PRELIMINARY RESEARCHES REGARDING THE USE OF A VFD CONTROLLER FOR THE VACUUM PUMP OF THE MECHANICAL MILKING MACHINE

R. Roşca, P. Cârlescu, I. Ţenu, C-tin Chirilă

Abstract
To maintain the stable vacuum needed for milking cows, air must be removed from the system at the same rate at which air enters the system through the pulsators, claws, leaks, unit fall-off and other equipment such as milk meters when present. Conventional vacuum control is accomplished by using a vacuum pump, sized for the maximum air flow into the milking system, running a full speed. The difference between the pump capacity and the actual air entering the system is made up by allowing air to enter the system through a regulator. In this paper a variable frequency driver (VFD) is used in order to drive the vacuum pump at a controlled speed, so that the air removed equals the air entering the milking system; in this case no conventional controller or regulator is needed during milking This technology for controlling vacuum in a milking system allows a dramatic reduction in energy use, while still producing equivalent vacuum stability. The VFD technology is able to adjust the rate of air removal from the milking system, by changing the speed of the vacuum pump motor. The preliminary tests proved that the used of the VFD controller led to a higher vacuum stability in terms of the error between the set vacuum value and the achieved values. The statistical analysis of the experimental results showed that there is a significant difference between the experimental results obtained for the two methods of vacuum regulation (with vacuum regulator and VFD controller).

Key words: variable frequency drive, milking equipment, vacuum stability