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Energy-efficient testing of hydraulic pumps and motors

Based on the idea of energy recovery, Prüfstandtechnik Leipzig GmbH and Jetschke Industriefahrzeuge have developed and built a test stand which allows testing of axial piston pumps and motors in any rotating direction, both in closed and in open circuit.

 

Hydraulic pumps and motors are implemented in highly productive machines worldwide. The demand for reliable and safe functioning of hydraulic components is continuously increasing, as a breakdown of the machinery would cause significant costs.

The same is true for components which are repaired by providers offering maintenance services. These parts should ideally be tested according to the same criteria that apply to the  manufacturer of the components.

The compression load of pumps is currently being tested using pressure control valves; hydro drives, just like the pumps, are generally hydraulically tested, i.e. without an external load.

The manufactured size of pumps and hydro drives has increased continuously over the past years based on the power needed, especially in mobile machines. Additionally, the admitted short-term point pressures for these components have increased drastically, resulting in test requirements of up to 480...500 bar. Apart from the energy consumption required for such testing, many companies don’t have the access to such high connection powers at their energy providers.

As an alternative, there are systems in which the test items (pumps) are loaded by hydro drives, which themselves emit driving power on the test items. Thus, pressure loads of any strength can be built up internally with the drive merely feeding in the total power loss of the system. These systems are often referred to as 'spinning systems'. Such systems are generally only used for testing in stable operating conditions as these circulations tend to be instable and fast control of the pressuring hydro drive is necessary for dynamic processes.

Based on the idea of energy recovery, Prüfstandtechnik Leipzig GmbH and Jetschke Industriefahrzeuge developed and built a test stand which allows testing of axial piston pumps and motors in any rotating direction, both in closed and in open circuit. The test items can be set with any variant of final controlling equipment of the manufacturer. Another important point is that the hydro drives are not loaded hydraulically, but through an external torsion moment, i.e. practice-oriented.


The core element is the dynamometer that was specifically modified by Hamburg-based company Jetschke, a reseller and maintenance provider of Linde Hydraulics. This particular double-axial piston machine is designed for the operation of pumps and drives in both rotating directions. The machine is directly linked to the test item via a torsion moment gauge bar.

The dynamometer and the test item work hydraulically in closed circuit. If pumps are to be tested for open circuits, the operator station is equipped with suction lines and the oil is discharged into a tank via a cartridge-valve after passing through the dynamometer. The operator informs the test stand control unit about the nature of the test item before the test run, be it a pump or a motor. According to this, the dynamometer works as a motor or pump.

The system is driven by an axial piston motor as the third component of the dynamometer. This hydro drive is operated in closed circuit, making the rotation speed of the test item controllable in a wide range.

The oil flow and the pressure in the respective high-pressure pipe of the test item are measured. Depending on the adjustment of the test item and the requirements to the test pressure course, the dynamometer is controlled through an adjustment of the proportional valves. The pressure cut-off valves of the dynamometer operate directly at the channels leading to the adjust cylinder, so they work directly and very fast.

Building the dynamometer as a double-axial piston machine allows for high rotation speed and an effective adjustment to the size of the test item.

With large test items, both units operate with the sum of their respective displacement; with very small test items, it is possible to control only the primary unit so that only a portion of the displacement of both machines is effective.

The test stand built for Jetschke is designed for maximum test performance of 160KW at a drive power of 75KW. The test-circuit is limited to maximum pressures of 450 bar; oil flows of up to 450 l/min, and rotation speed of up to 3,000 1/min.

The machine is completely operated via a control-PC displaying all relevant indicators on screen. Measurements and gradients can be documented and stored in databases. This test stand achieves universal applicability through modular programming and parameterization – and it saves energy by energy recovery.

 

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