Abstract:
A milking plant for milking animals, such as cows, wherein milk collecting means, prefeably in the form of teat cups, are attached to the teat of the animal whereafter milk is taken from the animal by use of vacuum. The milk is transported by a milk line system ( 31 ) to milks storage means comprising a cooling tank ( 30 ). For cleaning purposes the milk line system from each milk collecting means can be shut off from the milk tank by valve means ( 32 ) in order for separate cleaning of the milk line system. The invention is characterized by preventing any possible leakage of detergent from a cleaning fluid to the milk that has been collected in the milk tank, by providing a pressure difference between the two fluids. The pressure difference between the fluids is preferably achieved by connecting the cleaning fluid to the vacuum supply ( 4 ) of the milking plant.

Description:
TECHNICAL FIELD 
     The present invention relates to a milking plant for milking animals, such as cows, and preferably though not exclusively to plants comprising milking robots operating with vacuum to collect milk from the animals, wherein the milk is transported by a milk line system to a cooling tank. The invention relates particularly to the cleaning of milking equipment using a cleaning fluid such as water, or a detergent, flowing through the milk line system. 
     BACKGROUND OF THE INVENTION 
     In traditional milking with manual handling of the equipment a large number of cows are milked simultaneously one to four hours every morning and night. After each milking a manual adjustment is made wherein teat cups used to collect milk from the cows are placed on teat dummies. Rinsing water and later a detergent solution, is sucked from a washing machine through the teat dummies into the teat cups, and onwards through the milking equipment. The fluid transport is driven by a vacuum suction, for instance at an underpressure of 50 kPa, to a collecting chamber, usually called an end unit. Many different vacuum-driven milk transport arrangements have been disclosed, such as U.S. Pat. No. 4,432,700, GB 2095088 and DE 3422452 by WESTFALIA SEPARATOR AG, and DE 2548601 by Miele, which are hereby incorporated by reference. 
     Generally, the end unit comprises a pump, transporting fluid against the pressure difference out towards the atmospheric pressure. The pipe connection, which during milking is connected to the cooling tank, is moved out of the cooling tank before washing, into a cleaning sleeve. The cleaning sleeve has an output, which is connected to the washing machine. A closed cleaning loop is thus obtained for cleaning in place (CIP). The technique known as CIP is inherited from the dairy industry, and is intended to indicate that rinsing water and detergent solution are circulated through tanks, pipes and process lines without the equipment having to be dismantled. 
     For the traditional milking equipment, a cleaning loop is formed by manually disconnecting the milk line system from the milk-cooling tank and connecting it to a cleaning fluid system. The milk tank itself is cleaned separately after having been emptied. 
     When using so called voluntary milking systems, VMS, the milking plant is in operation all hours of the day, having milk stored and transported through pipe systems and tanks. There are thus no natural breaks in the milking providing the opportunity to traditional cleaning or washing. This makes it necessary to divide the milking plant into sub-systems, which are cleaned separately on different times. The only exception, which can be anticipated, is a common cleaning of the entire plants each time the cooling tank has been emptied. Since the tank is generally emptied with an interval of two days, the cleaning frequency is obviously inadequate. 
     As examples of such sub-systems, the following can be mentioned: 
     Teat rubbers are rinsed and sometimes disinfected between every cow that is: milked. The water that is used must not leak into the milk. 
     The quality of the milk is supervised for each milked cow, generally by inspecting the so-called pre-milk, obtained from the teat cavity from the animal. If the milk does not meet up to standards, all the milk from the present cow has to be dumped. All parts of the equipment that has been in contact with the milk are washed afterwards. 
     The pipe system of the milk line system, comprising pipes and valves, transporting milk from the robot to the cooling tank, often about 20 to 30 meters, needs to be washed a couple of times each day in order to prevent bacterial growth on surfaces that have been in contact with the milk. 
     Between robot and milking tank there is often a milk filter that has to be changed or washed several times a day, at the same time as the filter housing is washed. 
     A VMS plant can consist of one milking station only, but for larger plants a number of stations are by necessity working in parallel, but which can be cleaned individually. 
     In some type of plants the cooling tank is washed separately after being emptied. The milk that is produced during the cleaning of the milking tank is then temporarily stored in a buffer tank. The buffer tank is emptied and washed once the cooling tank is taken back into operation. 
