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View Full Version : OT/Why does my backhoe think it's a hydraulic jack??



torker
10-06-2008, 10:09 PM
OK...Hydraulic guys again...LOL!
I haven't a clue...
The only way I can get the main stick to raise up (Cylinder pulling) is to pump the control like a bottle jack. It will only raise in short bursts.... about 1/4" of the rod comes in for each "pump" of the handle.
Everything else works fine...with lots of power even at idle.
So "what's up hydro docs"?
Thanks!
Russ

garyphansen
10-06-2008, 10:25 PM
Russ: I am no expert but I would guess that you have air in your lines. Gary P. Hansen

Dawai
10-06-2008, 10:26 PM
Dirty spool valve...

I was using a New Holland, (rental) and the spool kept sticking..

Had a buddy who could really dig sitting on it digging my basement.. it stuck.. knocked the air conditioner right out of the window on the house.. He was near-heart attack.. pale.. I reassured him I would have torn the corner of the house off..

*a guy got buried in a ditch bank cave in.. Mr Green dug with the backhoe till he saw his shirt.. Saved the guys life.. he was the best I have ever saw.. Anyways, he did in a day what I could have in a week and half. *He's deceased now.. A really nice guy I miss a lot.. The guy who got buried, he got out of the ditch, quit work.. had a lil apron and a pair of scissors the next time I saw him.

wierdscience
10-06-2008, 10:31 PM
OK...Hydraulic guys again...LOL!
I haven't a clue...
The only way I can get the main stick to raise up (Cylinder pulling) is to pump the control like a bottle jack. It will only raise in short bursts.... about 1/4" of the rod comes in for each "pump" of the handle.
Everything else works fine...with lots of power even at idle.
So "what's up hydro docs"?
Thanks!
Russ

Will it develope any power while doing this?And will it hold position?

If not you may have a cut packing on the piston.

Tim Clarke
10-06-2008, 10:59 PM
Without being able to see the valve setup on the "hoe', I'll venture a guess or tow. First, I'm assuming that the control valve is an inline spoolvalve, with a handle for every pair of functions. As in 1 lever for bucket in/out, another for lift/drop, etc. Assuming this to be true, there will be a centering spring for each spool in the valve body. When alll the levers are in the released position, are all the ends of the spools the same distance from the casting? The reason I ask this is, is that from the end of the valve where the oil comes in from the pump, the spools move to block the flow from the pump, and send it to the function you need. So, if a spool has not returned to center exactly, it will effect the flow to the next spool in line. It's comon for a centering spring to break off a coil, or for the bolt that holds the assembly to back out a few turns. Either way, you need to be certain all spools return properly to center before moving on to the next step. Which is, to follow the likes from the function in question to the device.[inthis case, the cyl] Anything that isn't a hard line or hose will likely be suspect. A cast or machined block with ports in and out and maybe threaded caps other places will likely be a pilot operated check valve. Probably best to diss and inspect the thing, looking for busted parts, or tiny bits of debris holding the internals from doilg their intended job. Next up, there may be port reliefs on the valve. These will be inserted in the same section of the valve as the trouble is in. Usually a big hex fitting, with a spring and piston underneath. Sometimes with a visible adjusting screw and locknut.

Let me know what these checks reveal, and I'll try to help you noodle this out. I have no hoe specific experience, only 30 years of working on garbagewagons..............Doubtless others have experience on hoe's and will offer more help

TC

torker
10-07-2008, 12:02 AM
Thanks guys! Yes...it holds position....not for a long time but for an hour or so(if you leave the boom up after shutoff)(I did it to check for leakdown).
Hard to say on the power...it will lift pretty much what I ask but I have to pump the handle to lift it. It will jerk the boom up a little bit then it sounds like the pump is hitting a brickwall...sounds like it's at the end of travel or something...the slight squeal you get when you've maxed out travel...that's what this sounds like after every little "pump".(Oh Gawd...someone will have fun with all this sqealing and pumping stuff I bet)
Tim..David.. I'll check the spools etc tomorrow. Yes...this does have a valve for each function...old tymey! No fancy fourway controls on this ol' girl.
I'll check for valve centering etc.
Air in the lines.. I doubt that...but maybe.

