Open center or closed center hydraulic system: which one is on which vehicle?
In an open center system, oil returns freely to the tank when the valve is in neutral; the system waits at low pressure, generates less heat, and is built cheaply with a fixed displacement pump. In a closed center system, the valve blocks flow in neutral, the variable displacement pump destrokes, and the system generates pressure on demand. Open center is generally found on tractors and small construction machinery, closed center on large mobile machines.
Open center: The pump continuously delivers a fixed flow rate. When no lever is used, this flow returns to the tank through the center passage of the valve. Only pressure equal to line losses builds up in the circuit. Its advantage is simplicity and cost; its disadvantage is that the pump runs continuously even when no work is being done and generates heat in long lines.
Closed center: The valve blocks the inlet port in neutral. Pressure rises, the variable displacement pump reduces its stroke to nearly zero flow and maintains only standby pressure. When the lever is opened, the pump produces the flow rate that is demanded. Its advantages are efficiency, the ability to drive multiple functions simultaneously, and high pressure capacity; its disadvantages are cost and complexity.
How to tell in practice:
- If the hydraulic lines heat up while the engine idles and the pump makes continuous noise, it is most likely open center.
- If high standby pressure is measured in the lines in neutral, it is closed center.
From the point of view of a retrofit kit that moves the manual lever externally, this distinction does not matter: the kit does not enter the hydraulic circuit and drives the same lever the same way regardless of the center type.
Full coverage of this topic: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods