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Discussion Starter · #1 ·
I was looking around under my 4720 trying to understand how the hydraulics were all plumbed up. There is a valve block plumbed between the pump and the dual mid SCV's that I couldn't find on the JD parts breakdown. It has 2 wires coming out of it. What is that gizmo?
Also, After the dual mid SCV's the supply goes to the PB, then the 4th and 5th SCV's, then the 3rd EH SCV, then the rock shaft. I thought that was kind of odd, if you had the backhoe on, all of the hydraulics back there would be disabled. I guess you probably wouldn't be using them anyway. Maybe the 3rd loader function if you had a 4in 1 bucket or something like that. I have read here over and over about the PB tank port bypassing the rock shaft , but ALL of the rear hydraulics gets bypassed. Something to keep in mind if you have some odd application where you want those ports to be live with the hoe on. You would want to custom plumb your own setup.
Of course, it makes me wonder if the dealer plumbed it the way Deere intended. They had quite allot of trouble figuring out what lines they needed.
Another question. The 4th and 5th SCV block has a direct to tank line... the 3rd EH does not. Is that just for float operation?
 

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Arlen, please excuse my delayed reply-I am just getting caught up from being away in Florida this past weekend.

Can you please post a picture of this block with the two wires?

I will answer better shortly the best I can.:flag_of_truce:
 

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Discussion Starter · #3 ·
Arlen, please excuse my delayed reply-I am just getting caught up from being away in Florida this past weekend.

Can you please post a picture of this block with the two wires?

I will answer better shortly the best I can.:flag_of_truce:
Thanks Kenny,
I had to work for this picture! It is kind of hard to reach. It has one line coming directly from the pump and 1 line going into the Dual Mid SCV. Its located within 6 inches of the mid SCV. Maybe it supplies some kind of pilot pressure for the Hydro?
On a different note, I'm curious if the dealer installed hydraulics are plumbed in the proper sequence. What do you think of my observations?
 

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I thought about this trying to go to sleep last night-I have a feeling its the PTO Valve, you think?:

Text Line art Auto part Diagram Parallel


PTO VALVE
CartkeyPART NO.PART NAMEQTY SERIAL NO.REMARKS
1LVA801600Valve1 PTO
2M808250Screw With Washer3 M6 X 16, W/WASHER
3M808480Cover1 DRV
4CH14582O-Ring1
5M808479Plug1 DRV
6CH13526O-Ring2
7CH14607Ring1
8AM875154Valve1 DRV
9M800484Solid Shim2
10M87846Gasket2
CartkeyPART NO.PART NAMEQTY SERIAL NO.REMARKS
11M808477Spring1 DRV OUTER
12M808478Spring1 DRV INNER
13M800487O-Ring2
14M800486O-Ring1
15M800485Ring1
16AM878297Solenoid1
17M806692Nut1 PLASTIC
18CH14634O-Ring1
19CH17887O-Ring1
20M805942Gasket1 SOLENOID
CartkeyPART NO.PART NAMEQTY SERIAL NO.REMARKS
21LVA800760Solenoid Valve1
22M805945Spring1 SOLENOID
23M800635Plug1
24CH10567O-Ring1
25AM876921Plug4 1/8"
2615H559Pipe Plug3 1/4"
27LVU801642Housing1
2815H666Pipe Plug1 3/8"
29M808476Plug1
30CH14634O-Ring1
CartkeyPART NO.PART NAMEQTY SERIAL NO.REMARKS
31LVA801587Spool1 FLOW CONTROL
32M808475Spring1
3319M8504Cap Screw5-670000M8 X 80
19M8504Cap Screw5-680000M8 X 80 (EUROPEAN)
M87885Bolt5670001-M8 X 80
M87885Bolt5680001-M8 X 80, (EUROPEAN)
34M808332Gasket1 PTO VALVE
3511M7094Cotter Pin1 1.600 X 16 mm
3624M7088Washer1 6.600 X 12 X 1.600 mm
37M800653Spring1
CartkeyPART NO.PART NAMEQTY SERIAL NO.REMARKS
38M800652Valve Seat1
39M800651Poppet1 RELIEF
4012M7065Lock Washer5-6700008 mm
12M7065Lock Washer5-6800008 mm (EUROPEAN)
 

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On a different note, I'm curious if the dealer installed hydraulics are plumbed in the proper sequence. What do you think of my observations?
I think its probably correct. I doubt there is really many options for the installer, but I can believe its confusing due to the amount of options and variables. Add to that, JD usually does disable all rear hydraulics when backhoes are mounted.
 

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Discussion Starter · #6 ·
Yes, I think that is it. What does it do? Supply lubricating oil, or hydraulically shift the PTO in?
Why doesn't the 3rd EH SCV need a direct to tank line? Is it just because it doesn't have a float function?
Thanks for the info.
 

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Arlen,

Can you try to photograph the other lines. I am thinking that they plumbed the system wrong. While I only have the 3rd scv, it does vent right to the tank. Each individual block should have a return to the tank and I can't imagine that the engineers at Deere didn't do that, Even if the lines all tee into a manifold that then returns to the tank. See the diagrams in the empty thread I started last week in this section.
 

