Abstract:
A device for conveying powders through pipelines including at least one pumping device which in turn includes a suction inlet and a delivery outlet and a tubular chamber with opposite ends connected respectively to the suction inlet through an input valve and to the delivery outlet through an output valve. A vacuum source and a pressure source are connected upon command to the chamber in axially distanced positions to create a vacuum respectively and alternatively in the chamber in relation to the environment upstream of the device and a pressure in relation to the environment downstream of the device.

Description:
FIELD OF THE INVENTION 
   This is a nationalization of PCT/EP2004/007423 filed 7 Jul. 2004 and published in English. 
   BACKGROUND OF THE INVENTION 
   The present invention herein refers to a device for conveying fine powders through pipelines. 
   At the present state of the art there are various types of apparatus for transferring products in powder of various kinds from one container to another through special pipelines. In particular these types of apparatus are useful in painting plants that use paint in powder. In fact in such plants it is necessary to have an apparatus for the suction of paints in powder from any container whatsoever and for reconveying it to the spray painting guns. 
   Among the existing systems of conveying powder the Venturi-effect injectors can be mentioned. These injectors suck back the powder thanks to a jet of compressed air that is made to pass through a special convergent/divergent tube, and launch it along a conveyor tube using the same compressed air, often with the addition of supplementary conveying air. However, these systems present some problems, for example the consumption or the obstruction of the Venturi tubes, the inconstancy of the flow during prolonged use and the need for considerable maintenance. In addition the Venturi injectors require a high quantity of conveying air that then has to be discharged at the destination of the product in powder; this results in not being very convenient in various applications. 
   In addition to the Venturi injectors vacuum systems can also be mentioned. Such systems suck back the product in powder forming a vacuum in the conveying conduits. They have the problem of having to discharge the vacuum at the destination of the product; this makes it necessary to insert special devices that make the costs and complexity of the overall plant increase. In addition, the cleaning of the circuits of a vacuum system is rather difficult and problematic. 
   Recently the “volumetric” type of systems for the suction and reconveying of products in powder into pipelines have also been studied; nevertheless these systems use pistons with alternative movements and therefore, they are quite expensive. 
   Another system of conveying powders comprises a tubular chamber connected to the suction conduit by means of a first sleeve valve and to the delivery conduit by means of a second sleeve valve. Said chamber is positioned at a lower level than the tank from which the powders start, so as to allow the fall by gravity of the powders inside it. The chamber is fitted with an inlet of blowing air that enables the powder in it to be pushed into the delivery conduit. Such systems do not allow a continuous flow in output and have the disadvantage of having to be necessarily positioned at a lower level than the starting tank. To resolve the problem of the below-level positioning, the known technique of applying both a pressure source and a vacuum source alternatively to the hole was considered; in this manner it is possible to suck the powder into the chamber without relying only on the fall by gravity. In this embodiment, to find a solution between the need of suction and that of thrust of the powders, the hole is located in the chamber halfway between the inlet and the outlet. This causes strong disuniformity between the cycles of the pump and the quantity of powder injected at every cycle is variable and not easily controllable. To stabilize the flow in output from the device, it therefore became necessary to connect the two chambers in parallel with unsynchronized operating cycles. As a further disadvantage, the inlet valves of the two chambers are fitted with such a mechanical drive that when one of the two valves is open the other is closed. The two outlet valves are also fitted with a mechanical drive of this type. Such a device does not however permit the overlapping of the injection phases of the two chambers and thus does not allow a satisfactorily continuous flow of powder in output from the pump to be obtained. 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is to improve the abovementioned aspects by providing a device which, among other things, can support a continuous flow of powder, needs little conveying air and is economical compared to the devices of the know art. 
   In view of this aim it was decided to produce, in accordance with the invention, a device for conveying powders through pipelines comprising at least one pumping device comprising in turn a suction inlet and a delivery outlet, a tubular chamber with opposite ends connected respectively to said inlet through an input valve and to said outlet through an output valve, a vacuum source and a pressure source connected upon command to the chamber in axially distanced positions to create a vacuum respectively and alternatively in the chamber in relation to the environment upstream from the device and a pressure in relation to the environment downstream from the device. 
