I run all my returns to a header, the difference being that my return header is made from 1-1/2" steel pipe with big Tees for each flow to come back together. Then it all goes through a filter on the return before the tank. Now my machine is totally different than your as far as flows so those sizes aren't comparable. You could probably return all your flow through a 1" pipe.
Read what Bunk said 2 or 3 times. I am going to restate what he said. The pump only moves fluid. In a open hydraulic system, the pump only builds the pressure that it needs to to perform a particular function. If all the valves are in neutral (not pulled) and working correctly, the flow is simply going through the pump to a valve, then to another valve (power beyond) then back to the tank through the filter. In neutral this pressure should be low.
As said before it you try to pump 20 gpm through a 1/4" hose or fitting you will develop (just a guess example) 700 psi. The Horse power required for the pump to make 700 psi is based on the flow rate of the pump and the amount of flow, which is controlled by the displacement of the pump. If you exceed the HP of the engine it will bog down. If you take that same 1/4" restriction and remove it and install a 3/4 hose the pressure may go to 100 psi (again just a guess example). This lowers the engine HP required and keeps fluids cool.
This is why we have asked you for the neutral valve positions to see if you have a restriction. You need to do that test, and you need to post a pic of how you plump the pressure gauge because I want to make sure you have it in the right location.
So in the example above lets say you are getting 900 psi on your inlet line to the first valve with it in neutral, and when you deadhead the lift all the way to the top the pressure goes up to 2500. That would mean that your lowest pressure you will ever see is 900 which is too much, it would also mean that your pressure relief on that valve is set to 2500. When you dead head the cylinder, the pump is still pumping but the fluid can't go to the tank because its directed to the cylinder. The pressure will quickly build. If you didn't have a relief valve it would quickly break something or stall the pump/engine. Since that doesn't happen (usually), what is happening is that when the pressure reaches a certain point the relief valve opens and lets the fluid go back to the tank. This will keep happening till the valve is released.
Now you have a flow divider. That means that you have one flow from the pump that is being split by the divider. Basically the divider puts a certain amount of fluid to each circuit. That fluid then flows as described above.
Your problem could be on either side of your flow divider, the only way to know is to see what is generating the pressure when it shouldn't be. Pressure = heat buildup
You need to check the following and write down the results, and let us know what you get.
1. Put Tee with pressure gauge into line from pump to flow divider.
Neutral pressure
wheel valve forward pressure
wheel valve reverse pressure
steering valve pressure in each direction dead headed
lift valve dead head pressure any direction
2. Put Tee with pressure gauge between the flow divider and the wheel valve
Neutral pressure
wheel valve forward pressure
wheel valve reverse pressure
steering valve pressure in each direction dead headed
lift valve dead head pressure any direction
3. Put Tee with pressure gauge between the flow divider and the steering valve
Neutral pressure
wheel valve forward pressure
wheel valve reverse pressure
steering valve pressure in each direction dead headed
lift valve dead head pressure any direction
4. Put Tee with pressure gauge between the steering valve and the lift valve
Neutral pressure
wheel valve forward pressure
wheel valve reverse pressure
steering valve pressure in each direction dead headed
lift valve dead head pressure any direction
5. Put Tee with pressure gauge after the wheel valve outlet before it Tees into anything else
Measure the neutral pressure
Measure the pressure when operating the valve on the lift at dead head
6. Put Tee with pressure gauge after the last valve on the steering/lift side but before the common return
Measure the neutral pressure
Measure the pressure when operating the valve on the lift at dead head,
Measure the pressure when operating the wheel valve
Now all this may not be possible based on your connections or practical, but if you get all this info I think we will be able to point to your problem immediately.
Also post some pics of your whole machine with all the lines visible. Hard to help with just a pic of the valve.
