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This paper studies the proportional directional control valves design influence on the energetic behavior of a mid-power compact excavator. In particular, with reference to the hydraulic circuit actuating the primary workgroup, in the paper the hydraulic power metering performed with the boom cylinder proportional control valve is studied, and some design solution useful in reducing both the hydraulic power dissipation, and the power absorption from the machinery prime mover are highlighted. The analysis, experimentally performed for different operating conditions, is carried out highlighting the influence of a metering configuration both on the supply pressure modulation and on the flow-rate supplied to the actuator.

In this paper a lumped parameters numerical model is reviewed to study the meshing process of external gear pumps and motors, with the aim of highlighting the influence of some geometrical design parameters and operating conditions on inter-teeth volumes pressures. The inter-teeth space is modeled adopting a two-volume approach, properly tailored both for the pump and for the motor units behavior description. In both cases, the communications between the interconnected inter-teeth volumes and the high and low pressure ports are sketched as variable equivalent turbulent restrictors; flow areas have been determined as functions of the gears and of the meshing grooves main design parameters. The inter-teeth pressures, and the leakage flows, are calculated solving the incompressible and isothermal continuity equation, contemporarily applied to both volumes and properly combined with the classical turbulent orifice equation.

In this paper some design aspects related to external gear pumps balancing surfaces are studied, and some useful guidelines for designing bearing blocks balancing surfaces are suggested. In order to study bearing blocks axial balance, a numerical procedure for the determination of the pressure distribution inside the clearance bounded by gears sides and bearing blocks internal surfaces is firstly presented and applied. After, the influence of bearing blocks geometry and pump operating conditions on the widening thrust is highlighted, considering both constant and variable lateral clearance heights. Then, the computations are performed to evaluate the widening thrust variation as a function of bearing blocks relative tilt with respect to gears lateral sides, and both positive and negative bearing blocks tilts are evidenced and discussed.