Abstrakt

Starting hydraulic pumps in low ambient temperatures may cause: decreased hydraulic-mechanical efficiency, larger vibration of hydraulic installation, faster wear and more frequent damage to the elements of pumps, change of material properties of elements, increase of pressure drop. As a result of increase of resistance of cold oil flow in the suction pipe, large underpressure may be experienced, causing incomplete filling of pump working chambers with oil and reducing volumetric efficiency. Starting of cooled hydraulic pump in low temperatures may occur when pump is supplied with oil of the same temperature as the surroundings or the oil is warmed to higher temperature than the ambient temperature. During start-up of a hydraulic pump in thermal shock conditions, parts warm up in a nonuniform way, due to varying material and shape properties. This causes change of clearances between the co-operating elements and may lead to faulty operation of hydraulic pump or to its break-down. Experimental tests of hydraulic pumps in low ambient temperatures were conducted in the Laboratory of Hydraulics of the Faculty of Mechanical Engineering of the Gdańsk University of Technology. Tested pumps were placed in the low temperature chamber in which – 25 ºC temperature can be reached. The components were supplied with the warm mineral oil in the temperature ranging from 20 ºC to 60 ºC. In order to investigate of the heating process, temperature sensors were placed in moving and fixed parts of the pumps. In the research three types of pumps were considered: two axial piston pumps of different designs and one radial piston pump. It was proved, that in thermal shock conditions some malfunctions may occur, especially with large temperature difference between oil and pump. Experimental research of various hydraulic pumps operating in low ambient temperatures, undertaken by the author, allows to answer the question how the effective clearance changes in such conditions and what parameters does it depend on. To evaluate parameters for correct start-up of hydraulic pumps in thermal shock conditions, author uses and recommends two methods: analytical and computer simulation.

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