Reading my JD-790 hydraulic schematic...

[Willl]

Got some questions about my JD-790 hydraulic schematic and valve plumbing. (see attached)
The tractor has FEL, BH and rear PB ports. (BH runs off rear PB ports)

1) Beings my 790 has a SCV, to make this schematic less cluttered and easier to read, the lines I marked 1 and 2 are unused and I could erase them, correct ?

2) If I'm reading this correctly, this 790 SCV valve has both a PB output and a 'return to tank' output ?

3) If I was to install an extra hydraulic valve(s) off the rear remotes, would it
also have/need a 'return to tank' output ?
Obviously it'll need a PB output plugged into the return to power the rockshaft. Am I also going to have to plumb a extra 'return to tank' line from the new valve ?

4) If 3 above is 'yes', does the 790 have a 'return to tank' port ?

 

[Willl]

Anybody ?

 

[J_J]

Anybody ?

I believe that with all valves using PB, the work port fluid from each valve has to return to tank.

 

[Willl]

Hmm, so beings my BH has only 1 return it has to be a 'work port outlet' correct ?, which means my add-on valve must go before the BH ?

So looking at my schematic, does this also mean that as long as my BH is hooked up, my 3pt is nonfunctional ?

 

[spruce Deere]

O.K..... I think you are right on the schematic, but with that confusing thing aside......
A power beyond circuit always is constant live pressure and has to have 'return to tank' port. If you were to put a valve in a PB circuit, it must be an open center valve so you do not dead head the tractors pump when the valve is not open. The out or return port of the valve could then then go to the work port "inlet" of the BH valve OR back to the tractor via "work port outlet hose" of the power beyond. OR add-on valve could go AFTER the BH with work port outlet to the 'in' port of add-on valve and the 'out' port of the valve to the work port outlet line to the tractor.
The 3pt should still work with the BH or PB. Not that you could use 3pt implements with the BH in the way......
Mech put top/tilt and hydralic angle loader blade using the PB on his 790. He did a most excellent photo and description of the whole deal. A search on that might help 'ya to.

 

[Willl]

I reworked my schematic.

I went on the assumption that lines 1 and 2 were not applicable in my case and erased them. It does unclutter it a bit.
I also added where my backhoe is plumbed in at.

Couple things I noticed studying this, the rock shaft is the very last guy on
the line and there's not a whole lot of difference between a PB port and just tee'ing into the line. Sort of.

 

[kennyd]

Will,

Here are my thoughts...

First, what threw me was this statement (hence my PM to you):

The tractor has FEL, BH and rear remotes. (BH runs off rear remotes)

Just a terminology thing, but you do not have "rear remotes", you have what everybody calls "power beyond". "Remotes" usually means a valve, witch you do not have.

So now you want a rear remote valve... All you need is a valve without PB, and plump it in to the PB "loop" that you already have. If have done this on my machine, as well as quite a few others with JD's.

You will have to decide if you just want to lug the new in and use it when the backhoe is removed, or make it permanently plumbed in.

Look at these three threads:
Mine
Brad's
Jim's

 

[Willl]

Thanks for replying Kenny.

Just a terminology thing, but you do not have "rear remotes", you have what everybody calls "power beyond". "Remotes" usually means a valve, witch you do not have.

Yes, your correct. I should have called it PB instead and have corrected it.

I guess what's getting me confused is/was my thinking that a 'second' inline valve must be fed from a PB outlet from the first valve ?

Ya, permanent mount and permanent plumbed.

 

[AKKAMAAN]

wow....this was interesting...
First I must say after using JD educational litterture for many years, they are top of the line....
so is this drawing, even if JD seems to step away from the ISO standard a little bit.

I have a question to you guys, with experience of these JD tractors.
It is about the filter setup. I have never seen a design with a strainer in the tank, and a filter with a by-pass on the suction line. and no filter on the return line.
Is this a standard JD Tractor design or did the JD engineer make a mistake in the drawing, putting the filter on suction line instead of return line??
It wont effect the power steering pump because it is closed loop, but for sure the FEL, Rockshaft and AUX pump circuit.
See my picture!
If this is the design, it will for sure set up for a possible pump cavitation!

 

[kennyd]

I guess what's getting me confused is/was my thinking that a 'second' inline valve must be fed from a PB outlet from the first valve ?

Here is the way I look at it...Does your backhoe valve have a PB port? How many hoses are connected to it?

The main problem on the JD's is that the FEL valve is mounted directly to the transmission case (unlike most other makes) and does not have ports like a regular valve...The PB kit that you have is really all we have to work with.

IF you can find a "tank" port on your machine, then you can use a PB equipped valve with the PB port feeding the backhoe and/or the 3PH.

Attached are two pictures from my album that I marked up for another user. Basically there are QD's on the IN side of the new valve where you would plug in the backhoe. I am thinking of changing my setup over the winter like this so I can add a 3PH logsplitter., and I have the QD's from the original PB kit that I never used.