Abstract:
A check valve having an upstream inlet part mountable on a discharge end of a conduit, a downstream outlet part adapted to prevent backflow of fluid through the check valve, and a transition part located between the upstream inlet part and the downstream outlet part. A longitudinal dimension of the downstream outlet part extending in a direction transverse to a direction of flow is at least approximately 1.57 times the diameter of the upstream inlet part.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a check valve of the so-called “duckbill” type for use in drainage systems and effluent outfall lines. 
     2. Description of the Prior Art 
     A check valve is essentially a valve which allows fluid to flow in only one direction through a conduit, while closing and preventing back or reverse flow, when back pressure builds up downstream of the valve to a level greater than the upstream fluid pressure head. Check valves are used in various fluid transportation operations and must include some means of allowing the forward flow of liquid yet preventing any backflow. 
     Conventional rubber duckbill check valves have an inlet cuff, an outlet bill and a transitional middle part for connecting the cuff and the bill. The bill comprises a slit which opens when fluid is forced through the valve. Typically, existing “duckbill” type check valves have a bill slit dimension that is equal to or less than one-half the cuff (inlet) circumference. The reason for this is that if the bill slit dimension is larger than one-half the circumference of the cuff diameter, it becomes difficult or even impossible to remove a one-piece mandrel, which is used to manufacture the check valve through the cuff. 
     In most applications, it is desirable to have the maximum flow through the valve at the lowest possible pressure drop in the forward direction of the flow or, in other words, the lowest possible headloss. To improve the performance of duckbill check valves, valves have been recently developed in which the width of the bill is larger than the diameter of the cuff. The output area and the open position of the bill thus approaches more of the inlet area of the cuff, and the headloss decreases. For example, U.S. Pat. No. 5,931,197 to Raftis et al. discloses an asymmetrical check valve of this type. 
     It is therefore an object of the present invention to provide a duckbill check valve with an improved headloss over conventional valves. It is another object of the present invention to provide a check valve that overcomes the design problems encountered in the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention is a check valve with an oversized bill. The present invention includes a tubular inlet part, an outlet part and a transitional middle part, connecting the inlet part with the outlet part, wherein the width or height of the outlet part is at least approximately 1.57 times the diameter of the inlet part. The outlet part may be symmetrical about a longitudinal plane through the check valve. It can also have a curved bill. 
     The advantage of a valve of this size is the low headloss compared to conventional duckbill check valves. 
     With an effective outlet area larger than the inlet area of the valve, the headloss will drop below the headloss of an open pipe end at high flow rates. 
     The invention itself, both as to its construction and its method of operation, together with the additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  shows a top view of a conventional duckbill check valve according to the prior art; 
     FIG. 1 b  shows a side view of the conventional duckbill check valve of FIG. 1 a  according to the prior art; 
     FIG. 1 c  shows a front view of the conventional duckbill check valve of FIG. 1 a  according to the prior art; 
     FIG. 2 a  shows a top view of another conventional duckbill check valve according to the prior art; 
     FIG. 2 b  shows a side view of the conventional duckbill check valve of FIG. 2 a  according to the prior art; 
     FIG. 3 a  shows a top view of an embodiment according to the present invention; 
     FIG. 3 b  shows a side view of the embodiment of FIG. 3 a  according to the present invention; 
     FIG. 3 c  shows a front view of the embodiment of FIG. 3 a  according to the present invention; 
     FIG. 4 shows a front view of the present invention in a closed position; 
     FIG. 5 shows a front view of the present invention in a slightly opened position; 
     FIG. 6 shows a front view of the present invention in a further opened position; and 
     FIG. 7 shows a front view of the present invention in a fully opened position; 
     FIG. 8 shows a perspective view of the present invention with a curvilinear-shaped outlet part; and 
     FIG. 9 shows a side sectional view of the present invention attached to a pipeline via a flange. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 both show conventional duckbill check valves. These valves comprise an inlet portion  10 , a transitional portion  12  and an outlet portion  14 . The advantages of these designs are the low tooling costs and simple removal of a mandrel from the completed part. The check valve shown in FIG. 2 is slightly widening, with the width of the outlet portion  14  approximately equal to one-half the circumference of the inlet portion  10 . The mandrel is slightly more difficult to remove from the completed valve, but the headloss is lower. 
