Abstract:
A valve assembly is provided that is suitable for use as an air release valve. The valve mechanism is actuated by liquid forced through an orifice by a diaphragm under pressure from the main discharge and is less prone to valve chatter under varying pressure conditions. The use of an externally adjustable orifice and/or regulator allows the valve assembly to operate satisfactorily in a wide range of pressures. The mode of operation of the valve mechanism is externally visible.

Description:
TECHNICAL FIELD 
     The present invention relates generally to self-priming pumps and more particularly to a self priming pumping system including an automatic air release valve connected to the discharge side of a pump for venting air from the system. 
     BACKGROUND 
     The customary pumping arrangement employed in sewage lift stations and the like is comprised of at least one self-priming centrifugal pump, a suction inlet pipe connected to the intake side of the pump, a discharge main connected to the discharge side of the pump, and a one-way check valve in the discharge main which prevents liquid from flowing back to the pump when it is shut down. 
     When the pump is started up, the air in the pumping chamber and any air in the suction inlet pipe must be evacuated in order to achieve a full prime. The air which is evacuated cannot be forced past the check valve in the discharge main because self-priming pumps have limited air compression capability. For example, a typical four inch self-priming centrifugal pump, when in priming mode, may develop a maximum pressure of 7 feet of head at its rated speed. If such a pump is installed in a system with a discharge check valve that requires a pressure in excess of 7 feet to open, the pump will not develop sufficient pressure to open the check valve and initiate flow. It is therefore necessary to provide an air release valve between the check valve and the pump for venting air from the system. In order to have an efficiently operating system, the air release valve should automatically close when the pump is operating at rated capacity and head. 
     Many types of air release valves have been proposed. Many of these valves can become unstable under certain operating conditions, for example, low pressure conditions, and are prone to hydraulic chattering when pressure conditions are varying. Another drawback to known air release valves is that they can be easily plugged or fouled by stones, sticks, stringy material, an other solids commonly found in raw sewage and the like. 
     SUMMARY 
     A valve assembly suitable for use as an air release valve that is actuated by liquid forced through an orifice by a diaphragm under pressure from the main discharge is less prone to valve chatter under variable head conditions. The use of the orifice allows the valve assembly to operate satisfactorily in a wide range of discharge heads. 
     The valve assembly includes a valve inlet in fluid communication with a discharge from a pump and a passageway from the inlet to a valve outlet. A first cavity is defined by one or more first cavity walls and is in fluid communication with the passageway. A diaphragm is disposed within the first cavity that sealingly engages the one or more first cavity walls to form within the cavity a pair of adjacent pressure chambers: a first pressure chamber that is in fluid communication with the passageway and a second pressure chamber. An actuating fluid is disposed within the second pressure chamber and a valve mechanism is placed in fluid communication with the second pressure chamber. The valve mechanism is capable of being actuated between a closed valve position in which flow through the passageway is impeded by the valve and a open valve position in which flow through the passageway is substantially unimpeded by the valve mechanism. A flow orifice is disposed between the second pressure chamber and the valve mechanism that regulates a flow of fluid between the second pressure chamber and the valve mechanism. This flow orifice can be adjustable by external means. During operation, fluid in the second pressure chamber that is displaced by an increase in pressure in the first pressure chamber flows through the flow orifice and acts upon the valve mechanism to move the valve mechanism to the closed position. 
     The valve mechanism may include a plunger having a head and a plug connected to the plunger head. In this embodiment, in response to a flow of fluid from the second pressure chamber the plunger is moved between the open valve position in which the plug is flush with or protrudes slightly into the material passageway to impede flow through the passageway and the closed valve position in which the plug is fully protruded into the passageway. The plunger can be housed in a second cavity in which case the valve mechanism may include a diaphragm disposed on top of the plunger head that sealingly engages the second cavity to form a third pressure chamber such that a flow of fluid into the third pressure chamber from the second pressure chamber causes the second diaphragm to act on the plunger head to move the plunger to the closed valve position. The plug may have a chamfer at a distal end that defines a limited flow path for matter through the passageway when the valve is in the closed valve position. A biasing mechanism, such as a spring, compressible gas, or compressible material such as rubber, may be included that urges the plunger to the open valve position. An adjustable restrictor mechanism can be disposed in the passageway to regulate the flow rate of matter through the passageway. An optional back flow prevention mechanism, such as a check valve, may be placed in fluid communication with the passageway to prevent flow of matter toward the pump. 
