Single acting valve does not work correctly

[tree grower]

I posted my problem on Build it Yourself, but was unable to elicit a solution. To operate the snowplow setup on my little Ford 1210, I have a single-acting Prince valve attached with quick couplers to the hydraulic manifold--see pics. In the setup as pictured the valve allows the plow cylinder to collapse only if the tph links are lowered all the way . If the links are raised a little, the SA valve has working pressure in both (lift and lower) positions. What baffles me is that the tractor usually has a FEL with the manifold set as pictured, and it works just fine and the tph links raise and lower just as expected. I recently removed the power beyond hose from the loader valve, and plugged the pb return line in the manifold-see pic #1633. I really can't see a defect in the new valve. Is it possible there is an internal malfunction in the manifold? Diagnosis and recommendations requested.

 

[LD1]

HArd to tell without being more familiar with the hydraulic flow on THAT tractor....and/or having a hydraulic schematic.

But I am guessing that "manifold" that originally supplied a front loader.....used power beyond out of the loader valve to continue onward to feed the 3PH.

With the 3PH fully lowered....there is no backpressure on the return path of the hydraulic fluid out of your single acting valve.

Hopefully someone with more knowledge of the hydraulics on that series will chime in

 

[tree grower]

I can't dispute your thoughts, but the mystery is in the tractor's history. It was new in 1986 and used as an estate mower--no FEL. I bought it in 1992, and installed the loader. The valve is a two spool, open center, four way valve. With the manifold set as pictured, the loader and tph worked fine for years. I removed and re-attached the loader more than most owners, but everything always worked as expected. In the late 90s I activated the power beyond function, and needed to plumb in another return line into the manifold. As I recall, the main return line went into the extra port and the return from pb went into the main return port. I recall not understanding why, but those were the instructions. As such, all the loader functions worked properly, as did the tph. I recently discontinued the pb function, plugged the pb port in the loader valve, and switched the main return line from the extra port to the main return port. I added the new SA valve, and have the problem described in my OP. I suppose I could switch the return line from the main return port to the extra port, but I shouldn't have to. Further input requested.