Unlike other open-circuit hydraulic piston pumps, the XL Series from Denison Hydraulics, Marysville, Ohio (www.denisonhydraulics.com), has a smooth, round housing, so it is quieter.
It also lacks drum-type surfaces that amplify noise. Hydrostatic bearings give the compact pumps fast response times and longer lives. The pumps use static O-ring seals rather than gaskets.
The first model in the Series, the XL75, has a 75-cc/rev displacement pump with standard hydromechanical controls. A total of 10 models with outputs ranging from 10 to 260 cc/rev will be marketed over the next decade. They are aimed at high-volume, medium-duty applications, both mobile and industrial, needing high pressures (280 bar, 4,060 psi).