Abstract:
A vacuum receiver for a pneumatic conveyor for conveying, e.g., plastic pellets, having a receiving vessel with a material inlet, a material outlet and a conveying gas outlet. A first valve member is provided for opening and closing the conveying gas outlet, and a second valve member is provided for opening and closing the material outlet. Both valve members are connected to a common valve shaft and actuated by a single actuator mounted on a vessel lid. The vacuum receiver of the invention has the advantage of affording positive control and sealing of the material discharge valve while at the same time being economical to manufacture and easily cleaned.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a new pneumatic conveying receiver with positive dump valve control, particularly for used as a vacuum receiver for a pneumatic conveying systems for conveying a particulate material, such as plastic pellets.  
         [0002]     For many uses of bulk granular materials in the manufacturing environment a pneumatic transport system is the preferred method of bulk material handling. It allows the movement of a wide variety of materials through a simple tubular piping system. The low cost, easy installation, and when using vacuum as a motive power, minimal housekeeping since dust leaks are unlikely, make it a preferred selection. These systems will incorporate a power source such as a fan or blower, a source of material, a termination receiver, the connecting tube from the source to the receiver, and then on to the vacuum power unit, and a control device. In normal operation a simple system will load the individual receiver by engaging the air mover and allowing the source material to feed into the pickup end of the pipe, and separate at the receiver. This is done as a batch process to minimize costs associated with the valving of the material removal at the discharge of the receiver.  
         [0003]     A typical construction of these units has an actuator, either air or electric to connect the receiver to the pneumatic power source, and a power operated discharge valve with a second actuator to discharge the conveyed product from the vessel. It is known to use air cylinders to provide power for operation of these valves, but when there are two separate functions, there are always two separate power units to maneuver the valves. The market for these devices is very cost sensitive, however, and if two air operators are used, the expense of the second actuator represents a significant cost disadvantage. In the exceptionally price competitive market of basic pneumatic conveying systems, the additional cost of an actuated discharge valve at each termination point can become prohibitive.  
         [0004]     In a less costly arrangement, the expense of the second actuator may be avoided by using an un-powered, gravity-operated dump valve. A gravity operated discharge valve will allow the conveyed material to drop from the receiver after the vacuum dissipates when each batch has been completed. However, the lack of a positive actuation of the common gravity operated material dump valve mechanisms also leads to problems. In some cases this gravity operated valve will be blocked by stray granules of the material being handled, and consequently not transport a batch during the load cycle. Not infrequently such valves fail to properly seal due to the lack of a positive closing force. This failure to seal can prevent build-up of the necessary vacuum to draw further material from the pellet source to the vacuum receiver.  
         [0005]     Thus, the usual construction of vacuum receivers uses either a gravity dump valve for the simple device, or an actuated material dump valve for the more positive seal. But when a gravity operated dump valve is used, there will be the opportunity to have a missed load cycle if the valve is partially open due to trapped granules at the sealing surfaces. And although use of a power actuated valve will overcome the usual trapped material at the seal, the cost of a second actuator device may render the apparatus prohibitively expensive.  
         [0006]     The normal requirement for access to the internal vacuum receiver surfaces for cleaning and maintenance do not allow a convention linkage between the two valve devices to be used on a typical vacuum receiver. These units typically incorporate a funnel bottom, cylindrical vessel with the material dump valve at the lower end of the funnel. The upper end of the cylinder will be open, and a separate lid will cover the opening, and will usually hold or contain the air/material separator media, and the air outlet. Since the selection valve is associated with the lid and air outlet, a removable lid makes it unfeasible to link a dump valve device to the vacuum sequence selection valve on the air outlet.  
       SUMMARY OF THE INVENTON  
       [0007]     Accordingly, it is the object of the invention to provide an improved vacuum receiver with a positive dump valve control.  
         [0008]     It is also an object of the invention to provide a reliably operating vacuum receiver which can be constructed at moderate cost by eliminating the need for a second actuator to control the dump valve.  
