Abstract:
A hydrostatic tank floor relief valve of a construction described herein provides for equalization of hydrostatic pressure of fluid in a storage tank with hydrostatic pressure of ground water surrounding the storage tank. A high efficiency grate located in a flow channel of the hydrostatic tank floor relief valve blocks debris from entering the storage tank during pressure equalization, yet does not reduce effective flow rates through a flow channel of a given diameter. The hydrostatic tank floor relief valve optionally includes an elastomeric seal surface and a stainless steel seat ring that reduce the likelihood of particulate matter disrupting valve operation, and provide a more reliable seal.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part patent application of copending U.S. application Ser. No. 14/546,302, filed Nov. 18, 2014, entitled “HYDROSTATIC TANK FLOOR RELIEF VALVE”. The aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
       [0002]    The invention pertains to the field of hydrostatic tank floor relief valves. More particularly, the invention pertains to hydrostatic tank floor relief valves having a grate for blocking debris. 
       DESCRIPTION OF RELATED ART 
       [0003]    Various types of storage tanks may be buried underground, or partially underground, and heavy rains or flooding may saturate soils and raise the level of ground water so that the ground water surrounds the storage tank. As a result, if the storage tank is empty, partially empty, or contains a fluid that has a lower density than water, the storage tank may become buoyant. The buoyant forces acting on the tank may be sufficiently strong to cause the storage tank to “float”, and erupt out of the ground when buried, or out of a partially buried state. Storage tank float is undesirable not only because it disrupts tank placement, but also because piping that is attached to the storage tank may split or break, and allow the contents of the storage tank to spill from the storage tank, and possibly contaminate soil and ground water. 
         [0004]    Storage tanks constructed of concrete, for example, are also generally sensitive to buoyant forces and may crack and fail over time due to repeated exposure to potentially uneven distributions of buoyant forces as ground water levels rise and fall, even when those buoyant forces are not sufficient to cause the storage tank to fully float or erupt from the ground. 
         [0005]    Tank float is a major concern when storage tanks are used to hold gasoline, oil, or other fluids that pose a significant contamination hazard. Anchoring structures for these types of storage tanks exist in the prior art, but these anchoring approaches can increase installation costs and complexity, and may be best suited to storage tanks that contain fluids that also need to be protected from ground water infiltration. 
         [0006]    Other storage tanks, such as waste water storage tanks or septic tanks, need only prevent the contents of the tank from escaping into surrounding soil, and may freely accept rain water or ground water in addition to the biologically contaminated fluids they store. In these types of storage tanks, hydrostatic tank floor relief valves are integrated into storage tank construction to relieve buoyant forces and prevent tank float. 
         [0007]    In the prior art, a hydrostatic tank floor relief valve generally includes a valve body that is, for example, incorporated into the bottom of a concrete holding tank during concrete pouring operations, whether that tank will eventually be completely buried, or remain partially above ground. The valve body has an external shape that anchors the valve body into the concrete floor of the storage tank, and also prevents leakage of fluids between the valve body and surrounding concrete, or other storage tank construction materials. 
         [0008]    The valve body has a first end below the level of the storage tank floor that may be connected to a polyvinylchloride (PVC), cast iron, steel, or other type of pipe that is exposed to the water table when the water table rises to the bottom of the storage tank. A second end of the valve body, located inside the storage tank at the bottom of the storage tank, is generally sealed by a massive valve cover which may also include a gasket material between the valve cover and the valve body. The weight of the valve cover, and the hydrostatic pressure of fluids contained in the storage tank, hold the hydrostatic tank floor relief valve in a closed positon when ground water levels are below the bottom of the tank. Thus, the contents of the storage tank are prevented from escaping the storage tank. 
         [0009]    Ground water levels which rise above the level of the bottom of the storage tank may cause a significant increase in the hydrostatic pressure of ground water below the storage tank at the first end of the valve body. When the hydrostatic pressure of ground water exceeds the hydrostatic pressure of the fluid contained in the storage tank, a pressure differential forms and forces the valve cover away from the valve body, allowing ground water to flow into the storage tank until the pressure differential is equalized. Buoyant forces are thus relieved, and tank float is prevented. 
         [0010]    Hydrostatic tank floor relief valves also generally include a screen in the form of a disk with apertures placed in the valve body between the valve cover and the second end of the valve body. The screen may be provided with slots, perforations, holes, or other apertures that allow ground water to flow into the storage tank, but prevent gravel, stones, or other debris beneath the storage tank from infiltrating into the storage tank when ground water moves through the hydrostatic tank floor relief valve into the storage tank. 
