OT?-Hydraulic Winch Not Lifting Load

[alskdjfhg]

1997 F800 digger derrick truck, has a Pitman Polecat boom on.

Been a project for a long, but is the current focus. Alot of hoses were dry rotted and split, I've replaced $1800 worth of hose on it (every hose above the rotary).

Went to do a test lift yesterday, and it wouldn't lift a load. Engine was running at 2000 RPM, so should have plenty of flow. And wasn't loading the engine up. Would try to lift, but stop.

Was picking up a tractor axle that weighed probably 2000lbs, well within capacity.

Winch pays out line and raises without a load, boom lifts, and crane swings. So everything is getting oil.

Anything I should test before I pull the hoist motor?

 

[svs]

Does it have electric over hydraulic valves? Will the boom raise a load that stalls the winch?

I have an Altec derrick from same era. There is a lot of overload protection wizardry built into it that has to be adjusted properly, and might cause what you are seeing.

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[atomarc]

I would suspect a relief valve that was stuck partially open before I would suspect a bum pump. Is there a pressure gauge in the system?

Stuart

 

[alskdjfhg]

Does it have electric over hydraulic valves? Will the boom raise a load that stalls the winch?

I have an Altec derrick from same era. There is a lot of overload protection wizardry built into it that has to be adjusted properly, and might cause what you are seeing.

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Don't believe it has that, just big clunky in line spool valves.

 

[alskdjfhg]

I would suspect a relief valve that was stuck partially open before I would suspect a bum pump. Is there a pressure gauge in the system?

Stuart

No pressure gauge, but I supposed I can plumb one in fairly easily.

No idea where the relief valve/valves are on this beast

 

[Tony Quiring]

2nd pressure relief.

Get a gauge and a tee for a hose and measure pressure

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[gbent]

Worn out pumps and motors usually work ok with cold oil. Then they fade as the oil warms up and the viscosity falls.

 

[svs]

Don't believe it has that, just big clunky in line spool valves.

Mine has a pretty complicated proportional electric over hydraulic valve. It uses a pressure switch on main boom cylinder to essentially limit foot lbs. When it closes it prevents any motion that increases the overload. (Winch down, boom up, telescope in are allowed. )

I don’t know how this would be accomplished purely hydraulically, but that crane is recent enough I half suspect it was required, and I’d keep an eye open for innocuous looking plumbing that doesn’t seem to have a purpose.

On edit-Set the boom low and see what winch will drag horizontally. Would put my theory to rest one way or another.


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[john.k]

Pump is OK if the boom will lift rated load.......if the valve bank has spool valves ,then every valve section will have reliefs both ways .....and sometimes there are reliefs inside the spools...Can be complex.....this is especially the slew .....this will also have anti runaway valving.......However ,I note the winch is worm gear ......I would check the gears (check the oil for bronze),wouldnt be the first winch Ive seen stripped bronze........On my Atlas crane ,the previous owner had swapped relief shims and it would not slew uphill......even slight uphill .....I could have pulled the lot,but I just made a couple of spacer s and shimmed up the relief on the problem area.

 

[ChipSplitter]

Start checking pressures at different locations, kinda like chasing a loose connection with a multimeter.

I would start on the pressure side of the pump, then after the system relief, then after the spool valve, then after the pilot-operated check valve (to prevent the boom from drifting, not sure if yours is electrically controlled), and finally on the cylinder.

This will give you a map to start with.

 

[alskdjfhg]

So this crane is much older than the truck

I think the crane is mid 70s vintage. Nothing electrical, and all the hydraulics look very simple.

Hopefully I don't have any thing super complex wrong with this thing.

What sucks is I don't think this thing has pressure testing ports plumbed into it. So it'll be very annoying to hook up a gage.

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[metalmagpie]

You have to have pressure readings to diagnose this problem.

Remove hose. Put in tee. Put hose back into tee. Put pressure gauge in other leg of tee.

Also, listen very carefully. Shrieks and squeals all have meaning when dealing with hydraulics.

And start at the output. Measure pressure going into the winch. If you have pressure there and no output power then you know it's the winch. If you have no pressure there then you know your winch is OK, so you can move your testing upstream. Basic common sense debugging of a simple mechanical problem.

If you feel overwhelmed just leave it for a day or two until you can approach the job with some upbeat confidence.

It's a very cool problem to have!

metalmagpie

 

[ShaunM]

In my limited experience troubleshooting hydraulics, heat has been a decent give-away. If, after repeated cycling of the questionable circuit, one component is heating up quicker than anything else - that is usually the culprit. No cracking of lines necessary and simple to do.

 

[crossthread]

This is just a wild ass guess but since you had all the hoses off, could you have enough air trapped in the system to cause a problem?

 

[petersen]

Matt:

That is a "Commercial" brand gear pump or a copy thereof.

Those two hex plugs on the back plate are likely optional pressure ports
where you could get a pressure reading. They look like about a #12 ORB port
which you could screw an adapter into or if you know a clever young
machinist you could drill and tap them 1/4"NPT.

You may see very little pressure when only turning the drum but much more
pressure when attempting to lift a load. (on the upstream side of course)

Another possibility I have seen where a motor is "quill mounted"
to a worm like that, is a sheared key, galled up enough to drive a
light load. but not a heavier load (or on the drum shaft for that matter

petersen

Give me a shout when you are going to get back to work on the P&H.
I have had a couple of thoughts on that.

 

[alskdjfhg]

It's a very cool problem to have!

No not really, I need this one working

Give me a shout when you are going to get back to work on the P&H.
I have had a couple of thoughts on that.

Will do, haven't given up on it, going to use this crane to work on the P&H

 

[john.k]

When all the hoses are taken off a valvebank ,its not impossible for replacement to go onto the wrong valve fittings.........the old hoses have a "set",but new hoses dont ,so if the mechanic was relying on memory ,and the job ended up taking a lot longer than expected......Done that.................Ive also seen hoses swapped to reverse lever position....IE up for up ,instead of up for down ,.....and the reliefs are different pressures.

 

[alskdjfhg]

When all the hoses are taken off a valvebank ,its not impossible for replacement to go onto the wrong valve fittings.........the old hoses have a "set",but new hoses dont ,so if the mechanic was relying on memory ,and the job ended up taking a lot longer than expected......Done that.................Ive also seen hoses swapped to reverse lever position....IE up for up ,instead of up for down ,.....and the reliefs are different pressures.

Up and down on the hoist are hooked up backwards right now, that may be a factor.

I figured motor wouldnt care, but could have a reliefs set lower on down than up.

I'm going to swap that, then start checking pressures.

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[john.k]

The hoist will certainly have some sort of automatic brake mechanism,on the down direction........its also possible to wind the rope on the drum the wrong way and upset things.

 

[alskdjfhg]

Flipped the hoses around so Up is Up.

I can lift with the boom. Just not the winch. So don't think it's the main system reliefs the problem.

When I hold hoist up, I can hear the oil moving right at the control valve and feel it inside the return line. So thinking something is happening right at the valve.

The winch circuit is labeled 7A and 7B

I don't see where there is a relief valve in these pictures, am I missing something?

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