         [0009]     Yet another object of the invention is to provide a vacuum receiver with a positive dump valve control, which is inexpensive to produce and yet allows the vessel lid to be readily removed to facilitate cleaning of the receiving vessel.  
         [0010]     These and other objects are achieved in accordance with the present invention by providing a vacuum receiver for a pneumatic conveying system comprising a receiving vessel having a material inlet, a material outlet and a conveying gas outlet; a conveying gas valve for selectively opening and closing said conveying gas outlet; a discharge valve for selectively opening and closing said material outlet; and a single actuator for actuating said convey gas valve and said discharge valve.  
         [0011]     Further preferred aspects of the invention are described in the dependent claims.  
         [0012]     In accordance with the present invention, a single air operator is arranged in a unique way to actuate both the a valve connecting the vacuum receiver to a pneumatic power (vacuum) source and to actuate a positively operated dump valve for emptying the receiver into a hopper. In this way, it is possible to avoid the disadvantages of a non-positively acting, gravity-operated discharge valve for the dumping of the vessel and provide a positively controlled dump valve while eliminating the need for a second operator.  
         [0013]     In construction of these chambers, the need for an automatically compensating seal force is provided by an air cylinder. The use of a “Short Stroke” in both directions to alternately seal the air manifold (i.e., the connection to the conveying power source), and the material conveying vessel dump valve compensates for any minor differences in manufacturing tolerances or wear over time.  
         [0014]     The design of the terminal end of a pneumatic conveyor for granular bulk solids comprises a vessel with a material inlet, an air/material separator, an air outlet and a material outlet. In the present invention, the material outlet on the receiver is not a gravity operated dumping valve. Instead, a power actuated valve is employed as a more positive device.  
         [0015]     In many convey systems there are more than one vacuum receiver on a single air power (vacuum) source. In this configuration, a valve is required to access each individual vacuum receiver since only one convey receiver can be operating on line at a time. The construction of the vacuum receivers for these systems employs an actuator of the vacuum line access of the individual receiver.  
         [0016]     The vacuum receiver according to the invention uses a single operator with two attachment positions for both a vacuum sequence valve and an internal positive acting material dump valve. The method to accomplish this relies on the use of an air operated actuator for movement of both sealing devices. Positioning each of the seals in such a manner that the air cylinder will seat and seal its respective opening before reaching the end of the cylinder stroke affords a positive seal while still accommodating any small dimensional changes in the assembly or misalignment of components.  
         [0017]     By use of the lower conical portion of the vacuum receiver as the dump valve seat, it will automatically guide the seal to full contact with the cone. The upper air sequence valve seal is provided with a soft contact attachment so any minimal angular misalignment will be overcome.  
         [0018]     Another important feature of the new device is that the whole mechanism is mounted on the lid of the receiver so it removes with the lid allowing complete access to the internal surfaces of the chamber for cleaning.  
         [0019]     An additional benefit of a single actuator is that it avoids the use of two devices, and the attendant opportunity for breakage or other malfunction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawings, in which:  
         [0021]      FIG. 1  is a side elevational view of an embodiment of a vacuum receiver according to the invention.  
         [0022]      FIG. 2  is a sectional view of the vacuum receiver embodiment of  FIG. 1 .  
         [0023]      FIG. 3  is a perspective view of the dual valve arrangement of the invention.  
         [0024]      FIG. 4  is a side elevational view of an alternative embodiment of the invention provided with a glass tube chamber for monitoring the inventory of particulate material in the vacuum receiver. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]      FIG. 1  is a side elevation view of an embodiment of a vacuum receiver according to the invention. The vacuum receiver  10  comprises a receiving vessel  12  having a material inlet  14 , a material outlet  20  and a conveying gas outlet  36 . Receiving vessel  12  is preferably a funnel bottom vessel, with the material outlet  20  disposed at the bottom of the funnel portion of the vessel. A lid  26  is provided for the top of the vessel. In the illustrated embodiment, lid  26  is held in place by a plurality of clamps  30 , although it will be recognized that any suitable fastening mechanism could be used to affix the lid to the receiving vessel.  
