Abstract:
The invention relates to a method for vacuum conveying bulk material in a vacuum conveying system ( 1 ) which comprises: a plurality of tubes ( 2 - 6 ) for conveying bulk material, at least some of said tubes having flexible walls ( 71 ), a vacuum blower ( 10 ) disposed at a first end of said vacuum conveying system ( 1 ) for generating a conveying gas flow within said vacuum conveying system ( 1 ), a bulk material discharging section ( 22, 23 ) for discharging bulk material into said vacuum conveying system ( 1 ), and a bulk material receiving section ( 8, 9 ) communicating with said vacuum blower ( 10 ), for receiving bulk material conveyed by said gas flow from said bulk material discharging section ( 22, 23 ). According to the invention, the method comprises the steps of: disconnecting said vacuum blower ( 10 ) from said vacuum conveying system ( 1 ); and applying pressurized gas to said vacuum conveying system ( 1 ) or at least to a subsection thereof for stretching or inflating said flexible walls ( 71 ) to thereby reduce adherence of bulk material to said flexible walls ( 71 ). Other aspects of the invention relate to a corresponding vacuum conveying system, to a controlling device and a computer program product for controlling the vacuum conveying system in accordance with the above method steps.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to a method and system for vacuum conveying of bulk material and relates more specifically to a method, a system, a controlling device and a computer program product for preventing clogging of components of a vacuum conveying system used for vacuum conveying bulk material. 
       BACKGROUND OF INVENTION 
       [0002]    Vacuum conveying systems for vacuum conveying of bulk material are well-known. In vacuum conveying systems a vacuum blower usually generates vacuum or negative pressure in a system of tubes and/or hoses used for conveying the bulk material for conveying bulk material from a bulk material discharging section, which is used for discharging bulk material into the system, to a downstream bulk material receiving section, e.g. a storage container or processing stage. The vacuum blower generates an air flow in the tubes and/or hoses which conveys the bulk material. 
         [0003]    A general problem with vacuum conveying of bulk material, i.e. of material consisting of free flowing particles or powdery material, such as powder, ground stone powder or toner particles, in processing plants is adherence of bulk material to the inner circumferential walls of tubes or hoses used for conveying the bulk material, which causes clogging of the tubes or hoses and imparts an excessive load onto the vacuum blower generating the conveying air flow. 
         [0004]    One approach for avoiding adherence of powdery particles to the inner circumferential walls of the conveying tubes is to impose vibrations to the tubes by mechanical vibrators. However, imposing mechanical vibrations to the tubes may result in an excessive wearing down and even destruction of the tubes, which might give rise to the formation of small cracks and holes in the walls of the tubes. Such cracks and holes could cause an unwanted leakage and result in an uncontrolled leaking of powdery materials towards the outside, which is undesirable. 
         [0005]    On the other hand, the above mentioned approach of imposing mechanical vibrations to conveying hoses or tubes of a vacuum conveying system is not suitable, because the walls of the conveying hoses or tubes will be more prone to wear and tear and mechanical destructions. 
       SUMMARY OF INVENTION 
       [0006]    Accordingly, the present invention is directed to a method of vacuum conveying of bulk material or powdery material in a vacuum conveying system comprising a plurality of tubes for conveying bulk material, at least some of said tubes having flexible walls. 
         [0007]    It is an object of the present invention to provide an efficient vacuum conveying method and system for preventing adherence of bulk material or powdery material or clogging of a vacuum conveying system of the aforementioned type. 
         [0008]    According to still another aspect of the present invention there is to be provided a computer program product for use in the aforementioned vacuum conveying system for controlling the controlling device of the vacuum conveying system such as to efficiently prevent adherence of bulk material or powdery material and clogging of the system. 
         [0009]    The above and further objects are achieved by a method according to claim  1 , by a vacuum conveying system according to claim  13  and by a computer program product according to claim  21 . Further advantageous embodiments are the subject-matter of the dependent claims. 
