What is the difference between closed and open centre hydraulic systems?
We will try to answer it here.
Let’s start with closed centre systems
Closed centre hydraulic systems operate on the same constant pressure with variable flow. When the valve is in ON position/open the oil circulates through it to be then returned to the reservoir.
Once the valve spool is stroked, the flow focuses on a load and pressure is created.
In this system, turning the valve OFF will stop the flow at the valve port.
This causes the system to hold this pressure and not return it to the reservoir.
Pressure in this system increases up to the settings of your hydraulic system but once it gets higher than the system settings, the flow decreases.
Open centre hydraulic systems.
Open centre hydraulic systems let the oil flow travel through the valve ports to the reservoir even when the valve is in OFF position. As the name suggests, this system is open so unlike closed centre systems, here the flow through the valve and reservoir is constant even at no pressure.
When the valve is in ON position the oil circulates through the ports and then returns to the reservoir but because of the load sensing system that recognizes the flow and sends a signal to the pump, this creates pressure. This pressure then increases as per the system needs until it reaches the relief settings.
In open centre systems oil flows continuously through the directional valve regardless of it being used or not. In closed centre systems oil flows only when the valve sends signal to the pump, so this system is not producing large displacement of oil while not being used.
Open centre systems tend to be less expensive because of the fixed displacement pump being used as opposed to closed centre systems with variable displacement pumps. But closed centre systems albeit more expensive might be more efficient, as the oil is not being sent through the valve in Off position meaning there is less energy and fuel used.
It is important to understand and be able to recognize the system you are working with so you can choose the loader valve that suits best.
It is worth remembering that in an open centre system, flow is continuous, and pressure is variable
– which is the opposite of a closed centre system where the flow is variable and the is pressure continuous.
Hydraulic Planet offers loader valves for both systems.
Our closed centre loader valves also known as load sensing are manufactured in two sections with load sensing circuit and check valve for each section.
Open centre loader valves are also manufactured in two sections but with parallel circuit. Each section also contains a check valve but only the open centre valve contains preset for high pressure carry over plug (HPCO or also known as “power beyond”) that enables the pressure to be carried over to an additional valve- in most cases another directional control valve.
Check out our article on the compatibility of Hydraulic hose and fittings Here
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