Questions for you experienced hydraulic valve guys

[fastline]

I'm not ignorant to hydraulics, or at least understanding the engineering side of hydraulic power, but I am trying to repair a genie boom lift that is just pissing me off. Mostly because the schematics really suck, and I don't know what types of valves I am looking at just by looking.

I have SEVERAL problems, and I am about to set this POS on fire and walk away, but as a starter, this is an articulating boom lift that has sat for probably 10yrs I would guess. Original owners screwed it all up with wiring hacks, then a friend bought it and it sat some more. Now I am in there. God how I hate fixing other's work.

So first issue, boom raise and hold. When the boom section is commanded to go up, it fires a solenoid in the main hydro block and sends fluid to the piston side of cylinder. the cylinder has what I believe is counter balance valve or other "load check" device, with an emergency lowering handle, and a solenoid right on it. I have determined that lowering is all done at that point, as the rod end goes through this valve and the schematic shows the rod end otherwise to just return to tank.

2 issues.
1. When commanding boom up, engine labors hard like its doing something, I am just bumping the toggle. Eventually the boom will start to lift and the engine hardly labors. So I would consider the initial efforts to be dead heading for some reason. I suspect the valve on the cylinder.

2. Once boom is lifting, I can raise it fine, but as soon as I stop lifting, it will lower like I am holding the lower toggle. It's not like a little bleed down, that sucker is coming down!! I further opened the emergency lowering valve once and it lowered a touch faster, but not much.

The way I see this, everything is controlled in that valve, but I have NEVER seen one of these fail!? The fluid is healthy looking. It does not appear water has invaded this machine. Where I am at is either that valve has some sort of issue, or the piston seal is simply beyond toast! ??? BUT, like, should that valve not be able to account for that? Now, I do realize there is some lost math with the theories about fixed displacement in a cylinder, but if the piston is not sealing, the rod ends up acting, which increases pressures, possible beyond relief.

But this is fully sucked in, no people in basket, etc. I am just puzzled. I cycled cylinder a few times to try to get some heat from it, and nothing!


I will just go ahead and drop question 2 in, as it might relate. The basket "level" function does not work, but same deal here, when I activate either switch, up or down, the basket does not move at all, but the engine tells me something big is trying to happen. And I now have a head seal leak on what I believe is the "master" cylinder for leveling. If not familiar, when the boom goes up, the boom forces the aft cylinder to stroke, which is coupled to another cylinder under the basket so one cylinder forces the other to move just by stroking.

However, the cylinder under the basket does have a pair of valves on it, as I would expect, so if something happens, that basket cannot just dump humans on da flow. It almost seems like those valves too are having issues. Or I am missing something. When I boom up, It certainly moves that slave cylinder, and I can see it stroke, but I see zero movement at the basket. This is why I think the slave cylinder is now leaking. It just got some serious fluid pressure for some reason.

 

[Vetech63]

A model of your machine would help. Every cylinder on that machine will have a lock valve......a safety feature on anything that has a person on it. Depending on the type of lock valve, it will need a specific PSI for the valve to unlock and let fluid through for extend or retract. A properly functioning lock valve will then "lock" the cylinder in place once the fluid demand is lifted.

1. On your boom lift, you may be hearing the hydraulic load on your pump when it is building pressure for the lock valve release but usually the tone will only slightly change once the lift cylinder is moving. If your boom will not stay in position and comes down that fast there could be several reasons.....damaged cylinder and/or seals, junked out lock valve, etc...... You should hear a loud rush of fluid in the system when the boom is coming down uncontrolled. See if you can hear where that is coming from, it should point you in the right area.

2. You are correct on the operation of the master/slave cylinders on the basket. I will tell you that I have had to reseal numerous cylinders on those genies for improper operation. The lock valve manifold is also an area of concern on those.

 

[John C.]

You might also try to check the hose routings between the valve and the functions if that is possible. A machine sitting for many years can have all kinds of human caused issues. I've found hoses hooked up to the wrong things, Caps and plugs installed and hidden behind sheet metal, hoses crossed; etc.

