This shows the actual valve diagram you should see when ordering a valve....and explains the difference between open center and tandem center valves.
Intro to Directional Control Valves.
A and B are the work ports. And when the valve is centered (not being used), if you want the cylinders to stay where they are, you need A and B ports blocked off....IE: tandem center. A true open center opens them ports to tank and the cylinders are not held by the valve.
IF you look at the diagram/manual for the valve you sent me in a PM, It does show it being tandem center and power beyond capable. The diagram for the single spool valve is on the first page. and further down the page they show the PB adapter you need to get as well. It will thread into one of the tank ports.
So on the diagram.....Which I know is hard to follow if you dont understand hydraulic schematics.....shows pressure coming in and going straight out the T2 port which is PB. ANd the A and B ports are blocked off in neutral which is what you want. When the valve shifts either direction....PB flow is cut off.....and P goes to either work port A or B.....and the work port that pressure is not going to is free to return to tank through T port and NOT the T port which would be PB if the plug is installed
So looking at that diagram.....This is what it looks like
View attachment 759411
And in neutral.....Red is pressure passing through to PB. Notice the A and B ports are blocked so the oil in the cylinders cannot excape
View attachment 759412
When shifted (you have to visualize square 1 or 2 shifting into place of cube 0)....the flow would look like:
Notice how work port A is now receiving pressure to move the cylinder, while port B is open to return the oil discharged from the cylinder back to tank, and PB flow is cut off.
View attachment 759416
So when looking for a valve.....first and foremost you want one that is PB adaptable.
Second is you want to see that A and B port is isolated when in neutral like this:
View attachment 759417
And NOT one that is open to allow A and B to return to tank like this, which I suspect you may have.
View attachment 759418
The true open center valves are commonly used for hydraulic motors. Dont want to muddy the waters of your understanding of what you need, but when a valve is opened and a hydraulic motor is spinning.....if you had a tandem center valve....as soon as you let the valve return to neutral, you block off the flow of oil at the work ports A and B. This means that whatever the motor was spinning....has to stop IMMEDIATLY. Some things just cant do that.....think about the inertia of a rotary cutter on the front of a skidloader for example. The inertia of the cutter still trying to spin could cause a huge pressure spike and blow hoses. So true open center which is sometimes called "motor spools" allow it to spin down slowly. Thats not the only way to make that happen, and not the only use for a true open center valve....but just one example to help you inderstand.
I honestly dont know what logsplitter valves are. Whether they are tandem or open center doesnt really matter because they arent designed to hold a load like a loader.....and being a horizontal cylinder.....gravity isnt making it move on its own when in neutral.
Id still like to see a diagram or know just what valve you purchased initially to appease my curiosity. But at the end of the day.....get a PB capable tandem center valve (even if they dont use the term "tandem" just look at the diagram). ANd plumb it as I mentioned and you should be all set