Attn: Jeff Jackson: Super M Hydraulics Part 3

This is either going to make things clearer or confuse the heck outta you :)

From your last response to me, it sounds like you're using the belly pump as a reservoir only. It sounds like it's using that drilled hole that I mentioned earlier as the pickup, and the drain as the return, or vice versa. It also sounds like you don't ever pull the belly pump lever on the side of the tractor, but instead use a separate spool valve. Good. The picture is getting clearer.

Dad put a 5 gallon reservoir under the fuel tank of his Super M, but he doesn't have a belt pulley drive, and the tank does kinda stick out from the right side a little.

2.8 gallons will be better than a belly pump reservoir with the pump still installed. I'd go for it, and leave the belly pump intact. You'll either have to plug the two holes in the reservoir or connect them with a hose (personally, I'd plug them). You could then restore and use the belly pump as it was originally intended, for single-action hydraulics.

OR, you could get really fancy and combine the external tank with the belly tank. For this you gotta figure out which is the suction and which is the return. Install the new tank, then run the bottom outlet from this tank down to the return hole in the belly tank. Leave the pickup line from the belly tank to the live pump. Leave the line to the spool valve, and add additional spool valves by connecting them to the OUT port on your existing valve. Run the OUT port from the last spool valve to the top port on your new reservoir.

BTW, double-acting spool valves can also operate single-acting cylinders.

Pressure from the live pump is going into the belly pump control valve, then is dumping straight into the belly tank.

One thing people keep telling you is to Tee the pressure line off. You can't do that. This is an open center system, which means the hydraulic fluid flows straight through the system unless you're pulling the lever on the valve. If you put a Tee in the line, you'll never get any pressure because there will always be an open path back to the reservoir.

Nope, you MUST connect it this way:

RESERVOIR OUT --> LIVE PUMP --> VALVES --> RESERVOIR IN

If you continue to use the belly reservoir, you can simply plumb your new spool valves into the pressure line that runs from the live pump back to the belly pump.

The tough part will be setting this up with an external reservoir AND allowing you to still use the belly valve...

I think you can do it if you run the suction line from the belly reservoir to the return port on the new tank, then run the suction port from the new tank to the live pump.

Steven's right that a spool valve with float will work best with single-acting cylinders. You can use a basic double-acting valve, but for lowering the cultivators, you'll be forcing oil past the relief valve. It works, but it does lug the tractor down and puts stress on the pump.

Quite the can of worms we opened up, eh?