         [0011]    In the prior art, hydrostatic tank floor relief valve screens have a planar geometry with a number of perforations or apertures. An internal flow channel of the hydrostatic tank floor relief valve may have a given diameter, for example 2 inches or 4 inches, and a corresponding cross-sectional area. A total of the areas of all the apertures defined by the screen structure is necessarily smaller than the cross-sectional area of the internal flow channel of the hydrostatic tank floor relief valve because the structure of the screen defining the apertures blocks a portion of the flow channel As a result, the effective cross-sectional area of the flow channel is reduced by the presence of the screen. 
         [0012]      FIG. 1A  shows a top view of a prior art screen  2  and  FIG. 1B  shows a side view of the prior art screen  2 . The prior art screen  2  is a disk made of cast iron with a thickness T, and is provided with a series of slots  3  that that pass through solid portions  4  of the disk. A ring  5  surrounds the screen  2  to fit into the valve. The slots  3  allow fluid to flow through the prior art screen  2 , but prohibit the passage of gravel and other debris. Notches  6  are formed in the prior art screen  2  to allow the prior art screen  2  to be mounted in a hydrostatic tank floor relief valve, as described in detail below. 
         [0013]      FIG. 2A  and  FIG. 2B  show a prior art hydrostatic tank floor relief valve body  200  with a flow channel  230 . The valve body  200  includes a screen flange  210  that extends inwardly toward the flow channel  230  about an internal circumference of the flow channel  230 . Additionally, screen locks  220  are provided adjacent the screen flange  210 , and form tabs or posts extending into the flow channel  230 . The screen locks  220  are dimensioned and oriented so that the notches  6  in the prior art screen  2  may pass the screen locks  220  when the screen  2  is properly oriented. Thus, the screen  2  may be inserted into the flow channel  230 , past the screen locks  220 , and be held in the flow channel  230  by the screen flange  210 . As shown in  FIG. 2B , when the prior art screen  2  is positioned against the screen flange  210 , the prior art screen  2  may be rotated, for example one quarter turn, so that the notches  6  and screen locks  220  are no longer in alignment, and the ring  5  of the prior art screen  2  is held between the screen flange  210  and the screen locks  220 . Thus, the screen  2  is held in the flow channel  230  regardless of a fluid flow direction within the flow channel  230 , and may be easily removed to allow cleaning and maintenance of the hydrostatic tank floor relief valve. 
         [0014]    Prior art cast iron screens  2  are effective, but the casting process increases manufacturing costs. Furthermore, as can be seen from  FIG. 1A , for a flat disk prior art screen  2  with a diameter d, and an area A PAP =πr 2 , the slots  3  of the prior art screen  2  only allow fluid to pass through a limited portion of the area of the prior art screen  2 , flow through the prior art screen  2  being blocked by the screen ring  5  and the solid portion  4 . Since the flow channel  230  of the valve is a cylinder which also has a diameter d, the only available area left for fluid flow—the open slots  3 —is, by necessity, much less than the full area of the flow channel. Thus, the prior art screen  2  reduces the flow efficiency of a hydrostatic tank floor relief valve. 
         [0015]    In addition, due to the large tolerances necessary in metal castings, the prior art screen  2  has a large amount of play between the screen flange  210  and the screen locks  220 . This play may allow the prior art screen  2  to move, and even rotate, when fluid flows through the flow channel  230  and debris impacts the prior art screen  2 . Over time, motion of the prior art screen  2  may cause the notches  6  to orient with the screen locks  220  so that the prior art screen  2  is no longer held against the screen flange  210 . Thus, the prior art screen  2  may cease to function, and may interfere with the overall function of the hydrostatic tank floor relief valve. 
         [0016]    A reduction of the effective cross-sectional area of the flow channel limits the rate at which ground water may pass through the hydrostatic tank floor relief valve into the storage tank. Multiple hydrostatic tank floor relief valves may therefore be required to adequately react to high rates of change in ground water levels. Alternatively, the internal diameter of the hydrostatic tank floor relief valve, and the internal diameter of pipes connected to the hydrostatic tank floor relief valve must be increased to adequately respond to high rates of change in ground water levels. Both solutions increase tank construction costs. 
         [0017]    Prior art seats generally rely on a mating of two planar surfaces to form a seal between the valve cover and the hollow valve body when the hydrostatic tank floor relief valve is in a closed position. However, particulate matter may settle to the tank floor, or enter the tank through the hydrostatic tank floor relief valve when it is in an open position, and may become trapped between the two planar surfaces, thus reducing the effectiveness of the seal formed by the two planar surfaces. 
       SUMMARY OF THE INVENTION 