 

[fastline]

Vetech, I will do one better and add the hydro schematic. As for improper hose terminations, it could be possible! I have found so many things that prove the IQ of previous "techs"..... One being that they ran the engine fuel solenoid "pull" wire in the control instead of the "hold", so it was trying to move 30A in the control instead of just 1A, which burned traces on a relay board. The list is long!

however, it might be near impossible to confirm routing due to the length zig zagging through the boom system. I also don't want to blow one of those lines! I do notice that either the hydro schematic is wrong, or my thinking is. When the boom goes up, this pulls the rod out of the cylinder, building pressure at the head. That pressure should be piston side at the basket.

However, I am not sure routing issues would cause all of this. Even if routed wrong, when you toggle the basket tilt, fluid doesn't do anything inside the master cylinder, only the slave would move. So basically it might be backwards with the switching, but should still get movement up there.

Like, how likely is it that the valves have issues? What would cause this dead head situation? my only thought is possibly the piston seals are so screwed that pressure at one end is pressuring up both? But I still sort of think there would be some movement, somehow?

 

[Vetech63]

How about a full model and serial #. Take a few pics of the hold valve on the boom lift cylinder and the main control valve and post those also

 

[Vetech63]

Yeah, the schematic sucks. I can't read alot of it when I blow it up. Why don't you call Genie and tell them you want the tech services schematic and not that weak crap they put on their website for customers. Genie was great to work with back in the day. When Terex bought them, it went to Hell. It's a shell of its former self.

 

[fastline]

Update. I was able to get function on the basket tilt. I was able to get a much better hydro schematic and decided I may have been suffering from fluid loss on the master cylinder due to a major leak. I unpinned the top of the cylinder to confirm movement, then reconnected and stayed in the tilt switch a bit longer and got it moving, but that master cylinder is a massive leaker. Like shot oil in the air kind of leak. I think because there are two pairs of counterbalance valves, it takes some grunt to get over the hump!

On the boom, I raised it a couple times, then shut engine down while it dropped. You could hear the oil I believe inside the cylinder bypassing. The cylinder also started heated a bit just in a couple cycles.

But question, I thought these were built in such a way that even internal piston leakage would not allow the cylinder to move? I mean, I realize if the piston does not seal, the acting force comes from the rod in which the head pressure would shoot the moon, but I guess I am asking to confirm. The head seal is not leaking, but I guess gushing oil moving from the rod side through the tubing would cause noise regardless. I am hoping the cylinder heating gave me enough to confirm the issue.

I also had a 'no drive' issue but that was proved to be a low speed trip due to a bad boom up limit switch telling control to stay in creep, coupled with bad voltage adjustment on the anti stall board. It was obvious someone was playing with the pot on the board but was able to resolve this one.

So far I have all function issues resolved but I have several cylinders to build now........

 

[Vetech63]

There was a great thread on the subject of cylinder drift a while back. Maybe someone will link it for you. (I don't have time to look for it at the moment)

 

[colson04]

https://www.heavyequipmentforums.com/threads/vickers-solenoid-dump-valve-repair-jlg-component.90036/

I had a different but related problem with my JLG. I had an accesory manifold block crack. I didnt get the sudden dropping like you do, but my auto-level on basket was not correct anymore. Also ,this valve body dumped massive amounts of oil every time I went to function something. There are several of these dump valves inside the valve enclosure on my machine, and if they aren't wired and functioning properly, none of the functions will act appropriately.

Just some food for thought, knowing you said somebody has already hodge podged the wiring.

 

[fastline]

There was a great thread on the subject of cylinder drift a while back. Maybe someone will link it for you. (I don't have time to look for it at the moment)

Really as long as drift was confirmed due to piston seals, that is good enough for me. My experience has been just that.

Which leads to another question about cylinder "kits"? I really need to just buy prebuilt kits for this one to move this thing along. I suspect every seal in that machine is timed out.

 

[fastline]

Well..........fu**. Here is the next BS issue, and hoping someone can help me out here. Genie called this system "proportional".....Well, they sort of cheated. They use a single prop valve on the valve block to select how much flow (speed) you want. Full power to the Prop valve is full speed, and no power, is go nowhere.