     The division into separately cleaned sub-systems provides a need for a security system preventing mixture of detergent solution into the milk even if a system separating valve should leak. 
     In dairy industries the same problem was earlier solved by removing a piece of pipe between parts of the equipment that were washed and parts that contained milk. A similar procedure is used in traditional milking plants. The connection pipe or hose, from the milk-line system to the milk cooling tank is moved manually to a cleaning fluid supply connection for washing. 
     When the demand for automation made manual pipe removing in dairy industries impossible an analogue solution was developed in the form of valves. System separating valves were used in doubles and were provided with a drained pipe extension in between. In practice, a closing valve was used combined with a three-way valve. The latter opened for drainage of the intermediate pipe when the valves closed of the milk supplies. Later developments originating from the dairy industry has provided double seat valves with a different types of drained chambers between the seats. A drawback for the solutions provided for the dairy industry is that unwashed parts of the equipment are obtained between the sub-systems. The pipe system in a dairy is however enough extensive to provide possibility to shift between different sections so that also border zones are washed. For double seat valves of the “mixed proof” type one has often the possibility of washing and steam sterilising the mid chamber. 
     Milking plant systems, however, must for a foreseeable future, due to economical reasons if no other, be much simpler. Therefore the basic problem of preventing mixture of detergent into the milk has to be solved in another way. 
     OBJECT OF THE INVENTION 
     It is thus an object of the present invention to provide means and methods for cleaning of milking equipment in milking plants. More specifically it is an object to provide a safe and secure cleaning of the milk line system, with a low risk for detergent from the cleaning fluid to mix in with the milk, without the need of extensive piping or valve arrangement. 
     SUMMARY OF THE INVENTION 
     A The present invention is directed towards the milking plant for milking animals, such as cows, wherein milk collecting means, preferably in the form of teat cups, are attached to the teat of the animal whereafter milk is taken from the animal by use of vacuum. The milk is transported by a milk line system to a milk storage means comprising a cooling tank in which milk from all, or at least several animals, is stored. For cleaning purposes the milk line system from each milking station, that is milk collecting means, can be shut of from the milk tank by valve means in order for separate cleaning of the milk line system. The invention is characterised by preventing any possible leakage of detergent from a cleaning fluid to the milk that has been collected in the milk tank, by providing a pressure difference between the two fluids. 
     The two fluids are mechanically separated by the said valve means, but there is a always a risk for a valve to leak. By applying a higher pressure on the milk then on the cleaning fluid, the cleaning fluid cannot penetrate into the milk in case of leakage. Milk however can of course leak out through the valve into the cleaning fluid. Although neither this is desirable, the damage is limited to a somewhat decreased result of washing and a smaller amount of lost milk. Furthermore, leakage of milk will give rise to a substantial colouring of the water or detergent solution used as cleaning fluid, even at very low concentration, and is therefore easily spotted by suitable monitoring means. In a preferred embodiment of the invention, the pressure difference between the fluids is obtained by connecting the cleaning fluid to the vacuum supply of the milking plant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention and to show how the same may be carried into effect reference will now be made by way of example into the accompanied drawings of which 
         FIG. 1  shows an air separator and a cleaning fluid return pump, with a connection to the vacuum system of the milking plant in accordance with the invention; 
         FIG. 2  shows a preferred embodiment of the pump connected into the air separator, from  FIG. 1 , according to the invention; 
         FIG. 3  shows the milk tank, parts of the milk line system and parts of the cleaning system in an embodiment of the present invention; 
         FIG. 4  shows parts of another embodiment of the milking plant according to the invention, similar to that of  FIG. 3 ; 
         FIG. 5  shows parts of yet another embodiment of the present invention, in which the milking plant makes use of a buffer tank; 
         FIG. 6  shows a part of a milking plant according to the invention, illustrating pump and valve arrangements around the end unit; 
         FIG. 7  shows parts of the milking plant in an embodiment according to the invention, similar to that of  FIG. 6  but with a single pump arrangement; 
         FIG. 8  shows another embodiment of the invention, similar to that of FIG.  6 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     During cleaning of milking equipment it is common to suck in and rinse water, alkali washing solution, sour washing solution and disinfection solution through the teat cups from a container at atmospheric pressure. The underpressure in the connection point, i.e. the washing shelf with the teat dummies, makes the connection easy: the teat cups hold on by suction and no cleaning fluid leaks out. This method has turned out to be reliable and is useful also for milking robots. The cleaning fluid container is generally comprised as a part of a washing machine. The cleaning fluid is sucked and pumped through the milking equipment to a connection point were it is to be returned to the cleaning fluid container, thereby obtaining a circulation loop. In the vicinity of this connection point in a milking equipment, a system separating valve which must not leak is located. The system separating valve, which must be present, is placed between the milk transport line system (milk line system) and the milk-cooling tank. According to the present invention the risk for leakage of cleaning fluid into the milk is avoided by providing a pressure difference, so that the pressure of the cleaning fluid is lower than the pressure of the milk, on the respective sides of the system separating valve. 
