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It is a CLOSED-CENTER pump. It builds, and holds constant pressure, and then "goes out of stroke". The line that is pumping all the time is for the power steering and servo cylinder/valve for the hydraulically actuated variable ground drive. Simply cap it. (They DID use a pulsation damper on that line.) One port is for the "return" line from the power steering and variable speed servo. The internal valve is SINGLE ACTING, and there is only ONE cylinder port... with the control valve moved one way, oil is pumped to a SINGLE ACTING cylinder, to lift the header. When the valve is allowed to "center", the load (the header) is held in place. When the valve is moved the other way, oil is allowed to RETURN into the pump/reservoir, and the header drops by it's own weight. By using an external CLOSED CENTER valve, fed from the constant flow port, and returning into the other port, you could operate a double-acting cylinder, while ignoring the internal single-acting valve, and capping it's port. I hope I have explained this in an understandable manner!!! (I have two of the darned things, if you need any more!)
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