A variable delivery hydraulic pump system equipped with a power match control can effective save in saving energy and minimizing power losses. This power match control system provided with a load sensing (LS) valve senses the pressure differnce between the pump and load. The valve keeps the differnce at a certain value. The pressure diffiernce may be set at any value by the LS valve and the flow rate of the pump is controlled by the throttle and LS valves, irrespective of the load pressure. This paper discuss e s the establishment of a mathematical model for the pump with a power match, simulation and testing of the pump system.

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The performance of a newly developed bubble elimination system is an a lyzed. The system consists of a circular body for a swirled flow supplied tangentially, equiped with a throttle valve downward and a valve for discharging bubbles upward.
A strong swirl superimposed on an averaged laminar flow during the initial state is found to decay exponentially with the distance from the entrance at the far downstream. As a result, for Reynolds numbers greater than a suitable value an adverse pressure gradient is produced, exerting a backward force on the bubbles to be discharged. In additio n, universal velocity distributions and pressure contours downward are shown.

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This paper describes the effects of the asymmetricity of a pneumatic cylinder on the frequency characteristics of a valve-controlled cylinder system. Theoretical analysis is carried out on the system, wherein a valve, which has lap unevenness (i) and mean underlaps ( Δ, Δ'), is used, and an asymmetric cylinder which has an intertia load with Coulomb and viscous frictions is used, where the flow rate versus the pressurec haracteristicsc urvesf or the valve are approximatedp artiallya s polynomialso f degree 3 of the pressure ratio.
The effects of ratio of piston effective areas (r_am), lap unevenness, amplitude of the input sinusoidal spoold isplacement( y_o)and Coulomb friction of the asymmetric cylinder on the frequency responses of the system are studied.
Even though the valve has even underlaps, a suitableb ias ( δ) is necessary to the spoold isplacemen to keep the mean piston position of the asymmetric cylinder at some fixed point. The normalized value of bias (δ_o) changesa ccording to the changes of r_am, y_o and i. The(δ_o) versus frequency characteristics are studied. For an underdamped system, the value of δ_o has a peak around a resonance frequency.

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