     The pressure difference can be obtained either by raising the pressure on the milk side or by lowering it on the cleaning fluid side. A positive pressure on the milk side can be obtained by simply placing it high enough for the hydrostatic pressure in the connection point to provide sufficient security. This may however be inconvenient for other conceivable reasons. Another way of providing an increased pressure on the milk side is to use a pump directing the flow towards the system separating valve. Since the milk in the cooling tank is a delicate product, this is not a desirable solution. Neither is increasing the pressure in the cooling tank by pneumatic means, since the milk tank is fairly large. 
     The preferred procedure for obtaining the pressure difference, according to the invention, is instead to use the milking vacuum supply to lower the pressure on the cleaning fluid side in order to obtain the desired security against leakage. The return connection for the cleaning fluid must, with the proposed solution, have a return pump sucking the cleaning fluid at an underpressure and pumping it to the cleaning fluid container, which as mentioned is at atmospheric pressure. 
     The function of the return pump, or wash pump, is the same as for the end unit of the milking equipment, but the operational conditions are quite different. Milk requires delicate pumping without the mixture of air, where as for the case of cleaning fluid it is desirable to keep the volume in the pump equipment to a minimum in order to decrease the volume of the cleaning fluid. Thereby money is saved and the environmental stress is minimised. The desire to have a small cleaning fluid volume has a great impact for a VMS plant, which is washed several times a day. The flow of detergent solution, rinse water etc. which the return pump must handle is mixed up with air that is sucked into the cleaning loop.  FIG. 1  shows the return pump arrangement  1  in a proposed embodiment in the inventive milking plant. Due to the mixture of air in the cleaning fluid is provided an air separator  2  in immediate upstream connection with the return pump  6 , which preferably is a centrifugal pump. The return flow of cleaning fluid enters the air separator at  3 , and during transport in the air separator to the pump  6  inlet, any air present in the cleaning fluid rises to the free liquid surface and is thus released from the cleaning fluid. The milking vacuum system is connected to the air separator at  4 , serving both as an air recipient of the air separator, and as an underpressure provider for the cleaning fluid loop. The connection to the vacuum system at  4  is preferably preceded by a substantially vertical part  5  with such inner surface and such inner arrangement that any fluid drops present in the air stream falls back into the air separator  2 . When the return pump  6  is shut of the non-return valve  7  prevents suction back into the air separator. When the connection to the vacuum at  4  and a return valve at the inlet to the air separator  3  (not shown) are closed, the air separator is drained by means of a valve arrangement  8 . Down-streams the non-return valve  7 , the cleaning fluid is returned into a washing machine (not shown). 
     It is of outmost importance that the return pump arrangement has a larger capacity than the largest flow of cleaning fluid. Otherwise the air separator will cease to work and washing fluid will be sucked into the vacuum line. The air separator  2  and the return pump  6  will therefore often be emptied from cleaning fluid. The return pump  6  must thus be able to pump again once cleaning fluid flushes in. Centrifugal pumps of simple design have in these cases generally substantial start-up problems. Centrifugal pumps sucking in air-mixed flow of fluid separates the air in the central part of the pump. An air cavity is then obtained at the centre of the impeller of the centrifugal pump, so that only the outer portion of the pump house comprises a rotating ring of fluid. When the air cavity is large enough in diameter, the pump-work ceases completely. The amount of air that has to be collected before the pump ceases to work is dependent on the output pressure of the pump. It has, however, been found that an air separator connected directly to the pump inlet also has the ability to de-air the central part of the pump during operation. 
       FIG. 2  shows a proposed embodiment of the pump  6  with an impeller  20 , and its connection to the air separator  2 , which is designed to secure the functionality of the pump even if a fluid with a high degree with mixed-in air is sucked in. When a pump of the proposed design has been emptied it will also start to pump immediately once new fluid is provided through the air separator. The proposed pump as illustrated in  FIG. 2  thus makes it possible to work with a small volume of cleaning fluid and with sufficient over-capacity for the return pump. 