       [0018]    A hydrostatic tank floor relief valve of a construction described herein provides for equalization of hydrostatic pressure of fluid in a storage tank with hydrostatic pressure of ground water surrounding the storage tank. A high efficiency grate located in a flow channel of the hydrostatic tank floor relief valve blocks large debris such as rocks from entering the storage tank during pressure equalization. The grate is in the form of a cone or truncated cone, with solid bars interspersed with apertures, the total area of the apertures being at least equal to the cross-sectional area of the valve, and preferably is larger. Thus, the grate stops rocks but allows smaller particulate matter to pass, and does not reduce effective flow rates through a flow channel of a given diameter. The hydrostatic tank floor relief valve optionally includes an elastomeric seal surface and a stainless steel seat ring that reduce the likelihood of particulate matter disrupting valve operation, and provide a more reliable seal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0019]      FIG. 1A  shows a top view of a prior art tank floor relief valve screen. 
           [0020]      FIG. 1B  shows a side view of a prior art tank floor relief valve screen. 
           [0021]      FIG. 2A  shows a side view a prior art tank floor relief valve body with a prior art screen placed in a flow channel 
           [0022]      FIG. 2B  shows a side view a prior art tank floor relief valve body with a prior art screen locked in a flow channel. 
           [0023]      FIG. 3  shows a hydrostatic tank floor relief valve in a closed position, equipped with a truncated cone grate. 
           [0024]      FIG. 4  shows a hydrostatic tank floor relief in an open position, equipped with a truncated cone grate. 
           [0025]      FIG. 5  shows a perspective view of a truncated cone grate. 
           [0026]      FIG. 6A  shows a top view of a grate flange. 
           [0027]      FIG. 6B  shows a top view of a grate with grate retaining tabs. 
           [0028]      FIG. 6C  shows a top view of a grate flange and a grate with retaining tabs passing through the grate flange. 
           [0029]      FIG. 6D  shows a top view of a grate flange and a grate retaining tabs, the grate being rotated so that the tabs engage the grate flange. 
           [0030]      FIG. 6E  shows a detail of grate retaining tabs engaging the grate flange. 
           [0031]      FIG. 7A  shows a side view of a truncated-cone grate. 
           [0032]      FIG. 7B  shows a cut-through view of the grate of  FIG. 7A  along the lines  7 B- 7 B. 
           [0033]      FIG. 8  shows a detail of a hydrostatic tank floor relief valve seat ring, as shown in the dotted lines  8  in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    A hydrostatic tank floor relief valve of a construction described herein includes a high volume grate formed by a plurality of solid bars interspersed with apertures. The grate may be in the form of a cone, or a truncated cone with a bottom portion having holes for fluid flow. The truncated cone grate encompasses a larger surface area than prior art screens, which were formed of plates perforated by a plurality of relatively small holes. 
         [0035]    The bars of the grate are formed to be rigid and strong enough to prevent passage of rocks and other large debris, while the apertures are large enough to allow small particles to pass through the grate. The total area defined by all of the apertures of the grate are dimensioned to be at least as large as the cross-sectional area of a flow channel of a hydrostatic tank floor relief valve, and preferably are defined so that the total area is larger than the cross-sectional area. As a result, the truncated cone grate effectively prevents larger debris from passing through the hydrostatic tank floor relief valve, but does not significantly restrict flow rates for water and small particulates through the hydrostatic tank floor relief valve. 
         [0036]    The high volume grate is provided with two sets of grate retaining tabs that lock the grate in place on a grate flange. 
         [0037]    In addition, the hydrostatic tank floor relief valve of a construction described herein may include a stainless steel seat ring embedded in a channel of a seat flange of a hydrostatic tank floor relief valve hollow valve body. The seat ring engages an elastomeric boot covering a valve cover when the valve cover is in a closed position on the seat flange. The seat ring described herein provides an improved seal that is less susceptible to interference from particulate matter. The elastomeric boot and the seal ring may also be replaced in the event of damage without having to replace the entire hydrostatic tank floor relief valve. 
         [0038]      FIG. 3  shows a hydrostatic tank floor relief valve in a closed position. The hydrostatic tank floor relief valve includes a hollow valve body  10  with an inlet  30  and an outlet  20 . A pipe  40 , made of polyvinyl chloride (PVC), steel, cast iron or other material, is inserted into the inlet  30  of the hollow valve body  10  and sealed with an O-ring  41  or other suitable connection that prevents leakage between the hollow valve body  10  and the pipe  40 . A seat flange  15  and an inlet flange  17  extend radially outward from the hollow valve body  10 , and secure the hollow valve body  10  to the tank floor. 
         [0039]    The seat flange  15  is located at the outlet  20  of the hollow valve body  10 , and provides a seat surface  16  that includes a seat ring  60 . The seat ring  60  is also shown in detail in  FIG. 8 . A channel  50  is formed in the seat surface  16  of the seat flange  15  for accepting the seat ring  60 . The channel  50  is generally annular and concentric to the outlet  20  of the hollow valve body  10 . 
         [0040]    The seat ring  60  and the channel  50  are dimensioned so that the seat ring  60  is securely held in the channel  50  by pressing the seat ring  60  into the channel, and/or creating a bead  55  or other deformation along one or both sides of the channel  50  to retain the seat ring  60  in the channel  50 . In one embodiment, the seat ring  60  is made of stainless steel to provide strength and corrosion protection. However, any suitable material may be substituted for stainless steel, for example, to accommodate different fluid properties. The channel  50  in the seat surface  16  may be formed during casting of the hollow valve body  10 , or may be machined into the seat surface  16  during finishing operations on the hollow valve body  10 . Although the seat ring  60  is shown with a circular cross-sectional profile, other geometries are also acceptable provided they are capable of mating with the seal surface  85 . 