     After extensive testing at the Water Research Laboratories of Utah State University, it was determined that for submerged discharge, the headloss of a “duckbill” type of check valve is very closely equal to: 
     
       
         H=Q 2 /19.5gA 2   
       
     
     where H=Headloss in feet of water, 
     Q=Quantity of water flowing in gallons per minute, 
     g=Gravitational constant=32.16 feet/sec 2 , and 
     A=Effective open area in square inches. 
     Therefore, for constant flow conditions, the headloss is inversely proportional to the discharge area squared. 
     It was found that with a width or height (depending upon orientation) of the outlet portion  14  at least approximately 1.57 times the diameter of the inlet part, the headloss is much smaller than the headloss of conventional check valves. The present invention is a duckbill check valve  22  with an enlarged bill, as shown in FIG.  3 . the duckbill check valve  22  comprises an inlet part  16 , a transitional part  18  and an outlet part  20 , which appears as a pair of lips facing and engaging one another. The height h of the outlet part  20  (or bill) of FIG. 3 is substantially larger than the diameter d of the inlet part  16 . In fact, the height of the outlet part  20 , in its closed position, should be at least approximately 1.57 times the diameter d of the inlet part  16 . 
     It is important to note that the outlet part  20  may be oriented in different positions, rotatable about an axis perpendicular to the pipeline  30 . FIG. 3 shows the outlet part  20  of the present invention wherein the outlet part  20  (or lips) is oriented in a vertical manner, making the height h the operative dimension. Turning to FIGS. 4-7, the outlet part  20  is oriented in a horizontal manner, making the width w the operative dimension. According to the invention, it is the longitudinal dimension of the outlet part, in its closed position, that must be substantially larger than the diameter d of the inlet part  16 . 
     FIGS. 4-7 show the different opening stages of a duckbill check valve  22  according to the present invention. FIG. 4 shows a closed duckbill check valve  22 , FIGS.  5  and  6  show a progressively open duckbill check valve  22  and FIG. 7 shows a fully open duckbill check valve  22 . As can be seen from FIG. 7, depending on valve stiffness, the outlet part  20  will not open to a full circular opening, but will open to approximately 40% to 85% of the area of a full circular opening. 
     Valves built in accordance with the present invention, with an outlet part  20  bill slit greater than 1.57 times the inlet part  16  bore diameter, will have an open area about equal to, or larger than, the area of the inlet part  16 . Thus, the headloss is considerably lower than the headloss of conventional valves. Again, it is the width w of the outlet part  20  (in FIGS. 4-8) that should be at least approximately 1.57 times the diameter d of the inlet part. 
     The duckbill check valve  22  is preferably made from an elastomer, such as neoprene, or an elastomer reinforced with synthetic fabric, such as nylon or polyester, with construction similar to an automobile tire. The inlet part  16  is generally made of a stiff, durable material, such as styrene butadiene, with polyester fabric reinforcing, whereas the outlet part  20  is made of a flexible material to allow proper opening and closing of the outlet part  20 . Further, the outlet part  20  may be symmetrical about a longitudinal plane A—A through the duckbill check valve  22 . This longitudinal plane A—A is coincident with a center line of the inlet part  16 . In addition, it is also envisioned that the outlet part  20  may be curvilinear, as described in U.S. Pat. No. 5,727,593. The inlet part  16  may be fitted with a flange  32 , instead of the cuff shown in the drawings. 
     A duckbill check valve according to the preferred embodiment is manufactured similarly to a tire, using a multiple-piece mandrel. The mandrel will have to be disassembled to remove it from the inside of the valve. However, the great reduction in headloss will justify the added expense of manufacturing the invention. Furthermore, the duckbill check valve  22  can be provided with local reinforcements, such as embedded wire, plates, rings and tubes. 
     It will be understood by those of ordinary skill in the art that modifications may be made without departing from the spirit and scope of the present invention.