     Different embodiments of the milking plant according to the invention, comprising the return pump arrangement with the air separator as illustrated in  FIG. 1 , are shown in  FIG. 3-5 . The milk line system stretches from the milking robot, which is located at the milking stations were the animals are milked, to the milk room where the milk cooling tank is located. The milk line system from station to cooling tank is often about 20-30 meters long and needs to be washed 2-4 times a day, whereas the cooling tank generally is emptied and subsequently cleaned every two days. There are thus two main alternatives:
         a) The milk production is halted during the emptying and cleaning of the cooling tank. Therefore the entire milking plant is washed simultaneously.   b) The milk flow is led to a buffer tank during emptying and cleaning of the cooling tank.       

       FIG. 3  shows the milk-cooling tank  30 , to which milk is supplied from the milk line system at  31 . The cooling tank can be closed of from the milk line system by a valve  32 , and a valve  33  is able to connect the milk line system with the return pump arrangement at the bottom of the picture. As previously described, the output of the return pump arrangements at  34  leads to the washing machine for the cleaning fluid. At the bottom of the cooling tank there is an output connection  35  for emptying the milk tank to a milk transport vehicle. This output connection may also be connected to the return pump arrangement by valve  36 . At the top of the cooling tank a cleaning device  37  is shown, connectable to the cleaning fluid container (not shown) for cleaning the interior of the cooling tank. 
     During milk production valve  32  is opened and valve  33  is closed, so that milk from the milking robots is led from the milk line system  31  to the cooling tank  30  where it is stored until the milk transport vehicle arrives. In case the milk line system has to be cleaned although the milk tank is not emptied, valve  32  is closed and valve  33  is opened. In a manner as previously described the teat cups at the milking station are placed on cleaning fluid injectors comprising teat dummies, and the cleaning fluid is then sucked into the milk line system  31  and down through the air separator  2  and back to the washing machine by connection  34 . Thanks to the connection  4  between the cleaning fluid system and the vacuum supply, the pressure on the cleaning fluid side of valve  32  is lower than the pressure of the milk side. 
     When the milk tank is to be emptied valve  32  is closed and then connection  35  is connected to a milk transport vehicle. At the same time valve  33  is opened in order to drain the milk line system through the return pump arrangement. After the milk tank has been emptied the connection  35  is closed, the cleaning device  37  in the cooling tank is activated and the cleaning fluid supplied therefrom is drained through the opened valve  36  to the return pump arrangement. Also the valves  32  and  33  are opened, capabelising cleaning of the entire milking equipment. During this stage there is no vacuum connection at  4  between the return pump arrangement and the milking vacuum supply, the circulation of the cleaning fluid only being driven by the return pump  6 . 
     Another embodiment of the milking plant according to the invention is illustrated in FIG.  4 . This is a simpler design of that in  FIG. 3 , in the sense that filling and emptying of milk to the cooling tank  40  goes through the same opening  41 . During milking valve  42  is opened leading the milk line system  43  to the milk tank  40 , whereas valve  44  to the return pump arrangement is closed. During washing of the milk line system only, and not the cooling tank, valve  42  is closed and valve  44  is opened. The connection  4  to the vacuum supply of the return pump arrangements is opened whereby the underpressure guarantees that no cleaning fluid leaks into the cooling tank by valve  42 . 
     During emptying of the milk tank valve  42  is closed and the connection  41  of the cooling tank is connected to the milk transport vehicle. At the same time valve  44  is opened and the milk line system is drained through the air separator of the return pump arrangement. This may be, but does not have to be, aided by the air separator being connected to the vacuum supply at  4 , or by opening the draining valve means  8 . 
     Once the milk tank has been emptied the connection at  41  is closed and valves  42  and  44  are opened. Cleaning fluid supplied by the tank-cleaning device  45  is then drained through the air separator without using the vacuum connection at  4 . Therefore, the return transport pump  6  is working with atmospheric pressure at the suction side. 