         [0010]    According to a first aspect of the present invention, there is provided a method for vacuum conveying bulk material in a vacuum conveying system. A typical vacuum system comprises: a plurality of tubes for conveying bulk material, at least some of said tubes having flexible walls or flexible sections, a vacuum blower disposed at a first end of said vacuum conveying system for generating a conveying gas flow within said vacuum conveying system, a bulk material discharging section for discharging bulk material into said vacuum conveying system and said conveying gas flow, and a bulk material receiving section communicating with said vacuum blower, for receiving bulk material conveyed by said gas flow from said bulk material discharging section. According to the present invention the method comprises the steps of disconnecting said vacuum blower from said vacuum conveying system; and applying pressurized gas to said vacuum conveying system or at least to a subsection thereof for stretching or inflating said flexible walls or subsections to thereby reduce adherence of bulk material to said flexible walls. 
         [0011]    By applying high pressure gas the flexible circumferential wall or flexible section of the tube is inflated and thus locally stretched, which causes adhering particles to flake or peel off from the flexible circumferential wall or section. Thus, according to the present invention adherence of powdery or bulk material and even clogging of the vacuum conveying system is eliminated. 
         [0012]    Thus, in principle according to the present invention the vacuum conveying system may consist of both rigid tubes and flexible hoses depending on the design of the overall vacuum conveying system. In principle, the tubes may comprise subsections having flexible walls. However, preferably all conveying tubes of the vacuum conveying system are formed as hoses having flexible circumferential walls. At certain subsections of the system, in particular at bulk material discharging sections for feeding the powdery or bulk material and at bulk material receiving sections, such as filters or storage vessels, the circumferential walls may also comprise rigid walls. At such sections it is, however, preferred to provide a double-layer structure of these walls, including a tubular outer wall, which is rigid, and a lining of a flexible material covering the inner surface of the tubular wall. Preferably, the lining is linked with the inner surface only at discrete locations spaced apart from each other so that a free space can remain between the inner surface and the lining, which can be used for applying high-pressure air or vacuum to either inflate or stretch the flexible lining or to suck the flexible lining onto the inner surface of the respective section of the vacuum conveying system. Thus, adherence of powdery or bulk material on the inner surface of the flexible lining is effectively eliminated. 
         [0013]    According to another embodiment of the present invention valves disposed at respective ends of said vacuum conveying system and/or dividing said vacuum conveying system into subsections are closed, when said pressurized gas is applied to said vacuum conveying system or to a respective subsection thereof so that those sections of the system comprising flexible walls can be inflated to eliminate adherence of powdery or bulk material. 
         [0014]    According to another embodiment of the present invention the method comprises additionally the step of resuming a normal operation of the vacuum conveying system comprising the steps of: disconnecting the pressurized gas from the vacuum conveying system; and connecting the vacuum blower with the vacuum conveying system for generating the flow of conveying gas; wherein the step of resuming normal operation further comprises the steps of: slowly opening a valve used for disconnecting the bulk material receiving section while keeping closed valves used for connecting said bulk material discharging section for slowly letting off the high pressure gas prevailing within said vacuum conveying system and opening said valves used for connecting said bulk material discharging section for causing conveyance of bulk material from said discharging section to said bulk material receiving section. Thus, in a first step of the step of resuming normal operation the overpressure prevailing in the vacuum conveying system is let off and thus reduced to atmospheric pressure whereas, in a second step, the tubes and/or hoses of the vacuum conveying system are again connected with the vacuum blower for building up again the conveying gas flow used for conveying the powdery or bulk material in the system. Finally, valves or shutter means of the bulk material discharging sections are selectively opened again to disperse bulk material in the conveying gas flow and create a flow of fluidized bulk material to be conveyed in the vacuum conveying system. 
         [0015]    According to another embodiment of the present invention the steps of disconnecting said vacuum blower, applying pressurized gas and resuming a normal operation of said vacuum conveying system are performed repeatedly until a satisfactory condition, in particular a satisfactory effective conduit or flow cross section, of the vacuum conveying system is obtained. 
