A complete set of clusters comprises a claw and four fully assembled cups. The components are four sets of teat shells, liners, short milk tubes, short pulse tubes, the long milk tube and long pulse tubing.
Correctly setting up clusters
Clusters that are correctly set up will be easy to put on and take off and will require no intervention from the milker while a cow is being milked. They will also ensure no cluster slip which can compromise teat health and increase the risk of mastitis.
Ensuring the cow and the cluster are aligned results in a good seal between the teat and liner and is essential for even, fast and complete milking.
If clusters are attached between the back legs, the long milk and pulse tubes must line up with the cow’s backbone, with clusters sitting squarely under the udder.
Achieving correct alignment - all dairies
- Check the length of the long milk tube. Its length will depend on the width of the pit and the positioning of the cows. However, the tube should not be so long that it sags into the pit (see image), or so short that it pulls the cluster out of alignment. The long pulse tubes should be the same length as the long milk tube.
- Check for twisting of long milk tubes and correct as necessary.
- Cluster alignment may be improved by using a combination of relatively heavy cups with a light claw. Such a combination helps to maintain a more uniform distribution of cluster weight between the quarters. It can also be improved by using claws with more upright inlets.
- Check the milk line. When cups are attached between the back legs, shift the milk line (or the front gate) until the rubbers hang correctly and clusters are aligned with the udders. When clusters are attached from in front of the legs, the first inlet is usually between 0-300mm from the hinge post on the front gate.
- Install an appropriately designed zig-zag rail to position cows accurately for cluster alignment.
- In straight rump rail dairies, devices to support and align the clusters may be useful.
In rotaries, poor alignment is a common problem and cows often end up with udders that are lighter on one side as a result. Consider the following solutions:
Use rubber rings produced by manufacturers – prevents the tube sliding through the hole and pulling the cluster out of alignment
A hook attached to a section of stainless steel tube can be fitted into the long milk tube preventing it from sliding through the hole.
A band of metal welded around the outside of the platform can provide a slot that the milk rubbers are fed through which in turn creates friction to help hold the rubbers in place and improve cluster alignment.
Milk rubbers can be extended to allow them to come over the edge of the platform, rather than through the platform holes. This is possible only if there is a gap between the platform and the entry/exit platform.
A slot to feed the rubbers through can be included as part of the concrete platform construction. The cluster can align itself with the cow and when not in use pull back out of the way of cows as they exit and enter.
The weight of commercially available clusters varies from about 1.6 to 3.5kg. The optimum weight with the commonly used liners in New Zealand tends to be in the range of 2.2–2.6kg.
The main benefit of increasing cluster weight is to reduce the amount of milk (strippings) left in the udder when clusters are removed. However, there are disadvantages of increasing the weight of the cluster including increased milker fatigue, slipping and falling of cups, and teat damage.
The choice of an optimum weight usually involves a compromise, a match based on the cows, the type of liner used, and the preferred vacuum setting.
Cluster weight in relation to the vacuum level
The average vacuum level in the claw during the peak flow period of milking should be within the recommended range of 34-42 kPa.
Note: cluster vacuum is not the same as the working vacuum (as per the vacuum gauge) and requires specialist equipment to measure it.
Long milk tube
Uneven weight distribution between the four quarters of an udder is one of the most common causes of incomplete milking, uneven milk-out, and liner slips.
The milking unit should hang squarely on the udder so that cluster weight is evenly distributed across the udder’s four quarters. This rarely occurs in practice. Usually, the main culprit is the long milk tube, although udder conformation also has a major influence e.g. 3 titters.
Clusters not hanging evenly on the udder can be because the connecting hoses are too long, too short, twisted, or poorly aligned in relation to the cow.
To ensure the long milk tubes are the correct length cut rubbers to roughly the right length and then trim them during milking.
See cluster attachment for solutions to poor cluster alignment.
Short milk tube
A mismatch between the claw inlet and the short milk tube (SMT) can cause partial closure of the short milk tube where it joins the claw.
Flattened or kinked SMTs indicate common errors in matching liners and claws. In New Zealand, liner SMT bores vary from 8-14mm with a corresponding variation in claw nipple size. The same liner model is often produced with two different SMT bores to accommodate different claws.
Seek expert help to ensure the liner, SMT and claw are compatible or restriction to milk flow may occur.
The teat cup liner is the only part of the milking machine that comes into contact with the cow's teat, so it heavily influences milking performance as well as udder and teat health. It's therefore important that the liner length is correct for the shell.
Visit the Teat cup liners page for detailed information.
Insufficient constriction where the shell meets the short milk tube will allow air leakage. Refer to the Teat cup liners page for more detailed information.
Assessing cluster performance
When assessing the ability of clusters to milk out use the following measures:
Incomplete milking: A problem with incomplete milking exists if more than 20% of quarters contain strip yields (milk remaining) of 250ml or more. If there are consistent differences in strip yields between the same quarters on different cows it usually indicates poor cluster positioning or uneven weight distribution between the four cups.
Liner slip: If clusters and milking machinery are satisfactory, liner slips should not exceed more than 5 cows per 100 cows milked (excluding cows with very bad udder conformation).
Buying the right clusters
Most equipment companies will loan demonstration clusters to farmers who are doing an equipment upgrade. This is a good way to evaluate the personal feel and handling characteristics of different clusters as well as their milking performance. You could also visit other farmers who use the same clusters in their dairies.
Studies suggest that claws must have an effective volume of at least 150ml to provide stable vacuum below the teat, minimise crossflow and contamination between quarters, and minimise liner slip.
Other important characteristics of claws include:
- appropriate weight
- unrestricted inlet nipples and claw outlet to allow free flow of milk
- good visibility of milk flowing into the claw bowl from each quarter
- visibility of milk in the claw bowl to help detect problems and to indicate end of milking
- ruggedness in a tough environment
- easy to open and maintain
- good ‘personal feel and handling characteristics’