450A Bang Bang functions not working

[Knepptune]

And the funniest name for a part has to be....the bang bang dump valve.

First time I saw that in a parts book. It put a smile on my face.

 

[willie59]

JLG typically uses bang valves for functions like basket tilt or rotate and the oil is metered through an orifice to control speed. When they use a bang valve for boom functions, telescope or swing, they typically have a flow control knob at the platform controls to control the speed of the function which is what this unit uses.

 

[willie59]

It's tough for me to follow many details Donald as I'm simply looking at diagrams, I'm not there with the machine. It's easy to get lost in the big picture of these things as there is a big picture. When troubleshooting likes this, I try to focus on something specific and go from there. Again, you stated the steer works, so that indicates things are proper, we just gotta figure out what's not proper. And I would start with working with ground controls, less components (boom cables, etc) to be part of the problem. First of all, with engine running, dump valve is open allowing flow from P2 pump to simply flow to return (tank) line. Now I could be wrong, but if I'm reading that diagram correctly, with engine running, if you were to put a 12V jumper wire on terminal 14 you would power up the dump valve, which would close the return. At that point, pressure will build at the sequence valve input causing it to shift and open allowing flow to tank. At the same time, oil will flow through the .045 orifice in the steer circuit, flow to the LS shuttle valve, and flow to the spring side of the sequence valve causing it to shift to close the valve. But it's reacting to pressure on the input to the valve, and it's reaction is slightly greater because of the spring force, force on the LS side is slightly greater than on the input side, so the sequence valve is held slightly open holding a 230 psi standby pressure (at G2 test port) with the dump valve activated and no functions being operated. At least that's the way I'm reading it.

 

[JPV]

Thanks, your discussion is making a lot more sense now, I didn't notice Joe beat me to it until now. Carry on!

 

[Donold]

That is a great break down. I have no psi with the engine running and nothing selected. When I power up pin 14 I get 2,800 psi.
I had a can issue on a roll off to resolve so I had to walk away the rest of the day. I pulled the shuttle and it was clean and I could push it back and forth with a paperclip sticking in each end. There was very little resistance in either directions.

 

[willie59]

Well, again, I'm not 100% sure how that load sensing circuit works, been years since I've worked on those things. However, we know the dump valve is working correctly. Second, that 2800 psi, that's either we're seeing the sequence valve not working correctly and cramming oil past the main relief valve (just below the sequence valve in the diagram), or, the LS circuit input on the spring side of the, along with the force of the spring, is more than enough to counteract the force of the pump input to the sequence valve and cause that 2800 psi, I'm just not sure about that.

What puzzles me, since you get 2800 psi when you power up the dump valve (close return to tank for P1 circuit) then why don't the bang functions work? I mean, if you select, say, platform tilt up or down from ground controls, if you've verified the coil for platform up/dwn is getting power, have verified the flow control valve is getting power, and verified the dump valve is getting power, then why isn't the platform tilt up/dwn working because we know we are getting pressure when that dump valve activates? If you've verified all this, it keeps bringing me back to the flow control valve is not working correctly, that's the only thing between P1 pump circuit and the platform tilt valve if we have 2800 psi on G2 test port.

One thing of note, the swing and upper lift share the same sequence valve, and the bang functions have a sequence valve, those two valves are the same, you could always swap them and see if you get a different result. Likewise with the flow control valve, there are three, one for main upper boom, one for swing, and one for bang functions, same valve, you could swap them as well. If you do decide to pull those cartridges be sure and look at the o-rings and back up rings closely looking for signs of failure.

 

[willie59]

Thanks, your discussion is making a lot more sense now, I didn't notice Joe beat me to it until now. Carry on!

It's old JLG terminology JPV, I recall JLG using the terms bang bang valve and dump valve all the way back to the 40F from back in the late 70's early 80's, and they still use those terms today.

 

[Donold]

I swapped the lift and steer sequence valves. (again)Nothing changed. Next I removed P1 input to the manifold and capped it at the manifold and ran P1 directly back to tank. I wanted to see if some type of pressure was corrupting the P2 side. Nothing changed. Then I removed the level coil from its cartridge. Again nothing changed. I ran the unit and put power to pin 14 the pressure was 2,800 and when selecting a bong bang function the pressure goes away.

 

[Donold]

I just switched the load sensing shuttles and then I went through each coil to see if any coil in addition to the function selected are pulling in the cartridge and I found nothing out of the ordinary.

 

[willie59]

I have an early 450A (Ford dual fuel) with several functions not working. It will not swing, the basket level or pivot and the extension in and out do not respond when selected. The unit will drive, steer and it will go up as well as back down. The non working functions will work if I select a working function in concert with a non working function.

I have to admit I'm a bit stumped at this point as I've never seen this before and it's not making sense. Just to clarify your original post (quoted above), when you say the "non functions will work if I select a working function", does that mean if you're driving the machine or working the upper boom then it will allow you to work the non working (bang bang) functions?

