Patent Publication Number: US-6216285-B1

Title: Waste transport arrangement

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a vacuum sewer system for transporting waste to a collecting container, municipal sewer, or the like. 
     BACKGROUND OF THE INVENTION 
     One basic problem with vacuum sewer systems relates to the high noise they produce. The noise occurs when the sewer valve opens and closes and when air is drawn into the open sewer. The vacuum sewer technique requires a relatively great volume of air to rapidly flow into the sewer immediately following the material to be transported. Further, the sewer valve must open and close rapidly. These functions cause considerable noise reducing pressure variations. 
     Reducing the noise level in a large vacuum sewer system is particularly difficult, because a large system has a greater total volume. As a result, large vacuum sewer systems typically require an intake of large amounts of air. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to create a sewer arrangement that is entirely based on the vacuum sewer technique and is adapted for use in a large vacuum sewer system, in which arrangement the noise level is low and in which the function control is easy to perform. The characteristic features of the invention are stated in the claims. A vacuum sewer system of this kind combines the advantages of the vacuum sewer technique with a low noise level in spite of a large sewer volume. 
     The invention is based on two observations. First, less noise is produced if lesser amounts of air have to be let into the sewer through a sanitary unit, e.g. a toilet. Secondly, the noise level is reduced, if the average speed of the air stream in question can be lowered during the emptying of a sanitary unit. 
     According to the invention, the emptying of and the waste transport from a sanitary unit, e.g. a toilet, is made in two stages, both of which take part in a sewer under vacuum. In the first stage, waste transport is performed, as known per se, through a first sewer portion into an intermediate container under vacuum. This makes it possible to keep the transport distance short and the applied volume under vacuum relatively small. Irrespective of the total size of the vacuum sewer system, the first stage of waste transport can be carried out in a system of standard design, which improves functional reliability because a standard system can be trimmed to optimize its functionality. Small-size vacuum sewer devices having this type of initial function are known from U.S. Pat. No. 5,133,853. Their primary weakness lies in the fact that the vacuum induced waste transport ends in the intermediate container. From there on the waste must be transported by pressurized air or by another pressure agent, which would be really troublesome in a large system. According to the invention, the entire waste transport mechanism is based on vacuum sewer technique, and no pressure agent other than ambient air is needed in any transport stage. Consequently, a system according to the invention can be used in large vacuum sewer networks, such as in passenger vessels or hotels. Because of the specific characteristics of the invention, the size of the vacuum network has no negative influence on the noise level. 
     It is of advantage that a system according to the invention includes means for controlling the first stage of waste transport so that the air flowing into the intermediate container via the sanitary unit raises the pressure in the intermediate container to at least close to the pressure of the ambient air. This reduces the average speed of the air flow, which reduces the noise level. On the other hand, it is suitable to dimension the intermediate container so that, after the first transport stage, it contains a sufficient volume of air to allow the second waste transport stage to be carried out without feeding external air to the intermediate container or to the sewer portion downstream thereof. If no external air feed is needed, the system structure remains fairly uncomplicated and the number of possible leak points is reduced. If the sanitary unit is a toilet, it is recommended that the volume of the intermediate container be at least 4 liters. It should preferably be considerably greater, for instance 10 to 15 liters. 
     In a preferred embodiment, the downstream end of the first sewer portion is formed in an inverted U-shape which empties into the upper portion of the intermediate container. The downstream end of the first sewer portion should be at a clearly higher level than the surface of the sewage collected in the intermediate container. Thereby, the air volume contained in the intermediate container as well as in the first sewer portion is available in a technically advantageous manner for the second stage of waste transport. 
     If the first sewer portion is kept fairly short, the waste transport taking part therein causes as little noise as possible. Generally, it is of advantage, that the first sewer portion has a total length, from its sewer valve to its downstream end in the intermediate container, of at the most 3 m, preferably at the most 2 m. 
     In a vacuum sewer, the transport of material, in particular closely downstream of a sanitary unit, is generally performed most securely in a direction upwards. Hence it is of advantage, if the downstream end of the first sewer portion is at a considerably higher level than its upstream end. 
     It is of advantage to use the same vacuum level, the so-called “system vacuum” maintained by means of the vacuum generating means of the system, in the first as well as in the second stage of waste transport. This vacuum level preferably sets the absolute pressure in the sewer to about 75 to 30% of the pressure of the ambient air. The best operational reliability is generally achieved if the absolute pressure in the sewer is about 65 to 40% of the pressure of the ambient air. 
