6 September 2002


By Richard Allison

A NEW method for assessing teat liner performance is allowing one milking machine manufacturer to cut individual cow milking time by nearly one minute, while minimising liner slippage and teat stress.

All milking systems perform similarly under current testing methods without any milk flow, says Dairymasters head of research and development Edmond Harty. "But under high milk flow rates, differences become evident.

"This highlights the need to understand how milk flow affects vacuum changes at the teat end and liner wall behaviour. What are the vacuum changes under flow and how do different cluster designs affect liner behaviour?"

To answer this, a new method for assessing milking units under flow conditions was developed by Dr Harty and researchers at University College Dublin. The research took four years.

The test involves taking physical measurements, such as vacuum levels across the liner and slippage, during animal trials. In addition, liners are modelled for movement on a number of discrete points on the liner surface, based on a similar method for predicting stress in steel.

Data is then combined and a computer model accurately predicts liner movement involving several thousand calculations. It requires an understanding of the materials, shape and pressures acting around the liner, explains Dr Harty.

"It is now possible to apply computer simulations to different cluster designs to predict liner wall movement and teat-end vacuum level without having to build prototypes. We also have a better idea on how different liners collapse under different flow rates."

Designers can also assess whether existing liner design is sufficient and examine the effects of adjusting liner shape, short milk tube diameter, claw volume and weight.

A high vacuum when the liner is open maximises milking speed and a low vacuum when the liner is closed reduces stress on the teat. This is a large vacuum fluctuation and it is a good thing as long as it doesnt cause liner slip and the liner still collapses under the low vacuum level.

"This goes against current thinking. Excess vacuum fluctuation is thought by many to indicate liner slippage, but you can have a good fluctuation in vacuum without liner slippage. This needs to be taken into account when designing liners to stay on cows teats during the different phases."

Another important factor when designing milking equipment is vacuum level at the teat end. Dr Harty believes teat end vacuum level influences milking speed and stress on the teat.

"Teat-end vacuum levels are affected by cluster design, milk lift and pulsation characteristics. These influence how the liner responds and, therefore, the overall performance of milking equipment."

One advantage of being able to reduce vacuum at the teat end when liners collapse is reduced stress on the teat, because a vacuum tends to expand the teat. With the new testing method, we have been able to achieve a low vacuum when the liner collapses without liner slip, he says.

Dr Harty believes improved claw and liner design has resulted in milking time being reduced by one minute, while minimising teat stress.

"The new test method has also helped solve the question of whether all four liners on a cluster should collapse together or alternate two at a time as on many milking systems. Simultaneous pulsation was found to be better than alternate pulsation, as long as the correct liners and clusters are used."

Testing has also identified a potential problem with parlours with a cellar. Milk flow into the cellar creates a siphon effect leading to a higher vacuum in the liner than in the milking system. This means liners remain partially collapsed during the milking phase, which can lead to teat end damage.

Producers will also benefit from the likely adoption of this new test method as the international standard for milking equipment testing. The old method of testing pressure and pulsation cycles involved checking how far the pressure fluctuates up and down over a few minutes, says Dr Harty.

He believes a milking system and liner combination which produces a high vacuum when the liner is open and a low vacuum when the liner is closed is best for cows. "Ask for test data on milking equipment before you buy," he adds. &#42

Using a new cup liner testing method has led to a one-minute reduction in individual milking time, says Edmond Harty.

&#8226 New test method.

&#8226 Minimise teat stress.

&#8226 Increase milking speed.

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