The upper 'chamber' in the valve assembly, the smaller and not the 'main' or larger one, has a valve that sits against a plug there. 
Mine is stuck and I believe that is the reason that my blade will not stay raised. I work on alot of automotive, (read truck), machines along with tractor and farming equipment, but not much hydraulic items, so I am a little leary of messing this up in trying to free it. There are no soft parts in there so have applied some PB Blaster and set. Problem for me is how to apply force in this blind hole without messing up the valve or the chamber. Picture shows the valve. It is fairly shallow but needs to be pulled back out. 
When the valve assembly was detached from the pump there were a few scant drops of water evident that could have been trapped somewhere inside, not sure. Probably would have been enough to cause this problem, perhaps.
Are there some techniques or tricks in this situation? Been waiting for an 'aha' moment to strike, but hasn't happened, so am open to ideas. Haven't tried any heat yet either. Open to ideas. . ...
Will have to resize some pics 

You could try a small mapp gas torch and heat the housing around the valve.

Will give that a go, Rome.


(Aside , Looking for a good photo resizer if anyone has a good one)

When I have encountered something in a blind hole I have drilled and tapped a hole behind it to fit a grease zerk in it and used a grease gun to force it out. Then just plug the hole.

Making a note of this Jim.
This valve reminds me of trying to get a pilot bearing out of crankshaft !

many things have been shifted by the hydrualic power of grease. and its relatively gentle and even pressure.

i have heard of engines with stuck pistons being freed by bolting a plate over the bore and adding grease or oil.

Trainz, I have a grease zert cleaner that uses that principal. Works well.

Got this one out over the weekend. After the PB blaster soaked a day or so; I used a little heat to the body around the valve and then found a small curved pick tool and inserted in a small port or hole in the end of the valve and was able to twist it some. Afterward it was only a matter of working it forward and back in small degrees till it came out.
The chamber seems to have been slightly gummy with a residue, but the valve itself was in good shape.
Bad news is the pump looks like it is trashed........
Thanks for the replies, all
yellerc@