Ground control provides full power to the prop valve, but at the platform there is a "boom speed control" which is a potentiometer mated to a board. I am not convinced the board is bad because the LED light on it turns on when activated, it shuts off when a 12V input turns off, etc, but No matter what, It provides full power to the prop valve. Full voltage and I calculated the full current and that is what it is getting. So all you get is full speed in the basket, which is just too much.

I tried adjusting the pots on it labelled, 'maxout, threshhold, ramp, ' and another I can't recall. I am an electronics guy, but I got nothing here! They put sealer over the board so it will make PCB work very sucky suck.

To make this more fun, NONE of the books I have cover this board at all, I don't even have a part number, AND when I contacted Genie, they said, "as of April 1st, we no longer support products over 10yo".....LOL This is how you strategically kill the brand.

Oh, and I tried to just look up the prop valve so I could learn its drive characteristics. NOPE! Numbers on the side of it are useless. Genie must have played the cloaking game with their parts. This is SO not a CAT!!!

Any help or documents would be helpful! Happy to PM the machine info.

 

[John C.]

The last electronics component supplier I had luck with was Digikey. They have a search function on their web site that helped me a bunch when I had to get an old drill working. Even with that, there were components that were no longer being made.

Boards are problematic because they have gone from analog format to digital formats. Instead of potentiometers, voltage controls, amperage control and speed sensor frequency outputs, now you have PWM controls and micro processors that use software to make things work. Everything seemed to change between 2005 and 2010.

 

[fastline]

The last electronics component supplier I had luck with was Digikey. They have a search function on their web site that helped me a bunch when I had to get an old drill working. Even with that, there were components that were no longer being made.

Boards are problematic because they have gone from analog format to digital formats. Instead of potentiometers, voltage controls, amperage control and speed sensor frequency outputs, now you have PWM controls and micro processors that use software to make things work. Everything seemed to change between 2005 and 2010.

Judging by the design, I would nearly bet this is PWM output to the prop valve. I will have to tear down to confirm but there is a single power mosfet, and a FET only knows on or off. There is no way 2A is going through a potentiometer. Off the cuff, I would expect the pot drives the frequency of a 555 timer circuit which modulates the mosfet gate. The summing of the modulated signal would work to limit current to the prop valve.

I can probably fix the circuit if I can learn more about it. At the moment, I am not yet sure if someone just got the trimmers all messed up trying to 'adjust' things.

 

[fastline]

Speed controller is now right with the world again. Had to pull board and do a small bench repair and ton of test time with the scope to dial it in, but I'm very happy with it. Actually now that I know every function on it, I can tune it where I like it, not the OEM. Most certainly is a PWM controller with variable ramp rates and dwell. Wish all my issues were just electronic.

 

[John C.]

Sounds like the musings of the next generation of heavy equipment mechanic.

 

[fastline]

On to the next issue in this flaming dog turd

So after fixing some cylinders, speed controllers, wiring, etc, etc, etc, I finally set off to do some real function testing. I didn't get far.....lol Started driving and things seemed reasonable other than I noticed it seemed to sort of pull a bit to one side but it was a little muddy so I kept moving. Only talking 50ft fwd and back or so. I then tried to drive backward after doing some swing tests and had basket out of visual range for drive tires. It went backwards a bit, then stopped but I could tell it was likely that a tire was spinning. Again a little muddy, but I didn't think it was too bad. I confirmed one tire was spinning and other was doing nada.

So I realize there is a "traction" button which I believe is a counterbalance valve to equalize flow to each motor. "Posi". It indeed works and that got the MIA tire turning but just a small bit. As well, this put the engine under serious load....max load really. I could hear things grunting hard but not really going anywhere. The slipping tire was turning a little more than the 'stuck' one.

