Reweld on a hydraulic cylinder

admin

First, let me state that *I* am not going to attempt this repair.We have a hydraulic cylinder that appears to have a pinhole leak in the weld holding the end cap on.  It is not the end with the seal.Can this be welded in place, full of hydraulic fluid?  If so, what's the best way to go about it?I'd just as soon not drop the mast on a forklift to get this fixed.TIAdavid
Reply:If I understand the question, you're dealing with the back end of the cylinder.Chances are pretty good you can pull it off by raising the forks high enough to get the piston well clear of the weld area, and supporting them so there is no weight on the hydraulic system.Grind out the flau and reweld that spot, and allow complete cooling before putting weight back on the cylinder.The best thing would be to drain the cylinder of oil before attempting the weld, but it can be done with oil in the cylinder if you absolutely have to.Appreciation Gains You Recognition-
Reply:Sounds simple enough to me.....just make damn sure you are carefull not to weld right through the wall of the cylinder.....because if that happens, it will not be just a "pinhole" leak anymore.  I'll be the LAST one to let you down !
Reply:Thanks guys.I'm going to bring it up with a welder who does work for the scrap yard.He's a crusty old ******* and basically told me I'm an idiot because there's thousands of people that weld with 7018 on AC machines    It should be an interesting conversation.  I think I'll bait him with a box of 7018AC rod before I ask him to weld the cylinderRegarding the best approach, I'm not sure how we'd get all of the fluid out as I don't think the fitting is right at the bottom of the cylinder, unless you mean pull the cylinder from the mast.  Certainly doable but I'd like to avoid the downtime.
Reply:The problem I see with this type of repair is that the quality of the weld will suffer with hydraulic oil being present in the weld area. I'm sure it can be done without to much trouble but how long it will hold up is the only question. I would consider it a band-aid repair and the next time the equipment is out for some servicing. Repair it correctly. I am by no means a professional welder. I have been involved with high quality nuclear weld repairs in my previous career. In these welds, TIG was the only acceptable method and the root was Radiographically Tested as was the final pass. Any imperfections were reason for failure.
Reply:ahhh~ weldin on HYD in a scrapyard, eh?been there/done that MANY times! [how i started my own bizz, subbing maint. in scrapyards] i`v had to do this very same repair a few times, but mostly because the cap-head assembly absoloutly refused to unscrew for a re-sealing![ even on RINGHAVERS 40,000 lb hyd machine!] common practice was to air-arc the butt end off, cut the ram eye and shove everything out the butt end! [you can then re-seal the ram seal and wiper/piston seals...only thing you cant get to doing this is the Oring in the cap head assembly]why do i tell you all this? because nearly EVERY butt end cap i`v seen is a SOCKETT weld type arrangement[meaning the sockett potrudes into the cyl, beyond the weld area...kinda hard to screw up that type weld[as in a pinhole] i would look it over VERY good for a fracture in the weld[although anything is possible in a scrapyard, eh?] i would [and HAVE] repair it exactly as FRANZ suggest `ceptin i might try to pull the pressure up line just so`s to NOT biuld pressure inside the cyl during welding! and i wouldnt worry about the hyd fluid so much as i`v re-welded vibration fractured hard piping atop of HARRIS shears that regulerly ran 10,000 lbs pressure spikes 200/300 times a day!it never hurts to look,unless they`r WELDING!
Reply:I have done this type of repair many times.  I usually remove the cylinder from the machine then push the ram all the way in with the fitting down and drain as much oil out as possible.  Then I air arc all all but two spots of weld opposite to each other, being careful not to air arc all of the material out (this is to keep the cap from falling off).  Then I weld the spots that I cut out.  DO NOT cap the fittings on the cylinder when welding, it needs to be vented.  Then I air arc the two spots that I left and the ends of my new welds.  Weld the spots back in and you are done.  I usually weld the entire cap, not just the spot where it is leaking, it seems to work better this way.If its BLUE you're throughIf its GREY you stay
Reply:Thanks for the great additional info.If the owner decides to get it done right, we'll have to wait until the other forklift is back running.  I don't know why I didn't think of it being a socket.  That explains why the port is above the bottom.I think I'll have to change my username to kllrdave.  How you started is exactly where I'm at right now.  As you said, anything is possible in a scrap yard.  Here's an example:There is a T fitting on one forklift with what appears to be a schraeder valve (It was actually a MPT to hose adapter).  It was leaking propane so I pulled it apart.  Inside, I found a joist hanger nail with some  teflon tape wrapped underneath the head.  For some reason, this homemade valve wasn't sealing properly
Reply:It can actually be done pretty easily on the forklift.  I'm not quite a forklift mechanic, so I'll assume the following:1) The weld isn't near enough to a rubber seal to damage it.2)  The material is likely pretty thick...3/8"+3)  You want to avoid taking this thing apart if at all possible.4)  The only things that really matter is making it hold, and not taking it apart.If I'm correct about that...Grind a groove across the pinhole.  If you have 3/8" metal, grind 3/16-1/4" deep.  This assures that you aren't going to burn through it easily.  Burning through will get into large amounts of oil and you will NOT be able to weld it then.  Make the groove about 1.5" long, with the pinhole in the middle of it.  Clean the area about 3/4" back from the weld also.  Sometimes, even if you're not welding ON paint, the smoke from it burning near the puddle can get into your puddle and contaminate it.Clean the groove with acetone.You may want a small amount of torch preheat...not enough to turn red hot, but enough to burn the oil from the pinhole and help force the oil away from the hole.  It may help to do this but probably isn't really 100% necessary.  Then, fire up the welder (tig preferred, but can be stick), at the end of the groove.  What you want to do is get the heat going before you hit the pinhole in order to help burn the oil from the hole before you actually get to it.  Weld across the pinhole, and to the other end of your groove (providing you didn't see a pinhole pop back out of your weld.  If you see a pinhole, slowdown and/or grind and try again.This may take a couple tries of grinding and welding, but it may very well go the first time also.Proud to be a UNION worker.  Better pay, better benefits, better work environment.  UA Unions = working for the working class!!
Reply:well I for one, thinks KLLRDAVE sounds absoluotly KLLR! [lol]seriously;think of all the different disiplines you`ll have to master to keep that yard running!straight HYDstraight machstraight electricalthen you get to deal with; air over HYD [lotsa friction rig cranes, ANERICAN  come to mind]hyd over mech[shears,shredders and compactors]electrical over HYD[controll valving on most everything]mech over electrical[generators for mag cranes and such]and thats just in a SMALL yard![we have`nt EVEN began talking "eddy current separators", fluid separators, mag roller conveyors and such!]"if the owner decides to get it done right!" HAHAHAHAHAHAHA!if he`s ANYTHING like the guys who owned the yards I`V worked for he wants this thing running YESTERDAY!!!!!!!!!!!!!!been my experience that theres NEVER enough time to do it right, but we`ll MAKE time to do it over!pick your battles wisely, suggest the PROPER repair method, then give`m what he wants! [and DONT be afraid to say "I TOLD YOU SO!" when it breaks again after having to "jury rig" it back together!] he will grow to rely on you to tell him the "straight poop"[not that he`s gonna listen!]it never hurts to look,unless they`r WELDING!
Reply:I would grind it a little, heat it a little and zap it up.  A pinhole is minor and all it needs to do is seal.www.urkafarms.com