**Chenggang Yuan, Vinrea Lim Mao Lung, Andrew Plummer and Min Pan \***

Centre for Power Transmission and Motion Control, Department of Mechanical Engineering, University of Bath, Claverton Down BA2 7AY, UK; cy466@bath.ac.uk (C.Y.); vlml20@bath.ac.uk (V.L.M.L.); arp23@bath.ac.uk (A.P.) **\*** Correspondence: m.pan@bath.ac.uk

Received: 18 December 2019; Accepted: 4 February 2020; Published: 10 February 2020

**Abstract:** The switched inertance hydraulic converter (SIHC) is a new technology providing an alternative to conventional proportional or servo-valve-controlled systems in the area of fluid power. SIHCs can adjust or control flow and pressure by means of using digital control signals that do not rely on throttling the flow and dissipation of power, and provide hydraulic systems with high-energy efficiency, flexible control, and insensitivity to contamination. In this article, the analytical models of an SIHC in a three-port flow-booster configuration were used and validated at high operating pressure, with the low- and high-pressure supplies of 30 and 90 bar and a high delivery flow rate of 21 L/min. The system dynamics, flow responses, and power consumption were investigated and theoretically and experimentally validated. Results were compared to previous results achieved using low operating pressures, where low- and high-pressure supplies were 20 and 30 bar, and the delivery flow rate was 7 L/min. We concluded that the analytical models could effectively predict SIHC performance, and higher operating pressures and flow rates could result in system uncertainties that need to be understood well. As high operating pressure or flow rate is a common requirement in hydraulic systems, this constitutes an important contribution to the development of newly switched inertance hydraulic converters and the improvement of fluid-power energy efficiency.

**Keywords:** digital hydraulics; switched inertance hydraulic systems; high-speed switching valves; pressure booster; flow booster; efficient fluid power
