The Milking Machine

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The Milking Machine One of the 7 wonders of the
world How does it work? By Jenks Britt Western
Kentucky University
Part of this presentation is from Utah State
University extension service.
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Milking Machines This section will provide
illustration descriptions of the components of
a milking system explain how they function in
the daily milk harvest.                        
                                                  
                                
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How the milking machine works... Hand Milking
During hand milking of a cow, manual cleaning
massage of the udder stimulates milk let-down.
The teat is closed at the base of the udder and
then manual pressure is applied to the teat to
force the trapped milk out of the teat opening.
Hand milking is dependant on increased pressure
within the teat to overcome the resistance of the
teat sphincter. This is NOT the way milk is
removed by nursing calves or milking machines.
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Calf The presence of the calf and its "bunting"
of the udder stimulates milk let-down. As a calf
nurses a cow, it does not clamp off the base of
the teat nor put much pressure on the walls of
the teat. But as the calf sucks, a negative
pressure is produced in the mouth. The pressure
within the udder, created by atmospheric pressure
and by milk letdown is greater than the area of
negative pressure within the calf's mouth. The
resistance of the teat sphincter is overcome and
the milk flows rapidly into the calf's mouth (the
area of reduced pressure).
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How the machine works A milking machine functions
the same as a nursing calf. The reduced pressure
within the shell- inflation causes the milk to
flow out from the teat and udder and into the
milking system.
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Pulsation System The pulsation system allows the
inflation (shell liner) to close and apply
pressure to the teat end. It does this by
allowing atmospheric air to enter between the
shell and the inflation. The purpose is to
massage the teat end and force tissue fluids back
out of the teat end.
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If massage fails If the massage (or rest) phase
fails, the tissue fluids begin to collect, swell
the teat end and gradually shut off the opening
in the teat so little or no milk is removed. This
reduces milk harvested and may damage the teat
end.
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Shell "Creep" Teat problems are exaggerated if
the shell "creeps-up" onto the lower udder and
presses the tissues together at the base of the
teat. This closes off the opening from the gland
cistern to the teat cistern and stops milk flow.
It also prevents the outflow of tissue fluids,
even with proper massage.
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Simple Milking Machine This is a diagram of a
very simple, older milking machine system. Yet it
contains most of the components of the more
modern and more complicated system.
pulsator
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Complex milking machine A more complex milking
system and components is depicted here and the
individual parts are described in slides which
follow.
Automatic take off
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Vacuum Pump The function of the vacuum pump is
to remove or (exhaust) air from a closed system,
thereby creating a partial vacuum. Atmospheric
air creates a pressure on all surfaces, and when
measured with a mercury manometer, will cause
mercury to rise in a column to 29.9 inches high
at sea level. This is called barometric or
atmospheric pressure. Most milking systems will
create a partial vacuum of 10.5-12.5 inches of
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Rotary Vacuum Pump With a rotary vacuum pump the
"vanes" trap air and expel it out the exhaust.
Oil is required to reduce friction and also to
provide as an air seal. There are also liquid
(water) ring pumps and air lobe pumps.
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Vacuum Gauge The vacuum pressure may be measured
by a vacuum gauge instead of the mercury
manometer. It is still measured in inches of
mercury (Hg) to indicate the vacuum pressure
present. It may also be measured in units called
kiloPascals (kPa). One inch of mercury is equal
to 3.38 kPa. A vacuum gauge should be located on
the vacuum line. It should be observed at each
milking to be sure it is working and that it is
at the desired vacuum level for milking.
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Mercury Manometer The vacuum pump creates a
partial vacuum by removing part of the air from a
closed system, thus reducing the pressure of the
air. The difference between the (almost) 30
inches of mercury at atmospheric pressure and the
reduced air pressure is the vacuum created and it
is expressed in inches of mercury (usually
10.5-12.5"). A mercury manometer, as pictured,
can be used to measure this vacuum pressure. The
size of the vacuum pump is usually expressed in
terms of cubic feet of air removed from the
system per minute (CFM).
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Vacuum Controller (regulator) The vacuum
controller admits air into the milking system to
limit the vacuum in the pulsator and milk lines.
The CFM rating of the controller must be equal to
or greater than the vacuum pump capacity. The
controller should be installed in a clean area
where moisture and dirt will not affect its
proper operation and where it will not freeze in
cold weather if condensation accumulates. The
preferred site is near the sanitary trap.
