I finally got a number to the engineer (at my company)that specs these valves, I plan on giving him a call tomorrow. I still think just hooking up a garden hose and running some water thru it will give me the info I need. If it doesnt run out, with the extra port plugged, its closed center, if it runs out the extra port and not the excess port, its open center with power beyond. If the water runs out the out port and the extra port. If i plug the extra port but remove the plug and it runs out the out port, it open center. I know the a/b ports run to one hydraulic motor for forward and reverse. I should be able to shift the spool and water run out either a or b. If i connect the two a/b ports to make a loop and shift the valve, water should run out the out port. If i loop a/b,reinstall the power beyond plug, but dont plug the extra port, and shift the valve, the water should run out the out port. If I do all of those things and everything works as described, I think it would be safe to say the valve is a open center valve. Now f I leave the power beyond plug installed and plug the extra port, and water runs out the out port, I might have a problem as i am sure the reliefs should be high enough that my garden hose wouldnt dump over the reliefs back to tank. If there s some other way to double check this valve, I dont know what it would be.