How the milking system works

The milking system is divided into the milking side and the pulsator side.  When the system is turned on, vacuum is created everywhere by a vacuum pump that removes air from the system.  When the cows are not attached to the milking system,  the vacuum created will be the same on both the milking side and the pulsator side of the system.  When the cows are attached to the milking system by the milking claws, milk and vacuum are present on the milking side.

This will cause the vacuum on the milking side of the system to be somewhat lower than the vacuum on the pulsator side.  The pulsator side will never have milk, only vacuum or air.

The easiest way to understand the milking system is to look at the action taking place at the teat cup level.   There are 4 teat cups with liners attached to the milking claw.  The area between the liner and the claw is part of the pulsator side of the system.  The area between the teat and the liner is on the milking side of the system.   The pulsators are devices that sit on top of the pulsator lines on the pulsator side of the system.  They alternately expose the area between the liner and the shell to air and vacuum.  

When exposed to vacuum, the liner is pulled open around the teat and milk flows.  Milk flows because the teat is exposed to vacuum.

When exposed to air, the liner collapses around the teat, and the teat is not exposed to the vacuum on the milking side of the system, so milk ceases to flow and the teat rests.

This is how the cow is milked.   This pulsator action generally takes place around 60 times a minute.

The Milking system consists of the following parts:


The pump removes air and creates the vacuum.   The vacuum pump is measured by the amount of cubic feet per minute of air the pump can move measured at 15" hg.

Vacuum Regulator

The vacuum regulator admits atmospheric air in and out of the system to keep the vacuum at a predetermined set level.  If the vacuum gets too high, the vacuum regulator will open and let air into the system to lower the vacuum.

The Milk flow System

The milk line conveys milk, air and vacuum.  Vacuum goes up through the receiver jar to the milking unit.  Milk flows from the milking unit to the receiver jar.


High line versus low line.  Vacuum should be 11.5-12.5 " Hg at teat end during milking.  So before cows are attached and milk flows, the vacuum on high lines will be set higher ( 14-15") compared to low lines (12-13").  More vacuum is required if milk has to be moved above the cow, compared to letting milk flow into a low line.

The Pulsator System

The pulsator speeds are 60/minute.

The pulsator ratios equal 100%, 50/50, 60/40, 70/30 are typically ratios.  the first number refers to the amount of time the pulsator draws vacuum to open the liner and withdraw milk.  The second number indicates the amount of time it admits atmospheric air to collapse the liner and massage the teat.  A 70/30 ratio milks cows faster than a 50/50 ratio.  Uniform pulsation milks all 4 quarters simultaneously.  Alternate pulsation milks two quarters at a time, while the other 2 quarters rest.  Dual pulsators allow the quarter to be milked at different ratios, such as 60/40 behind and 50/50 in the front quarters. 


Balance Tank and vacuum piping

Connects vacuum pump, balance tank, sanitary trap, milk lines and the pulsator pipeline.  The vacuum supply tank provides a great vacuum source of limited duration.   It prevents excessive fluctuation when instantaneous air admission is greater than pump capacity.


Sanitary trap and milk receiver

The sanitary trap separates the milking part of the system from the just vacuum side of the system.  The receiver collects milk from the milking units, and the milk pump pumps milk from the receiver jar to the bulk tank.


Bulk Tank

The Milking Machine and its relationship to Mastitis

1.  Abrupt reduction of milk vacuum can cause movement of air towards the teat end, and droplets of milk may strike the teat end.  If the droplets have bacteria, the impact may force the bacteria into the teat ducts.  


Remember water is bad!!

2.  It can be a carrier of mastitis pathogens from one cow to the next.  (Strep ag, Staph aureus, and mycoplasma)  Teat dipping is important to kill bacteria left on the teat after milking.

3.  Bacteria can probably be transferred during milking from an infected quarter across the claw piece to an uninfected quarter through the impact mechanism.


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Copyright 1999-2001
New Bolton Center Field Service Department
Students:  Keith Javic - Class of 2003, C. Nikki Conroy - Class of 2003