         [0026]     A conveying gas source  40 , such as a vacuum pump, is connected via a connecting tube  38  to the conveying gas outlet  36 . Material inlet  14  is connected to a granular material source  16  via a connecting tube  18 . A mounting flange  32  is secured to receiving vessel  12  to facilitate mounting the receiving vessel in a desired position above a receiving hopper  24 , which may, for example, be a supply hopper for a plastic molding machine.  
         [0027]     As seen more clearly in  FIG. 2 , which is a sectional view of the vacuum receiver  10 , a screen  34  is provided in front of the conveying gas outlet  36 . Screen  34  serves to separate conveyed particles, e.g. plastic pellets, from a stream of conveying gas, e.g. air, inside the vacuum receiver. Also visible in  FIG. 2  is a lid seal  28 , which is disposed between the receiving vessel  12  and the receiver lid  26  in order to provide a gas-tight closure.  
         [0028]     A conveying gas valve member  46  is provided in order to open and close the conveying gas outlet  36 . Likewise, a material discharge valve member  52  is provided to open and close the material outlet  20  at the bottom of the receiving vessel  12 . Conveying gas valve member  46  and material discharge valve member  52  are both connected to a common valve rod  44 . The valve rod, in turn, is connected to an actuator  42 , such as a compressed air cylinder, by which valve rod  44  can be extended or retracted. In the illustrated embodiment, extension of valve rod  44  moves conveying gas valve member  46  downwardly in order to unblock the conveying gas outlet  36 . Extension of valve rod  44  also moves material discharge valve member  52  downwardly to a position in which is seats firmly against the lower walls of the funnel portion of the receiving vessel  12 , thereby closing material outlet  20 .  
         [0029]     In operation, the vacuum pump which serves as conveying gas source  40  is switched on to draw a stream of air out of the vacuum receiver  10 , so that a reduced pressure is created therein. The reduced pressure in vacuum receiver  10 , in turn, draws granular material entrained in a stream of conveying gas from granular material source  16  through connecting tube  18  and material inlet  14  into the vacuum receiver  10 . An accumulation of granular material  22  is shown in the bottom of receiving vessel  12 . Screen  34  prevents any of the granular material  22  from passing with the conveying gas through conveying gas outlet  36 .  
         [0030]     When the granular material  22  in receiving vessel  12  reaches a desired level, a controller  48  is actuated to admit compressed air from a compressed air source  50  to the bottom of air cylinder  42  so that valve rod  44  is retracted, or in other words raised. This moves conveying gas valve member  46  upwardly over the mouth of the conveying gas outlet  36 , thereby blocking the flow of conveying gas and terminating the pneumatic transfer of granular material from granular material source  16  into the vacuum receiver  10 .  
         [0031]     At the same time, the retraction of valve rod  44 , also moves material discharge valve member  52  to a raised position, so that material discharge  20  is opened, and the granular material  22  can flow out of the receiving vessel  12 , thereby delivering a desired batch of the granular material  22  into receiving hopper  24 .  
         [0032]     After the vacuum receiver  10  is emptied, controller  48  is again actuated, this time to deliver compressed air from compressed air source  50  to the top of air cylinder  42 , thereby driving valve rod  44  downwardly to its extended position. This urges the material discharge valve member  52  with a positive force against the mouth of the funnel bottom of receiving vessel  12 , thereby tightly closing the material outlet  20 . At the same time, conveying gas outlet valve member  46  is moved downwardly away from the entrance to conveying gas outlet  36 , thereby enabling the vacuum pump  40  to draw a new stream of conveying gas with entrained granular material  22  from granular material source  16  into the vacuum receiver  10 .  
