QDoes anyone know what the valve is called that Timberwolf uses on the back of the ram cylinder to bypass valve and go straight to the tank? Q
I couldn't find anything on the site referring to it, but it may be a fairly common industrial circuit using a pilot operated check or poppet from the closed end of cylinder directly back to tank. The pilot signal comes from the rod side of the manual valve. Anytime the cylinder is being retracted, the pressure to the rod side also pilots open the bypass and the high flow coming out of closed side skips the main control valve and goes directly to tank. (It could be done to both ports, for both directions, but there is no reason to do so on the rod side.)
Any pilot operated (PO) check valve or PO spool valve can work. A remote ported unloading valve (similar to what is in a two stage pump, but in an external body all of its own), or remote ported counterbalance valve, can all be made to do the same thing. Basically, any valve that can open a path to tank when piloted with a pressure signal from the rod side of the circuit.
This type of circuit could work well on a splitter when the load is always resistive and doesn’t run ahead of the control. If the cylinder can overrun (say a log lift going down), a PO check can work but it may be unstable and chatter. Counterbalance may work better, but beyond the scope of this discussion.
There is some explanation here from Bud Trinkels book posted on HydrPneumatics website
http://www.hydraulicspneumatics.com/200/eBooks/Article/True/45149/
Sun Hydraulics is a big name. Hydraforce, Parker/Sterling, Modular Controls/Vickers/Eaton probably all have them.
I haven't checked surplus center, they may have. They had surplus remote piloted relief/unloading valves, but only three left and I bought all three this summer at $10 each.
This type of valve is not something Northern Tool or Harbor Freight would have.
The reason for the unloading is to reduce the pressure drop back to tank in a large flow portion of the circuit. In industrial equipment the flow differences can be huge if the cylinder has a large rod compared to its bore size. Logsplitter, not so much difference, and I doubt worth the complexity unless you have a large cylinder and large pump flow.
When a circuit is FLOW limited, i.e. like most small pump logsplitters, flow at the cylinder is defined by the pump output. Retract speed is faster than extend because the rod side area is smaller. Same gpm into smaller area = cylinder moves faster.
However, the flow out of the closed side is more than the pump flow into the rod side because of the larger area, so there can be quite high flows out through the main control valve. Pressure drops can get high, flow forces can make the valve malfunction, but using larger valves can get expensive. Then this circuit can make some sense.
Bunny trail, but in an extreme case, the circuit can become PRESSURE limited and the retract speed is actually SLOWER than extend speed. This is due to the high backpressure pushing against the larger area on the closed side of piston. The balance of pump flow ends up going across the relief valve. Servovalve circuits all work this way, but they use pressure compensated variable pumps. Retract is slower than extend. Not common sense at all, but if you work out the math it is obvious why.
kcj
Like mine that's gotta be a biatch to move unless you hook it to something. Next thing is to put a piece of timber on that monster instead of kindling wood for a photo shoot :hmm3grin2orange:
) I do have a log lift on the processor that is real unique but I dont have a pic of it to show ya'll. 
