Patent Publication Number: US-6341387-B1

Title: Safety device and method for swimming pool drain protection

Description:
RELATED APPLICATIONS 
     This is a continuation in part of application Ser. No. 09/439,875, filed on Nov. 12, 1999, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a drain suction relief device and method for installing it on swimming pools and more particularly concerns a prefabricated safety device for installation in new and existing pools to avoid an object or person being trapped below water or harmed by a swimming pool drain inlet from the suction from a swimming pool recirculating pump system. 
     Unfortunately, accidents occur whereby individuals, usually children and young adults, are trapped by the suction created in a swimming pool recirculating system at the inlet of a main drain in such a system. The hair of the individual may be sucked into the drain and/or a body part may obstruct or block the drain, thereby forming a vacuum in the main drain line. This vacuum may prevent the person, particularly a child, from escaping; often leading to serious injury, drowning when trapped below the water surface or even disembowelment where a person is seated on the drain. 
     This severe problem has resulted in many attempted and varied solutions. Examples of such prior art are U.S. Pat. No. 4,115,878 to Johnson, et al., U.S. Pat. No. 4,602,391 to Shepherd, U.S. Pat. No. 5,499,406 to Chalberg, et al., which disclose safety devices which are integrally designed and incorporated into the structure of the whirlpool baths or spas for which they are intended. Further attempts in the prior art are disclosed in U.S. Pat. No. 5,682,624 to Ciochetti, and U.S. Pat. No. 5,822,808 to Gallagher, et al. which use valves with moving parts that are triggered upon the creation of a vacuum. Other attempts, such as U.S. Pat. No. 5,167,041 to Burkitt, utilize pressure sensors and water level sensors that activate switches that turn off the pump. Also, vacuum release vertical pipes have been used on pools before. The present invention, as distinguished from the prior art, takes the form of an “add on” kit that is prefabricated and suitable for retrofitting existing swimming pool recirculating systems, as well as for use in new systems. The invention has no moving parts, is made from simple pipes familiar in the art, and is not subject to wear nor requires maintenance. It eliminates the need to do calculations, design work or fabrication work when installing such a safety device on a pool. The invention is suitable for virtually any swimming pool recirculating system, regardless of pump capacity, line size, or pool depth, and maintains the integrity of the existing recirculating system without need for reconfiguration or redesign. 
     SUMMARY OF THE INVENTION 
     The present invention entails a safety device capable of eliminating the vacuum created in the main drain line of a pool when an object or person obstructs or becomes trapped against the drain or other suction line inlet of a swimming pool recirculating pump system. The vacuum elimination safety device is installed in the main drain suction line of the swimming pool recirculating pump system. The present invention is constructed through installing one end of an interior vertical pipe fluidly connected to the main drain suction line in a “T”-type connection with the second end opening downward. The interior vertical pipe is enclosed within an exterior vertical sump pipe of larger diameter that is closed at the bottom end and vented to the atmosphere at the top. The configuration of the vertical pipes creates a column of water that is vented to the atmosphere during normal operation of the swimming pool recirculating system. When the main drain of the swimming pool is blocked or obstructed, thereby creating a vacuum at the point of the obstruction or blockage, the water within the column created by the present invention is evacuated and the suction is broken as air is pulled through the open vent of the invention. Suction is interrupted, and the vacuum created at the point of the obstruction or blockage is eliminated, thereby allowing removal of the obstruction or blockage. 
     A principal object of the present invention is to provide an improved safety device for use in a swimming pool recirculating pump system that eliminates the vacuum created when the intake to the recirculating pump system is obstructed or blocked. The pump intake may be obstructed or blocked by a person, and more particularly a child or young adult, resulting in serious injury or death through suction disembowelment, or drowning through suction entrapment or hair entanglement. 
     Another object of the present invention is to provide a safety device that is not dependent on electric, mechanical, or magnetic components for operation in eliminating the vacuum created when a pool suction line is obstructed or blocked. The present invention uses gravity and a simple pipe configuration rather than valves, sensors, or switching components. It is therefore very unlikely that the device will fail as a result of wear or interruption of power. Further, the components of the present device will not need maintenance or replacement. Lastly, the present device is not capable of a “false” shut off of the swimming pool recirculating pump system through the inadvertent activation of a valve or sensor. 
     Yet another object of the present invention is to limit the suction head created by a swimming pool recirculating pump to a minimum usable level regardless of the size or strength of the pump. 