         [0041]    A valve cover  70  is located at the outlet  20  of the hollow valve body  10 . The valve cover  70  is covered with an elastomeric boot  80  which provides a seal surface  85  at a side of valve cover  70  facing the seat flange  15 . Thus, when the valve cover  70  is in a closed position and pressed onto the seat flange  15  by its own mass and hydrostatic pressure P T  of fluid in the tank acting on the valve cover  70 , the seat ring  60  is pressed on to the seal surface  85 , creating a positive seal as the elastomeric material of the elastomeric boot  80  conforms to the seal ring  60 . The elastomeric boot  80  is made of ethylene propylene diene monomer (EPDM) rubber in one embodiment and is removably fitted to the valve cover  70  to facilitate ease of replacement if necessary. However, other elastomeric compounds may be substituted for EPDM in other embodiments, and the elastomeric boot  80  may take other forms or be permanently attached to the valve cover  70 , provided a seal surface  85  is formed on the valve cover  70 . 
         [0042]    The valve cover  70  is movable by ground water pressure from the closed position, shown in  FIG. 3 , to an open position shown in  FIG. 4 . In these figures the valve cover  70  includes retaining tabs  90  that project into the outlet  20  of the hollow valve body  10 . The retaining tabs  90  are spaced about an inner diameter of the valve cover  70 , and pass through mating gaps in a valve cover lock  100  that protrudes inwardly from an inner surface of the hollow valve body  10  adjacent to the outlet  20 . Thus, when the valve cover  70  is inserted into the outlet  20  of the hollow valve body  10  and rotated, the gaps in the valve cover lock  100  no longer mate with the retaining tabs  90 , and motion of the valve cover  70  away from the outlet  20  is limited by a length of the retaining tabs  90 . 
         [0043]    A grate  110  is located in the hollow valve body  10  in a flow channel  25  between the outlet  20  and the inlet  30 , and is attached to a grate flange  130 . As shown in  FIG. 6A , the grate flange  130  is an annular ring with gaps  130   a  spaced about an inner circumference that is open to the flow channel  25 . 
         [0044]    As shown in  FIG. 6B , a top edge of the grate  110  includes a first series of retaining tabs  120   a  that protrude radially from the grate  110 . A second set of retaining tabs  120   b  also protrude radially from the grate  110 , and alternate in location with the first set of retaining tabs  120   a.  As shown in  FIG. 6E , the first set of retaining tabs  120   a  are offset toward an inlet  30  end of the grate  110 , and the second set of retaining tabs  120   b  are offset toward an outlet  20  end of the grate  110  such that the first set of retaining tabs  120   a  and the second set of retaining tabs  120   b  are separated by a distance approximately equal to a thickness Tf of the grate flange  130 . 
         [0045]    The grate  110  may be inserted into outlet  20  of the hollow valve body  10 , and when properly oriented, as shown in  FIG. 6C , the first set of retaining tabs  120   a  may pass through the gaps  130   a  in the grate flange  130 , while the second set of retaining tabs  120   b  are blocked by the grate flange  130 , stopping further insertion of the grate  110  into the hollow valve body  10 . 
         [0046]    As shown in  FIG. 6D , when the grate  110  is then rotated, the first set of retaining tabs  120   a  is oriented at an inlet  30  side of the grate flange  130 , while the second set of retaining tabs  120   b  is oriented at the an outlet  20  side of the grate flange  130 . Thus, the grate flange  130  is held between the first set of retaining tabs  120   a  and the second set of retaining tabs  120   b  . In this manner, motion of the grate  110  toward either the outlet  20  of the hollow valve body  10  or the inlet  30  of the hollow valve body  10  is prevented. 
         [0047]    Additionally, the first set of retaining tabs  120   a  and the second set of retaining tabs  120   b  may be separated with close tolerances relative to the thickness of the grate flange  130 , or provided with a structure that is lightly sprung with a bias toward the grate flange  130 , so that the grate  110  is prevented from inadvertently rotating after installation. In some embodiments, the grate flange  130  may be provided with surface features such as indentations, protrusions, or detents that accept the first set of retaining tabs  120   a  and the second set of retaining tabs  120   b  after the grate  110  has been rotated so that the grate  110  may only be removed by intentional manual manipulation. 
         [0048]      FIG. 5  shows a perspective view of a truncated cone shaped grate  110  that more clearly illustrates the construction of the grate  110 . In this example, the grate  110  has a cone section made up of solid bars  124 , with apertures  122  in between each of the solid bars  124 , and a bottom  128  with at least one hole  126 . Each aperture  122  and hole  126  has an area which can be denoted as A(n), where n=1, 2, 3, . . . N, where N is the number of apertures  122  and hole(s)  126  Summing the area A(n) of all the apertures  122  and holes  126  in the grate  110  provides a total flow area A f  through the grate calculated as: 
         [0000]    
       