         [0016]    According to another embodiment of the present invention the vacuum conveying method is performed fully automatically under the control of a suitable controlling device for controlling the timings for opening/closing the valves of the vacuum conveying system. Accordingly, another related aspect of the present invention is directed to a controlling device for controlling a vacuum conveying system such as to perform the steps of the above vacuum conveying method. For determining the degree of adherence or clogging of the vacuum conveying system, a measured value indicative of the degree of adherence or clogging of the vacuum conveying system or of a subsection thereof is determined. Based on the measured value the steps of disconnecting said vacuum blower and applying pressurized gas are initiated automatically, by the controller device, if the measured value exceeds a predetermined threshold value representative of a satisfactory degree of adherence or clogging of the vacuum conveying system. The measured value can correspond e.g. to a power consumption of the vacuum blower and/or to a pressure drop in the vacuum conveying system. For controlling the vacuum conveying method, the valves and the vacuum blower of the system are controlled automatically in accordance with the above method steps. 
         [0017]    Another related aspect of the present invention relates to a software or computer program product, comprising computer program code means for causing the afore-mentioned controlling device to perform the steps of a method according to the present invention, when executed by a data processing means of said controlling device, such as a general-purpose computer, a dedicated data processor, an application specific integrated circuit (ASIC) or the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Hereinafter the present invention will be described with reference to exemplary embodiments and drawings, from which further advantages, features and objects will become apparent to a person skilled in the art and wherein: 
           [0019]      FIG. 1  shows a schematic diagram of a vacuum conveying system according to the present invention; 
           [0020]      FIG. 2  is a schematic cross section of a hose for use in the vacuum conveying system according to  FIG. 1 ; and 
           [0021]      FIG. 3  is a schematic flow diagram of a control method according to the present invention. 
       
    
    
       [0022]    Throughout the drawings identical reference numerals relate to identical or substantially equivalent elements or groups of elements. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0023]    In the following, the overall configuration of the vacuum conveying system  1  will be described with reference to  FIG. 1  first. Referring to  FIG. 1 , the vacuum conveying system  1  consists of a plurality of conveying hoses  5  to  7  for connecting the bulk material receiving sections  8 ,  9  with bulk material discharging sections  2 ,  4 . More specifically, the first bulk material discharging section consists of a tube  2  having a hopper  22 , which is unitarily provided with the tube  2 . The first bulk material discharging section  2  is connected, via rotary valve  24 , with a silo container  20  used for storing bulk material, such as a powder. The first discharging section  2  is connected, via connecting hose  3 , with a second bulk material discharging section  4  of similar configuration. More specifically, the second bulk material discharging section  4  consists of a tube  4  having a hopper  23 , which is unitarily connected with the tube  4 . The second bulk material discharging section  4  is connected, via rotary valve  25 , to a bag  21  used for storing bulk material, such as a powder. Squeeze valves  15 ,  16  are disposed at the ends of the connecting hose  3  for disconnecting the first discharging section  2  and the connecting hose  3 , respectively, from the remainder of the conveying system  1 . 
         [0024]    The second discharging section  4  is connected, via hose  5 , to a diverter valve  26  used to switch vacuum conveyance either to the first bulk material receiving section  8  (as indicated in  FIG. 1 ) or to a second bulk material receiving section  9 . In the exemplary embodiment according to  FIG. 1  both bulk material receiving sections  8 ,  9  are indicated as filter receivers each having a filter structure for separating the air used for conveying the bulk material from the bulk material itself. In operation, the powdery particles of the bulk material collide with the respective filter structure and then fall down towards a hopper and are discharged, via rotary valve  29  and  28 , respectively, to a first outlet OUT 1  or a second outlet OUT 2 , respectively, whereas the separated air stream is sucked, via hose  12  and  11 , respectively, by the common vacuum blower  10 . Via valves  35 ,  36  a pulsating stream of air can be selectively applied to the filter structure of the respective filter section  9  and  8 , respectively, for imposing mechanical vibrations and loosening adhering powdery particles from the respective filter structure. 
         [0025]    As shown in  FIG. 1 , squeeze valves  18 ,  19  can be used for closing the ends of the hoses  6 ,  7  and disconnecting the vacuum blower  10 . The filter sections  8 ,  9  are disposed in pressure-tight boxes. On the top cover of the filter sections  8 ,  9  there is provided an orifice so that the interior of the filter sections  8 ,  9  communicates with the hose  12 ,  11  and the vacuum blower  10 . Butterfly valves  34 ,  33  are provided for disconnecting the filter sections  8 ,  9  from the vacuum blower  10 . 
