Abstract:
In a device for pumping meat-containing products, such as pieces of meat, meat paste and meat pulp (dough), it is aimed at avoiding problems of the meat forming bridges in a feed space, of meat remaining in the device during a too long time, of too much churning up of the meat and to provide a simple device adapted to discharge at will a continuous meat discharge flow under constant pressure or at a constant flow rate. Thereto, there is a feed space with means for feeding the meat under pressure to one of a number of cylinders with reciprocating pistons or the like, acting in parallel, with a controlled valve in the delivery line between each piston and a common discharge duct. Several feed means are proposed, depending on the application of the devices for pieces of meat on the one hand or for paste or pulp.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for pumping meat-containing products, such as pieces of meat, meat paste and meat pulp (dough), in an essentially uniform stream, having a number of displacers such as pistons, which alternate during the pumping. 
     Such meat pumps are used to pump the meat to systems where further operations are carried out, for example making sausage, meat metering to all kinds of casings, for example for hams, checking of the meat for, for example, pieces of bone and other characteristics etc. 
     Meat paste and meat pulp constitute a fairly uniform mass with at most very small cohering original meat particles (in any case less than 1 cm maximum transverse measurement) and can be obtained by grinding or cutting and, for example, from bone presses, in which (remaining) meat with bones is placed under high pressure in order for the meat to be separated from the bones and leave the press through fine holes as a paste. 
     Devices for pumping meat are known in various designs. For example, rotary vane pumps for meat are known, to which the meat is fed from a feed hopper via a worm screw under vacuum, something which is suitable only for pieces of meat. Meat pulp and meat paste have the tendency to tunnel formation, in other words, meat which is at a standstill for some time, here for example above the worm screw, does not move downwardly very well or not at all, for example into the range of the screw, and thus forms a bridge. 
     Devices of the type referred to in the preamble, with alternating displacers, have become known, inter alia in order to eliminate the disadvantage of such tunnel formation. 
     For example, meat pumps are known in which a reciprocating displacer forces a stream of meat product batchwise towards an outlet, at which outlet is connected a second displacer which moves back to allow its delivery space to be filled by the first displacer when the latter is pressing, while the second displacer empties its thus filled delivery space while pressing towards the outlet when the first displacer is moving back. A disc-shaped non-return valve between said delivery spaces makes this possible. The meat is greatly churned up in the process, particularly by the first displacer when it is moving back into the feed space, and in this case some of the meat can easily remain too long in the feed space. 
     Meat pumps with two parallel reciprocating displacers in the bottom of a feed space are also known, connecting to a common outlet, while at the place where the outlets of the two displacers meet to form a common outlet a reversing valve moving under the influence of the pressure of the meat is provided. In order to ensure that the displacers are capable of forcing the meat towards the outlet under a desired pressure, each displacer has a cylinder which encloses it tightly, and which is also reciprocatable for the purpose of being moved between a retracted position, in which it is retracted from the feed space at the side opposite the outlet, and an extended position, in which it is entirely positioned in the bottom part of the feed space and connects to the appropriate outlet. When each displacer is retracted away from the meat outlet, its cylinder moves with it. On the delivery stroke the cylinder first moves to the extended position, following which the displacer can put pressure on the meat mass taken up therein by the cylinder on that movement, and which is separated from the rest of the feed space, and can force it towards the meat outlet. 
     The cylinder with sharp front edge makes this system unsuitable for pieces of meat, while the cylinder each time the meat above it at a standstill for so long that the above-mentioned tunnel formation occurs in the case of meat paste and meat pulp, so that it does not sink down again quickly and completely when the cylinder is retracted. 
     The object of the invention now is to improve this and to provide a device of the type referred to in the preamble, suitable not only for pieces of meat but also for meat paste and meat pulp, in which the above-mentioned disadvantages do not occur, a uniform meat flow through the device and to the outlet can be achieved, and the residence time of all meat in the device is approximately equally short. 