kennyd4110
10-07-2008, 06:51 AM
It sounds like the relief valve for that spool is set to low...so when your raising the boom the relief valve pops off and the system goes into bypass mode-just like when a cylinder reaches the end of it's travel. You will need a gauge to properly set the relief pressure.

kennyd4110
10-07-2008, 06:52 AM
Russ: I am no expert but I would guess that you have air in your lines. Gary P. Hansen

These systems are "self bleeding"

J Richardson
10-07-2008, 07:47 AM
Hi,

What type of hoe is it? If it's a newer model, most likely it will have a variable displacement pump, and it sounds to me like the pump maybe be cycling between high volume mode to low volume mode. A little more info or pump manufacturer would help.

John

GKman
10-07-2008, 08:29 AM
Because you gave 29 cents for it?:D

torker
10-07-2008, 09:22 AM
John...most of the guys here already know..it's an old girl...a 1969 MF 40 with a plain ol' front drive pump. Very simple...but pretty foreign to me.
I am not a hydraulic guy...yet!
Gkman...it doesn't matter what I paid..it doesn't work.

Dawai
10-07-2008, 09:32 AM
Russ...

A spool valve is ported, has lil orings to separate the spool cuts.. PRESSURE is applied to parts to balance it.. when you apply pressure there on the lever it imbalances it allowing the pressure to "overcome the force" and it switches and rebalances.

A bad oring on the spool.. a restricted port via a piece of degraded hyd hose stopping it up.. all these things are bad.

My wrecker wants to stick.. I have to jiggle the levers.. old hydraulics..

VERY DAMN expensive to work on, unless you can figure it out yourself.. so expensive people part with the machine. A four port valve was $6,000 for a machine I was working on.

I'd love to do the robot lawnmower one more further.. imagine setting the "ho" up on the corner of a lot, it traveling to the site, digging a foundation level and to grade as laid out on computer cad program.. then beeping the horn when done... Lil unseen things like rocks.. well that'd make a programmer cry and pull his hair. Dozers do that routinely now.. people just sit on them being a saftey switch..

Metalmelter
10-07-2008, 12:24 PM
Hey Torker,

I have the same line of thought about your pressure being off like the previous poster said or a bad o-ring in the valve. I have one, a JD 410B, EVERYTHING is hydraulic. When i got it the first thing I did was to replace every filter I culd find and change the gallons of oil. You MUST use the proper oil which is spec'd for the machine. What you find in the oil change, oil included, may give you an idea of what is going on in the system.

Lastly, make friends with these guys here : http://www.heavyequipmentforums.com/Forum/forumdisplay.php?f=51

There's a wealth on knowledge there to be had ;)

Good luck!

Eric

M_C
10-07-2008, 04:35 PM
OK...Hydraulic guys again...LOL!
I haven't a clue...
The only way I can get the main stick to raise up (Cylinder pulling) is to pump the control like a bottle jack. It will only raise in short bursts.... about 1/4" of the rod comes in for each "pump" of the handle.
Everything else works fine...with lots of power even at idle.
So "what's up hydro docs"?
Thanks!
Russ

Most likely the piston seal has failed on that ram.
When you pressurise the rod side of the ram to retract, the oil bypasses the piston seal, and essentialy pressurise both sides of the piston creating a displacement ram, so it pretty much hydraulic locks itself.

A quick test without dismantling anything is to fully retract the ram, then bump the lever to try and retract the cylinder again. If it moves out slightly, then the piston seal has failed.
Other way to confirm, is to fully retract the ram, disconnect the non-pressurised hose, and try applying pressure to the remaining hose. If il comes out the disconnected port on the ram, then the seal has failed.

