In hydraulic equipment, a jet cavitation occurs frequently at points wherein oil flows through an orifice and a gap that is due to a high pressure and large pressure difference. These jets typically erode equipment surfaces when the cavitation bubbles collapse. Although the erosion characteristics have been studied for cases wherein jets impinge on surfaces at normal or oblique angles, cavitation erosion has not been studied in cases wherein jets flow parallel to the wall surfaces. This study uses the method outlined in ASTM G134-17, Standard Test Method for Erosion of Solid Materials by Cavitating Liquid Jet, to perform 8-hour-long erosion tests on aluminum specimens and to visualize cavitation jets in transparent acrylic specimens. We test specimens with chamfers and tapers in different orientations and compare the results with numerical simulations to better understand the mechanisms behind cavitation erosion. The inner walls of the chamfered specimens were partially eroded near the downstream chamfered edge, regardless of the chamfer location. During the testing time, the chamfered surfaces and outer surfaces on both ends were not eroded. Erosion pits were visible locally along the convergent and straight paths in the tapered specimen, but the pits did not appear in the divergent-tapered specimen. Visualization and numerical results offer some insights into the pressure dynamics that explain why divergent tapers seem to be effective countermeasures against cavitation erosion in hydraulic equipment.