         [0026]    As shown in  FIG. 1 , the first bulk material discharging section  2  is connected, via hose  14 , with an air inlet  13 . In a normal operating condition and in the condition of the diverter valve  26  as indicated in  FIG. 1 , the valves  15 ,  16 ,  17 ,  5 ,  18 ,  34  are open so that the inlet of the vacuum blower  10  generates a stream of warm air, which flows e.g. from air inlet  13 , via hose  14 , tube  2  of the first discharging section, the connecting hose  3 , the tube  4  of the second discharging section, conveying hose  5  and conveying hose, towards the bulk material receiving section  8 , from where the air is sucked, via line  12 , towards the inlet of the vacuum blower  10 . Thus, bulk material, which is falling down from the silo container  20  and/or storing bag  21 , is dosed by the rotary valves  24 ,  25  into the associated hopper  22 ,  23  in accordance with the stream of air in the vacuum conveying system. Furthermore, the bulk material is finely dispersed in the air flow. The resulting fluid bulk material is conveyed by the air flow towards the bulk material receiving section  8 , where the bulk material is again separated from the air and discharged, via rotary valve  29 , from outlet OUT 1 . On the other hand, if the diverter valve  26  is switched to the illustrated alternative position, the resulting fluid bulk material is conveyed by the air flow towards the bulk material receiving section  9 , where the bulk material is again separated from the air and discharged, via rotary valve  28 , from outlet OUT 2 . 
         [0027]    As shown in  FIG. 1 , a filter  30  is provided upstream from the inlet of the vacuum blower  10  to protect the vacuum blower  10 . Upstream from the filter  30 , there is provided an air inlet valve that is opened when the butterfly valve  33  is closed, for establishing a stand-by operating condition of vacuum blower  10 , as will be explained in more detail below. In a normal operating condition of the vacuum conveying system  1 , the vacuum breaking valve  32  is closed so that the vacuum blower  10  generates a vacuum in hoses  11 ,  40 , depending on the state of the valves  33  and  41 , respectively. Furthermore, a pressure indicator  38  is disposed upstream from the vacuum blower  10  for measuring the pressure upstream from the vacuum blower  10  for obtaining a measured value representing a pressure drop upstream from the vacuum blower  10 . As an alternative or auxiliary measure, also the power consumption of the vacuum blower  10  can be measured. As will become apparent to a person skilled in the art, the above or other measured values are representative for the effective conduit or flow cross section of the vacuum conveying system  1  and thus are a good indicator for monitoring the adherence of bulk or powdery material to the inner walls of the conveying tubes and/or hoses of the vacuum conveying system  1  and for the degree of clogging of the vacuum conveying system  1 . 
         [0028]    According to the exemplary embodiment shown in  FIG. 1 , the hopper  22  and the tube  2  of the first bulk material discharging section consists of a metallic casing with a lining of a flexible, pressure-tight material, such as rubber. Preferably, the flexible lining is not bonded to the casing but instead only clamped to the metallic casing at a plurality of discrete locations spaced apart from each other, e.g. at the connecting flanges between the tube  2  and adjacent hose  14  and  3 , respectively, and at the connecting flanges between the hopper  22  and the adjacent rotary valve  24 . The second bulk material discharging section  4  has a similar configuration so that a detailed description thereof can be omitted. 
         [0029]    As shown in the bottom part of  FIG. 1 , according to the present invention the vacuum conveying system further comprises a source of pressurized air, i.e. of high pressure air or of air under a pressure above the suction pressure in the vacuum conveying system. In  FIG. 1 , the source of pressurized air is schematically indicated by arrow  50 . More specifically, the source of pressurized air comprises an inlet  50  for high pressure air, which communicates, via lines  52  and  63 , with a space between the tube  2  and hopper  22  and the associated inner lining of flexible material of the first bulk material discharging section, via lines  52 ,  64  and  65 , with a space between the tube  4  and hopper  23  and the associated inner lining of the second bulk material discharging section, and, via line  54 , with hose  5 , if diaphragm or solenoid valve  60  and diaphragm or solenoid valve  57  are opened. Pressure reducing valves  58 ,  55 , with associated pressure indicators  38 , can be used for adjusting the pressure of the high pressure air. Pressure safety valves  61 ,  62  are provided, for safety reasons, for discharging high pressure air, e.g. in case of emergency or for maintenance purposes. 
