Still new to hydraulic systems , Could i not use a regular hydraulic pump ran of the engine , then from that pump go to control valves and to each hydraulic motors ? Why is it better to use variable displacement pump vs any other pump ? Any help in helping / advice is great .
You could go that route, but a few things.
I'd suspect the hydraulic pump is sized to equal out the power for drive and lift/tilt. If you have a pump that is too big, when you lift the arms and drive forward the motor will stall, so they will have worked that out so it may use a max of say 20% of total available engine power, so you'd need a bigger pump to use almost 100%
A vairable displacement piston pump is ideal for drive systems due to the fact it's more effecient (you pump fluid ONLY when you need it so no wated heat or energy waste) No valves are required for this setup, in the neutral position no fluid moves, forward, you move the plate one direction to pump fluid, same with reverse.
Using valves to control drive motors does work BUT it;s not smooth, you will never get the nice smooth operation that you will with a hydrostatic drive. The biggest issue you will have is heat, your pump will be pumping fluid at all times, this will heat up, no matter what you do, it will heat up unless you have a large oil cooler. Remember the piston pumps only pump when required and will only pump as much fluid as required, so it cuts down on a lot of heat.
Again, i'm not saying it can't be done, it will just cost you too much, and the outcome will not work as well as a hydrostatic machine would.
