The History of Vacuum Regulation Technology

An inordinate amount of time, money and anguish has been invested in changing the ways that vacuum is controlled in milking machines. These extraordinary efforts have not resulted in a commensurate improvement in milking performance. There are two fundamental methods of influencing the vacuum in the milking machine: 1) a device to regulate ‘system’ vacuum, usually located near the receiver and 2) design and configuration of system components to reduce the vacuum difference between the regulated system vacuum and the vacuum at the teat end. The ‘system’ regulation devices are the primary emphasis in this paper but the influence of components and design will also be covered to put these two contributions to milking vacuum stability in perspective. System regulation devices control the vacuum at a point downstream (in the direction of airflow) of the receiver. This control strategy tragically, CANNOT have any influence on the major causes of vacuum drop between the milkline and the milking unit and vacuum stability at the teat end, namely (in approximate order of significance): • Vacuum drop in the long milk tube and the associated vacuum fluctuations caused by slugs of milk in the tube and intermittent air admission to the milking unit. • Vacuum drop and vacuum fluctuations produced in the short milk tube due to milk slugs. • Vacuum fluctuations at the teat end caused by the opening and closing of the liner • Slugging in the milkline The vacuum measurement of most interest to the cow and her teats is the average vacuum in the claw during milking. The only legitimate function of most vacuum regulators is to provide a relatively stable reference vacuum in the receiver. If the milkline is designed correctly this same vacuum will also be supplied to the entire length of the milkline. The milkline vacuum together with knowledge of the relationship between milk flow rate and the milkline-claw vacuum difference will allow the competent evaluator to adjust the regulator vacuum to achieve the desired average claw vacuum for the majority of the time that milking units are attached to cows. As we will see, the history of vacuum regulation has shown an improvement receiver vacuum stability but the history of vacuum stability at the “business end” of the cow, her teat ends, has not progressed in this same orderly manner. The Beginning of Recorded Machine Milking Time This brief history of vacuum regulation is taken from the well researched and entertaining works by Hall (1959 and 1977) and Dodd and Hall (1992). Milking machines were first introduced in the late 1800’s. It is presumed that the vacuum was set by trial and error to arrive at a vacuum level that worked reasonably well.