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Diagram of Controller The controller allows air
to enter the line, as needed. Or, it closes down
to exclude excess air in order to maintain a
specific vacuum level. A controller that is too
small or partially plugged may result in an
excessively high vacuum level, which could cause
damage to the teats.
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Various Regulators Several types of vacuum
controllers (regulators) are available.
Weight-type controllers usually do not provide
the vacuum stability desired. They should be
replaced with the newer style controllers that
are now available.
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Vacuum Balance (Distribution) Tanks The vacuum
balance tank is also referred to as a vacuum
reserve, air distribution, or a header tank. It
serves as the point of entry for header pipes so
serves as a distribution tank. Its content volume
has a cushioning effect on the vacuum level when
small amounts of air are admitted into the
system so it is a balance or cushion tank.
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Teat Cup Shell and Teat Cup Liner (Inflation)
Form a vacuum chamber which allows milk to be
removed from the teat and also provides massage
of the teat end. The size inflation used should
correspond to the shell size. Most companies
recommend the use of narrow bore liners (3/4 inch
or less in internal diameter). These have less
tendency to creep up the teats and shut off milk
flow from the udder into the teats.
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Teat Cup Liner (Inflation) The inflation (or
shell liner) is made of synthetic rubber or
silicon and is the only part of the entire
milking system which comes in contact with the
cow. The surface becomes pitted with use and
cleaning and they must be changed on schedule. If
not, they are more likely to aid in the spread of
infectious bacteria which cause mastitis. They
also lose their elasticity, with use, and will
not provide proper teat massage.
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Twisted Inflation It is essential that
inflations be installed properly and in the
correct shell. Twisting will prevent normal
function. Some inflations are square, others have
ribbed sides or special tops. Some admit air into
the tailpiece of the liner and are called a
vented inflation. This is done to avoid flooding
with milk. Most manufacturers control claw
flooding by admitting air into the claw. Vented
inflations may cause problems in systems that
have inadequate reserve air flow. When vented
inflations are used, the air inlet in the claw
should be closed (covered or sealed).
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Roughened Inflation with Milk Deposits It is
very important that inflations are changed on
schedule as recommended by the manufacturer.
Otherwise they become worn, allow buildup of milk
deposits and bacteria and assist in the spread of
contagious forms of mastitis.
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Pulsator The function of the pulsator is to
allow intermittent massage of the teat end to
prevent swelling. It does this by alternating
between a partial vacuum (milking phase) and
atmospheric air pressure (massage phase). Some
systems require that a specific side of the
pulsator be attached to the teat cups for the
rear quarters. For these systems, be sure the
hoses are connected correctly.
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Pulsation Air Filter Some systems use air
filters to help keep dust out of the pulsation
system. This aids in reducing wear and in
preventing "sticking" of the pulsators.
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Milking Phase During the milking phase, the
space between the inflation and shell and the
space inside the inflation have the same partial
vacuum. This causes the inflation to open and
milk to flow from the teat because the pressure
is lower outside the teat end.
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Massage (rest) Phase During the massage (or
rest) phase, air at normal atmospheric pressure
enters between the shell and inflation. Due to
the partial vacuum inside the inflation, the
inflation collapses around the teat. The pressure
of the collapsed inflation helps massage the teat
end, preventing congestion of blood and body
fluids in the teat skin and tissue.
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Alternating Inflation Most pulsators are of an
"alternating" type. This results in alternately
milking the front and then rear quarters. This
helps to even out the milk flow and reduce
flooding of the claw. Two hoses connect the
pulsator to the connections on the claw to allow
this alternation. Be sure they are properly
connected.
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Pulsation Rate The number of times per minute
that the pulsator alternates between the milking
and massage phase is called the PULSATION RATE.
Rates vary from about 40 to 80 pulsations per
minute, depending upon the manufacturer. A rate
between 50 to 60 is usually recommended.
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Pulsation Ratio The ratio of time the inflation
is in the milking phase compared to the time it
is in the massage (rest) phase is called the
PULSATION RATIO (or milk to rest ratio). Ratios
vary by manufacturer, from 5050 to about 7030.
Cows will usually milk slightly faster with a
wider ratio, such as 7030. However, the longer
milk phase and shorter rest phase may cause teat
end trauma and damage if the milking equipment is
not working properly and if good milking
practices are not followed. Ratios near 6040 are
less likely to contribute to problem situations.
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Milking Claw The milking claw connects and
supports the four shells and inflations and
serves as a collection site for the milk from the
four quarters. The "tail piece" of the inflation
carries the milk from the teat end into the claw
(its also called the short milk tube).
