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Relatively Simple Method for Measuring Teatcup Liner Opening and Closing Pressures and Liner Ratio¹

Department of Animal Science, Animal Physiology, North Carolina State University, Raleigh 27650

ABSTRACT

This paper fills the need for a simple method for estimating the liner ratio during a pulsation cycle. The method can be used with any liner or shell combination.

Ordinary 22-gauge wire was sutured into the inner opposing walls of a teatcup liner. These "electrodes" were connected to a bridge amplifier, and contact closure was recorded by ultraviolet oscillograph.

When the liner walls touched or parted, the resulting signal had the form of a square wave, which allowed precise estimates of liner opening and closing to within 10 ms. Additionally, the pulsation chamber pressure was measured and the recording superimposed on the liner opening and closing, thus providing an estimate of the pressures at which the liner walls parted and touched.

Liner ratio has been measured by others both by determining the pressure at which the liner walls touched and parted in the absence of pulsations (static) and in the presence of pulsations (dynamic). In an example of the method's usefulness, liner ratio was set by the static method; and three pulsation rates, two ratios, and two liner wall movement speeds were compared for their effects on liner ratio determined by the proposed method (dynamic). At slow liner movement dynamic liner ratio was affected; liner opening pressure was affected more; liner walls remained parted longer. The greatest increase, 9%, occurred at 65 pulsation/min at a static ratio of 70:30. Additional considerations of the method include limitations.

¹ Paper No. 8609 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named nor criticism of similar ones not mentioned.