Pumps can also be used as a motor, drive unit or key element in a variable speed drive

Paul Boughton

The QX system from Bucher Hydraulics can be used not just as quiet internal gear pumps, but also as powerful motors, high-accuracy flow dividers or as very reliable pumps for low-viscosity fluids.

A QX unit can also be used as a pump in one specified direction and as a motor in the opposite direction (known as two-quadrant mode), as a universal drive unit that can switch between pump and motor function and operate in any direction (four-quadrant mode), or as a key element in a variable-speed drive.

Their straightforward and robust construction makes these units the pumps of choice where quiet running, low pulsation levels and high operational
reliability are required.

All six frame sizes are designed for pressure ranges of 100, 160, 210 and 320bar, and for peak pressures up to 400bar. The geometric displacements extend from 5 to 500cm3/rev and their close and systematic spacing gives a range of 72 single pumps and 1764 double pumps. Including triple and quadruple versions, more than 10000 pump combinations are possible.

The principal components of QX internal gear pumps are pinion and internal gear ring, housing, and shaft. There are only three moving parts in each pressure stage, which results in low wear and long service life. The standard components of single pumps can be combined into double and triple pumps with the help of intermediate flanges. Thanks to the special design features of these internal gear pumps, the axial or radial clearances do not require any hydrostatic compensation.

The cutting-edge design delivers its full potential when operating with low-viscosity fluids. Even with viscosities lower than 1mm2/s (cSt), continuous pressures as high as 250bar can be achieved by connecting up to five pump stages in series. QXV pumps are used with diesel fuel, gasoline/ petrol, aviation jet fuel, brake fluids, Pentosin, HFC and HFA hydraulic media, and many other fluids.

The symmetrical design of the QX internal gear pump means that, with only minor modifications, it can be transformed into a drive unit that can be used in two-quadrant or four-quadrant mode. This unit offers numerous possibilities for application in both open- and closed-loop circuits. A current trend, and one that is particularly noticeable in injection moulding machine design, is the growing use of frequency-controlled drives, an application to which QXM internal gear drive units are also ideally suited.

Naturally, QXM units can also be used simply as motors. The special gear tooth geometry creates particularly good inlet behaviour, and motor speeds of more than 10000rpm are attainable.

Bucher Hydraulics GmbH is based in Klettgau, Germany. www.bucherhydraulics.com

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