     SUMMARY OF THE INVENTION 
     For this purpose, such a device is according to the invention characterized in that a feed space for the meat product connects to at least two reciprocating displacers or pistons disposed outside it and acting in parallel, in that at least one further moving pressurizing piston is disposed in said feed space in order to place the meat product under pressure, in such a way that it can flow towards each cylinder of said displacers acting in parallel when the latter in their reciprocating movement free the connection to the feed space, and in that a controlled valve is fitted in the delivery line between each of said cylinders and a common discharge line. 
     Said pressurizing means need not obstruct the sinking down of the meat in the feed space, and can easily work in such a way that no meat is left too long in the feed space and that the meat is not churned up too much. Since the above-mentioned valve in the outlet is controlled, it can be given a much better shape for the purpose than a non-return valve operating through pressure, which gives a troublesome disruption of a uniform through-going meat flow, particularly at the downstream side. 
     The connections of the feed space to said cylinders are preferably fitted in the side wall of said cylinders, in such a way that each displacer passes its connection on its reciprocating movement. The cylinders can thus be filled from the side, which permits an advantageous positioning of said displacers to the side of the feed space and allows a simple design of the said pressurizing means in the feed space. Said pressurizing means is according to the invention preferably a single reciprocating double-acting piston which can move from the connection of one of the parallel-acting displacers to the connection of the other one for the infeed of meat product alternately to one and the other of these displacers. Such a piston can move fairly quickly and need be moved only during a small part of the total pumping cycle, so that no tunnel formation occurs in the feed space and the meat always sinks down well for filling of the space in which this piston is operating. 
     The invention makes it possible in a simple manner to use the device as desired for the supply of a constant meat output or for the delivery of a meat product at constant pressure, as will be described below. 
     The invention also relates to measures which are intended for improving the use of the device either for pieces of meat, or for meat paste and pulp. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained in greater detail with reference to the appended drawings, in which: 
     FIG. 1 is a side view of a device according to the invention in a preferred embodiment; 
     FIG. 2 is an end view, and 
     FIG. 3 is a top view of said device; 
     FIG. 4 is a schematic illustration of the situation during pumping, and 
     FIG. 5 is such an illustration in a different phase thereof; 
     FIG. 6 is a circuit diagram, showing the relationship between the positions of the different moving elements of said device and time; 
     FIG. 7 shows the feed part of the device if used for meat paste or pulp; and 
     FIG. 8 shows said feed part in a different design, intended for pumping pieces of meat. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a frame there is a meat feed space 1, having on two opposite sides thereof an upright cylinder 2, 3, each with a displacer 4 and 5 respectively, fitting therein, and an outlet line 6 and 7 respectively at the bottom of each cylinder, meeting in a common outlet 8. Each outlet line contains a valve 9 and 10 respectively, shown in dotted lines, and each operated by a pneumatic cylinder 11, 12. 
     Two horizontal pneumatic cylinders 13 engage at 14 on a fixed point in the frame and at the other side engage with their moving part a yoke 5 on which two horizontal rods 16 extend through sliding stuffing boxes into the bottom part of the feed space 1, where they are connected to a piston 17. 
     In FIGS. 1 and 2 the feed space at the top end is not shown in detail. Depending on the purpose, a feed device according to FIG. 7 or according to FIG. 8 can connect thereto, as will be discussed in greater detail. In FIG. 3 the top part of the feed space is left out, so that said piston 17 is largely visible. 
     FIGS. 4 and 5 show how the feed space 1 is connected internally to the space inside the cylinders 2 and 3 by horizontal cylinder parts 18 and 19 in which piston 17 fits, part 18 connecting to an opening 20 in the side wall of cylinder 2, and part 19 connecting to such an opening 21 of cylinder 3. 
     This device operates as follows: As shown in FIG. 4, the displacer 5 is moving downwards at a particular moment, and the valve 10 is open to allow the meat thus displaced through to outlet 8. Displacer 4, which in principle moves in opposing phase to displacer 5, is in its highest position, and valve 9 is closed. Meat placed in the feed space 1 is now conveyed by piston 17 to cylinder 2, so that the latter is filled. Piston 17 is shown in the centre position here. The pneumatic cylinders 13 give the piston 17 a variable end position in both directions, so that after complete filling of cylinder 2 and the exertion of a certain pressure thereon by piston 17 the latter stops. This ensures as well as possible that the cylinders 2 and 3 are filled completely. 
