Energy consumption of milking pump controlled by frequency convertor during milking cycle

P. Vaculik*, M. Prikryl, J. Bradna and L. Libich

Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Prague 6 – Suchdol, Czech Republic
*Correspondence: vaculik@tf.czu.cz

Abstract:

The article deals with selected parameters affecting the energy consumption of a vacuum pump in a milking system during the whole milking cycle in variants with and without regulation by a frequency convertor. When put into practice, the latest research of creation, control and stabilization of vacuum in milking devices allows dairy farmers to obtain a vacuum system that ensures maximum stability of milking pressure, which is a basic requirement affecting the health of dairy cows. The choice of vacuum system prioritizes in particular high performance, maximum operational reliability, minimum maintenance, long service life, environmental friendliness and economy. The vacuum pump was a Roots vacuum pump with a rotary piston which is typical for this use. Use of a frequency convertor significantly affected the efficiency of this pump for control of vacuum pressure level and pump performance by varying the rotation frequency according to the actual airflow requirement. Using this control system, only as much vacuum pressure is produced as necessary. By measurement of an experimental setup, it was found that the average power requirement of a setup with a control valve was 3.8 kW compared to 1.7 kW in the case of the variant with frequency convertor. Measurements and calculations have shown that this system is capable of saving more than 50% of electric energy.

Key words:

Effect of altitude and vacuum pressure on flow rate of vacuum pumps on milking machines driven by gasoline engine and a generator

H. Unal*, S. Arslan and H. Erdogan

University of Uludag, Faculty of Agriculture, Department of Biosystems Engineering,
Nilufer, TR16059 Bursa, Turkey
*Correspondence: hunal@uludag.edu.tr

Abstract:

The objective of this study was to compare the performances of two vacuum pumps driven by an internal combustion (gasoline) engine (Vacuum Pump 1) and a generator powered electrical motor (Vacuum Pump 2) under different altitude and vacuum pressures. The vacuum pumps delivering a flow rate of 350 l min^-1 at 50 kPa vacuum pressure were tested, which are commonly used in bucket type milking machines. Atmospheric pressures, maximum vacuum pump pressures, and air flow rates at milking pressures (38–50 kPa) were measured at altitudes from 0 to 2,000 m with 200 m increments. Maximum pump pressure reduced by 3.8, 11.3, and 19.9% for Vacuum Pump 1 at altitudes of 400, 1,200, and 2,000 m, respectively whereas Vacuum Pump 2 had 4.4, 12.3, and 20.4% less maximum pressure at the same altitudes. Air flow rate (457.7 l min^-1) of Vacuum Pump 1 at the sea level at 38 kPa working pressure reduced by 22.7% at the altitude of 2,000 m. The air flow rate reduced more (28.1%) at the operating pressure of 50 kPa for Vacuum Pump 1 at 2,000 m, compared to the sea level. Similarly, for Vacuum Pump 2, the measured flow rate at 38 kPa showed 19.1% reduction at 2,000 m while at 50 kPa the air flow rate reduced 26.4%, corresponding to 352.3 l min^-1. Differences in the air flow rates of vacuum pumps 1 and 2 under different vacuum pressures were insignificant (P > 0.05). However, the effect of altitude and vacuum pressure on measured air flow rates was significant for each pump at 5% level. The regression equations were also obtained for atmospheric pressure-altitude, maximum pump pressure-altitude, air flow rate-altitude, and air flow rate-pump vacuum-altitude. High determination coefficients that were found for these relationships suggest that pressure setting can be accurately done as the altitude at which milking needs to be changed without suffering from air flow rate during milking with bucket type machines.

Key words:

air flow rate, Altitude, gasoline engine, generator, Milking machine, pump pressure, vacuum pump