An Improved Air Admission Method for Use on Milking Machine Claw Pieces

New Zealand Journal of Agriculture, Volume 84, Issue 1, 15 January 1952, Page 48

An Improved Air Admission Method for Use on Milking Machine Claw Pieces

By

W. G. WHITTLESTONE,

Physical Chemist, Department of Agriculture Animal Research

Station, Rualcura, and

W. G. BATT,

Supervisor of Farm Dairy Instruction, Department of

Agriculture, Hamilton

IT has been evident for some time that the milk tube of the claw piece of certain milking machines does not clean satisfactorily. This article describes a simple modification of the claw cap air admission method which obviates this difficulty. The new claw cap was developed at the Department of Agriculture Animal Research Station, Ruakura, and has been shown after a year's trial in the field to be superior to other attempts to solve the problem.

YEARS ago it was customary to supply air admission in the claw by piercing the claw cap with a small twist drill or by filing a groove in the thread on the end of the claw milk tube. Both methods were found to be unreliable because of blockage by dirt or the drawing in of insects.

To avoid the effects of dirt it has become customary to drill the air admission hole between the nipples, so protecting the orifice against the collection of dirt caused by its being rubbed against a dirty surface. This results in the air being drawn into the milk tube some distance from the closed end, so creating a “dead end”. During the cleaning process milk may remain in this dead space to decompose between milkings and so become a fruitful source of bacterial contamination in the machine. That this will sometimes occur is evident from the nature of the cleaning process, which depends ,on the scrubbing action of air mixed with the cleaning solution. There is no turbulence or scrubbing in a “dead end” and hence milk deposits may build up.

The solution lies in putting the air admission hole back in the end of the claw in such a way that flies and dirt are not drawn into it. Why is it common to find an insect or a piece of straw or the like drawn into an air admission hole? The answer is that when a small hole (l/32in. diameter) is connected to a 15in. vacuum it draws in a lot of air. All of this air has to concentrate at the tiny opening and so it moves in at a high speed. An insect or a floating piece of straw is immediately drawn into the hole if it comes near this region of fastmoving air. Further, when the air hole is in the end of the claw it is likely to bump against a dirty surface of a cow. This results in the blocking of the hole.

In the diagram on this page is shown a claw cap which obviates the troubles outlined. The cap is made with a boss in the centre. Through this boss the l/32in. air admission hole is drilled. Across this hole is a Jin. hole drilled at right angles and opening to the air on opposite sides of the boss. This simple device meets both objections raised to the hole described above. All of the air passing through the l/32in. hole now first enters the two jin. holes. A jin. hole has 16 times the area of the l/32in. hole and there are two entry ports. This means that the speed of the air going into the two ports is only 1/32 times what it is at the small l/32in. hole. This reduction in speed reduces the chances of an insect or piece of straw being drawn in. Further, the chances of a fly being trapped are now greatly reduced

because it would be necessary for two flies to sit on the opposite ports at the same time before they would be firmly caught by the vacuum. This is rather unlikely. A glance at the diagram will also show that bumping the cap against a dirty surface is not likely to result in a blockage. The outer l/32in. hole being blocked does not matter. Its only purpose is to enable the farmer to push a piece of wire through into the inner hole as a routine check on its being clear.

The new type of claw cap with protected air admission was given trial, under R. W. Naylor, Farm Dairy Instructor, Department of Agriculture, Te Awamutu, on five different milking machines in use last season and the duration of the tests ranged from 1 to 3 months.

Machines which had previously shown considerable deposits between the air admission hole and the cap were selected, and the new type of claw cap was used in one or two bails, the older type being used on the remaining sets. Both claws therefore received the same cleaning treatment and were subjected to the same shed conditions.

In each case the claws fitted with the new type of cap were found to be in satisfactory condition at the close of the trial, while those of the older sets contained deposits to a varying extent.

The “dead end” or “pocket” formed on claws where the air admission hole is placed on the claw tube has been the cause of considerable contamination from a quick accumulation of deposits. The range has been from a trace to the' extremes in which the “dead end” becomes almost filled. It is expected that the new type of cap will be well received by milkingmachine manufacturers and be of benefit to the dairy industry.