may be overall a lot hotter than the tank, when cooling it pulls a crack in the last edge.

basilisk

[Swingman]

24 hours later and holding 120 psi steady as a rock. By jove, I think we've got it!

[dpb]

...[various inputs elided for brevity]...

OK, followup here--

After consideration of the points raised, decided perhaps it was a heat/cooling issue after all.

So, went to a larger tip and reflowed the problematical area and voila!

-- seem to have a good seam all the way around now. We'll see how it stands up to pressure and temperature (it's in unheated shop and winter's coming on) cycling over next few months...

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[Swingman]

Good luck ... just checked mine this morning and it's still holding rock steady at 120psi since Sat AM ... since this is about the longest its gone without being used in a couple of years I'll hold what I got.

Good to get rid of that little irritant/thorn in the side ... I'm keenly aware of each and everyone of my tools that is not performing up to spec and it bugs me no end/get no rest until that's rectified. :)

[dpb]

The big compressor holds when off but the valve at the tank leaks around the stem when open. It _should_ be replaced at some point but it's been that way from the time I was a kid so it's a feature that tells you when you didn't turn the air off if the compressor cycles w/o being used... :) That's my story and...

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[Larry W]

The big compressor holds when off but the valve at the tank leaks around

That is sort of like older Harley Davidsons; You could tell when they were really low on engine oil because they stopped leaking...

[dpb]

First Charger we bought was from a dealership in small Piedmont VA town. Shop head was old-timer who crew-chief'ed for Lee Petty in the MoPar factory days. He told me when I complained "when a MoPar engine _doesn't_ use a little oil, then it's got a problem..." :)

So, it went nearly 200k w/ an extra qt/change...

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[Morgans]

Nearly always cleanliness of the parent metal. Get all corrosion gone, and grease or oil. Use acid resin, and het it and use a stainless steel brush (only) on it, then braze.