There are various sizes currently in use for milk transfer lines, from 52 mm to 76 mm in diameter. Their capacity is determined by ISO standards. When selecting a pipe's diameter, the number of milking points and the design of the parlour must be taken into account as well as possible later incorporation of ACR/measurement systems, the number of milkers, the production, and the milking speed (difficult to predict). Along with the ASAE standards, the NMC recommendations take these conditions into account and provide guidance on the type of pipe needed. It is important to select a milking system that will not cause problems, regardless of whether future modifications are introduced.
The pipes must have more or less inclination based upon their capacity to receive milk, but without altering the vacuum inside of them. Installation of pipes that are longer at the beginning of the parlour than at the end must be avoided. Any possible accessories must not interfere with the milking. Some ACR systems are installed directly on the pipe, while other are joined through the use of tubes. In either case, the slope and height must allow proper extraction that does not affect the removal times.
There are three types of joints between pipes: plastic fittings, stainless steel fittings, and welded joints. Each one has its own characteristics, with the cost of the last two being relatively low.
Milk pump and pressure pipe
The pump's power will be determined by the pumping height and the length of the pipe (the most common power levels are between 0.55 and 1.1 kW). The system must have a drainage valve (some pumps have automatic valves that are activated during washing), and these must be appropriately maintained in order to prevent possible breaks from filling the receiver vessel.
The pressure pipe must be made of stainless steel. The use of stainless steel fittings is also highly recommended since these offer stability and ensure adequate cleanliness. The pipe design is the same as for any other milk or vacuum system, with the number of curves and the length minimised.
It is important that the tank input does not have narrow points if the final system uses ribbed hose or rubber tubing. One increasingly interesting possibility is to locate the input in the lower part of the tank, which requiresit to have a backflow prevention valve.
The milk filter is located inside the pressurised milk transfer line and is made of stainless steel. Its diameter must not be less than that of the pipe, since otherwise the extraction capacity (of milk or water) will be reduced. There are single and double systems (two filters in the same pipe). The filters must have high mechanical strength and the correct flow capacity, and must retain sediments.
There are one-piece and two-piece teat liners (liner and tube). These can be made of either silicone or rubber. The first type allows a higher number of milkings, although their cost is higher. Variations in the hardness of the materials will modify the collapse vacuum.
The various types of teat liners also differ from each other in the size of their opening, both in relation to diameter and length ("mouth" of the liner and height of the part in contact with the teat).
The equipment parts must be replaced based upon the number of milkings, not based on the number of months since they have been installed.
The capacity of the collecting bowl in the claw can vary between 150-450 cc, and its consumption can vary as well (determined by the entry of atmospheric air through an orifice). The claw output usually has a diameter of 16 mm, although this can vary from 12-18 mm. The short milk tube openings range from 8 mm to 12 mm.
The closure (the valve that uses pressure to interrupt passage of the vacuum) can be located in the claw itself or in the long milk tube. An ACR system breaks the vacuum in the mechanism located on the milk tube.
The claw must be maintained to ensure that the air entry orifice is kept clean and air entry does not increase (which would increase consumption and affect the milking stability). It must be verified that no leaks through the tube connections exist and that the liners are appropriately fit in order to break the vacuum during attachment (it must also be ensured that the vacuum breaking is correct).