As for the spool valves being the problem, given the age, they'll be a basic open centre direct acting spool. The only seals are between the outside, and the return ports. They rely on a lapped fit to provide good sealing between all the pressure lines.

torker
10-07-2008, 04:40 PM
Sorry guys...one REALLY important thing I should have said...I can push down just fine with the main boom...it just won't pull the rod in. MC...if the seal was buggered..wouldn't that cause the cylinder to lock in both directions?

M_C
10-07-2008, 04:46 PM
Sorry guys...one REALLY important thing I should have said...I can push down just fine with the main boom...it just won't pull the rod in. MC...if the seal was buggered..wouldn't that cause the cylinder to lock in both directions?

No.
There's more piston surface area being pressurised when extending, so it'll still extend perfectly well, albeit with less power if the seals failed.
Could also be something like a collapsed hose acting like a one way valve, but it's very rare for that to happen.

I'd be checking the ram first, as that's the most likely part to fail.

torker
10-07-2008, 05:02 PM
Thanks MC.. as soon as this hurricane quits I'll do the checks you mentioned.
Holy smoke...the wind is just screaming thru here...rain coming down in buckets! Good weather for....ummm ummm...hmmmm

macona
10-07-2008, 06:46 PM
Sometimes, lime M_C said, a bad hose can cause this. The internal rubber becomes delaminated from the steel braid when there is a small hole or cut. The pressure fills the space between the rubber and braid and it acts like a balloon sealing off the hose.

Patch
10-07-2008, 08:00 PM
I suppose based on what little information has been disclosed thus far I
would have to opine a best estimate of breakdown. That being said, I believe that it is more than possible that the control valve spool operating the boom cyl. is broken into two pieces within the valve.

Patch

Tinkerer
10-07-2008, 08:15 PM
When I was in your spot with a 59 Massy 404 the first thing I'd did is swap the lines from the none working cylinder to a know functioning control valve my case the down rigger valve would act like it was dead heading and bog the pump down along with the motor. Swapped and it worked fine so I know it was in the spool. End up being a nylon ball stuck in the port removed it and replaced with a steel ball that fixed it up. Also mine had a diverter valve the swapped the pump feed from the FEL to the Hoe it you forgot to switch it the thing would act like that little jerks at a time caused by lack of fluid volume needed to run the ram out. Does yours have a diverter valve?

KDuffy
10-07-2008, 11:12 PM
Look for a smallish block on the end of the cylinder in the opposite direction to the travel desired. It should have a obvious extra plug or a bushing looking section at the end of the line. There should be a spring and check assembly inside that will have a counter assembly to open this when pressure builds on the cylinder side. Without this opening you will only get the reduced pressure oil to move, allowing the small steps that you see.

Note: This may be at the control block end of the lines as well on such a machine, it is common now to have them on the cylinders. The control block may have a counterbalance valve built in that could hang up and cause such a problem too. These units are to ensure that there is pressure on both sides of the piston prior to moving so as to not have a rapid uncontrolled movement (especially larger movements than desired).

It is not magic, just parts that must be in the right order to work, and broken springs and small bits of material or corrosion will stop the motion of the release mechanism.

Like Tinkerer said swap the lines, and see if the problem moves.

torker
10-08-2008, 09:24 AM
Oh GREAT...now the FEL main rams are doing the same thing. Gotta pump the handle to get it to raise. The reservoir is FULL. Well.. I knew I'd be havin troubles...what happens when "You get a deal" :D

kennyd4110
10-08-2008, 04:16 PM
Oh GREAT...now the FEL main rams are doing the same thing. Gotta pump the handle to get it to raise. The reservoir is FULL. Well.. I knew I'd be havin troubles...what happens when "You get a deal" :D

Again I will suggest you find the main relief valve...

