I’m in real trouble…..AT620 Grove boom uncommanded up

Setting some light purlins, lifted the load, and while slowly swinging around, the boom uncommanded raised to full up then blew the return hose. Now I’m stuck with the load in the air. Tried reconnecting return line, and lower boom, boom raised and immediately blew off the return line again while lever was in lowering direction. So much oil is coming out of the line I can’t manage it. All of the lines, cables, valve spools seem to be doing what they are supposed to. What are my options?? 1980’s Grove AT620

Id be pulling the spool out of the valve for that function if it where me i have no idea if that machine has pilot controls or not but it screams the spring end of the spool fell apart or broke. Odd tho that it blows the hose right off seems it should go though the main relief first. Im assuming its one of the cylinder hoses its popping if its the return from the control valve to the tank it reasons that theres a blockage of some kind in the return

Call a tow truck a rotator out there take load off & help support the boom

Pull the boom valve apart. As tyler says, it could broken and jammed, and its putting all the oil to boom up, and "return to tank" portion of the valve isn't taking the oil. The other possiblility is a problem in the hydraulic swivel, with pressure bleeding over into return . You can do some swapping around of hoses and use other control valves to get the boom down out of the air, but you really need to know what you are doing with rerouting the hoses, and you will need tobe bypassing what isn't working right. You'll need to know how the system works, and I guess I'm not real comfortable giving that sort of advice, because you can really hurt yourself if you don't know what you are doing. The boom isn't going to fall out of the sky, because the holding valve in the cylinder should have it locked. As far as the load- a rotator wrecker isn't going to do you any good, they have about 30' of stick, and likely won't reach what you need. If you really want the load out of the air, another crane or telehandler would be my choice. Also, my suspicion is this is a RT620, not a AT620 .

Tyler d4c said: Id be pulling the spool out of the valve for that function if it where me i have no idea if that machine has pilot controls or not but it screams the spring end of the spool fell apart or broke. Odd tho that it blows the hose right off seems it should go though the main relief first. Im assuming its one of the cylinder hoses its popping if its the return from the control valve to the tank it reasons that theres a blockage of some kind in the return Click to expand... I pulled the spool from the boom valve, looks flawless, pulled the one next to it , also look flawless, removed the pressure relief cartridge, everything looks as it should no broken spring. The return hose that keeps popping off is off the main return manifold, so any of the other stacks could be dumping. I looked at the hydraulic schematic, I’m still puzzled as why the return circuit is under fairly high pressure. Enough to blow double hose clamps off a barb nipple. Maybe the massive pressure drop is inadvertently by some black magic causing the boom to raise over 68 degrees, (75 degrees is max) my purlin is still in the air, no good way to lower the load or the boom. What am I missing?

crane operator said: Pull the boom valve apart. As tyler says, it could broken and jammed, and its putting all the oil to boom up, and "return to tank" portion of the valve isn't taking the oil. The other possiblility is a problem in the hydraulic swivel, with pressure bleeding over into return . You can do some swapping around of hoses and use other control valves to get the boom down out of the air, but you really need to know what you are doing with rerouting the hoses, and you will need tobe bypassing what isn't working right. You'll need to know how the system works, and I guess I'm not real comfortable giving that sort of advice, because you can really hurt yourself if you don't know what you are doing. The boom isn't going to fall out of the sky, because the holding valve in the cylinder should have it locked. As far as the load- a rotator wrecker isn't going to do you any good, they have about 30' of stick, and likely won't reach what you need. If you really want the load out of the air, another crane or telehandler would be my choice. Also, my suspicion is this is a RT620, not a AT620 . Click to expand... Yes it is an RT 620, my bad, mostly manual activated valves. You may be on to something with the rotator, we were swinging when the hose popped off and it was the joint at the rotator housing. I agree on not rerouting lines Willy nilly! Too much stored energy at play. What is the best way to diagnose the rotary union? The valve spools looked good on removal and reinstall, spring was good in the pressure relief in that valve stack. I’ve never had a union apart that was that big, As I look at the layout of the rotary union, can it be separated, leaving the bottom half attached to the crane?

