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Without changing the original valve control hydraulic system, a kind of hydraulic transformer, called four-port hydraulic transformer (FHT), is proposed to recover the energy loss caused by system throttling. The remarkable feature of FHT is that the flow rate at inlet and outlet ports are equal. This means that FHT can be connected into the load circuit of hydraulic system to recovery energy without refreshing flow rate. This paper investigates the flow characteristics of FHT, including instantaneous flow rates, average flow rates and flow pulsations in each port. The relationships between the structure of port plate and the flow characteristics are given. The variation rule of number of plungers connected to four ports is shown, and the relationship between the variation and the flow pulsation is revealed. The simulation results show that the flow rates and displacements of symmetrical ports are same, and the instantaneous flow rate of symmetrical ports has the same rule. The results also show the frequent changes of the number of plungers connected with each port lead to more flow jump points in instantaneous curves, and the jump point is the basic cause of its loud noise. The test shows that the flow rates of measurement data of the experiment are very close to the theoretical analysis, proved the theoretical analysis of flow characteristics for FHT are appropriate and reasonable, which has a certain reference for the development and energy-saving application for FHT.

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