M_C
10-08-2008, 04:54 PM
Think you might want to invest in a pressure gauge and an assortment of suitable T-peices to see what pressure you're getting, and if it's making to where it should be.

torker
10-08-2008, 07:23 PM
Thanks MC...that's what I'm going to do. Get the right pressure guages etc.
There is something screwy here.
I've found a bunch of troubleshooting info for hydraulics on google. Most of it is guys trying to sell their books but some is relavent.
Russ

kennyd4110
10-08-2008, 10:18 PM
Here is a great FREE reference:

Army Hydraulic Manual (http://www.derijcke.com/dl/manual.pdf)

Patch
10-08-2008, 10:38 PM
Oh GREAT...now the FEL main rams are doing the same thing. Gotta pump the handle to get it to raise. The reservoir is FULL. Well.. I knew I'd be havin troubles...what happens when "You get a deal" :D

Ah ! This is good.
The additional info now relates to 2 disfunctions which actually narrows a most probable cause and removes most of the doubt it being a spool valve.

Probable--relief valve in one or the other hyd. valve bodys.

Russ, simple check even before you get your gauges (which you will eventually need to adjust relief pressures).
Take a box wrench and remove each relief valve and check to see if a spring is broken.
It only takes a few minutes to remove and check.
They are not complicated. Cup your hand over the top of each relief valve as you remove it. If a broken spring--replace. Pressures are adjusted with round shims or depending on what valve is used it could be of a pressure screw you turn to obtain correct psi.
With(when you get) pressure guage T-d into line adjust pressure by adding shims or adjusting pressure screw.

Oh by the way, I did find a site that offered repair manuals at about $70.
Let me know if you want info.

All the best,

Patch

torker
10-09-2008, 12:38 AM
Thanks Patch, I'll check it out in the morning.
I'm STILL waiting for the previous owner to find the manual. He's slower than the second coming....cept when it comes to cashing cheques.
Kenny..Thanks for the link!
Russ

doctor demo
10-09-2008, 01:43 AM
I'm STILL waiting for the previous owner to find the manual. He's slower than the second coming....cept when it comes to cashing cheques.
Russ
Russ, in those ''tools You don't know You own'' do you have a flow gauge that reads up to around 30 g.p.m. and a pres. gauge to about 3,500 psi ?

You realy need that manual, but I am still leaning in the direction of the diverter/dump valve between the fel and hoe.

Sure wish I could just pop in and have a look for myself, ya know ''a pic is worth a thou. words'' situation.

I have a flow gauge I could ups to you if you would like. Although at this moment I'm not sure how hi it reads as I haven't used or seen it in a while.

I can even throw in a press. gauge in the same box if it would help, I'm sure postage couldn't be more than $20.00.

Steve

jcarter
10-09-2008, 08:27 AM
Without any diagnostic tools it's really an educated guess and trial and error method to find the problem and you can waste a lot of time. Steve has the right idea-get a flow/pressure gauge on it and start tracing through the system. The majority of our equipment at the golf course is driven hydraulically. Without the gauge shown in the link below I would be wasting a lot of time and possibly money replacing components unnecessarily.This gauge incorporates a needle valve with which I can restrict flow and put a load on the pump or other components to test them under pressure. It's a fast and absolute process. The only problem is you need a box full of fittings to connect to various systems.It's amazing how many pumps I have tested that have good flow until you put a load on them. As soon as you turn in that needle valve the flow drops right off and pressure only comes up slightly. Fast and easy diagnosis.http://img.photobucket.com/albums/v679/j-carter/100_0267.jpg

R W
10-25-2008, 07:47 PM
This is a very interesting problem, have you found the solution to it.
Please keep us informed.

torker
10-26-2008, 01:15 AM
Yes..I did find the problem It was the main relief. I turned up the pressure a bit and it cured it. However.. I have to get the proper fittings/guauges etc. I have the relief set a bit too high and blew the main pressure hose.
It's kinda weird...the curl on the bucket...you limit it "in" and it almost kills the machine. None of the other cylinders do this.
The relief valve is VERY touchy. I've been trying to find a new spring as I believe that is the problem.
Russ

R W
10-26-2008, 05:05 AM
Pleased to hear that you have it sorted it out, thanks for the reply.