Can I tee into PB and return for extra valve?

[CTGuy]

Not knowing what is going on inside the DO3 is a bit of a problem. But the schematics are probably available. It may be that they are so simple that everyone but me already knows how they work.

Attached is a schematic of the valve. I don't know about the subplate.

What feeds flow to the rear remotes? Is there some sort of push/pull valve? Why does the drawing show two lines?

The tractor came with a 3-spool loader valve. Two of the spools operate the loader via a single joystick. The third spool was spare. I purchased and installed the 3rd SCV kit - LVB25089. A drawing is attached. That 3rd (rear) SCV kit uses up the third spool on the loader valve. It has a push/pull lever and two lines to operate both sides of an implement's cylinder(s).

What do you think is happening inside the DO3 when the solenoid is activated? Does it do all the things that the loader control spool valve does? Specifically, lets say that the "a" circuit is activated to extend the cylinder. As it extends, the piston moves and forces fluid out of the other side of the cylinder. But circuit "b" is closed. Does that expelled oil have a path out? Where?

I believe that:

When the A solenoid on my grapple valve fires, it opens the A side of the grapple valve to the pressure on the subplate's P port, and sends that pressurized fluid to the A side of the grapple cylinders. At the same time, it opens the B side of the grapple valve to the unpressurized T port of the subplate to allow the B side of the grapple cylinder to empty back to the tank.​

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When the solenoid is uncharged again, the valve returns to neutral (closed) and the continuous flow resumes through the subplate (in the P port and out the T port), essentially bypassing the grapple valve entirely.​

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When the B solenoid on my grapple valve fires, it opens the B side of the grapple valve to the pressure on the subplate's P port, and sends that pressurized fluid to the B side of the grapple cylinders. At the same time, it opens the A side of the grapple valve to the unpressurized T port of the subplate to allow the A side of the grapple cylinder to empty back to the tank.​

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Does the schematic tell what it does? I was pretty sure I bought the right one for my application. Nobody said anything about needing a separate return line to the tank. In fact, I don't believe I have ever seen a D03 subplate that has a Power Beyond port separate from the T port. But I suppose they exist.

 

[rScotty]

Perfect. The schematic showing how it works matches your explanation of hour A & B work. We both agree that the T on the solenoid operated Grapple Valve is the unpressurized flow back to the tank when he solenoid is actuated..
So we are on the same page. We probably could have done this over a single beer, but of course this is more fun.
It is interesting that in the drawing, you show the T on the solenoid operated Grapple valve as a PB line. I now see your thought process - When the solenoid was NOT actuated, then pressure would just flow through the valve and out the T line so that line would be available as a PB line to the log splitter - which has a control valve (not shown) but with its return own line to the tank. Then when the solenoid was activated, the expelled fluid would be ... uh.... hmm....would still be fed to the splitter at very low pressure - but hopefully still at enough pressure so that it could make it through the splitter control valve and to the tank.

It is bizarre, but I don't see any reason why that wouldn't work - although i have no idea if you will be able to get eough flow to the tank after all that plumbing and losses to avoid getting some backpressure in one of the tank lines. And my experience is that backpressure from set of high resistance tank lines leads to odd behavior.

Consider that all those lines have resistance and resistance is additive. At some point the resistance adds up enough so that it acts as though you had deadheaded that pump.
I do not know at what point that the sum of all the fluid resistances puts more torque on the pump drive shaft than it can stand. But hydraulic pumps are rather high dollar items.

Here's an idea. Relief valves are cheap and adjustable. You've got some spare places you could put one or more. And 5000 psi glycerin damped pressure gauges are in the $20 range. Put one of each on that DO3 and cross your fingers that will protect the pump.
And keep an eye on the temperature of your hydraulic fluid. Resistance is heat, and hydraulic fluid itself has a defiinite temperature limit. Seals too. So you should also consider putting a temperature guage somewhere. Another $30.

I'm kind of curious myself.... hope you build it.
rScotty

 

[CTGuy]

I'm kind of curious myself.... hope you build it.

Thanks. I am in the middle of building it. I'll let you know how it goes. Also, another reason I chose that particular subplate is because it has big ol' connections. Most of the subplates I saw, used #6 SAE connections all around. This one uses #10 SAE for the T & P ports and # 8 SAE for the A & B ports. That allows me to use bigger hoses with less friction. In the end, I will only be adding about 3 feet of 1/2" hose and one 90-degree angle, plus the subplate. I doubt that will add much resistance, but I guess I will find out. Thanks again.