         [0030]    As shown in  FIG. 1 , the inlet of vacuum blower  10  also communicates, via hoses  40 ,  43 , with the space between the tube  2  and hopper  22  and the associated inner lining of flexible material of the first bulk material discharging section and, via hoses  40 ,  42 , with the space between the tube  4  and hopper  23  and the associated inner lining of the second bulk material discharging section. Thus, if the ball valve  41  is opened any overpressure existing in hoses  40 ,  42  and  43  can be released. 
         [0031]    In the normal operating condition of the vacuum conveying system  1 , the inlet  50  for high pressure air and/or the valves  60 ,  56  are closed so that no overpressure is generated in order to push away the inner linings of flexible material from the tube  2 ,  3  and the hopper  22 ,  23  of the first and second bulk material discharging section, respectively, for stretching the inner linings and thus removing or reducing the adherence of powdery or bulk material to the inner linings. Furthermore, in the normal operating condition of the vacuum conveying system  1 , the ball valve  41  is open so that the vacuum blower  10  generates a vacuum on line  40  in order to suck the inner linings of flexible material to the tube  2 ,  3  and the hopper  22 ,  23  of the first and second bulk material discharging section, respectively, for ensuring an optimum conduit in the first and second bulk material discharging section, respectively. 
         [0032]    As shown in  FIG. 1 , the outlet of the vacuum blower  10  is connected with hose  44 , which ends in a hopper-shaped outlet  45  directly opposite to the air inlet  13  of the vacuum conveying system  1 . Thus, the warm and dry air exiting from the outlet of the vacuum blower  10  is recycled and enters the air inlet  13 . Thus, the conveying flow of air in the tubes and/or hoses of the vacuum conveying system  1  is relatively warm and dry, which further prevents clogging and adhering of powdery or bulk material in the vacuum conveying system  1 . 
         [0033]    According to a preferred embodiment according to the present invention the main conveying lines of the vacuum conveying system  1  consist of hoses of the type shown in  FIG. 2  or at least comprise portions having flexible walls, like the hose shown in  FIG. 2 .  FIG. 2  shows a partial cross sectional view of a hose  70  for use in the vacuum conveying system according to the present invention. As shown in  FIG. 2 , the hose  70  comprises a tubular wall  71  of a flexible material, such as rubber. Typical outer diameters of the hose  70  lie in the range between approx. 50 mm to approx. 130 mm, depending on the throughput of the vacuum conveying system. At equidistant intervals of e.g. 800 to 1,000 mm, supporting coils or bearing rings  73  are embedded in the circumferential wall  71  of hose  70  in order to prevent an uncontrolled collapse of hose  70  and to ensure an appropriate effective conduit of hose  70 . Furthermore, a flange  72  is embedded in the circumferential wall  71  at the end of hose  70 , for connecting to an orifice  74  of another member of the vacuum conveying system, as will become apparent to a person skilled in the art. Typically, a hose used in a vacuum conveying system according to the present invention is adapted to withstand overpressures up to approx. 3 to 10 bar, depending on the effective throughput to be achieved. 
         [0034]    Referring to  FIGS. 1 and 3 , a process cycle for removing adherence of powdery or bulk material to the circumferential walls of the hoses and/or to the inner linings of the bulk material discharging sections and of the hoppers will be described. 
