TJ 230A Forwarder crane control woes

[Burntberry]

Hopefully someone here has seen this issue before and can help...

We've got a 230A with an F60 crane that's got a Danfoss PVG32 valve bank and electronic joysticks. 

Everything was working ok, then a vandal decided to fill the hydraulic tank with water.

We drained, blew out, and flushed everything several times.  When we tested it several of the functions weren't working at all, or would work intermittently.  After taking the valvebank apart (original to the machine) we found a fair bit of wear/scoring, so we ordered a new valve bank.

Put the new bank on and all functions are working at low idle.  But once RPMs increase, all the functions except the boom act up:  

The grapple rotate and open/close slow then stop working at all fairly early,
The boom rotate slows/gets weak,
and the jib moves in a jerking motion.

There's no boom extension on this unit, though it originally had it. It's since been welded shut.

When you're watching the manual actuators you can see them close or start jerking, like it's losing pilot pressure.  Except the boom.  The functions do work when operated manually (although the grapple rotate seems really slow at high idle). Monitoring pressures corresponds to the actuators - it either drops to a few hundred psi, or it jerks back and forth between, eg. 800-1200 PSI.

If you move a cylinder to end of stroke, however, you can bring the idle up to max RPM and it'll hold steady at the system relief pressure (2500PSI).

We've tried bypassing the brake valve to see if it was the accumulator charging somehow doing it (the accumulator pressure is low, so it recharges more than it should), and we played with the system relief pressure settings.  Both had no effect.  Steering and blade both function normally.

We also tried swapping actuators, but an actuator that works on the boom won't on the jib (or other troubled function) and vice versa.  We also swapped hoses from Jib to Boom with no discernible effect on either (boom worked, jib jerked)

Anybody out there ever seen this before, or have any idea what to check next?  I'm running out of ideas...

Thanks

[moodnacreek]

I know this is way to simple and even insulting but could any hoses be crossed?  I just went through this on a simple front end loader and it did all kinds of jerking, stopping and starting.  A restrictor in the wrong port can do funny things sometimes.

[BargeMonkey]

 Sure the water didn't trash your hydraulic pump ? 

[Firewoodjoe]

Yeah a gauge needs to be put as close to the pumps as possible. And monitor pressure. Both main and pilot. It should have actually test ports. Also run all reliefs in and back out to they’re setting. Count revolutions of your wrench. It may have washed junk through the sytem. If the pumps check out then it could be a long hard road. Also it sounds like you’ve had a lot torn apart. Could be air in it? How much have you ran it after the fact? And it may take a few filters. It’s hard to get water out of an entire system. Hydraulic oil is designed to suspend water in it. 

[slowmiller]

Not sure what that machine runs for a hydraulic pump but sound like an issue with the load sensing circuit (assuming it is a variable displacement pump). Seems like the pump failing to stoke up when demand increases would cause most of those issues.

[Burntberry]

Hi all and thanks for the help.

It's an open-center system, no load sensing.  But that's exactly what it's acting like, like the pump won't keep up with demand. 

But the weird thing is the pump has no problem keeping up with the boom, and it can reach and hold max system pressure.  Flow seems ok but I haven't had a flowmeter hooked up to the system, just measuring the return rate old-school with containers.  

And something that may have gotten lost in my first post:  All functions work normal when actuated manually.  Low idle, fast idle, doesn't matter - they behave as you'd expect (except the grapple function doesn't seem to get much faster with idle increase).

I'd like to be able to measure pilot pressure but the Danfoss PVG32 valves apparently have no ports for it, except on banks with an  external pilot pump, which this one doesn't have (there's an integral pressure reducer in the valve that takes the pilot feed off the main hydraulic circuit). 

I might try hooking up an external pump to the system to eliminate that variable, or bring in a flowmeter.  But beyond that the only thing I can think of is the actuators.

[kiko]

The pvg32 is a load sense control valve. The load sense happens in the valve itself not the valve sending a signal to a variable displacement pump.  I found the technical info on that valve on line.   The pilot pressure or standby as danfoss calls would be measured at the M port on the inlet section. This should be 450 psi when in neutral. This is the same port you would measure main relief pressure. There are also load checks for each sections.  Will another function work properly while you have the boom traveling. Like jib and main up at the same time?   

[bushmechanic]

Kiko is right on about the valve being a load sensing one and those pumps are gear pumps. You said there is no issue with the steering or blade functions and I think it's because they are manually operated valves. The older 230A had only one hydraulic pump bolted to the side of the Cummins 4Bt, the later and 610 models also had another pump driven from the crankshaft in the front of the engine, still gear pumps. You said manually operated it works fine, so the issue may not be hydraulic but electric. If it has Danfoss joysticks then you will have IPS boxes and those can certainly give you the jerky functions. By all means check your pressures, but if you still can't see anything wrong you best check your electrics.   

[Burntberry]

The pvg32 is a load sense control valve. The load sense happens in the valve itself not the valve sending a signal to a variable displacement pump.  I found the technical info on that valve on line.   The pilot pressure or standby as danfoss calls would be measured at the M port on the inlet section. This should be 450 psi when in neutral. This is the same port you would measure main relief pressure. There are also load checks for each sections.  Will another function work properly while you have the boom traveling. Like jib and main up at the same time?  

Are you sure about the M port for the pilot pressure?  My understanding is that it's the system pressure.  It ties directly to the P port and the troubleshooting manual says if there's a check valve for external pilot pressure to use a test tee to check relief pressure. 

I actually have a tee on the P line now and the pressure matches the M port.   I'll try to attach a couple pics from the manuals I was looking at.


Also, for the neutral pressure, wouldn't it be the same as the standby pressure in the tech manual (145psi)?  That's right around where it seems to be sitting, although that's based off judging it with a 3000psi gauge

[Burntberry]

Kiko is right on about the valve being a load sensing one and those pumps are gear pumps. You said there is no issue with the steering or blade functions and I think it's because they are manually operated valves. The older 230A had only one hydraulic pump bolted to the side of the Cummins 4Bt, the later and 610 models also had another pump driven from the crankshaft in the front of the engine, still gear pumps. You said manually operated it works fine, so the issue may not be hydraulic but electric. If it has Danfoss joysticks then you will have IPS boxes and those can certainly give you the jerky functions. By all means check your pressures, but if you still can't see anything wrong you best check your electrics.  

Hi bushmechanic, I'm not far away! (near Springdale) 

This must be the older 230A style (makes sense since it has 230A on the door), there's a Cessna pump bolted to the side of the 4BT as you described. 

The Danfoss claw joysticks were removed a while ago and replaced with new proportional joysticks.  Signal voltage seems to be good - it's a steady variation around 0.5V up to 14V or so, and I actually tried running it off a powerpack with a 10k potentiometer and it behaved the same.  So I think you might be right about the electronics.

[bushmechanic]

Ok so the joysticks were replaced, but does it still have the IPS boxes? I've had lots of troubles with those. So much shaking in the machine tends to knock the wiring loose or the soldered connection on the circuit boards. Last bit of trouble I had was on a Rottne harvester. It would stop working on one joystick, I'd give it tap with my boot and way she'd go for another while. It was in the circuit board of that one. Make sure the seat switch is not the culprit too! Good to have another Newfie on here👍