Design improvement of screw pump power sources for hydraulic elevators to reduce noise emissions

Three-screw pumps are often used as the pressure power source in hydraulic elevators. In some cases the pump and the motor are both submerged in the oil tank. This solution improves the cooling of the motor and the noise emission is low. In the case of big plants, the pump and the motor are both outside of the oil tank. With this layout, the noise emission of the pump cannot be disregarded, especially if the pump is used in civil building. In this paper first experimental tests on the noise emission of the pump in real conditions are presented. They were made using in-field measurements by means of sound intensity. Then, a theoretical study is presented on the possibility of reducing the quasi-impulsive load components, which act on the rotors of the three-screw pumps in the rotational axial direction. These forces can be related to the noise emission of the pump. The analysis is carried out by the systematic variation of one of the design parameters of the rotors, i.e. the semi-amplitude of the threaded zone of the screws, by using the analytical tools previously set-up for the study of the dynamic loads on the standard rotors. Finally, it is shown that a suitable choice of this design parameter on one hand allows cancellation of the quasi-impulsive load, on the other hand it has a positive effect on the radial loads.