     The piston 17 preferably has a larger surface area than the pressure face of the displacers 4 and 5. In the figures the piston 17 is presumed to be non-circular, lower than wide. The rods 16 can thus run along the cylinder 3 at the side. The shape of the cylinder parts 18 and 19 is, of course, adapted thereto. 
     Before displacer 5 has reached the end of its downward delivery stroke, displacer 4 is moved quickly downwards under a pressure which is lower than the delivery pressure, until it just shuts off opening 20 or has slightly passed it, with a variable end position determined by said pressure. This means that there is more certainty that the space in cylinder 2 is completely filled. Said lower pressure is higher than the pressure which piston 17 exerts, so that some meat can be forced back into space 18 if desired. 
     Once displacer 5 approaches its downward pressing end positions, this is observed by one or more sensors 41 and passed on to the control system, which now quickly closes valve 10, quickly opens valve 9 and makes displacer 4 more further downwards at a higher pressure, the delivery pressure, for pressing, while displacer 5 moves quickly upwards. Once this displacer 5 is reaching its top end position, piston 17 is moved quickly to the right for the filling of cylinder 3, following which displacer 5 is moved downwards to shut off the connection opening 21, as discussed for displacer 4. The moving parts now take up the position shown in FIG. 5. Since displacer 5 can then start its delivery stroke as soon as displacer 4 has reached the end of its delivery stroke, a virtually continuous meat flow can be obtained through the outlet 8. 
     If one now wishes to pump the meat with constant output (quantity per unit time), one makes the displacers 4 and 5 carry out a uniform movement (of constant speed) during the pumping, irrespective of the delivery pressure. If a practically uniform delivery pressure is desired, one ensures that a constant downward pressure is exerted by said displacers during their delivery stroke. All this is easy to achieve with a hydraulic drive of the displacers 4 and 5, where either a constant quantity of liquid can be taken into a hydraulic drive cylinder or liquid under constant pressure with a quantity per unit time which adjusts itself thereto. Since the displacers must move back quickly and, before forcing, first have to move in the delivery direction under a lower pressure to shut off the connection openings 20 and 21, two hydraulic drives can advantageously be selected for this, with rapid reversing and with mutually differing pressures. 
     FIG. 6 shows the relative movement of the parts. The time in seconds is plotted on the horizontal axis, and the vertical axis shows the stroke of each of these parts individually. The solid lines show here the situation in which piston 17 always reaches the same end positions and stops there, and in which the displacers 4 and 5 always reach the same position on closing of the connection openings 20 and 21, and move uniformly on the delivery stroke. At the bottom of FIG. 6 numbers IV and V indicate what situation corresponds to the position of the parts of FIG. 4 and 5 (in which, because the situation of FIG. 4 is reached earlier than that of FIG. 5, FIG. 5 actually belongs to a subsequent cycle). 
     The system works in such a way that the delivery stroke of a displacer begins immediately when that of the other displacer ends, in order to obtain a continuous delivery flow. All other movements are made subordinate thereto in their phasing. FIG. 6 assumes a normal cycle of 22 seconds, in which, for example, 3,000 dm 3  of meat per hour is pumped. There are various causes through which the phasing shown can change. If pumping takes place at constant delivery pressure, then a displacer 4 or 5 can follow a line different from the straight slanting line 22 for the uniform movement of displacer 4 and thus reach its end position slightly earlier or later. 
     Moreover, in the event of (for example, temporarily) insufficient meat in the feed space 1, the filling of a cylinder 2 or 3 can be incomplete, so that a displacer 4 or 5 moves slightly further down when closing its connection opening 20 or 21, and before the delivery stroke begins. The meat can also show differences in compressibility, which influence this initial position of the pressing. The system described will, however, always react well to this. FIG. 6 shows by dotted lines (and exaggerated for the sake of simplicity) what then happens. Assume that displacer 4 does not move along solid line 22 for the delivery stroke, but along line 22&#39; or 22&#39;, and its delivery stroke ends in A&#39; instead of in A. Then said displacer is quickly retracted along 23&#39;, and piston 17 begins on its next filling stroke along 24&#39;, while displacer 5 presses from B&#39; instead of B and the valves 9 and 10 close and open respectively according to C&#39; and D&#39;, instead of according to C and D. 