     The efficiency of the first stage of waste transport is improved, if the volume of the intermediate container is made variable and controllable by means of a movable means, for instance a membrane, a piston or the like. The idea is to keep the volume of the intermediate container small at the beginning of the first stage of waste transport and enlarge it at the end of the same stage. This enhances the efficiency of the first stage of waste transport. In an advantageous embodiment, the means controlling the volume of the intermediate container is pressure operated, preferably operated by means of the “system vacuum”. Thus, a change of the volume of the intermediate container can be adapted to the first stage of waste transport, so that the volume of the intermediate container is automatically considerably smaller at the beginning of the first stage of transport than at the end of the same stage. It is of advantage to have a time related interconnection between the function of volume control means and the function of the sewer valve. This can be obtained if the volume change is pneumatically controlled through the operational means of the sewer valve. Such a system gives the best prospects for controlling the volume of the intermediate container in a manner best serving the function of the system. At the same time the structure of the control means remains fairly uncomplicated and is based on a control technique already previously used in vacuum sewer systems. 
     The structure of a system according to the invention can be simplified by arranging the connection of the intermediate container to a second sewer portion through a second sewer valve, having its opening and closing movement functionally connected to the function of the sewer valve of the sanitary unit connected to the first sewer portion. The basic idea is that when one sewer valve opens the other closes and vice versa. Such a functional connection can be easily obtained by arranging the sewer pipes so that both sewer valves are close to one another so that their operating mechanisms can be mechanically interconnected. Alternatively, both sewer portions may be connected to the same disc valve, so that a through-flow opening in the valve disc can take a position in line with one or the other of the two sewer portions. 
     Reducing the noise level is in practice best obtained by installing the sanitary unit in a room space and the intermediate container outside the wall or any other limiting surface of that room. The limiting surface of the room acts as a noise insulation for the noise produced when filling the intermediate container in the first stage of waste transport and when emptying it in the second stage of waste transport. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be explained more fully with reference to the accompanying schematic drawings, in which 
     FIG. 1 shows a system according to the invention adopted to serve a toilet, and 
     FIG. 2 shows how the two sewer valves of the system of FIG. 1 may be functionally interconnected. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the drawings,  1  indicates a vacuum toilet and  2  a first sewer portion connected thereto. The first sewer portion  2  leads to an intermediate container  3 . The transport of waste material from the toilet  1  is controlled by means of a sewer valve  4 , which normally is kept closed, but which can be opened, if, in the sewer  2 , there is a vacuum strong enough for effective transport of toilet waste. The vacuum of the system is generated by a vacuum pump  5 . 
     Another sewer pipe  6  is leading out from the intermediate container  3 . This pipe has, at its upstream end, a sewer valve  7  that works in principle in the same manner as the sewer valve  4 . When the sewer valve  4  is closed, the sewer valve  7  stays open, but is closed when the sewer valve  4  is to be opened. The sewer pipe  6  leads to a receptacle  21 , which may be separated from the pipe  6  by a device (not shown) that allows the receptacle to be under atmospheric pressure in spite of the fact that the vacuum pump continuously maintains, in the pipe  6 , a vacuum of about one half of atmospheric pressure. Devices of this kind are known, for instance, from the patent publications U.S. Pat. Nos. 3,629,099, 4,184,506, 4,034,421, and U.S. Pat. No. 4,246,925. As used herein, the word “receptacle” includes any type of destination for the waste, such as a collecting container, as illustrated in FIGS. 1 and 2, or a community sewer line. 
     The function of the arrangement shown in FIG. 1 is the following: A pressure sensor controls the vacuum pump  5  so that the pump continuously maintains, in the sewer pipe  6 , a vacuum of about one half of atmospheric pressure with some variation between preset upper and lower limits. In the quiescent state of the arrangement this same vacuum prevails also in the intermediate container  3  and in the sewer pipe  2 . For emptying the toilet  1  the valve  7  is closed and the valve  4  is opened. Thereby, the pressure of the ambient air rapidly pushes the waste present in the toilet into the sewer pipe  2  and therethrough to the intermediate container  3 . The valve  4  is kept open long enough for raising the pressure in the intermediate container  3  to about the level of the pressure of the ambient air, which happens in one or a few seconds. Thereafter, the valve  4  is closed and the valve  7  is opened, whereby, due to the vacuum prevailing in the pipe  6 , the air under atmospheric pressure in the intermediate container  3  pushes the waste collected in the intermediate container into the pipe  6 . The valve  7  remains open, whereby the vacuum created by the vacuum pump  5  again spreads into the intermediate container  3  and the pipe  2 . 
