By Jose M. Garcia Bravo, Ph.D., CFPS
The International Standards Organization (ISO) helps hydraulic pump and motor users, manufacturers, and researchers identify key performance characteristics of these components. Hydraulic pumps and motors are widely used in heavy mobile equipment and industrial applications, where pumps are used to transmit power hydraulically to different functions of a machine. Engineering designers and system integrators use pump performance data to identify the suitability of a hydraulic machine to accomplish the job.
The image above shows a graphical representation of the performance of an orbital internal gear pump under varying pressure and flow conditions. This type of plot is quite useful for the engineer to identify optimal operating conditions of the machine. For the particular case shown in the figure, it is seen that the maximum efficiency is reached at approximately 4000 lb.in. and 100 revolutions per minute.
Each manufacturer or user may choose to use the preferred testing method for determining the component performance characteristics. However, having a standardized procedure for obtaining the required measurements reduces the amount of time required to designate a test specification and at the same time improves the repeatability of the results in case the test needs to be conducted multiple times or at different locations.
An example of such pump or motor normative is the ISO 4409:2007 standard (Hydraulic Fluid Power – Positive-Displacement Pumps, Motors, and Integral Transmissions – Methods of Testing and Presenting Basic Steady-State Performance). This unified testing method specifies the required procedure and equipment needed for determining the pump, motor, or integral transmission efficiencies (volumetric, mechanical, and overall) over a range of manufacturer-recommended operating conditions. It also specifies the accuracy of the testing equipment and the recommended practice for presenting the experimental data. The end result of this standard is the data obtained from the prescribed experiments, where such results are used to produce tables and/or plots that indicate the performance of the tested machine. Arguably, the OEM manufacturer may use these results as a guide for selecting one pump or motor over another. The ISO 4409 standard is currently under revision by an international panel of experts from industry and academia. This revision process is recommended periodically so that the document is ensured to be current and valid.
With the advent of computer modeling and simulation in hydraulic systems, engineers and researchers have also benefitted from the existence of these standardized test methods. A computer model of a pump, motor, or transmission can be experimentally validated in laboratory conditions utilizing the standard method. Garcia, Johnson, and Michael (2015)1 proposed a method where pump performance could be normalized using rating indexes for individual operating conditions; such indexes were estimated using histograms corresponding to field data and combined with polynomial models derived from the performance data obtained via ISO 4409 measurements.
Another useful example of ISO standards for pumps is ISO 8426 (Hydraulic Fluid Power – Positive-Displacement Pumps and Motors – Determination of Derived Capacity), a method for experimentally determining the discharge characteristics of a pump or volume intake of a motor. This characteristic is especially important because it allows the designer or user to determine the real efficiencies of the machine from measured data.
Other important standards include ISO 4392 parts 1, 2, and 3 and ISO 17559. The 4392 normative provides specific directions for testing unique motor torque characteristics at speeds as low as 1 RPM and how much hydraulic power is required to break away friction or general performance at constant flow and pressure.
While each pump, motor, and hydrostatic transmission is intrinsically different, the engineer should use experimental data as important criteria for selecting a hydraulic component. The validity and repeatability of that data depends on the experiments used to collect it. The ISO standards provide experimental procedures backed by years of experience and multiple hours of discussion among members of ISO technical advisory groups around the world. These standards, and other similar ones, provide a readily available, valuable, and reliable tool to accomplish credible characterization of a machine without having to waste time or money designing unverified experimental test procedures.
For more information: Jose M. Garcia Bravo, Ph.D., CFPS, is assistant professor at the School of Engineering Technology, Purdue University. He can be reached at email@example.com.