Nowadays, hydraulic systems have a wide range of applications in our daily life. The common applications of the hydraulic system perform lifting, holding and gripping. Hydraulic systems will transmit power using the pressure of incompressible fluids. In most of the cases, the fluid is taken from a reservoir using pumps. These are simple, safe, and economic systems that can be controlled easily and accurately. Providing constant force regardless of the speed is an advantage of the hydraulic system.

Open loop hydraulic system and closed loop hydraulic system are the two types of hydraulic system. In an open loop system, when the actuating mechanism is idle, there will be fluid flow but no pressure. For a closed loop system, when the pump operates there will be pressure for fluids. The fluid will flow continuously between the pump and the actuator without entering into the reservoir for a closed loop system. Whereas, for an open loop system, the fluid flow from the actuator to the reservoir and then fresh fluid flow towards the pump inlet. Open loop systems use a directional control valve and closed-loop system use an additional pump called charge pump or feed pump. Less heat generation is the advantage of open loop hydraulic system and precise response of actuation is the advantage of the closed-loop hydraulic system.

In order to eliminate the presence of foreign contaminants and to assist fluid flow, all open loop hydraulic circuits will use sealed or pressurized reservoirs. Conventional open loop hydraulic circuit used a large reservoir to allow air bubbles to escape from the fluid used.

The internal combustion engine, bomb calorimeter, reciprocating air compressor, refrigerating systems, piston-cylinder arrangements without valves, Rankine cycle(operating fluid is continuously evaporated and condensed), etc.. are examples of the closed-loop hydraulic system. Turbine, compressor, pump, boiler, heat exchangers, etc.. are examples of the open loop hydraulic system.
For simple applications, open loop hydraulic systems are efficient and cheaper. But for complex applications having independently working multiple subsystems, closed-loop hydraulic systems will be a better choice.

Also, Read: Examples of hydraulic system

Open and Closed Hydraulic Systems Difference

• Open loop hydraulic systems are suitable for low-pressure applications(below 3000psi) and closed loop systems can operate under high pressure with less fluid flow.
• Closed loop systems have more control options and the direction can be reversed without using valves.
• Closed loop systems are more difficult to diagnose and repair compared with open loop systems.
• Continuous pressurization of the system is eliminated in the case of an open loop system.
• Some designed hydrostatic transmission will be there in closed-loop systems.