Compact pumps offer higher flow

April 1, 2004
Two new pumps from Sauer-Danfoss are helping mobile-equipment designers meet today's demand for compact, quiet, high-performance machines.
Series 45 open-circuit piston pumps feature high flow, fast response, and quiet operation.

Two new pumps from Sauer-Danfoss, Ames, Ia. (, are helping mobile-equipment designers meet today's demand for compact, quiet, high-performance machines. Part of the company's Series 45 line, the new open-circuit piston pumps, Frames E (100 to 147 cc) and J (45 to 75cc), offer several sought-after features in mobile-hydraulic systems. For instance:

Compact size. "Based on maximum product dimensions, the Series 45 pumps are smaller than much of our competition by up to 15%," says Stuart Archer, product manager. Eliminating a bias piston in some models and redesigning swashplate bearings and pistons have all contributed to a smaller package size. "For the OEM and end user, the benefit of small package size is real estate," says Archer. Space becomes a premium as machines grow more complex. Thus, the Series 45 pumps leave more room for other system components.

Quicker response: The pump's servo pistons are located near the pump controls. This speeds response because it minimizes the flow path for the control oil and produces benefits for load-sense, pressure-compensator, electrohydraulic, and other types of control. "Close proximity helps eliminate the effect of bulk modulus and reaction time," says Archer, and minimizes time lag between an input signal from the operator and a change in flow at the pump.

Low noise: Quiet operation is essential to meet vehicle regulatory requirements and reduce operator fatigue. To minimize noise levels, Sauer-Danfoss used analytical tools to optimize valve-plate performance (torque and pressure ripple) to reach the best noise level.

One-piece housing: A single-piece housing assembly maximizes housing strength, reduces stress points, requires less machining and fewer parts, increases rigidity, and minimizes potential leak points on the pump. "All these features help increase robustness and quality," says Archer. Sauer-Danfoss applied DFM (Design For Manufacture) principles by including manufacturing and assembly engineers throughout the design and development process, he notes, which streamlined manufacturing once production began. "Total costs actually decreased due to reduced assembly time," he adds.

Higher speed: "Frames E and J were developed with state-of-the-art design and manufacturing techniques, including computational fluid dynamics, creating pumps that can withstand higher input speeds than pumps made from traditional designs," says Archer.

Pump input speed limits are a function of several factors, he explains, but one of the major hurdles is "fill." In other words, how quickly oil can enter the pump without cavitating. "CFD lets us closely analyze and model inlet-flow passages to optimize the design for naturally aspirated inlet conditions, that is, with no charge flow. Of course, the major benefit of operating at higher input speeds is flow," Archer explains. Higher operating speeds may permit the use of smaller pumps, which can reduce system costs. "For example, a 51-cc pump may run at a maximum speed of 2,500 rpm, giving a flow of 128 lpm. If a 45-cc pump can run at 2,850 rpm, the end user will get the same flow from a smaller pump at a lower price," he says.

Charging (applying positive pressure to) the inlet to the Series 45 pumps also permits higher input speeds. A built-in design margin avoids consequences such as premature pump failure. The Series 45 pump family includes six frame sizes, covering displacements from 25 to 147 cc/rev. Maximum pressures are 310 bar (4,495 psi) continuous and 400 bar (5,801 psi) peak. Typical applications include cranes, telehandlers, forklift trucks, wheel and backhoe loaders, as well as forestry and agricultural machinery.

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