       FIG. 5  shows another arrangement for a milking plant in accordance with b) above. In the illustrated arrangement, the flow of milk is led to a small buffer tank  50  during emptying and cleaning of the cooling tank  51 . Once the cooling tank is back in use, the buffer tank is emptied by gravity feeding, simply by being placed in a elevated position relative the milk cooling tank  51 . The buffer tank can be cleaned separately or together with the milk line system.  FIG. 5  shows an arrangement with separate cleaning, making use of the cleaning device  52  in the buffer tank  50 , similar to the cleaning device  53  in the milk cooling tank. 
     During milk production milk is passed from the milking robot via the milk line system  54  through valves  55  and  56  to the cooling tank  51 . Valves  57 ,  58  and  59  are during filling of the cooling tank closed. When the milk line system is washed only, valves  55  and  58  are held opened whereas valves  57 ,  56  and  60  are closed. The air separator is connected to the vacuum at  4  in order to secure that no cleaning fluid leaks into neither the cooling tank by valve  56  nor to the buffer tank  50  by valves  57  or  60 . 
     When the cooling tank is full valves  56  and  60  are closed, whereas valve  57  is opened. The milk from the milk line system is then transported to the buffer tank  50 . The connecting pipe  61  between the cooling tank  51  and the milk line system is then removed and the cooling tank is then connected to the milk transport vehicle by a connection at  62 . When the cooling tank  51  has been emptied it has to be cleaned, and also during cleaning milk from the milk line system is transported to the buffer tank  50 . Valves  60  and  55  are thus still closed and valve  57  is opened. 
     Also valve  56  is closed whereas valve  58  is open. The air separator is connected to the vacuum supply at  4  during cleaning of the cooling tank, in order to prevent cleaning fluid to leak into the buffer tank. The connection  61  is re-installed and valve  59  is open so that cleaning fluid can be circulated in a tank cleaning loop by pump  63 , thereby cleaning the cooling tank through means of the cleaning device  53 . A separate cleaning fluid container and washing machine (not shown) is preferably provided in the tank cleaning loop. A drain valve (not shown) is also comprised in the tank cleaning loop, for dumping used cleaning fluid. 
     Once the milk-cooling tank is reinstated, valves  55 ,  56  and  57  are opened, leading milk both from the milk line system  54  and from the buffer tank  50  to the milk-cooling tank  51 . Valves  60 ,  58  and  59  are closed, separating the cleaning fluid from the milk. Once the buffer tank  50  has been emptied through the force of gravity, valve  57  is closed and valve  60  is opened. Cleaning fluid is supplied to the buffer tank  50  through the cleaning device  52 , and by use of the under pressure connected at  4  the cleaning fluid is drained by the return pump at the pressure that is lower than on the milk side of valves  57  and  58 . 
     The embodiments of the invention as illustrated in the preceding  FIGS. 3-5  all show how the proposed procedure together with the proposed return pump arrangement for cleaning fluids can be used to prevent mixture of cleaning fluid into the milk. An important aspect of cleaning of milk equipment is to get rid of any residue of rinse water in the pipes and hoses of the milk line system. The risk for residual rinse water to be present when the milk production starts is especially large in the long transport lines from the milking station, i.e. the milking robot, to the cooling tank. Due to the length of such a connection it is difficult to arrange it with a constant fall towards the output end. With the proposed method and apparatus a possibility is provided to suck air through the milk line system to the air separator of the return pump arrangement, with a flow such that any residual rinse water is dragged out leaving a dry milk line system. 
     As previously mentioned, there is in vacuum milking equipment an air separating container usually called an end unit. To the end unit arrives a flow of air mixed milk from the teat cups of the milk station. The air is passed out through the end unit through the connection to the vacuum supply and a vacuum pump, whereas the milk is pumped out by means of milk pump. 
     In  FIG. 6  there is an illustration of such an end unit  600  with connection  601  through which air mixed milk is supplied to the end unit  600 . At the top of the end unit there is a connection  602  to the vacuum supply, by a liquid separator  603  divised to capture any drops of fluid flowing towards the vacuum at  602 . The end unit arrangement presented in  FIG. 6  is provided with two pumps  604  and  605 . Pump  604  is devised to pump milk from the end unit to the cooling tank and can be specially devised for gentle pumping. Pump  604  is of course also used for cleaning the subsequent milk line system at  606 . Pump  605  is devised for milk that is to be dumped and for cleaning of the milking equipment. The system separating valves  607  and  608  are held fully opened in order to ensure that the pumps are filled with fluid at start-up. The non-return valves  609  and  610  are there to prevent back-suction and the draining valve  611  is devised to prevent cleaning fluid or rinse water to be retained in the pump  605 , which could leak into the milk. The arrangement according to  FIG. 6  with two pumps makes it possible to work with a high capacity cleaning pump  605 , such as a centrifugal pump. During cleaning of the end unit, with valve  607  closed, pump  605  together with the vacuum connection  602  ensures that the pressure on the cleaning fluid side of  607  is lower than on the milk side. 
