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In principle, there are different methods being used to clean milking plants. The most common is circulation cleaning, which will be described in the following pages. With this method the cleaning is performed in three to five steps, where at least one involves circulation of the cleaning fluid.
The different phases during cleaning.
When using a combined cleaning agent, i.e. containing both detergent and disinfectant, in most cases the cleaning is performed in the following three phases:
1. A pre-rinse, usually with lukewarm water, to get rid of most of the milk residues after milking. The rinse should continue until the discarded effluent water is clear.
2. A circulation cleaning with a cleaning solution containing the combined cleaning agent. The water temperature is usually around 70° to 90°C (160° to 190°F) at the start and is decreased to about 40° to 50°C (105° to 120°F) at the end of the circulation. The end temperature should never be below 40°C, since this could cause the formation of fatty coatings.
3. A final rinse, usually with cold water, to remove any residuals of the cleaning solution.
In systems using detergents and disinfectants separately, two further phases will be performed. After the detergent cleaning, the plant is rinsed and then a disinfection circulation follows. After the disinfection, a final rinse will usually be performed.
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Sophistication of cleaning systems vary. Seen from a global point of view, cleaning is mostly controlled manually. However, automatically controlled cleaning systems are also widely used.
The most basic form of cleaning is still utilised on smaller farms where bucket milking takes place. In this situation the milking bucket is cleaned manually using hot water, a brush and some detergent. This method incorporates the key factors required for cleaning and will give a good cleaning result on a bucket milking plant.
In a manually controlled (or semiautomatic) cleaning system the farmer must control:
- the amounts of hot and cold water,
- the suction and return pipes (hoses),
- the adding of cleaning agents,
- the time for the circulation cleaning phase.
In an automatically controlled system parts of or all these measures are controlled by the cleaning unit. Sophisticated systems also supervise the cleaning process and signal using an alarm if something goes wrong during the cleaning. However, some operations in an automatically controlled system still need to be done manually, e.g. washing the clusters, connecting them to the jetters and setting the machine for cleaning and milking.
Two different ways are usually used to create the water flow during cleaning. In the first part of the milking plant (the milking units, the milk line and the receiver) the vacuum pump is used to create the flow. In the second part, the delivery line, the milk pump is used to pump the water back to a wash trough. The following sections describe how the water flow is regulated during the cleaning of these parts of the milking plant.
The flow in the milk pipeline is usually formed by sucking water from the wash trough into the pipeline system. Depending on the system used, air and water are sucked into the pipeline, either at the same time or separately. Due to the pressure difference between the vacuum level inside the pipeline and the atmospheric pressure outside, water will be accelerated by the fast moving air and travel towards the receiver. Apart from entering through the suction pipe, air also enters through the milking cluster and through leaks in the system, thus making the flow more turbulent.
With a transparent pipeline the flows shown in the picture below often can be observed. The flow often changes from one type to another within a few seconds. Common to all these flows, is that the pipe is filled with both water and air.
Common flows in a milk pipeline during cleaning.
The most desired flow during cleaning is the slug flow. A slug can be described as a moving cylinder of water measuring from a few centimeters to several meters in length. The slug fills up the whole pipe section over its length. This means that all surfaces in the pipe will be reached by the cleaning water, including the roof of the pipe.
In some cleaning systems several slugs travel through the system at the same time. These slugs often break and travel for some distance as a wave until they are caught by a following slug.
The water flow can be controlled in one of the following ways:
- continuous inlet of air and water at the same time,
- spontaneously alternating inlet of air and water or
- controlled alternating inlet of air and water.
Today all of these are commonly occurring, sometimes they can also be combined. They are described in the following sections.
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Water is sucked into the wash line from the trough by means of vacuum. An air admission hole is drilled to the recommended size in the suction pipe above water level, thus letting air flow into the system continuously. In order to assure a continuous water intake the water level in the trough should not sink below the water intake of the suction pipe. With this method, air and water will be sucked into the system in more or less constant proportions.
This is called spontaneous slug flow formation.
Another way of controlling the flow of water is by varying the water level in the trough intermittently. As soon as the water level is below the suction pipe intake, air is sucked in. When water is pumped back into the trough and the water level rises to the suction pipe intake, another water suction cycle starts.
This is called spontaneous flushing pulsation.
In flushing pulsation systems intake of water and air are intentionally separated using an automatic air inlet valve.
This valve is usually close to or in the wash trough. Air is let in until the slug has reached the receiver, thereby ensuring that all pipe surfaces are exposed to the fast moving water.
To get sufficient control it is appropriate to use an automatically controlled air valve.
In a controlled system only one slug at a time is travelling through the pipeline. The water suction for the following slug starts as the preceding slug enters the receiver. The time for the water suction determines the size of the slug. The speed of the slug is controlled by the flowrate of air admitted through the air inlet and by the size of the slug.
