getting the right part

I need to replace the control valve assembly on my 445 Moline. It is a pto powered pump and two control valves for the bucket and loader. I know just enough about hydraulics to be dangerous and I want to make sure and get the right part. I would like to add a third valve in case that I wanted to add a cylinder in the future. I don't know for sure the difference between closed and open center hydraulics. Could someone help me out to make sure I order the right part?
Thanks,
Ted

I don’t know what system your tractor has I’d guess open center .
Hydraulic system

Surplus center sells valves that can be converted from open center to closed center with a conversion plug .

I agree with the guess sv made that your system is open center. The pump in a closed center system is more complex. Is there any brand or other ID on the pump that might help identify what you have. I assume by your explanation of it being a PTO pump that it is not part of the stock hydraulic system of the tractor. Is it possible to post a picture of it? One way to determine what you have may be a little messy, but can you determine which hose returns fluid to the pump unit from the valve? If so you could disconnect it and direct the flow out of the valve into a clean bucket. Then start the pump, if oil flows continually out of the valve you have an open center system.

As far as I know all 445 MMs were made in the late 50s, Closed center hydraulics were not around very much back then.

I agree with the others. The closed center demand driven hydraulic systems are built into modern tractors and have complex pumps and complex valving. Neither is likely to be found on a PTO pump. Open center valves have an intake port from the pump, and a return port to the reservoir, that are connected (open to each other) when the control handle is in the middle of its movement. This allows the pump to just push oil right through the center of the valve creating zero pressure. Two other ports (usually on the ends) connect to cylinders or hydraulic motors. When the lever is moved, the passage through the center is blocked off causing the flow to go out to the cylinder on one hose, and back to the reservoir from the cylinder on the other port.
Closed style valves do not allow oil to flow through when in the middle position. This would immediately cause your pump to go to max pressure and get things very hot very rapidly. Go with the open center valve. If you want a third valve, buy them all as a stack of valves at one time. The open center type can only be used one valve at a time when operating a loader, so don't use more than one handle at a time. Jim