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The PTO clutch is hydraulically activated. The wires open/ activate the valve and allow the pressure to engage the clutch and run the PTO.:hi:
 

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Discussion Starter · #10 ·
Arlen,

Can you try to photograph the other lines. I am thinking that they plumbed the system wrong. While I only have the 3rd scv, it does vent right to the tank. Each individual block should have a return to the tank and I can't imagine that the engineers at Deere didn't do that, Even if the lines all tee into a manifold that then returns to the tank. See the diagrams in the empty thread I started last week in this section.
I'll get some pictures. How does the plumbing go in your unit? Pump, PTO clutch, Dual mid, 3rd SCV, rock shaft? Maybe I'm confused about how the rock shaft is supplied?? I assumed it was last, after the 3rd SCV. My third SCV was factory installed, the 4th and 5th and PB was dealer installed. There was only 2 lines coming out of the EH block from the factory. Maybe what I thought was the rock shaft supply is actually going back to tank. It will be nice to get a service manual.
 

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I finally took a look under my tractor today. The 3rd EH SCV is supplied by the power beyond on the dual mid scv. The return from the 3rd scv appears to go to the back of the transmission case near the top and the nearest thing to that is the rockshaft so the 3rd scv may supply the rockshaft. It was too dark for photos. The Dual mid also appears to have a short line into the transmission case which must be the return for the valve. This would be the place to tee into for a return line.

I am starting to see how to add valves to the 4520....
 

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Discussion Starter · #12 ·
Charley, It sounds like your tractor is plumbed up basically the same as mine. The only difference is on mine the dual mid feeds the power beyond option, then 4th and 5th SCV before going to the 3rd SCV. So that begs the question: Why doesn't the 3rd EH SCV need a tank port? Everything else appears to have one. I was wondering if the tank port was only needed when the valves have float. I did look at that Prince diagram that you posted; that's what got me thinking about all of this. There are a couple of cartridge valves in the 3rd EH manifold. Any idea what those are for? I'll post a pic.
As far as a tank port for adding valves... there should be a plug in the case just below the right draft arm. That's where the PB and my 4th and 5th SCV dump to tank. It would probably be easier than where the dual mid goes to tank.
 

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The way these are plumbed would be wrong in the world of mechanical hydraulic valve because momentary spikes in pressure would be backward transmitted to valves up stream and potentially blow the seals. The only thing I can think of is that the EH valves are more pressure tolerant because they are pilot operated valves so you can plumb them in series and not have a separate tank vent or power beyond line on them.

All speculation on my part. I just don't know enough about EH valve specs. I know that none of the EH valves for sale on line have a power beyond function which makes me think they don't need it. It may be one reason why Deere is moving to them- because you can daisy chain them......
 

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Arlen, it matters not whether the valve has float or not-it is simply a design on the valve body itself. Most if not all EH valves are mounted to a "subplate" that is machined from a solid billet of material and not cast like a regular spool valve so that can take the pressure better, that's my theory anyway :)
 

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Discussion Starter · #15 ·
Arlen, it matters not whether the valve has float or not-it is simply a design on the valve body itself. Most if not all EH valves are mounted to a "subplate" that is machined from a solid billet of material and not cast like a regular spool valve so that can take the pressure better, that's my theory anyway :)
Kenny, thank you, that helps clear things up. In regards to float, would it be safe to say you MUST have a tank port to have float? I really couldn't imagine it any other way in my head.
Thanks for your help. I'm just learning this gear pump/open center business. I'm from an industrial (closed center, variable displacement piston pump) world.
 

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Discussion Starter · #17 ·
No, not at all. Here is one that has float regardless if it has the OC, CC, or BYD sleeve installed:

Surplus Center - 1 SPOOL 30 GPM PRINCE RD512GG5A4B1 OC VALVE W/FLT

It is all about the internal porting and spool design that determines this.
I was thinking that in the float mode, without a tank port, if pressure built up in the line due to a down stream valve activating a function, the cyllinder in the float mode would extend.

I'm not trying to be argumentative, just trying to learn a few things.
 

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I was thinking that in the float mode, without a tank port, if pressure built up in the line due to a down stream valve activating a function, the cyllinder in the float mode would extend.
Wow, great point to which I have no good rebuttal.:unknown::think:




I'm not trying to be argumentative, just trying to learn a few things
I didn't take it like you are/where argumentative at all Arlen, that thought NEVER crossed my mind.
 

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So, on the 4x20 series, where can you tie in to drain to the tank? Obviously the 3rd valve feeds the rockshaft so that's not the best location for an independant drain. I can't tell which pipe out of the loader scv is the return.

Additionally, opposite the filter return on the trans there is a plugged port. I suppose that could be used as a return on the left side of the tractor. I would like an independent return because I am seriously thinking of using a standard valve for SV 4/5 rather than EH.

Charley
 
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