Study Of Cavitation Of Constant Pressure Variable Displacement Pump In Swing System Of Concrete Pump

Concrete pumps with S-type distribution valves are one of the most popular products in the market. Great attention has been paid on constant pressure variable displacement pumps of swing systems since cavitation frequently happens when concrete pumps work, which severely shortens their lifetime and reduces operational reliabilities. In this thesis, reasons for cavitation generation and methods for its suppression in constant pressure variable displacement pumps are investigated, through theoretical study, simulation and test. The work is summarized here.1. Features, applications and developments of swing systems of concrete pumps are reviewed; mechanism of cavitation, its resultant dangers and suppression methods are analyzed; aims of this thesis are then determined.2. By investigating operational mechanism and conditions of both swing systems and constant pressure variable displacement pumps in concrete pumps, it is found that the major cause for cavitation is that when the pump shifts from the unloading stage to high-flow-rate stage, the output flow rate suddenly increases and therefore the instantaneous input flow rate is insufficient. This results in the decrease of the pressure in the pump inlet and cavitation is then induced.3. Based on the reasons for damages and operation properties of pumps, the method that damping orifices are installed in the control circuit of pumps to depress the variation of output flow rate is proposed, by analyzing forces and velocities of the swash plate of the pump during the process of the change of flow rate and investigating the influence of the hydraulic resistance network on the flow change rate; further discussions on the effect of the flow change rate on systems performance are given.4. The mathematical model of constant pressure variable displacement pump and AMESim simulation model of the swing system of the concrete pump are built, and the occurrence of the sudden change of flow rate caused by pump condition shifts is verified; the effect of damping orifice before and after its use and its diameters on the flow change rate and operation properties of systems are simulated, which indicates that damping orifices with proper diameters play a significant role on suppressing the sudden change in the flow rate when pumps shift to another operation condition.5. Tests are conducted on a concrete pump prototype, which show that the decrease of the instantaneous pressure in the pump inlet during operation conditions shifts have been greatly improved after the installation of a damping orifice with a proper diameter in the control circuit.