     These and other objects, advantages, and features of the exemplary embodiment of the invention are described in detail in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a typical pumping station that employs an air release valve constructed in accordance with one embodiment of the present invention; 
         FIG. 2  is a perspective view of an air release valve constructed in accordance with one embodiment of the present invention; 
         FIG. 3  is an exploded view of the air release valve of  FIG. 2 ; 
         FIG. 4  is a side view of the air release valve of  FIG. 2 ; 
         FIGS. 5 and 6  are cross section views of the air release valve of  FIG. 2  in two modes of operation; and 
         FIG. 7  is a cross section view of an air release valve constructed in accordance with an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a pumping system  1  which includes a conventional self-priming centrifugal pump  2 . In the illustrated arrangement the pump  2  is disposed above a wet well  6  which collects the liquid to be pumped. A suction inlet line  4  is connected to the intake side of the pump  2  and extends down into the wet well  6 . A discharge main  8  is connected to the discharge outlet of the pump  2  and extends upwardly. The discharge main  8  is provided with a one-way check valve  9  that prevents the liquid downstream from the valve from return to the pump  2  when it has been shut down or is not operating. The pump  2  is driven by an electric motor  3  operated through suitable electronic controls  7 . 
     An air release valve  10  constructed in accordance with the present invention is installed in the illustrated pumping system between the pump  2  and the check valve  9  so that the inlet of the valve  10  communicates with the discharge outlet of the pump  2  through the main  8 . An exhaust line  5  is connected to the outlet port of the valve  10  and extends into the wet well  6 . The purpose of the valve  10  is to vent the air that is evacuated from the suction inlet pipe  4  and the pumping chamber of the pump. The valve  10  automatically closes when the pump is fully primed to prevent the venting of liquid through the valve during the pumping cycle. 
     Referring now to  FIGS. 2-6 , the air release valve  10  is shown in greater detail. The valve  10  is made up of a housing  15  and a cover  21  that are bolted together. The housing  15  includes an inlet  20  that is connected to the main discharge  8  from the pump  2  (see  FIG. 1 ) and an outlet  30  that connects to the vent line  5  (see  FIG. 1 .) A flow passageway  16  is formed between the inlet and outlet. The housing also includes a first cavity  17  and a second cavity  18  while the cover  21  includes an interior bore that forms a fluid path between the first and second cavities indicated generally as  22  in  FIG. 3 . The housing and cover are molded from a corrosion resistant material that can be molded in the desired final color to eliminate the need for paint. The use of this type of material provides sufficient corrosion resistance for use in most corrosive environments. 
     Referring now to  FIG. 3 , an exploded view of the valve  10  is shown. A diaphragm  33  is mounted in the first cavity  17  so that its outer edge is captured between a groove on the upper surface of the housing and a groove on the bottom surface of the cover. The diaphragm is flexible and divides the first cavity  17  into two pressure chambers, one of which is filled with a flowable material as will be described below. The second cavity  18  houses a valve mechanism that includes a plunger  37 , a cup seal  39 , a spring  41 , and a second diaphragm  35  also having an outer edge that is captured between a groove on the upper surface of the housing and a groove on the bottom surface of the cover. The spring may be replaced by other biasing mechanisms such as compressible gas or material like rubber (not shown). The interior bore  22  is accessible for filling by removing fill plug  57  from a reservoir  53 . An orifice  55  is inserted into the reservoir  53 . The orifice is then located in the interior bore  22  that connects the first and second cavities  17 ,  18 . An adjustable restrictor  83  with sealing o-ring  84  is threaded into a threaded bore in the housing  15  that intersects the passageway  16 . The restrictor is held in place with a cotter pin  85 . 
