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| The main difference between the two is the hydraulic pump. There are a very few exceptions to the rule, but in 99% of today's agricultural hydraulic systems.
OPEN-CENTER (OC) 1- the pump is usually a gear-type pump with a constant or "fixed" displacement,
2-the gear pump puts out a constant volume (fixed displacement) of oil for every revolution,
3-the pumped oil goes through a system of "open" valves that do not internally restrict or divert the flow of oil until the valve is activated, so the hydraulic system stays at a relatively low pressure until a valve is activated.
5- The pressure rise in the system is caused solely by the resistance of the hydraulic work to be done (i.e., the weight of the disk harrow against the hydraulic cylinder raising it)
6- when the work is done, the open center valve is returned to neutral, and the oil flow through the valve is unrestricted once again. The pump's flow doesn't change from neutral to full pressure; just the pressure in the system changes.
CLOSED-CENTER (CC) 1- the pump is an axial-piston pump with a control device (compensator) which can vary the pump;s output from almost nothing to maximum volume.
2- The pump's output per revoltuion is variable, depending on the "demand" fed back from the hydraulic system valves to the pump compensator
3- the pump's output flows to a system of "closed" valves that internally stop all flow through the valve until the valve is activated.
4- the hydraulic system's flow and operating pressure vary, and is determined by the load at the moment, which can be relatively low or very high
5- the pressure rise in the system is also chiefly determined by the resistance of the hydraulic work to be done, but this is exactly matched to the system's demand by the compensator,
6-when the work is done, the closed-center valves return to neutral, oil flow is shut off once again, and the compensator instantly adjusts the pump's output to match current system demands.
This explanation is over-simplified; I am not trying to get into the physics and engineering of even the oldest open-center hydraulic systems, let alone today's complex variable flow systems.
In brief you most likely will damage an open-center hydraulic system if you connect the remotes to a closed-center application such as that 455 drill, without getting the special kit to divert OC remote valve flow.
Edited by Redwrench 2/14/2008 22:27
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Open Center and Closed Center Hydraulics?
