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'generic' test-pressure & setup for hydraulic tubing segments

Pants

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I found some damage to some rigid segments of steel hydraulic tubing (rust pitting that looks like it just barely penetrated from spot-abrasion in some cases, physical-damage kinking in others) and bronze-brazed to repair them so they at least "look good," but I'd like to do some down-and-dirty hydro testing of those segments before I go through the acrobatics of installing them, perhaps only then to find there's still some problem. I plan to bleed all air from segments, and use either:

1) a porta-power with ATF, or
2) a grease-gun with water

I'm thinking I'll test to 1.25x some typical working pressure, but don't have any specs to correspond to my machine in particular, since it's a gray-market CAT (307SSR). Hydraulic tubing segments are 7/8", none longer than 3', with lots of bends, and -8 o-ring face-seals at both ends. I still need to come up with adapter fittings to go from porta-power/grease-gun to ORFS and a gauge somewhere, and also probably have to wait for that pressure-gauge to get here since my max on-hand gauge is just 3000psi.

Any do's/don'ts regarding the above? Would 5000psi x 1.25 be reasonable?

Any particular safety concerns? I'm thinking the obvious measures apply: keep a little distance (porta-power hose is only so long...), wear safety-glasses, place test segment in drum or similar to keep any mess contained. My thinking is that if something fails, it's going to present as a brief jet or rapid weeping of the ATF, and not as anything spectacular or worthy of an epic-fail video, but I'm interested to know what happens from the perspective of anyone who has been through this.

Thanks - Dave
 

Delmer

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I'd vote for the porta power. How would you release the pressure with the grease gun?

Shield everything with heavy cloth, rubber or carpet. You do know about oil injection, right?

If the working pressure is really 5,000 psi, then I'd hook up the gauge direct to the porta power and see how much force it takes to get 2,500 psi, then triple that force for your test.
 

Pants

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Delmer,

So you're thinking it might take more muscle than I might muster to get the porta-power up to, say, 7.5K psi? Or just suggesting I could guesstimate based on arm-force to get to the 2500 psi mark, and not have to wait for another gauge? It's been a while since I used a porta-power to that level, but I think I recall getting to the relief-valve-open point without feeling like I was going to bust a nut. 'Fact now I'm wondering whether mine is actually rated for 10K...maybe 4K. Uh-oh.

As to the 5K psi I mentioned, that's based on some not-necessarily-related references to relief pressures being set somewhere in the high 4K psi range. Good point on the grease-gun pressure release - I guess I'd have to crack open a temp connection, which isn't ideal (or provide a bleed valve in my plumbing) but then again it would be nice to work with water vs. oil, for...laundry's sake as much as anything else.

--ds
 

John C.

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Why would you want to go to all that trouble and expense? It will just be a leak in the future that is fairly cheap to repair. If there has been any repairs by brazing then the piece must be replaced completely. If all you want to do is see if something leaks then hook up air pressure to it and spray it with a soap solution looking for bubbles.

The normal engineering safety factor for hydraulic pressure lines and vessels is four times the working pressure. If you have a working pressure of 5,000 PSI then your safety factor is 20,000 PSI. That kind of pressure is very dangerous.
 

Pants

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Why would you want to go to all that trouble and expense? It will just be a leak in the future that is fairly cheap to repair. If there has been any repairs by brazing then the piece must be replaced completely. If all you want to do is see if something leaks then hook up air pressure to it and spray it with a soap solution looking for bubbles.

The normal engineering safety factor for hydraulic pressure lines and vessels is four times the working pressure. If you have a working pressure of 5,000 PSI then your safety factor is 20,000 PSI. That kind of pressure is very dangerous.

Sorry John, I have to disagree on all counts.

These steel lines can't be found in the USA (maybe not in Japan even), so would have to be custom-bent - which is very expensive, especially where I am. I'd go with new hoses before even trying to find them.