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Claw Size The claw is connected to the milk line
by the long milk hose and milk flows from the
claw to the milk line through this long milk
hose.
Excess milk hose length
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Claw Size The claw should be of adequate size to
avoid flooding. Most claws admit air through a
small hole in the claw to aid milk flow. Claws
should not have filters in them. Be sure the
ferrules (tubes where the liners are attached to
the claw) are not bent or damaged as this will
block milk flow, slow milking and cause teat
irritation.
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Long Milk Hose The long milk hose carries milk
from the claw to the milk line. Be sure the long
milk hose is in good condition, does not leak, is
not too long and does not contain a filter. Avoid
loops in this line that may cause a "backup" of
milk flood the claw.
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Milk Line The milk line receives milk through
the long milk hose and carries it to the receiver
jar. "Low- lines" are located lower than udder
level and "high lines" are located higher than
udder level. Low-lines result in less claw and
hose flooding during peak milk flow and also
reduce vacuum fluctuation.
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Milk Line Function The milk line must transport
milk (allow the milk to flow in it) and also
provide room for air to move above the milk.
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Eliminate Risers in Milk Line Eliminate any
risers in the milk line. Lifting milk leads to
flooding of the line and vacuum fluctuations.
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Milkline slope Adequate slope in the milkline
throughout the system is essential for the proper
flow of milk. Flat spots will cause flooding of
the line and vacuum fluctuations.
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Receiver Jar Milk flows by gravity through the
milk line and into the receiver jar. The receiver
jar serves as a small holding reservoir until the
milk can be pumped into the bulk tank for cooling
and storage. The valve between the receiving jar
and the milk pump should not admit air. If a
bubbling action occurs in the receiver jar, air
is leaking past the valve and it should be
corrected or replaced.
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Sanitary Trap The sanitary trap is usually
located close to the milk receiver jar. Its
purpose is to trap any milk or wash water that
goes past the receiver jar, so it doesn't enter
the vacuum balance tank or get on into the vacuum
pump. The pipes connecting the trap with the
balance tank should be the same size as the
milkline and should slope toward the trap.
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Milk Pump The milk pump turns on when milk
reaches a certain level in the receiver jar. It
pumps milk through another milk line into the
bulk tank. This is a separate small pump which
pumps milk and is unrelated to the vacuum pump,
which pumps air. Be sure the lines and valves are
properly set prior to milking to deliver the milk
from the receiver jar to the bulk tank.
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Bulk Tank Milk is stored and cooled in the bulk
tank until it is picked up by truck for transport
to the milk processor. Be sure that no wash water
or discarded milk enters the bulk tank. If this
should ever occur, shut down the entire system
and notify the manager (owner) immediately. Be
sure the bulk tank is properly cleaned after the
milk is shipped.
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Weigh Jars Weigh jars are glass jars calibrated
to measure the volume (and weight) of milk
accurately. They are used to record the daily
production of each cow. Weigh jars should be
placed so the milk inlet ports are about the same
height as the cows' udders. This reduces the
lifting of milk from the udder, which can cause
vacuum fluctuation at the teat end. Weigh jars
also have other disadvantages (1) emptying the
jar after each cow can slow down the efficiency
of the parlor, (2) they tend to congest a parlor
pit area and reduce ease of operator movement,
and (3) they are expensive to replace if broken.
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Metering Devices Other, smaller metering devices
are available which avoid the disadvantages of
the weigh jars but still provide information on
milk production.
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Cleaning in place (CIP) units CIP units allow for
internal cleaning of the milking cluster in the
parlor rather than transferring to thr milk room.
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Automatic take-offs When milk flow is below the
set flow rate the vacuum operated rope cluster
remover is activated by the milk meter after
cluster vacuum is shut off.
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Touch pad The touch pad operates the milking unit
and allows fore computer data input on the cow
being milked.
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Milk line slope After it reaches the milk line
milk flows by gravity to the receiver.
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Automatic wash system The automatic wash system
runs the rinse, clean and acid cycles which are
the three phases of the system cleaning after
each milking.
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Air Injector The air injector allows slugs of air
to enter the pipeline to form a slug flow of
water through the line.
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Milk Line Size The milk line should be of
adequate size for the number of milking units
used. Milk lines are made of glass or stainless
steel. Stainless steel is preferred because of
its durability. Most stainless steel lines are
welded on site and joined at some connections
with clamps and gaskets.
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Basement Barn The milk line , pulsators, meters
, etc are in a clean space under the parlor floor.