The Basics of Hydraulic Vane Pump Failure

22 April, 2010- To understand the anatomy of hydraulic vane pump failure in a precise manner, lets take an example of a hydraulic power unit where a 15HP electric motor is directly connected with a vane pump. It generates a high pitched noise when the unit runs. If we consider that the motor bearing does not effect the pump and neither does the motor overload even after connecting a pressure line to the tank line to stimulate pressure. Though the noise remains persistent and varies with varying pressure then what could be the possible reason for noise? Now here if the symptoms remain consistent with the restriction at the pump inlet, a suction filter (which increases at high viscosity while the element clogs) in such a case can increase the chances of part vacuum development at the pump inlet. This pump inlet vacuum if in excess, can lead to cavitation erosion and mechanical damage.

Cavitation erosion

The decrease in absolute pressure while a partial vacuum development in the pump intake line can lead to the formation of vapor bubbles within the hydraulic fluid. Eventually when these bubbles are exposed to high pressure at the outlet pump, these implode vehemently and then later the collapsing of these bubbles against metal surface leads to erosion. Resultantly, hydraulic fluid gets contaminated with erosion and affects sensitive surfaces.

Mechanical damage

The mechanical forces rendered by the vacuum itself can lead to catastrophic failure during the partial vacuum development at the pump inlet. In case of vane pump designs, the vanes should extend from their retracted point in the rotor during inlet. While it happens, the void in the rotor created by the extending vane is filled with fluid through pump inlet. Exit of excessive vacuum at the pump inlet can make the vanes lose connection with cam ring while inlet which consequently, lets the vanes get hammered back onto the cam ring for the pressed fluid acts on the base of the vane during outlet. This to and fro activity distorts the vane tips and cam ring resulting into catastrophic failure.

Both cavitation bubble collapse and hammering vanes can be the reason of persistent noise in this particular hypothetical situation. The simple solution for it is to either replace the suction filter or alternatively, discard it completely.