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

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.