I have to extend and retract a cylinder (and i must be able to control it) with out the use of a DVC this can be done using 1, 2 or 4 componants. i was just wondering if someone could give me an opinion on whether or not the circuit i have come up with will work or if i am on the right track. i am not the best at hydraulics.  (*note: a vertical cylinder may be used instead of the horizontal)
thanks

500psi system pressure (the pump has a relief valve already incorperated) goes to both ends of the cylinder (horizontal with no load on it). the blank end will have a T on it also going to a neelde valve which then goes to the tank.
when the needle valve is closed(no flow going though) the pressure will build up on both sides of the cyclinder. because of the area on the blank end, the fluid will be pushed out from the rod end and back to the blank end (causing regeneration). the cylider extends.
when the needle vavle is opened, the fluid on the blank end will travel back to tank and the pressure will build up on the rod end. this should cause the cylinder to retract.

The pressure drop through the valve being equal to or more than the pressure required to move the unloaded cylinder, then yes the cylinder will move as you suggest.

In actual fact, the force required to break the seal contact with the bore of the cylinder will be more than the pressure drop through the valve.

The pump will put all of the oil on the floor!

Its a two to one cylinder so it would stay extended i guess. do you have any ideas? i have spent a few hrs trying to figure out something but so far thats the only one i thought would work  
the componants i have are : sequence valve, reducing valve, 2 needle valves, 1 flow control valve and two check valves.

yes there are alot of similarities in the theory but for me, applying the theory to a wiring diagram is much eaiser then to a hydraulic one.  right now we really dont cover DC theory either. mainly Ac because that is the most common  in the indusrty. i think we need a little more time in the class to really understand and maintain the knowlege.
sounds like you have a lot of fun doing your part time job.

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