To make hydraulic excavator more efficient, numerous studies to reduce throttling losses being major losses in hydraulic systems have been conducted. However, less throttling losses are likely to lead to inefficient operation considering the ICE efficiency map. In order to solve this issue, a hydraulic system called STEAM being one of the constant pressure systems has been proposed to improve overall system efficiency. Important features of this system are that the ICE can be operated at the most efficient point, and recoverable energy is allowed to be recuperated by accumulators. However, it might be difficult to be accepted by the industry due to using a multitude of valves. Alternatively, a three pump open center system allows engineers to design simple layout of the machines and enables machines to provide fluid efficiently by three pumps with less throttling losses. It seems that there is a new possibility by merging both architectures. Therefore, the purpose of this study is set to design a new hybrid architecture which combines an open center system with STEAM. In this thesis, basic principles and a design guideline to develop a hydraulic circuit of the new hydraulic architecture are discussed. To confirm the improvement of the system efficiency, simulations and experiments with the test rig are carried out and achievements are discussed.