This study examines the dynamic characteristics of different aspect ratios (length/diameter, L/D) of small hydraulic orifices. A homemade pressure square wave generator (PSWG) was employed to excite inlet pressure square waves The responses of time-domain and frequency-domain were measured by piezoelectric pressure sensors and a Spectrum Analyzer. Experimental conditions: At a pressure of 2 MPa, frequency was adjusted by the frequency converter to 200 Hz, orifice diameters range from 0.5 to 2.0 mm and lengths are from 0.5 to 3 mm (aspect ratios from 0.25 to 6). In the wave form of the time-domain response, a square waveform at the inlet of the orifice becomes a triangular waveform after the hydraulic fluid flows through the orifice. The pressure-drop via the orifice results in a delay of pressure increase and decrease. Results show a considerable pressure decay of over 90 % on the large aspect ratio of small orifices. For characteristics of dynamic control, it is necessary to improve hydraulic technology to reach the high precision field.
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