         [0035]    As shown in  FIG. 3 , the process cycle assumes that the system is initially working in a normal vacuum conveying operating condition (step S 1 ) that will be described hereinafter. In the normal vacuum conveying operating condition (or normal operating condition), the valves  15 - 18  and  34  are open so that air entering the vacuum conveying system  1  via air inlet  13  is sucked by the vacuum blower  10  for generating a conveying air flow in the vacuum conveying system  1 . The rotary valves  24 ,  25  are selectively opened so that bulk or powdery material stored in the silo container  20  and storing bag  21  can enter the associated hopper  2  and  4 , respectively, to be dispersed in the conveying air flow in the respective bulk material discharging section  2 ,  4 . The conveying air flow conveys the powdery or bulk material from the bulk material discharging section  22  and/or  23  to the bulk material receiving section (filter section)  8  and bulk material outlet OUT 1 . In the normal operating condition, the valve  41  is open so that the inner linings of flexible material are sucked against the associated casing of the respective bulk material discharging section  2 ,  4 . Furthermore, the high pressure air inlet  50  and valves  60 ,  57  are closed in order to prevent that the inner linings of flexible material lift off from the associated casing of the respective bulk material discharging section  2 ,  4  and that the conveying hoses  3 ,  5  are inflated by the high pressure air. 
         [0036]    During the above normal operating condition, powdery or bulk material may adhere to the inner walls of the hoses and/or inner linings, caused e.g. by agglomerating of powdery particles due to moisture of the conveying air flow. Adherence of powdery or bulk material to the inner walls of the hoses and/or inner linings will reduce the effective conduit or flow cross section of the vacuum conveying system  1  and will finally result in a clogged state, which is to be avoided. For this purpose, a measured value representative of the effective conduit of the vacuum conveying system is derived, e.g. the effective power consumption of the vacuum blower  10  or a pressure drop within the vacuum conveying system  1 . 
         [0037]    As shown in  FIG. 3 , in step S 2  it is determined whether the vacuum conveying system is in a clogged state. For this purpose the measured value is compared with a predetermined threshold value representative of a minimum acceptable effective conduit of the vacuum conveying system  1 . If it is determined in step S 2  that the system is not in a clogged state, the process returns to step S 1 . On the other hand, if it is determined in step S 2  that the system is in a clogged state, the process continues with step S 3 , which will be explained in the following. 
         [0038]    First, in step S 3  the rotary valves  24 ,  25  are closed to stop discharging of bulk or powdery material into the conveying air flow. Furthermore, the air control valve  31  of the vacuum blower  10  opens so that the conveying air flow in the vacuum conveying system stops and a stand-by operation of the vacuum blower  10  is started. As a next step, the squeeze valves  15 - 18  and  34  are closed to disconnect the vacuum blower  10  from the conveying hoses  3 ,  5  and  6 , from the bulk material discharging sections  2 ,  4  and from the filter section  8 . As a next step, the high pressure generating section is activated, by opening the inlet  50  for high pressure air and the valves  56  and  60 . Thus, an overpressure regulated by the pressure reducing valves  58 ,  55  is applied to the bulk material discharging sections  2 ,  4  and to the conveying hoses  3 ,  5  and  6 . Thus, the inner linings of flexible material are separated from the casings of the bulk material discharging sections and the flexible hoses  3 ,  5  and  6  are inflated or stretched to thus reduce or eliminate adherence of powdery or bulk material to inner walls of the vacuum conveying system  1 . In this manner, steps S 4  and S 5  according to  FIG. 3  are performed. 
         [0039]    As will become apparent to a person skilled in the art, the valves  41 , on the one hand, and  56 ,  60 , on the other hand, may be actuated in such a manner as to inflate and deflate the flexible walls of the vacuum conveying system to thereby reduce adherence of bulk material to the flexible walls of the vacuum conveying system. As an alternative, the valves  41 ,  56  and  60  may also be actuated in such a manner that, before resuming normal operation of the vacuum conveying system, an idle pressure is measure in the vacuum conveying system and such that the flexible walls of the vacuum conveying system are inflated and deflated again if the idle pressure should still be too high, which usually is indicative of a clogging state of the vacuum conveying system. 
         [0040]    Finally, the adhered particles are removed from the inner walls of the vacuum conveying system to a satisfactory extent, which can be controlled by varying the time period of the process cycle consisting of the steps S 2  to S 5  according to  FIG. 3 . 
