Condition monitoring and fault diagnosis for vane pumps using flow ripple measurement

Vane pumps are simple in principle and can be mass produced inexpensively, making them well suited to the automotive industry. They also have many other applications, such as in the chemical industry and food industry. A common type of damage to a vane pump is cavitation erosion on the side plates. If this damage is not detected in time, it could cause failure of the pump, which depending on the type of system may have safety implications, and in some cases a high cost from lost production whilst the system is shut down. This kind of damage is common on other types of pumps such as gear pumps and piston pumps. So a practical method for fault diagnosis of hydraulic pumps is required which does not necessitate removal of a pump from the working system. This paper presents a method of detecting and identifying cavitation damage on pump side plates via pump flow ripple. Power steering vane pumps are used for this study, although the principles may also be applicable to other types of vane pump, and indeed to piston and gear pumps. The investigation has been done through measurement and simulation. A numerical model of a vane pump is described, and simulated cavitation damage is introduced into the model. This damage is shown to have a clear effect on the simulated flow ripple. The pump flow ripple has also been measured experimentally using the Secondary Source Method, and artificial damage has been introduced into the pump. The damage is shown to have a clear effect on the measured flow ripple, consistent with the simulation results. Whilst the secondary source enables the measurement of flow ripple in laboratory conditions, it is generally impracticable for in-situ measurement for condition monitoring. A simplified method for calculation of pump flow ripple from in-situ pump pressure ripple measurements and system impedance is discussed.