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Hydraulic Pumps

Hydraulic system is the basis of modern highway engineering. Hydraulic pump is the basis of a hydraulic system. Without going into technical details of design and operating principle of one pump or another, we would like to draw your attention to an unpleasant fact of damage of this unit, which is often very expensive.

Equipment maintenance schedules for each equipment unit are specified in the technical documentation. They include replacement of filtering elements and replacement or purification of operating fluid (usually hydraulic oil). A simple calculation reveals that operation for min. 8 hours per shift annually results in ca. 2000 running hours. Maintenance schedules recommend replacement of filters and oil after every 1000 hours. Earlier, seasonal replacement of operating fuel together with replacement of filtering elements was recommended for domestic machinery. It was very practicable. All-weather operating fluids which depend more on the region of application (north, middle area, tropics) are used today. A change of a season always leads to various problems, related to inevitable moisture collection in each vessel regardless of its application.

I would like to describe a case from my own experience. A high-pressure pump station, 350 bar, located in the Moscow region. The station exists for about 3 years, but its running time is only ca. 500 r.h. and it is commissioned at the end of October. During start-up, high level of vibration is detected while pressure does not rise higher than 80 bar. Safety valves inspection did not show any results. Operating fluid was drained, the pump was removed and pump piston abruption was detected.


There was no operating fluid in the pump housing

As a result of long-term storage, condensate has collected in the operating fluid, water has entered the pump housing and frozen. The result can be seen in the pictures. It was enough to heat the station prior to start-up and the pump would not be damaged. Timely separation or replacement of operating fluid would also save the pump.

An experience in operation and maintenance of hydraulic pumps tells to pay close attention to one well-known moment. Axial-piston, radial-piston and, in particular, vane-type pumps shall be provided with a certain backup in the suction line. The initial pump start-up shall be performed only if the pump housing is filled with operating fluid. Otherwise the pump gets “burnt” which can be clearly seen at the damaged parts.

Absence of operating fluid in the pump housing

Trace of overheating is clearly seen in the picture, which is the evidence of operating fluid absence in the pump housing.

The same happened with the axial-piston pump, while the maintenance personnel usually report of a sufficient level of operating fluid.

The parts are almost fritted, which is possible only in case of very high temperature.

Time and again we received complaints from our clients, that abnormal typical noise has appeared at the equipment in the area of pumps location. Typically, a suggestion to open the pump housing vent plugs eliminates the suspicious noise. At the same time we recommend to check the filtering elements on the hydraulic tank breather and replace them. Axial- and radial-piston pumps are supposed to have an operating fluid backup in the suction line as well as the corresponding level of operating fluid.

At this pump distributor a trace of short-term operation with no operating fluid are clearly seen. This pump was lucky to be restored almost with no damage to its operability, as the maintenance personnel has reacted to the abnormal noise before it was too late.

By publishing this material I would like to attract the attention of all concerned to the fact that observance of simple operational requirements helps to avoid all the unwanted problems. In institutions, where necessary attention is paid to preventive measures, all machinery operates for a long time without any unpleasant damages.

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