MinnesotaEric
Super Member
What this photo is shows is that on an open center* hydraulic system hydraulic pressure (P for pressure or power) flows throught the valve if not divered to run the lift or curl functions of the loader. Flowing out of the loader valve, a double-acting divertor valve is installed inline on the hose between the three point valve and the loader valve. This divertor valve is also open center (meaning that when at rest, it too allows hydraulic P to flow straight through. You'll use a DO3 open center subplate, and a double-acting electric over hydraulic divertor valve to provide your tractor's loader with a third function.
Your base third function diagram looks like this:
Unless you buy a kit, when ordering a DO3 valve, you want is hydraulic diagram of the valve to match what I've drawn in the diagram above (open center, work ports A and B blocked in neutral).
The valve is mounted to a subplate. The subplate has four hydraulic ports: P for fluid coming in, T (tank) for fluid going out (which gets tapped into the three point's inlet), and A and B for doing work. You'll want a DO3 subplate as well. Here is the very subplate you'd need, a SFP 10101 DO3.
On my tractor, I mounted my subplate atop my transmission out of harms way. I used LED DIN connectors so that when power was applied, I'd have a tell-tail light to help determin faults if the third function failed. Power to activate the double-acting valve come from solid state relays (for low failure rates) wired directly to the battery. Control power came off of a piggy-back plug on the radio at the fusebox which I fused to 5 amps and that ran through the switches on the joystick and then to the control side of the relays.
Hoses where all custom sized using my local hydaulic jobber to crimp them up. I made a total of three mounting plates and included a quick disconnect for removing the loader while keeping the third function's hard lines of the loader.
* Closed center is like the water system in your house: always under pressure and fluid does not move till the valve is opened. Open center is like a spray pump where the water goes round and round the system till it is needed, then diverted off in another direction by a valve.