     For displacer 5 it is indicated how the latter can reach the start of the delivery stroke in E&#39; instead of in E, and so has left a shorter delivery stroke. It then begins to press in B&#39; when displacer 4 has followed the solid line and in B&#39; when displacer 4 has followed the dotted line discussed. During that shorter delivery stroke displacer 4 starts to press earlier etc. Since each displacer has a fairly long standstill period after the closure of its connection opening (the horizontal line parts of 10 seconds when running along the solid lines), there is no objection to shortening thereof through such circumstances (for example, to the distance E-B&#39; or E&#39;-B&#39;). 
     The feed system will now be described with reference to FIGS. 7 and 8. A partial vacuum is maintained in known manner in the feed space 1 for the purpose of extracting the air from the meat, preventing the meat from being adversely affected through lengthy contact with air, preventing the appearance of the meat from being adversely affected, for example through air bubbles in sausages, and preventing too much air from being released during heating of, for example, sausages, which could break the skin. 
     FIG. 7 shows a feed hopper 25 for meat pulp or meat paste, from the bottom end of which a pipe 26 leads to a valve 27 and from there to the feed hopper 1 of the pumping device described. The valve 27 preferably has in the fixed housing a tubular diaphragm with connection for a pressure medium in the space between housing and diaphragm. Through infeed of said pressure medium, for example at a pressure of 5 bars, the diaphragm can be pinched together elastically and the valve can thus be closed. If it is open, the partial vacuum in the feed space 1 sucks in the meat pulp or the meat paste from the hopper 25. In the top of the feed hopper 1 is a dish 28 which leaves a gap free between its peripheral edge and the top wall of the space round the feed opening from pipe 26, through which meat pulp or meat paste flows in and moves downwards therein as a cylindrical screen 29. This thin screen gives good air extraction from the pulp or paste in this space which is under partial vacuum. The gap can be accurately set by moving the dish 28 up or down, for example by hand. A level sensor 30 observes the meat level in space 1. If this becomes too high, the height of the meat screen 29 becomes too small and air extraction is no longer adequate. Sensor 30 therefore closes valve 27 before this meat level becomes too high. The feed space 1 is the same as that of the preceding figures. 
     FIG. 8 shows a feed hopper 31 for pieces of meat. By means of a valve 32, which can be of the same design as valve 27 of FIG. 7, but in which the feed of pressure medium thereto can be controlled in any desired manner, for example by hand, the pieces of meat are fed to the hopper 31. This hopper is under partial vacuum (pipe 33 to vacuum pump), and the meat is thus easily sucked in when valve 32 is open. 
     The hopper 1 contains a shaft 34 having thereon stirring elements 35 to keep the meat moving slightly, so that it is deaerated well through the vacuum prevailing, without being damaged. There is great freedom in the choice of these stirring elements, for example as a flat slanting ring 35, as blades 36 parallel to or slanting relative to the shaft and at a distance from it, as slanting blades 37 directly on the shaft etc. and in all possible combinations thereof, as known in many different designs. 
     Located thereunder is a rotating conveyor screw 38 in a bottom part of the hopper 31, which encloses said screw in a close fit along the bottom half of the periphery. This screw conveys to the right in the figure and at the right end extends to the outside of the hopper 31 over a short distance into a part 39 which is built onto the hopper and encloses the screw along the entire periphery. In the bottom of part 39 there is a delivery opening 40 which connects to the feed space 1 of FIGS. 1-5. Said feed space can thus be fairly small. Sensors can be fitted to stop the screw 38 when the feed space 1 behind it is full, which is possible in all kinds of ways, for example by observing the resistance of screw 38, the latter then going into operation again for example after a fixed time lag or under the influence of a level measurement in the feed space. The valve 32 can also be connected to this control system, for example to be closed if screw 38 stops. 
     If the feed space 1 is shaped in such a way that the meat from opening 40 can reach the connection openings to the displacers, for example 20 and 21, in a supple and flowing way, then piston 17 can be omitted, and the screw 38 can take over its function.