         [0033]     If it is necessary to clean the vacuum receiver, for example if the vacuum receiver is to be switched to a different source of plastic pellets, this may be easily accomplished by removing lid  26 . Since the actuator  42 , valve rod  44 , conveying gas valve member  46  and material discharge valve member  52  are all connected to lid  26 , they will all be moved out of the way when the lid  26  is removed, thereby providing unhindered access to the receiving vessel  12  for cleaning.  
         [0034]      FIG. 3  is a perspective view of the valve assembly of the invention showing how the conveyance air valve member  46  and the dump valve member  52  are both mounted on a common valve rod  44 . Dump valve member  52  has a conical configuration to achieve a positive conic seal with the funnel bottom of receiver vessel  12  when valve rod  44  is urged downwardly by actuator  42 .  
         [0035]      FIG. 4  is a side elevational view of an alternative embodiment of the vacuum receiver of the invention in which like parts are identified by the same reference numerals as in the first embodiment illustrated in  FIGS. 1 through 3 . The operation of this embodiment is essentially the same as the embodiment of  FIGS. 1 through 3 . However, the funnel bottom of receiving vessel  12  is provided with a glass tube chamber to enable monitoring of the particulate material in the apparatus. In this embodiment, the funnel bottom of the receiving vessel is provided with an upper clamping flange  54 , which in turn, is connected to a lower clamping flange  56  by a plurality of rods  58 . The bottom clamping flange  56  is connected to a support base or mounting base  62 . A transparent glass tube  60  is clamped between the upper and lower clamping flanges  54  and  56 . If desired, resilient seal members (not shown) may be arranged between the clamping flanges and the glass tube to assure that the system remains vacuum tight. Transparent glass tube  60  allows visual observation of the supply of particulate material in the vacuum receiver. The glass tube chamber is typically sized to maintain five shots or five minutes of material at the feed throat of the apparatus. Easy access to the glass tube chamber for cleaning or other purposes may be obtained by simply unscrewing the rods  58 .  
         [0036]     To facilitate automatic control of the level of particulate material in the system, the glass tube chamber  60  optionally may be provided with a level sensor  66  mounted in a sensor support bracket  64 . Sensor  66  can provide a control signal to operate the vacuum valve to fill and empty the receiving vessel  12 . Sensor support bracket  64  is movably mounted on one or more of the support rods  58  so that it can be raised or lowered as needed to adjust the position of the level detector and the amount of particulate material maintained in the glass tube chamber  60 . In the illustrated embodiment, a thumb screw  68  is provided to hold the bracket  64  and sensor  66  at the desired level, but any other suitable clamping arrangement could be used instead.  
         [0037]     The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.  
       List of Reference Numerals  
       [0038]      10  Vacuum receiver  
         [0039]      12  Receiving vessel with funnel bottom  
         [0040]      14  Material inlet  
         [0041]      16  Granular material source  
         [0042]      18  Connecting tube  
         [0043]      20  Discharge outlet  
         [0044]      22  Granular Material  
         [0045]      24  Receiving hopper  
         [0046]      26  Receiver lid  
         [0047]      28  Lid seal  
         [0048]      30  Lid clamps  
         [0049]      32  Mounting flange  
         [0050]      34  Separator screen  
         [0051]      36  Air outlet  
         [0052]      38  Air connecting tube  
         [0053]      40  Convey air (vacuum) source  
         [0054]      42  Actuator (compessed air cylinder)  
         [0055]      44  Valve rod  
         [0056]      46  Convey air valve  
         [0057]      48  Controller  
         [0058]      50  Compressed air source  
         [0059]      52  Discharge valve  
         [0060]      54  Upper clamping flange  
         [0061]      56  Lower clamping flange  
         [0062]      58  Rods  
         [0063]      60  Glass tube chamber  
         [0064]      62  Base  
         [0065]      64  Sensor support bracket  
         [0066]      66  Material level sensor  
         [0067]      68  Thumbscrew