Open & Closed Center Systems


  • Differentiate between the terms open loop and closed loop.
  • Read a schematic to correctly identify an open or closed center hydraulic system.

Terminology Clarified

Discussions around hydraulic system designs often result in confusion when terms such as open loop, closed loop, open center, and closed center are used.
Open Loop
Closed Loop

When we are talking about the loop, we are referring to the system as a whole. Open loop systems start and end at the reservoir whereas closed loop systems start and end at the pump.

Open Center
Closed Center

When we are talking about the center we are referring to the center position of a directional control valve. Open center valves connect the P and T ports when centered. Closed center valves block the P port from the T port when centered.

Open Loop Systems

An open loop hydraulic system is any system where all of the fluid starts at the reservoir and is returned to the reservoir.

The pump takes in fluid from the reservoir, then sends the fluid to the valves and actuators, and then ultimately, back to the reservoir via a filter.

Now that we know what an open loop system looks like, let's have a look at open and closed center systems that are common in open loops.

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