       FIG. 7  shows an arrangement similar to that of  FIG. 6 , but with only one pump  702 . The valve  701  connects the output from the valve  702  to the vacuum system. This connection can be made to the liquid separator  703  of the end unit  704 , were potential leakage is taken care of. This arrangement can be combined with an air intake  705  with low capacity so that leaking fluid is guaranteed to be sucked out. 
     When cleaning the end unit  704  but not the subsequent milking equipment at  708 , valves  701  and  702  are closed thereby obtaining an atmospheric pressure on the milk side (upper side) of valve  74 . The lower side of valve  74  however is still in contact with the vacuum from the end unit  76 , guaranteeing that no leakage of cleaning fluid occurs into the milk. 
       FIG. 8  shows yet another embodiment of the present invention using an end unit  800 . As previously described in conjunction with  FIG. 6 , the pump towards the milk tank  801 , corresponding to pump  604  in  FIG. 6 , can be especially devised for pumping milk. Such a pump can be a positive displacement pump, for instance a peristaltic pump. When using such a peristaltic pump, with a good suction capacity, the arrangement can be simplified as illustrated in FIG.  8 . Since the pump  801  is capable of suction even without being contained with milk or water at the start-up, the non-return valve  802  can be placed at the inlet of the pump  801 . The non-return valve  802  then becomes the system separator during cleaning. The underpressure in the line from the end unit both provides sealing power to the non-return valve  802  and security towards leakage of cleaning fluid into the milk. 
     In order to lower the demands of the milk transport pump  801 , the connection  803  of the end unit  800  to the vacuum supply can be provided with a three-way valve  804 , so that the end unit only works with underpressure during milking. After milking of each cow the valve  804  is adjusted so that air is let in whereby atmospheric pressure is obtained on the pre-milk surface. In accordance with the invention, valve  804  is of course adjusted to open the connection between the end unit  800  and the vacuum supply during cleaning of the end unit. This way leakage of cleaning fluid into the milk in the milk line system after the pump  801  is avoided, by means of the non-return valve  802 . 
     An embodiment of the present invention using a so-called releaser instead of a milk pump can be used. Such milk transport arrangements are well known in the prior art and have been used for a long time. In the embodiment there is a non-return valve in the milk line system. It is placed in immediate connection to the end unit. The mid chamber of the releaser, “the lock chamber”, is placed in the milk room above the cooling tank and is provided with the non-return valve for preventing back suction. The lock chamber is vacuum provided in a well-known way by valve means, so that the milk can flow in from the end unit. When the valve is adjusted so that the lock chamber is provided with atmospheric pressure, the non-return valve closes towards the end unit and the milk in the lock tank is emptied into the cooling tank. Since only milk from one cow at the time flows into the end unit, and the entire milking procedure as well as the valve is controlled by a central unit (not shown), the end unit can after each finished milking be provided with atmospheric pressure by means of a valve. Thereby the underpressure in the lock tank can also be used to lift and transport the milk. 
     When dumping milk that for some reason does not fulfil the demands on quality, and during cleaning, the pump is used. The end unit is then provided with vacuum, preventing mixture of cleaning fluid into the milk through the lock chamber, by means of the non-return valve. When cleaning the milk line system and the lock chamber of the releaser, the return pump is preferably used in order to provide a continuos flow of fluid. In coherence with what has been described for previous embodiments in conjunction with  FIGS. 3-5 , the air separator preceding the return pump is connected to the vacuum at a connection when there is milk present in the cooling tank and the milk line system is being cleaned. 
     Several embodiments and procedures for using those embodiments have been described in the proceeding text. Common for all embodiments is the inventive concept to use an underpressure provided by the vacuum supply of the milking plant, to the cleaning fluid in order to prevent cleaning fluid to leak into the milk when cleaning sub-units of the milk plant, in the context of the present invention the milk animal may of course be a cow, however, any other milk animal such as sheep, goat, horse or buffalo may also be intended.