The safety-factor has nothing to do with test pressure, and I think you need to check your source for that 4x figure. Tubing might be *designed* (and never tested) not to fail at some multiple of working pressure (eg the tubing factory certifies it to fail at no less than, say, 20K psi, so the designer specifying that tubing can then choose a fraction of that failure psi to suit a chosen factor of safety), but test pressures for boilers and pipelines are typically not even double the working pressure.

--ds
 

John C.

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Bit of difference between a 600 or 1,200 PSI steam plant and and excavator working at 4,500 to 5,000 PSI. So what brand of excavator are you working on that allows anything to be brazed with brass? What makes this tubing so special you can't order stock and put your own fittings on the ends? I might be missing something here but I have built more than one or two of these over forty years in the business.

Hydraulic hoses specified for any system is required to have a burst pressure of no less than 4 times the working pressure. I can't cite the engineering standard at this time but that has been the requirement I've had to work under. That's why some systems use two wire hose, others four wire hose and the biggest ones require six wire hose. Hydraulic tubing will not be any less. If you are talking test pressure then why would a hundred PSI air pressure be any different than 5,000 PSI of fluid. If it leaks at a hundred it will leak at 5,000. If there is any chance it could rupture at 5,000 you need to replace it. If there is a rust pit in the tube deep enough that it could develop a leak and cause a hazard, then any safety inspector will require replacement. In reality though it will just leak a little to start with and the operator will see it and shut the machine down to repair or replace it.
 

Pants

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Bit of difference between a 600 or 1,200 PSI steam plant and and excavator working at 4,500 to 5,000 PSI. So what brand of excavator are you working on that allows anything to be brazed with brass? What makes this tubing so special you can't order stock and put your own fittings on the ends? I might be missing something here but I have built more than one or two of these over forty years in the business.

Hydraulic hoses specified for any system is required to have a burst pressure of no less than 4 times the working pressure. I can't cite the engineering standard at this time but that has been the requirement I've had to work under. That's why some systems use two wire hose, others four wire hose and the biggest ones require six wire hose. Hydraulic tubing will not be any less. If you are talking test pressure then why would a hundred PSI air pressure be any different than 5,000 PSI of fluid. If it leaks at a hundred it will leak at 5,000. If there is any chance it could rupture at 5,000 you need to replace it. If there is a rust pit in the tube deep enough that it could develop a leak and cause a hazard, then any safety inspector will require replacement. In reality though it will just leak a little to start with and the operator will see it and shut the machine down to repair or replace it.

John,

You lost me with "...why would a hundred PSI air pressure be any different than 5,000 PSI of fluid." Where'd the "100 psi of air" reference come from? And of course there's a huge difference between them that you'd certainly know given your background, so...not sure what you really meant there.

Your citation of hose burst-pressure = 4x working pressure seems reasonable, but let's not confuse burst pressure with test pressure...and I'm not talking about hoses to begin with - just steel tubing. As mentioned in first post, this is essentially an orphaned Japan-only gray-market CAT, for which parts are either unaffordable or just not cataloged - I've been there many times with this machine. As to safety inspectors, well, that'd be me, god help me, since my wife isn't particularly interested in my equipment...though I'm also the oiler, coal-tender and occasional dishwasher. That said, I have enough confidence in my metalworking skills to think my brazed repairs will work, and enough safety-inspector/test-engineer in me to require that I test them to verify - hence this post.

If it were easy/inexpensive to replace the tubing, I'd not have bothered with repairs, as per my first post.
 

mikebramel

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Most Japanese excavators use pipe, not tubing, hence the weird sizes. If you want a custom replacement bent you will need new clamps or wrap them in shim stock.
 

digger doug

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Porto power with gage....enerpac makes 1 model that goes to 40k psi if you need higher than the standard 10 k psi.
 
Last edited:

wrangler

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I have never had great luck brazing steel lines on ag equipment.They may hold for a while but fail in the end in the brazed area.The best way I have found to make this work is to wrap the line with wire like rebar tie wire and braze over the whole thing.I wrap as tight as possible,like a tightly coiled spring.Is it possible to replace this line with high pressure hose?
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
IMHO you don't EVER braze steel hydraulic tubing (or any type of hydraulic fittings for that matter) unless you have a death wish........