We had a 530 I seem to remember a override in compartment under operators seat where the batteries were

If it is boom up and the drum still works, can you line it down across the outriggers? pick it off with anything at all. The rotator, a forklift etc. Best of luck with your fix.

DannoMcfwano said: Yes it is an RT 620, my bad, mostly manual activated valves. You may be on to something with the rotator, we were swinging when the hose popped off and it was the joint at the rotator housing. I agree on not rerouting lines Willy nilly! Too much stored energy at play. What is the best way to diagnose the rotary union? The valve spools looked good on removal and reinstall, spring was good in the pressure relief in that valve stack. I’ve never had a union apart that was that big, As I look at the layout of the rotary union, can it be separated, leaving the bottom half attached to the crane? Click to expand... If it is in the swivel, the repair procedure I prefer is to remove the whole swivel from the crane, reseal, and reinstall. I would be doing a little more figuring out, before pulling swivel, which is a pretty involved repair. Just because the spool looks fine, doesn't mean it is fine, and doesn't eliminate the possibility of a crack in the valve body. You could start by routing the return to tank oil directly to tank, by extending the hose that has popped off, rather than through the swivel. See if you have pressure being generated at the return to tank port on the swivel, by capping the swivel part and putting a gauge there. Or just leaving the port open on the swivel, and bump the starter, checking if its making oil there, and then cap it. If you don't have to swing, this should enable you to run and get the load out of the air, and confirm you have a problem in the swivel.

I have a drop release hook, I was able to get a fiberglass pole and hook over to the release and drop the purlin on soft ground. Still have to work the problem. I’ll go grab some fittings and gauges. Thanks for info so far.

crane operator said: If it is in the swivel, the repair procedure I prefer is to remove the whole swivel from the crane, reseal, and reinstall. I would be doing a little more figuring out, before pulling swivel, which is a pretty involved repair. Just because the spool looks fine, doesn't mean it is fine, and doesn't eliminate the possibility of a crack in the valve body. You could start by routing the return to tank oil directly to tank, by extending the hose that has popped off, rather than through the swivel. See if you have pressure being generated at the return to tank port on the swivel, by capping the swivel part and putting a gauge there. Or just leaving the port open on the swivel, and bump the starter, checking if its making oil there, and then cap it. If you don't have to swing, this should enable you to run and get the load out of the air, and confirm you have a problem in the swivel. Click to expand... I re-routed the return line from the manifold back to the tank with a 2” clear line. Put a cap and pressure gage on the rotary port (where return is plumbed) started up, no pressure at all on the rotary port. Still able to operate all controls properly, but the temporary return line was flowing full at a pretty high rate. I might get a clean bucket and see what the actual flow rate is. I went thru each pressure relief device on each valve sub stack. Didn’t see any glaring issues. Tomorrow I’ll slide each valve spool out an inspect all of them. Anybody have any other suggestions?? Could the main pump be in full flow position? Each valve appears to be working as it is supposed to. I’m stumped…..

DannoMcfwano said: Still able to operate all controls properly Click to expand... everything is working correctly with return straight to tank? DannoMcfwano said: Could the main pump be in full flow position Click to expand... The pumps are always in full flow, the only increase or decrease is by rpm of the engine.

Well I finally figured out the problem, it was in plain sight the whole time. There is a stiff arm link link on the rotating union. Well the bolt that fastens it to the turret backed out and the screw bound underneath and caught in another bolt head, which ripped the low pressure line out , not over pressure causing this issue but shear brute jerking the line out. After two weeks of checking everything else I was feeling around the now oil well and felt the bolt in a bind underneath, 30 minutes later new bolt and nut, back running again! Thanks for all the support !

Thanks for the update. It is nice when the conclusion is posted.

So was this trapping the return line, backing up return to tank oil - and that's what was causing the boom up? Essentially collapsing the line before pulling it off? Dead heading the system and the weakest centering spool spring was the one for boom up? Because I'm having trouble seeing that.