Because the machine initially drove decent, I really don't think the drive motor is shot, I think the seals in the brake are toast, allowing pressure to equalize in the brake, thus pressure is not acting on the piston to release it fully? I am just trying to think of some simple tests to prove my theory before I tear down AGAIN. I was thinking if I jack up that side of the machine and try to drive, without posi, it should normally force that tire to spin more, correct?

The brake lines are connected to each other so I feel confident if one is releasing, the same pressure is going to both. I thought about trying to test for case drain action but the hoses look odd. I need to see what sort of motor I have here. Again, just not real confident the motor is at issue here. I would think all that grunting means something is trying to happen. IE, motors are digging in.

 

[fastline]

At a loss here. I uncoupled the problem side drive motor while still hosed up. As suspected, in the open differential mode, power went right to the uncoupled motor and ran it fine, no engine laboring at all. When I uncoupled the motor, there was a brief gasp of pressure, and there was a little oil that came out. Probably 1/2cup or less. However, I realized the brake cannot be removed as an assembly! You have to pull the entire torq hub just to get access to the back bolts, so I pulled the face cover off the brake so I could get the guts out. The damn piston seals are NICE! Actually nothing in there looked out of order.

So I am either missing something here, or we might have issues in the hub, which I sort of don't agree with right now. Mostly because they don't exactly get a workout like other equipment, and I see no signs of contamination or that a bomb went off.

What is frustrating me at the moment is after disassembly, it became obvious the inner shaft has no seal on it on the piston/motor side so any major pressure is more likely to go to the torq hub and there is no indication of an over full condition. Per the book, it appears the oil that came out when I popped the motor loose was SUPPOSED to be there! That is the only oil for the friction discs. I have no clue how much because the book says "flip it on end and fill to top of plates"!!!! WTF! That is basically impossible in situ without pulling all hydro lines to drive motor and couple all of this as an assembly! Why would they do this????

This has me so baffled that I think my next plan is the assemble the brake with the stub shaft, and omit the friction plates and piston (bypass the brake) just to see if I can get drive! Really the only thing I can think of here. It appears other bad stuff would happen before a brake piston leak would cause a fail to unlock situation.

Any thoughts on this, or maybe HTF I am supposed to get oil to those plates? I am shocked there is not a fill hole!

 

[colson04]

Did you pull the cover off your torque hub for a quick inspection? My jlg sheared a quarter of a tooth off and it locked everything right up tight. I had to pull my drive motor and brake (as one assembly) in order to swap torque hubs.

 

[fastline]

No, this one is not locked up. Actually it will initially drive for 10ft for so. A friend was questioning the drive motor but at the moment, it's lowest on the list because it seems to run uncoupled free as a bird, and the load against the engine indicates something is working hard. I guess I did not check for motor heating, but IMO, it's either that brake or in the hub. Hoping for the brake!

The way this is acting is "drag". Like a frozen bearing, dragging brake, or similar. I cannot help but wonder if the neutral for freewheel button on the hub has anything at all to do with this. It was in freewheel for years as it was pulled into position. Button is fully out though and otherside woke right up.

I just don't know how that button works so hard to make a guess there.

And I could be totally off and the FRONT wheel is froze up...lol but those are smooth, and it is sitting on grass so I would think I would see it trying to push and slide up there.

 

[fastline]

I guess this is becoming like my diary/log, and apparently I get to eat some shi& on this one. After my suspicion that left brake was hanging up, I pulled it apart and did not find the drama I was looking for. That caused me to pause and rethink. I decided I would assemble the brake, minus the discs because it is not much hassle, and will confirm things for sure. Sure enough, it drives like a dream without the brake goodies!

However, it got me thinking......I never even checked to ensure the brakes were getting pressure and went off assumptions because the RH brake is free willy. I did not even need to test for pressure because I confirmed the """""BRAKE RELEASE SOLENOID""" is not getting power....... Yep, I chased my tail on this one. I figured out that the travel alarm is wired with that release solenoid, so no " beep, beep", no brake release. I guess I just took the good brake apart and confirmed it is good.....lmao. I will mess with the other one when I have time. Seems evident that one is toast for one reason or another.

This was yet another electrical gremlin. I would be so screwed without my meters.