Milking Machine, Top Cover with Four Suction Devices

Milking Machine Top cover for collecting bowl, or "claw" with handle with four suction devices, or teat-cups. Stainless steel and aluminum. Mid-20th century, c.e.

Gift of Jon Gilbert Fox, Hanover, New Hampshire.

rl.563.2358.su

Mechanical Milking Overview

Dairy cattle are milked by machine. Milking machine design and function is critical for rapid and efficient removal of milk without damage to the teat or gland and with minimal risk for transmitting pathogenic microorganisms that might cause mastitis.

The machine includes teat cups that contact the cow’s teats and remove the milk, a claw where milk pools as it is removed from the four teats, vacuum tubes that provide vacuum to the teat cups and a milk tube that removes milk away from the claw, a source of vacuum for the machine, and a pulsator that regulates the on-off cycle of the vacuum. Many milking machines today have an automatic take-off (ATO or detacher) device that removes the machine from the cow when milking is completed.

Most cows have four functional teats. Therefore, milking machines are designed with four teat cups. These are composed of an inner rubber liner and an outer shell, usually made of metal. The rubber liner is relatively thin in the section that sits inside of the shell, while the liner’s tube below the shell is thicker rubber.

If you consider this arrangement for a moment, you will realize that the teat cup assembly results in two chambers (see below): A) one inside of the liner and B) one between the metal shell and the outside of the liner. A vacuum is pulled in both chambers; the vacuum in chamber A is continuous, while the vacuum in chamber B alternates between atmospheric pressure and the vacuum.

When the teat cup is applied to the teat, the end of the inside chamber is filled by the teat. During the milk phase the vacuum applied inside the liner is constant and keeps a constant negative pressure at the end of the teat, drawing milk (in yellow) from the gland. The vacuum applied to chamber B, between the shell and the thinner walled part of the liner, keeps the liner from collapsing under the vacuum. During the rest phase, the vacuum inside chamber B is monetarily off. Air (in green) enters chamber B instantly reaches atmospheric pressure, colapsing the rubber liner around the teat end, massaging the teat and maintaining blood flow. The lower part of chamber A maintains its vacuum (lower part of right diagram), while the upper part around the teat momentarily loses vacuum. This alternating vacuum-atmospheric pressure in chamber B is controlled by a pulsator.

To prevent teat-end trauma, This alternating vacuum-atmospheric pressure, referred to as pulsation, is important for maintaining teat end health.

A proper pulsation rate, that is the number of cycles of vacuum on - vacuum off (in Chamber B above), or milk phase – rest phase cycles, usually is about 45-60 per minute. The ratio of time that the machine is in milk phase vs rest phase should be between 50/50 to 60/40 (pulsation ratio). In some systems, pulsation ratios are slightly different for teat cups milking the fore quarters vs the rear quarters. This is done because typically the rear quarters are larger and contain more milk than fore quarters. Therefore, rear quarters usually take slightly longer to milk out compared with fore quarters. The adjusted pulsation to rear vs. fore can account for this difference so that the rear quarters milk out faster and all quarters are properly milked out when the automatic take-offs detach the machine.

References

http://www.americanartifacts.com/smma/milker/milker.htm http://classes.ansci.illinois.edu/ansc438/Mastitis/milkmachine.html