This is called controlled flushing pulsation.
For several reasons the controlled slug formation is advantageous in comparison with the other types of water flow:
- It is easier to adjust appropriate flow rates in installations with nontransparent pipes.
- The circulation volumes could be smaller, which reduces the required amount of detergent.
- The mechanical action of the water is improved.
- Average flow rate is lower, which causes lower demands on the milk pump capacity.
Compared to the flow in the milk pipeline, the flow in the delivery line is easy to control. This pipe should be fully flooded with water moving at the correct speed.
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In pipeline (or RTS, Round-The-Shed) milking systems, spontaneous slug formation is a common way of controlling the water flow. Controlled flushing pulsation, however, can also be suitable for these systems.
In a simple pipeline milking system the water travels as shown in the picture below. Water is sucked from the wash trough, passes through the milking units and moves through the entire pipe system until it reaches the receiver. From the receiver it will either be pumped back to the trough by the milk pump or go to the drain.
To avoid having the water travelling the shortest way to the receiver a wash valve is closed during cleaning. A controlled leakage through the valve assures that the short pipe between the wash valve and the receiver is cleaned.
The flow path of cleaning solution through a pipeline (RTS) milking system.
Sometimes the pipe system could consist of two loops. The flow through such a system is difficult to control, especially if the loops are of varying length.
In order to accelerate the water, air is let in close to or in the trough. After the air inlet the milking units are arranged in parallel. The units are mounted in the upright position on a rack of teat-cup jetters which are connected to the washline. When a controlled slug flow is used, the air inlet often is placed after the units.
The parlour plant is principally cleaned in the same way as the pipeline or RTS plant. The major differences are that the milk line is shorter and that the milking units will be cleaned in the same place as when operated during milking, i.e. they will be placed in an upright position on the cluster cleaner assembly, or attached to jetter cups, at the milking point.
A parlour plant can have the milk and wash line or lines at a low level below where the cow stands, known as a Lowline installation, or at a level above the milkerís height, known as a Highline or Midiline installation. A parlour installation can also contain recorder jars.
The same basic washing principles apply to all types of parlours.
There are many different ways of letting the water flow in a parlour plant. The reason for this diversity could be that local traditions regulate the way of cleaning, or that milking plants have varying characteristics. Both spontaneous slug formation and controlled flushing pulsation are used to control the water flows. In many cases, however, the controlled flushing pulsation is preferred.
The two pictures below shows examples of installations which occur. For all parlours water is sucked into a wash line. The milking units, and sometimes also milk recorders, are connected to this wash line and fed with water. From the units the water reaches the milk line and continues to the receiver. Often water also is sucked directly into the milk line.
Below, two designs are described which could be used in the cleaning of parlours. However, the reader should bear in mind that this only constitutes two examples. The way the flow is controlled could vary widely among parlours.
The picture below shows a flow pattern that is common for small parlour plants. The flow of water is controlled by spontaneous slug flow formation, i.e. no air inlet valve is used to control the flow.
The flow path of cleaning solution through a smallsize lowline milking parlour.
In parlour plants with large bore milklines controlled slug flow is usually used. The way the system is configurated could vary largely. The picture below shows a system with two suction lines, one for the wash line which feeds the units, and one feeding the milk line. Each of them have an air inlet valve close to the trough. Since the milkline forms a loop, a wash valve is needed.
The flow path of cleaning solution through a large lowline milking parlour.
It is also possible in large plants to add additional equipment which creates a water slug at the end of the milk line. This will ensure that the total length of the milk line comes in contact with the water slug and therefore gives a total clean.
After cleaning the milking plant has to be drained. The pipelines are drained by gravity but sometimes also by mechanical means, i.e. sponges. Furthermore, the pipelines are often dried by means of blowing air. The delivery line is also drained by gravity and is equipped with a manually operated drain valve close to the milk pump. If equipped with a plate cooler, another drain valve could be needed.
Often the slope of the pipeline in an RTS plant is insufficient to assure a proper drain relying on gravity only. Therefore one or more sponges often are sucked through the pipelines in order to force the remaining water out of the system. These sponges could either be let into the system manually or automatically. The sponges end up in the receiver, from where they have to be removed manually.
Since the pipeline in a parlour plant often is rather short, it is possible to have enough slope to ensure proper draining. For RTS plants and parlours, the cleaning programme for the parlour usually ends up with a drying phase by letting air through the plant.
Compared with milking, some extra equipment is used solely for the cleaning process.
These are:
- the wash trough,
- the wash line,
- an air inlet valve (optional, depending on system),
- a water heater (depending on system),
- the teatcup jetters,
- the wash valve and
- a control box which can vary from simple to sophisticated.
In practice, the wash trough, the heater, the air inlet valve and the control box form the unit, which can be called the cleaning unit.
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