What is open loop and closeloop system?

Systems in which the output quantity has no effect upon the input to the control process are called open-loop control systems, and that open-loop systems are just that, open ended non-feedback systems.

- Hydraulic fluid will flow from pump to actuators i.e. hydraulic motor and actuators to pump continuously. Hydraulic fluid will enter at inlet of pump after passing through the actuators. One hydraulic pump might be used for driving the multiple hydraulic motor in case of closed hydraulic system. 

- hydraulic pump will suck fluid from reservoir and will deliver the high pressure fluid to the actuators i.e. hydraulic cylinders via passing through pressure relief valve , pressure regulating and flow control valve. After passing from actuators, fluid will go to heat exchanger and then reservoir and again pump will take fresh fluid from reservoir via its inlet port and this process will be continuous during operation of hydraulic actuators. 

If you ask about hydraulic systems so , Open system is : 1-Fluid Tank must 2-different pressure after and before the pump Closed system is : 1-no tank 2-no different pressure after and before the pump , the pressure is constant at any point on the lines Example: the blood circuit in humans.