         [0041]    Referring to  FIG. 3 , as a next step the normal operating condition of the vacuum conveying system is resumed in step S 6 . For this purpose, the valves  56 ,  60  and/or the high pressure air inlet  50  are closed first. As a next step, the valves  17  and  18  are opened slowly so that the overpressure developed in the conveying hoses  5 ,  6  is slowly reduced. As a next step, the remaining squeeze valves  15  and  16  and the valve  34  are opened and the air control valve of the vacuum blower  10  are opened so that the conveying air flow in the vacuum conveying system builds up again, as described above. As a next step the rotary valves  24 ,  25  of the discharging sections are selectively actuated and reopened to cause dispersion of powdery or bulk material in the conveying air flow. Furthermore, the valve  41  is opened again so that the inner linings of flexible material of the discharging sections  2 ,  4  are sucked against the rigid casings of the discharging sections  2 ,  4 , as described above. Finally, the normal operating condition is resumed and the process reverts to step S 1 . 
         [0042]    If it is determined, in step S 2 , that the vacuum conveying system is still clogged, as derived by comparing the measured value with the predetermined threshold value, the cycle consisting of the steps S 3  to S 6  is performed again, until a satisfactory effective conduit of the vacuum conveying system is obtained again, as indicated by the afore-mentioned measured value. 
         [0043]    As will become apparent to a person skilled in the art, the control valves of the vacuum conveying system according to the present invention are preferably electronic control valves that can be actuated in accordance with control signals output by a suitable controlling device. Accordingly, another closely related aspect of the present invention relates to a controlling device configured for performing the method steps as described above. According to the present invention, such a controlling device may be implemented using any kind of general-purpose computer, processor, application-specific integrated circuit (ASIC) or similar data processing means. Of course, such a data processing means may comprise a volatile or non-volatile memory for storing a computer program code configured to execute the method steps as described above when run on the data processing device of the controlling device. Thus, according to another preferred aspect of the present invention, the vacuum conveying method can be performed fully automatically, under the supervision of such a controlling device. 
         [0044]    As will become apparent to a person skilled in the art, the vacuum conveying method and controlling device according to the present invention can be applied to conveying any kind of powdery or bulk material, including, but not limiting the present invention, powders of TiO 2 , kaoline, chalk, in particular black chalk, and carbon black. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  vacuum conveying system 
           2  bulk material discharging section 
           3  connecting hose 
           4  bulk material discharging section 
           5  central conveying hose 
           6  conveying hose 
           7  conveying hose 
           8  bulk material receiving section 
           9  bulk material receiving section 
           10  vacuum blower 
           11  tube/hose 
           12  tube/hose 
           13  air inlet 
           14  hose 
           15  squeeze valve 
           16  squeeze valve 
           17  squeeze valve 
           18  squeeze valve 
           19  squeeze valve 
           20  bulk material container 
           21  bulk material containing bag 
           22  hopper 
           23  hopper 
           24  rotary valve 
           25  rotary valve 
           26  diverter valve 
           28  rotary valve 
           29  rotary valve 
           30  filter 
           31  air inlet valve 
           32  vacuum breaker 
           33  butterfly valve 
           34  butterfly valve 
           35  vibrator/inlet for pulse air 
           36  vibrator/inlet for pulse air 
           38  pressure indicator 
           40  tube 
           41  ball valve 
           42  connecting tube 
           43  connecting tube 
           44  line for recycled air (from vacuum blower  10 ) 
           45  outlet for recycled air 
           50  inlet for high pressure air 
           51  tube/hose 
           52  tube/hose 
           53  tube/hose 
           54  tube/hose 
           55  pressure reducing valve 
           56  hand valve 
           57  diaphragm or solenoid valve 
           58  pressure reducing valve 
           59  hand valve 
           60  diaphragm or solenoid valve 
           61  pressure safety valve 
           62  pressure safety valve 
           63  tube/hose for high pressure air 
           64  connecting tube or hose 
           65  tube/hose for high pressure air 
           70  hose 
           71  tubular hose body 
           72  flange 
           73  supporting coil or bearing ring 
           74  flange