Machine milking
The basic principle of the milking machine is shown in Figure 1.6. The
milking machine extracts the milk from the teat by vacuum. A vacuum
pump, a vacuum vessel, a vessel for collecting milk, teat cups and a
pulsator are essential parts of the milking machine.
The teat cup unit consists of a teat cup containing an inner tube of
rubber, called the teat cup liner. The inside of the liner, in contact with the
teat, is subjected to a constant vacuum of about 50 kPa (50% vacuum)
during milking.
The pressure in the pulsation chamber (between the liner and teat cup) is
regularly alternated by the pulsator between 50 kPa during the suction
phase and atmospheric pressure during the massage phase. The result is
that milk is sucked from the teat cistern during the suction phase. During
the massage phase, the teat cup liner is pressed together allowing a period
of teat massage. This is followed by another suction phase, and so on, as
shown in Figure 1.7.
Relief of the teat during the massage phase is necessary to avoid
accumulation of blood and fluid in the teat. Such congestion in the teat can
be painful to the cow, and milk let down and milking performance can be
affected. Repeated congestion at successive milking sessions can even
have an influence on the udder health. The pulsator alternates between
suction and massage phases about 50 to 60 times per minute.
The four teat cups, attached to a manifold called the milk claw, are held
on the cow’s teats by suction and the friction between the teat and the teat
cup liner. Vacuum is alternately (alternate pulsation) applied to the left and
right teats or, in some instances, to the front teats and rear teats. The
applying of vacuum to all four teats at the same time (simultaneous
pulsation) is less common. The milk is drawn from the teats directly to the
milk pail or via a vacuumised transport pipe to a receiver unit.