   To clarify the explanation of the innovative principles of the present invention and its advantages in comparison to the known technique, herein below is described, with the help of enclosed drawings, the example of a possible embodiment applying such principles. In the drawings: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  represents a view in section of a device in accordance with the invention, and 
       FIG. 2  represents a view in section of a detail of the apparatus of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an embodiment of the invention comprising two identical pumping devices  10   a  and  10   b  connected in parallel by means of a tubular “Y” element  20  upstream and by means of a tubular “Y” element  21  downstream. The powder starting container (not shown in the Figures) is connected upstream from the tubular element  20 , while the delivery tube (not shown in the Figures) into which the powders are to be sent is connected downstream from the tubular element  21 . Each pumping device  10  comprises a rectilinear tubular chamber  11 , a suction inlet  12  and a delivery outlet  13 . The tubular chamber  11  is housed inside a containing body  22  and its two opposite ends are connected respectively to the suction inlet  12  by means of an input valve  14  and to the delivery outlet  13  by means of an output valve  15 . Said valves can be, for example, “vacuum pinch valves”, as will be described herein below. The internal cylindrical wall of the tubular chamber  11  is fitted with two segments of porous tube  18  and  19 . The wall of these segments of porous tube allows air, but not powder, to pass. An inlet hole  16  and an outlet hole  17  respectively are made in the containing body  22 , in correspondence with the segments of porous tube  18  and  19 , and both have a small ring-shaped chamber. The inlet  16  and outlet  17  holes place the chamber  11  in communication respectively with a pressure source (not shown) and with a vacuum source (not shown). This pressure source is suitable for raising the internal pressure of the chamber to above the pressure level existing downstream from the tubular element  21 . The vacuum source is suitable for lowering the internal pressure of the chamber below the pressure level existing upstream from the tubular element  20 . The pressure and vacuum sources mentioned above can be connected to and disconnected upon requirement from the chamber  11  by means of suitable command means (not shown in the Figure). The inlet hole  16  and the relative porous tube  18  are located in proximity of the inlet valve  14 ; the outlet hole  17  and the relative porous tube  19  are located in proximity of the outlet valve  15 . This arrangement favors the suction and delivery of the powders in input to and in output from the chamber  11 . 
     FIG. 2  shows a “vacuum pinch valve”  14  in detail. This is a valve of the sleeve type in the body  29  from which a drive chamber  34  containing a soft tube  30  is made. The drive chamber  34  can be connected through the input hole  31  to a source of compressed air for closing the soft tube. In addition an outlet hole  32  is present that puts the drive chamber  34  in communication upon command with a vacuum source to force the re-opening of the valve passage section. 
   We shall now describe the operation of the device described above. In doing this, the operating cycle of one of the two pumping devices  10  shall be described, considering that the operating cycle of the other pumping device  10  is perfectly identical, but simply out of phase in relation to the first as will be clarified below. 
   In a first phase, the valves  14  and  15  are closed by effect of the pressure applied to the holes  31   a  and  31   b,  and the chamber  11  is put into vacuum starting from the outlet hole  17  by means of the porous tube  19 ; after which the valve  14  is opened, by effect of the vacuum applied to its outlet hole  32   a.  With this configuration of pressures the powder is sucked inside the chamber  11  through the opening  12  that communicates with the powder starting container. 
   In a second phase, the valve  14  is closed by effect of the pressure that is applied to its inlet hole  31   a,  after which the chamber  11  is put in pressure starting from the inlet hole  16  through the porous tube  18  and the valve  15  is opened by effect of the vacuum that is applied to its outlet hole  32   b.  With this configuration of pressures the powder is pushed out of the chamber  11  through the outlet opening  13  and goes into the conveying tube positioned downstream of the device. 
   When the suction/reconveying cycle of the powders has finished, the pumping device, for example the  10   a,  starts again with the first suction phase described previously, thus carrying out a periodic type of operation. The other pumping device, for example the  10   b,  carries out the same operating cycle, but with a delay in comparison with device  10   a  equal to half the period of the cycle. In this manner the powders are delivered with continuity, as the suction phase of one of the two devices  10  is compensated by the simultaneous delivery by the other device  10 . 
   The flow can be regulated both by varying the time of duration of the single phases and by varying the values of the conveying air pressure and of the suction air. 
   Following the description the numerous advantages that can be achieved with the present invention in comparison with the known technique appear evident. In fact, in comparison to the Venturi systems a very constant flow of powder over time, use of highly reduced conveying air, and a limited dimension of the conveying tubes have been achieved; in addition the new device undergoes less wear, needs less maintenance and can be easily cleaned automatically. 
   In comparison to the known volumetric systems of the technique, on the other hand, the device in accordance with the invention permits greater constructive simplicity and lower costs of implementation thanks to the absence of moving devices. The new device needs less maintenance also in comparison to the volumetric type of systems. 
   In comparison with the known systems of pumping with tubular chamber, suction and injection phases have been optimized thanks to the presence of the two holes axially distanced for the connection of the chamber to the pressure and vacuum sources. In addition, thanks to the type of drive of the inlet and outlet valves, it has been possible to overlap the injection phases of the two chambers, thus obtaining a satisfactorily continuous flow of powder in output. 
   Nevertheless, one pumping device  10  can be used when the pulsing flow of powder in output is satisfactory. 
   Naturally, the above description of an embodiment applying the innovative principles of the present invention is given as example of such innovative principles and must not therefore be taken as limiting within the sphere of the patent right claimed. For example, the range of flows that can be reached by the new device can be widened, as well as suitably dimensioning its components, also placing in parallel any number whatsoever of pumping devices  10 , instead of using only two as previously described. 
   When continuous flow in high grade is required, many pumps devices can be used in parallel. For example, advantageously the pumping devices with different phase to each other (one loading, one full and one discharging) can be used.