Novel pilot pressure-controlled two-stage flow-distribution radial piston motor

Hydraulic motors provide low-speed stability, system flexibility, and cost advantages for many industrial applications. However, conventional flow-distribution systems have limited reliable high-pressure operation, e.g., Staffa-type low-speed high-torque motors typically operate at pressures ≤25 MPa. To address this limitation, in this study, a novel pilot pressure-controlled two-stage flow-distribution radial piston motor was developed, in which the main flow is apportioned by pilot-operated seat valves to improve sealing compared with a conventional spool or plate distribution system. System behavior was examined by performing AMESim simulations to evaluate the steady-state torque and volumetric responses. The simulation results showed that the concept can tolerate operation up to 30 MPa with acceptable trends in torque and volumetric efficiency. A prototype with a geometric displacement of 207 mL/r was fabricated and bench tested to validate the practicality of the configuration. Prototype tests were primarily conducted as feasibility checks. The experimental measurements showed smooth operation and volumetric efficiencies of up to 85% under low-load conditions, which confirmed the viability of the pilot pressure two-stage distribution concept. However, at elevated pressures, the leakage arising from limited manufacturing precision, undeveloped distribution optimization, and pilot-signal dynamics substantially decreased the volumetric efficiency (approximately 45% at 18 MPa). The results showed that the developed pilot-operated seat-valve two-stage distribution system addresses the key sealing limitations of traditional designs and establishes a feasible route for high-pressure radial piston motors. Future improvements in sealing, machining tolerance, and pilot-stage dynamics will enable high-efficiency and high-pressure performances.