 

[Donold]

Here is what I have: From the platform it will drive and steer. I was working on the issues from the ground control to keep it simple. I am using platform right as my go to bang bang function to be consistent. At G2 Platform right at idle 200 PSI no movement. Power up pin 11 to get high idle 2,500 psi is seen when selecting platform right but no action on the platform. Selecting Platform right and tower lift up I see 2,500 psi and the platform goes right and the tower goes up. I see the tower is on the P2 circuit and takes a different path back to tank via the re-level valve. If I select upper lift (P1) and platform right it does not move the platform right. I am truly confused because the Upper lift takes the same path back to tank that I think is not working for the bang bang functions and it works. Quoting Charles Schultz, "good grief."

 

[willie59]

Upper lift (P1 circuit) should have no connection, or reaction, to the bang valve functions (P2 circuit) as they have no connection whatsoever aside from the tank return lines, which everything concerning the hydraulic circuits of the machine share pretty much the same tank line.

Yes, the tower circuit does have a "different path" to tank through the re-leveling valve, but that a hand operated valve to connect to the tank circuit, that tank return doesn't come into play unless you open that hand valve, the normal return to tank for the tower circuit is via the 4 way directional valve that controls the tower boom, just like all the other function valves.

What's curious to me, whether ground controls or platform controls, if I got this right, bang functions don't work, except steer (platform controls), steer works (bang valve function), but none of the other bang valve functions work by themselves. You select platform rotate from platform controls and nothing happens, yet you select platform rotate and tower lift from platform controls and now the platform rotates. But, does tower go up?

What about any other combination of bang functions to make the platform rotate?

Or steer, what happens when you select steer (since it works proper) and all the other bang functions individually?

 

[Donold]

The way I explained that last part was confusing. I see main lift in the operation manual and upper lift in the parts book are the same. When operating the main lift it works however; working a bang function along with the main lift only the main lift works. When working the tower lift we get bang bang functions. All the platform functions work at the same time tower lift up or down is selected. For example it will be going down and platform moving right at the same time. The telescopic function will work only when tower lift up or down is selected. The lift will not move up or down when the telescopic function is selected but works fine by itself. Telescopic overrides the tower lift but the platform functions do not. The bang bang functions do not work from the platform. From the platform or the ground control the bang bang functions can be heard spooling up (deadhead?) but no flow.

 

[Donold]

I went and tried all the possible combinations. Only the tower selection gets the bang bang functions to work, from ground or platform. Steer will only steer drive only drive. Selecting two bang bang functions at once does nothing.

 

[willie59]

Let me see if I got this right.

• The only bang function that works and that works independently is tower lift (lower boom) up and down
  
• No other bang functions work either independently or any combination selected
• Yet you can operate tower lift (up/down) and all other bang functions now work while you're operating tower lift up/down
• Telescope (bang function) will work when tower lift is selected up/down but tower does not move, only telescope operates

Is this correct?

 

[Donold]

That is correct. The telescope appears to have a demand that is less than the lift so it gets priority. I tried all combinations today and only tower lift combined to the other bang bans will get them to work.

 

[willie59]

I have to admit, at this point you've kicked my a$$, I can't even see how this problem is even possible either by the electrical diagrams or by the hydraulic diagrams. In over 30 years of working on machines I've never seen a problem like this that defies explanation, but I just don't see one. I'll keep looking because my curiosity works that way, but just damn!

 

[willie59]

I know you're looking for answers but I don't have any for this one, I really don't see a reason how this is even possible. Forget about steer, the fact that the tower function (bang valve circuit) works proper indicates that the dump valve, the sequence valve, and the flow control valve works proper, end of discussion. That other bang functions don't work, a bunch of ??? I've considered low voltage, but that don't fly since you can make other bang functions work in conjunction with tower function, they all share the same power source. I've considered a faulty 4 way valve, all the functions use a 4 way valve, and closed center at that, if one were faulty, dumping oil to tank, it would affect all bang functions, including tower, add to that the fact that you can make all bang functions work by working the tower function indicates the other bang functions are not faulty. So we focus on the tower circuit, the common denominator, as the cause of the problem, but I just don't see it, no matter how I slice and dice it looking at the diagrams. Makes me wonder if it's a fault that can't been seen on diagrams, such as a failed o-ring on a valve cartridge. For example, I once worked on a Skyjack scissor that had no functions. After following the pretty much same path of "this isn't possible according to the diagrams", I pulled the entire main control valve and took it apart. I found where they had to drill passages in the valve manifold, one drilling in particular intersected with tank circuit, other passages in that drilling didn't need to be connected to tank. To remedy this manufacturing method they fitted a set screw to block that drilled port. Over time that set screw "plug" came loose, allowed that drilled passage to send every function command to tank circuit. I reset that set screw plug with red Loctite.

 

[Donold]

Damn it man.
I told the owner of the machine I was going to remove the block put it on the bench and remove everything on it for cleaning and inspection. At the end of my rope and out of options, I called yesterday for a price on the main block and the block is sold as a complete assembly. I don’t have a price yet if I end up going that route. I guess they overloaded their calculator. If just the flow cartridge was about 250 the entire ball of wax can be 7k. I hope I find a smoking gun in the inspection of the stripped down block.

 

[willie59]

If you're going to tear down the main control valve you may want to consider replacing the o-rings on all the fittings. Most likely will have 900 series o-rings for all the o-ring boss port fittings and the valve cartridges will likely have something like 100 series o-rings and back up rings. And be sure to be looking for evidence of o-ring failure on some component