Marquipt won't hold load

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Some of you guys may remember my previous thread about my 1K# Marquipt that was leaking hydraulic fluid several months ago.

Well with a little encouragement from the forum and a $10K estimate from Marquipt I decided to dig into it myself. It was as advertised pretty srtaight forward and mainly grunt work. And as usual this turned into a major "restoration".

The original leak was basically the upper wiper seal on the cylinder. So I had the cylinder rebuilt, new hydraulic lines made up. Sand blasted and powedercoated the whole thing. New cable and some HW and we're all back together. I run the dang thing in the garage. It goes up and down fine. Me and two other guys install it on the boat and it, runs up and down fine.

I get tight on this San Sal trip and never get to test it by launching the dink. Well you guessed it. We get all the way down there and it raises the tender about three feet, makes a godawful noise and then the load comes down. Maybe air? We try it several more times. Fluid is coming out the vent cap and onto the deck. So needing a liferaft for the return trip we get the tender back into the chocks and that's it for this trip.

I guess I have finally found something worse than carrying a scuba tank that is out of hydro all around the Behamas....

So the boat is back home now and I'm trying to figure out what's going on. A guy mentioned to me that there are "reversing" valves or poppets in the cylinder and if those were'nt seated right when the cylider was rebuilt that would cause this. Seems like the only option, however, I did have an electric motor guy try to fit this with a newer or more modern control. Basically a two button hoist control. He never could get it right and we went back to the original control, with the orignal wiring and terminal block in place.

Electrically it works fine with the cable going in and out as it should. But when this thing makes that awful noise and the cable is stripping out the 2 solenoids on the motor get hot and seem like they're gonna burn up.

So I'm wondering if the solenoids got damaged when this guy was messing around with the new controller. Marquipt is telling me they have gone to 12 and 24 volt DC systems (this one being 120 vlt AC) and that's part of the reason their ETN was so expensive. So there's really no motivation to help with this 1989 model. So.....has anyone seen something like this on a hydraulic system? I'm ready to take the cylinder back to the rebuild guys, but that means a complete and total disassembly of the unit again. Thanks in advance.

 

[Trojan]

You need to tell me where this spewing vent is located? On the cyl. or the pump? How many lines go to the cylinder. Is it single or double acting. What does the cyl. connect to. I'm not familiar with the unit or system you have, but I know hydraulics. It does not sound like the cyl. is bad. But need more info on the system. Valves or poppets are not usually built into the cyl.. Sounds more like a bypassing pressure control valve. Is there some place I could look up the system?
BILL

 

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Thanks Bill. The system has only two hydraulic lines. The vent cap is on top of the resevoir which is bolted onto the hydraulic pump (and where the fluid leaks from). It's 120volt AC. There are two solenoids that correspond with the hydraulic lines and possibly sometype of manifold (hard to tell but it's a machined aluminum block.) I understood the motor guy to say the pump motor only turns in one direction and these solenoids reverse the flow of the fluid. That was part of the reason he couldn't get new contoller to work. But the cylinder itself seems quite simple except for the pulley block welded on the ram. It only has the two lines attached as well and reversing these just changes the direction.

I'll take another look at that "manifold" and see if there are some other fittings on it. If there's a reversing or bypass valve or seat in there, maybe some grit or sand got in there from the sand blasting. Although we tried to be careful. Thanks for your thoughts.

 

[REBrueckner]

Sounds like the solenoids activate one at a time to control the direction of fluid flow.

 

[Brian Degulis]

You should have solinoid control valves and pilot checks or lock valves. For it not to hold load 2 valves have to be inoperative (unlikely). Fluid blowing out the vent is caused by air in the system which will also cause the load to drop. Did you cycle this thing with no load several times to purge it?

Brian

 

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Brian, I like what you're saying, but yes I raised and lowered that cable wieght maybe 15 or 20 times. I'd much rather do that 100 more times than take this dang thing apart again. And yes, the hydraulic fluid is foaming when it spills over, so there is air in it for sure.......The manual says "cycle" the boom "several" times to "purge" air.

Think I should keep cycling it? Thanks.

 

[Brian Degulis]

No don't keep cycling. Look for an air leak on the suction side. That would be where the fluid exits the resevoir and enters the pump. It sounds like your picking up air somewhere. Also check any filters or valves on the suction side. If you have a restriction on the fluid supply that will do it also. If it were just not holding the load I would say it's the piston seal in the cylinder but the fluid blowing out the resevoir is pointing toward air.

Brian

 

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Thanks Brian, appreciate the toughts on this. One question, if it's an air leak, would that also mean there's a fluid leak when the system is static? I'll be going by the boat tomorow and will try to gat a better look. Thx.

 

[Brian Degulis]

Thanks Brian, appreciate the toughts on this. One question, if it's an air leak, would that also mean there's a fluid leak when the system is static? I'll be going by the boat tomorow and will try to gat a better look. Thx.

Sometimes but not always. A small leak may draw air under suction but not leak fluid. You could also have something wrong within the tank. I don't know how it's designed but if it's a pick up tube within the tank and it's leaking it can draw lots of air yet leak no fluid.

Brian

 

[Trojan]

You said you cycled the unit, but did you stroke the cylinder to full extension and back. It does sound like air. Make sure you stroke out the cylinder in both directions a couple of times. Air also would prevent you from lifting at full load.

BILL