         
           
             
               A 
               f 
             
             = 
             
               
                 ∑ 
                 
                   n 
                   = 
                   1 
                 
                 N 
               
                
               
                 A 
                  
                 
                   ( 
                   n 
                   ) 
                 
               
             
           
         
       
     
         [0049]    The grate  110  is therefore constructed to provide a number of apertures with a total flow area A f  that is at least as large as the cross-sectional area A p  of the pipe  40  bringing ground water to the inlet  30 , calculated as: 
         [0000]      A p =πr 2 (where r is the radius of pipe  40 )
 
         [0050]    Provided A f ≧A p , the grate  110  will not significantly restrict fluid flow from the inlet  30  to the outlet  20 . 
         [0051]    In operation, the hydrostatic tank floor relief valve is held in a closed position, illustrated in  FIG. 3 , by hydrostatic fluid pressure P T  of fluid contained in the tank. When ground water levels rise, water enters the pipe  40 , passes through the grate  110 , and ground water hydrostatic pressure P G  acts on the valve cover  70  at the outlet  20 . When ground water hydrostatic pressure P G  exceeds the hydrostatic fluid pressure P T  of fluid contained in the tank, as shown in  FIG. 4 , a pressure differential is created, ground water forces the valve cover  70  away from the seat flange  15 , and flows into the tank. When ground water hydrostatic pressure P G  and hydrostatic fluid pressure P T  of fluid contained in the tank equalize, the valve cover  70  moves under the force of gravity and the weight of the valve cover  70  back toward the seal flange  15 , closing the hydrostatic tank floor relief valve. 
         [0052]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.