       FIG. 5  show a cross section of the air release valve  10  with the valve in the open position in which the valve connects the discharge of the pump with the wet well for venting purposes. The air release valve  10  will typically be in this position at any time the pump is not operating. The first cavity  17  is divided into two pressure chambers, a first pressure chamber  36  and a second pressure chamber  43  by the diaphragm  33 . The diaphragm is retained between the housing  15  and cover  21  and serves as a sealed barrier between first and second pressure chambers  36 ,  43 . Likewise, the diaphragm  35  divides the second cavity into two pressure chambers, a third pressure chamber  45  (seen best in  FIG. 6 ) and a fourth pressure chamber that houses the plunger. A fluid  34  is placed in the second and third pressure chambers  43 ,  45 , as well as the internal bore  22  and rests there during this steady state condition. The biasing spring  41  in the second cavity  18  holds the plunger “up” so that the passageway  16  is fully or substantially open and the flow of air out of the outlet  30  is unimpeded. A cross shaped fluid channel  58  is grooved into the cover  21  above the diaphragm  33  and the diaphragm  35  to prevent the diaphragms from sealing off the pressure chamber when the valve is in the up position. When the pump comes online and media begins to be pumped through the pump discharge and through the passageway, resistance to the flow builds up causing an increase in pressure in the first pressure chamber  36 . The level of resistance to flow within the passageway and, consequentially, the rate at which pressure builds in the first pressure chamber triggering actuation of the valve can be adjusted by threading or unthreading the restrictor  83 . 
     As the pressure builds in the first pressure chamber  36  and acts against the diaphragm  33 , the fluid  34  on the other side of the diaphragm in the second pressure chamber  43 , the internal bore  22 , and third pressure chamber  45  is also pressurized. The fluid is forced to pass through the orifice  56  in the internal bore  22  at a controlled rate determined by the orifice characteristics. More fluid flows into the third pressure chamber  45 . Because of the differential in the areas of the top of the plunger and the end of the plunger  38 , a force is produced to compress the spring. When the applied force overcomes the biasing force of the spring, the plunger moves “down” and substantially blocks the passageway as shown in  FIG. 6 . The air release valve  10  remains in this position as long as the pump is operating and the head pressure in the discharge is maintained. A small chamfer on the end of the plunger  38  helps to keep the flow passages from becoming clogged by allowing a small continual flow. Another feature of the air release valve is an indicator window  75  (shown in  FIG. 4 ) that shows the position of the plunger and hence the present mode of operation of the air release valve. In  FIG. 4 , it can be seen that the valve is in the closed position because the bottom edge of the head of the plunger, which is molded in white or other contrasting color, lines up with the arrows labeled “closed.” 
     A cup seal  39  is housed in the housing and is disposed around the end of the plunger to clean the plunger prior to retraction into the second cavity  18 . The cup seal is well suited for this application because it causes little friction when the plunger is moving down, facilitating operation in low head conditions. However, another type of seal such as an o-ring may also be used in place or in combination with the cup seal. 
     The orifice  55  controls the rate of flow of the fluid between the second pressure chamber  43  and the third pressure chamber  45 . In this manner, the orifice also damps the effects of abrupt changes in the pressure in the first pressure chamber  36  and reduces valve chatter that might otherwise occur under varying pressure conditions. Because the fluid is maintained in a sealed region defined by the second pressure chamber  43 , the internal bore  22 , and the third pressure chamber  45 , it is not susceptible to clogging and no mechanical components that require lubrication are utilized. 
     When the pump is turned off and the flow of media through the passage  16  falls, the pressure in the first pressure chamber  36  is reduced to the point that the biasing spring lifts the plunger and opens the valve to its open position. The operating characteristics of the pump can be easily compensated for by adjusting the restrictor  83  thereby reducing the need for changes in internal hardware such as the spring  41 , which may be more difficult to access. 
     To provide additional adjustability, the orifice can also be externally adjustable as is shown in  FIG. 7 . In place of the orifice  55 , a needle valve  95  is threaded into the housing  21  so that it protrudes into the internal bore  22  near the passage from the second pressure chamber into the bore. An o-ring  98  seals the threaded bore  96  from the fluid path. The end of the valve  99  co-acts with the passage to form an adjustable orifice. 
     It can be seen from the foregoing description that an air release valve that is actuated by liquid forced through an orifice by a diaphragm under pressure from the main discharge is less prone to valve chatter under varying pressure conditions. Although the invention has been described with a certain degree of particularity, it should be understood that various changes can be made by those skilled in the art without departing from the spirit or scope of the invention as hereinafter claimed.