Liner Design Influences Milking Characteristics
From the NMC Newsletter "Udder Topics", August 1996
Liner design usually has a greater effect on milking characteristics than
any other machine factor. For example, six-fold differences in strip yield,
eight-fold differences in the incidence of teatcup slips, and 33% differences
in milking times between liner types have been reported.
Machine-induced congestion and edema is reduced by milking with a "narrow-bore"
liner having a soft mouthpiece lip. The internal diameter of a liner is
usually measured at a point 3" (75 mm) below the mouthpiece lip. Liners
should have a barrel diameter about 1-2 mm less than the average diameter
of the teats after milk letdown (this means a diameter approximately 21-22
mm, or 0.83-0.87", for typical U.S. herds). Liners should be designed to
fit the teatcup shells. The mouthpiece should not be distorted by the shell,
but the liner should be held firmly enough not to twist easily in the shell.
Teatcup shells should all be the same length (within 2 mm) to ensure uniform
liner tension and to distribute the cluster weight more evenly between
the four quarters.
Liners should be long enough to collapse below the teat. Pulsation fails
if the liners are unable to collapse because the teat penetrates too deeply.
The minimum effective lengths of liners, made of natural rubber or synthetic
rubber, should be: 130 mm (5.1") for liners up to 20 mm (0.8") bore; 135
mm (5.3") for 21-22 mm (0.83-0.87") bore; 140 mm (5.5") for liners of 23-24
mm bore (0.9-0.94").
Liners should have no cracks in the short milk tube connecting to the claw,
and no surface roughness or swelling evident around the mouthpiece lip.
Mouthpiece deterioration usually results in increased squawking and liner
slips. Swelling of the liner barrel usually results in increased strip
yields and, possibly, higher SCC in sub-clinically infected quarters. Because
liner life varies with how they are stored, used, and cleaned, adjustments
from standard manufacturer's recommendations may be needed. Such adjustments
should be based on milking performance. If there is a significant change
in milkability when liners are replaced, then the liners were used too
long.
Source: 1996 NMC Annual Meeting Proceedings, pg. 235
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