A bit of a moot point when considering the above but test pressure for steel hydraulic tubing & flexible hoses on machinery is generally 120% of the maximum system working pressure and the same conditions of operating temperature, so something around 200F/90C. In your case the maximum working pressure is 4550psi in the travel circuit so that would be 5500psi test pressure, the main hydraulic system is 4000psi so the test pressure would be 4800psi.

Regarding John C's comment regarding bursting pressure being 4x working pressure, that is included in all SAE standards for hydraulic hose & tubings such as standards SAE100R12, R13, & R15 to name but three.
 

John C.

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I believe all the Japanese excavators I've worked and all the American ones a well us seamless tubing. The easy way to tell the difference is that tubing is measured on the OD of the tube while pipe is measured on the ID.

You can purchase hydraulic tubing in twenty foot lengths at nearly all the places you obtain hydraulic fittings from. They will also sell you nearly any type of end you might want to fit your machine. Cut it to length, install the fittings on each end that you want to use and I generally bend the tubing using a old hammer handle as I install it in the clamps. The cost going this way is only a fraction of what a dealer will charge. Remember to paint it before you install in on the machine for good.

Thanks Nige for the standards.
 

Pants

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Thanks for all the replies...

mikebramel - not sure whether technically pipe or tube, but it behaves like a heavy-wall tube. I take it the reason the ID is so much larger than necessary (nominal fitting sizes are -8) is just because they didn't want it to be terribly subject to damage when something, er, fell on it... yeah, that's another story. Suffice it to say it wasn't heavy enough. "Unbending" this stuff involved either a lot of leverage, porta-power jigging, heating, and some completely-unsuccessful attempts to engage a hydraulic pipe bender (I'd need one made for 1/4-scale models, I think).

digger doug - wish I could drop by and borrow your porta-power. Having spent so much time over the weekend doing lovely brazed repairs to the pitted sections, followed by lovely multiple coats of industrial epoxy, I'm still game to test these, though I'm short on both fittings and an easily-controllable pressure-source. Trusted local hydraulic shop told me today their standard excavator hose is rated somewhere in the 3Kpsi range, and that when they hydro, it's to 4K or 4.5K max, so my 4K pump might be up to the task - though Nige has some probably-comparable actual specs for a similar machine that suggest the test-pressure should be more like 5.5K. I suppose for some spectacularly quick white-knuckle testing, I could engage my air/hydraulic pump, but I might suggest my wife go shopping prior to that event.

wrangler - thought you were kidding at first, but that method actually sounds like it might help in a pinch...as long as no bubble-gum contaminates the joint along with the bailing-wire...

Nige - you don't think that passing a conservative hydro integrity test would be a reasonable way to go? I'm thinking as long as I don't run any body-parts over the pressurized tubing to check for leaks, but rather maintain some distance, the dropoff in any leak's energy is so rapid with distance that reasonable separation and general caution will suffice. Really, I'm more worried about making a mess than getting injured, and I definitely don't want to have to remove any of these nastily-cramped tubing segments from the machine later if something fails then. Let me know if you know of other specific concerns.

John C - If I replace them, it's going to be with hose. Honestly, I wish I'd gone that way to start with, but I was up against a weekend, and all I could "make progress" on was the tubing repairs, so I ran with that, also knowing that replacement hoses are not inexpensive. These are not simple bends - they include some short-radius 180s and lots of out-of-plane bends - and even if I found the same steel tubing, I've got nothing even close to being up to the task of bending it. Like I was saying, the "unbending" sessions gave me pretty good familiarity with its toughness, and the bends are demanding in terms of where they have to land at the retaining clamps. In terms of hose replacements, local shop gets about $16/swaged fitting, plus about $5/foot of hose, so my seven segments, averaging about 6' each...hell, I don't even want to do the math yet... Before I go there, I will do some hydros and see how the repairs do. If they fail, I'll be secretly happy to be able to justify another unexpected expense...