     The function of the system is controlled by a control device  9 , to which the toilet&#39;s flush demand push-button  10  is connected. The function of the control device  9  is known per se and is therefore not explained here. The control device  9  may be a device generally used in vacuum sewer systems and sold under the trade name EVAC 90 by Evac International Oy of Helsinki, Finland. Through a check valve  17  this device is connected to a portion of the vacuum sewer that is continuously under vacuum. By pressing the push-button  10  the function of the control device  9  is started. The control device  9  includes means for connecting the different operating devices present to the vacuum source  5  of the system, thereby controlling the function and time of the opening and closing movements of the sewer valves  4  and  7  and of a closure valve  18  of a flush water pipe  22  that is connected to the toilet  1 . 
     The function described can be effected by providing the intermediate container  3  with a device controlling the volume therein. In FIG. 1 such a device has the form of a movable airtight flexible membrane  11  installed in the upper portion of the container  3 . When the container  3  is under vacuum, the membrane  11  is in its lower position, pressed by ambient air against a support plate  12 . The inner volume of the container  3  is then at a minimum, which in the illustrated embodiment is about 5 to 7 liters. When the sewer valve  4  is opened, the control device  9  connects, through the pipe  14 , the space  13  above the membrane  11  of the container  3 , which space is also about 5 to 7 liters, to the vacuum source of the system, whereby the membrane  11  takes the position shown in dotted lines, at or close to the interior surface of the upper portion of the container  3 . The membrane  11  stays in this position, until the sewer valve  4  has again been closed. In this state, before the opening of the sewer valve  7 , the pressure in the container  3  is atmospheric, which keeps the membrane  11  in its upper position, even when the device  9  no longer maintains a vacuum at the upper side of the membrane. 
     The arrangements described give the following advantages: The volume of the intermediate container  3  is initially small, which means that the amount of air required for transporting waste from the toilet  1  to the container  3  is also relatively small. This supports a reduction of the noise level. When the volume of the container  3  is enlarged by means of moving the membrane  11 , additional air flows into the container  3  through the sewer valve  4 , but the speed of this flow is relatively low, so that much noise is not produced. 
     For preventing the waste present in the intermediate container  3  from flowing back into the pipe  2  it is of advantage that the downstream end of the sewer position  2  empties into the upper part of the free inner space of the intermediate container  3 , preferably so that the downstream end of the sewer portion  2  is formed with an inverted U-shape, for instance as shown in FIG.  1 . The total length of the sewer portion  2  from the valve  4  to the downstream end of the sewer portion is, in the embodiment according to FIG. 1, about 1.5 meters. Of this length, the major part is directed upwards, which is of advantage for obtaining an effective vacuum induced transport of waste material. 
     In the embodiment shown in FIG. 2, the sewer valves  4  and  7  are arranged in the form of a disc valve. A valve type suitable for this purpose is shown, for instance, in U.S. Pat. No. 4,713,847. The valves  4  and  7  are combined into one valve device  15  connected to the pipe  2  as well as to the pipe  6 . In the housing of the valve device  15 , there is a rotatable circular valve disc  23  receiving its movement power from an operating device  16 . The valve disc  23  may have one through-flow opening  24  that alternatively takes a position in line with the pipe  2  and with the pipe  6 , or two through-flow openings, of which one moves away from the position of the pipe  2 , when the other moves to the position of the pipe  6  and vice versa. If two through-flow openings are used, it is possible, in the illustrated embodiment, to arrange the movement of the valve body (the disc  23 ) so that a smaller turning angle of the valve disc  23  is needed than when one through-flow opening is used. This is also possible when there is only one through-flow opening, if the pipes  2 ,  6  are not diametrically disposed relative to the turning axis of the disc  23 , as shown in FIG. 2, but are instead angularly closer to one another. Instead of a rotatable circular valve disc, the valve body may be provided in a variety of different forms, such as a sector plate (which is a disc having only a portion, or sector, less than 360° disposed in the valve), or a linearly moving plate. The operating unit  16  of the combined valve  15  may be provided as a vacuum controlled device, powered by the pressure difference between the “system vacuum” and the ambient air, an electrically powered device, or other arrangement. 
     The toilet  1  is installed in a room  19 . The intermediate container  3  and the control devices connected thereto are preferably located on the other side of a wall  20  of the room  19 , thereby to reduce the noise level in the room  19 . 
     The invention is not limited to the embodiments shown, but several modifications thereof are feasible within the scope of the attached claims.