Technical Help .   OPEN CENTRE CIRCUIT Most common type of oil circuit Oil is pumped from the oil reservoir through the control valve and back to the tank in a continuous flow CLOSED CENTRE CIRCUIT Common on JD tractors with piston type pump. Oil is pumped to control valve (dead end) until it reaches working pressure. At this point the pump stops pumping oil - only when the oil has somewhere to go (ie. control valve is activated and work cylinder moves) does the pump resume pumping oil. There is no continuous flow of oil. Only spent oil from work cylinder is returned to reservoir. OPEN CENTRE CIRCUIT WITH POWER BEYOND   With Power Beyond kit fitted it is possible to fit a control valve in the existing hydraulic system without affecting the operation of either new control valve or existing system. Flow is maintained to both valves during operation CLOSED CENTRE CIRCUIT WITH POWER BEYOND   Same as closed centre hydraulic system. No need for special kits to have power beyond.