--Dave
 

Garrie Denny

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whats the point of testing a steel line that has had been either Brazed,silver soldered or subject to any other force or heat that it wasn't designed for,all that will happen will prove wheather the person repairing was compentent Brazer/welder/silver solderer or the applied heat when making that repairweakened the true safe working pressure when the heat was applied and sent the safe working pressures of that pipe out the window.?
 

digger doug

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, I could engage my air/hydraulic pump, but I might suggest my wife go shopping prior to that event.

Dave don't doo that....the air over pumps are too fast. I took a 5k system test overpressure, (and to failure) with "one extra pump please"
the pump cycled one more thump, and bang, a tube ruptured.
You really need a hand pump.

Try Harbor freight.
 

Karl Robbers

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Perhaps brazing hydraulic lines was reasonable when standard hydraulic pressure was 1 or 2000 PSI, but the game has changed with 5000+ PSI being commonplace. Some of the older mechanics will remember the difficulty that was had keeping the oil inside the lines of O&K excavators which were the first high pressure machines I believe.
I would caution the OP to not take high pressure fluid injection lightly as high pressure fluid has the ability to reach out further than he may think.
Apart from the potential weakening of mechanical properties, welding and brazing can create nasty scale internally that can play havoc with pumps etc.
I guess it's a free country and you an adult, so you can make your own choices.
 

Pants

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Perhaps brazing hydraulic lines was reasonable when standard hydraulic pressure was 1 or 2000 PSI, but the game has changed with 5000+ PSI being commonplace. Some of the older mechanics will remember the difficulty that was had keeping the oil inside the lines of O&K excavators which were the first high pressure machines I believe.
I would caution the OP to not take high pressure fluid injection lightly as high pressure fluid has the ability to reach out further than he may think.
Apart from the potential weakening of mechanical properties, welding and brazing can create nasty scale internally that can play havoc with pumps etc.
I guess it's a free country and you an adult, so you can make your own choices.

Well, maybe Oz is free, but Amerika's been trading a lot of freedom in recent years...yeah, that's a subject for a different forum.

I don't know what you mean by "high pressure fluid has the ability to reach out further than he may think" - in terms of a failure, and being able to nail someone from across a jobsite, or...? Are you aware of injuries from failures like pinholes etc that DON'T result from an unfortunate victim being positioned within a foot or two of the failed hose or tube - or more likely, running an unprotected hand over a line to feel for a pesky leak? I think such 'bullseye' stories would be commonplace if indeed they were a concern. I found that other forums were full of pro-brazing, pro-welding repair methods, with no one who'd actually DONE such repairs reporting anything worse than "it didn't last for all that long", and many had been doing such repairs regularly for years.

I got back to my testing once my 10K gauge arrived, and found that my rusty porta-power was easily capable of getting to 6K psi (amply above my target of 5500). All lines tested fine over periods of hours of holding, sometimes overnight depending on what else I was busy doing. Of course, pressure varies considerably with temperature (both ways - from sun or lack thereof) especially if the air has been well purged, owing to thermal expansion of the oil, so I'd sometimes come back to a test I'd set up that morning and found it had gained a few hundred psi as the sun got to it. That variability, and the occasional ever-so-slight leak in the porta-power's return and/or check-valves made me more conservative than I might otherwise have been, so I left the tests for hours at a minimum and pressurized a bit higher than I'd planned. Since I'd gotten into the habit of solvent-wiping the pipes just before testing, any oily spots that developed would have pointed me towards suspect sections, but there were none. My only problem was with a female-swivel ORFS nut that had been warped such that it couldn't evenly squeeze the accompanying o-ring flange to its face, so that end will need replacement.

Anyone know of a source for ORFS tube-end braze-on components? I can't Google 'em. I bought a hose-end type intended to be crimped in, and a fitting-adapter with that end on it, but I'm not wild about either, since the neck's very short and so doesn't lend itself to a sleeve-brazed repair by mating within the old socket, but rather looks like it's going to need a butt-weld, which I'd prolly have to TIG vs braze.
 
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