     An additional object of the present invention is that it may be installed as a “kit” on virtually any pool, whether new or existing. The invention is intended to be self-contained and made of materials familiar in the art, preferably polyvinyl chloride (PVC) piping, The exact limiting quantity of suction is determined by the internal dimensions and arrangement of the piping and sump. 
     The device is not limited by the configuration of the swimming pool recirculating pump system and drains, the pump or line size, the depth of the pool, or whether the elevation of the swimming pool recirculating pump is located above the level of water in the pool, at water level, or below water level. Regardless of the pool&#39;s configuration, the device can be installed in the main drain suction line with the top of the device extending approximately 6″ above the pool water level. Moreover, the hydraulics of the device will operate uniformly regardless of the pool configuration. Therefore there is no need for measuring or modification specific to the pool system on which the safety device is being installed. Also, because the device only requires that a relatively shallow excavation be dug close to the edge of the pool, installation in new systems and retrofit of existing systems is simple and inexpensive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof will be more fully understood hereinafter as a result of a detailed description of preferred embodiments of the invention when taken in conjunction with the following drawings in which: 
     FIG. 1 is a cross-sectional view of a portion of a swimming pool illustrating the configuration of a standard swimming pool recirculating pump system, and further showing the invention installed in the main drain suction line. 
     FIG. 2 is a cross-sectional side view of the present invention. 
     FIG. 2 a  is a cross-sectional front view of the vertical top pipe of the present invention. 
     FIG. 2 b  is a cross-sectional front view of the present invention. 
     FIG. 3 is a cross-sectional front view of the interface between the coupling of the vertically disposed pipes and the horizontally-disposed suction line of the present invention. 
     FIG. 3 a  is a perspective view of a connector piece. 
     FIG. 3 b  is a cross-sectional front view of the interface between the coupling of the vertically disposed pipes and the horizontally-disposed suction line of another embodiment of the present invention. 
     FIG. 3 c  is a cross-sectional front view of the interface between the coupling of the vertically disposed pipes and the horizontally-disposed suction line of another embodiment of the present invention. 
     FIG. 4 is an exploded side view of the vented cap and the notched coupling that connects the vented cap to the vertical top pipe of the present invention. 
     FIG. 5 is a side view as in FIG. 4, but with the vented cap fitted on the notched coupling and illustrating the flow of air into the present invention. 
     FIG. 6 is an top view of the vented cap fitted on the coupling in relation to the suction line. 
     FIG. 7 is a cross-sectional side view of the present invention in the form of an alternative embodiment wherein a solid cap with spacers is fitted directly on the top end of the vertical top pipe and illustrating the flow of air into the alternative embodiment. 
     FIG. 8 is a cross-sectional elevation view of an alternative embodiment of the present invention utilizing a solid cap as shown in FIG.  7 . 
     FIG. 9 is a side view of the present invention in the form of an alternative embodiment wherein the suction line from the pool into the invention and the suction line out of the present invention to the pump are separate pipes, each having a 90 degree bend and extending down into the exterior vertical pipe in substitution of the single interior vertical sump pipe connected to the suction line. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention illustrated in the Figures provides a safety device capable of eliminating the vacuum created in the main drain line of a pool when an object or person obstructs or becomes trapped against the drain or other suction line inlet of a swimming pool recirculating pump system. 
     Shown in FIG. 1 is a representation of a swimming pool  108  having a floor  110 , a side wall  112 , and a deck  114  that is conventionally equipped with a conventional pump and filter system  15  having a filter  105  and recirculating pump  104  that draws water from the pool  108 . The specific design and configuration of the conventional filtration or recirculation system  15  is not part of or critical to the operation of the present invention. As illustrated, the pool  108  is equipped with an outlet  100  located in the floor  110  of the pool  110  at its deepest point, although it is foreseeable that the pool  108  could be equipped with multiple drains or suction line inlets at various locations in the pool  108 . The outlet  100  illustrated in FIG. 1 is commonly referred to as the main drain of the pool  108  because a majority of the water W pumped from pool  108  through the filtration or recirculation system by pump  104  is drawn through the outlet  100 . As is conventional, a suction line  12  is provided that fluidly interconnects the outlet  100  at connection  102  and the pump  104  at connection  106 . Suction line  12  is most commonly cylindrical, has an interior surface  14  and an exterior surface  16 , and is commonly buried at a variable depth beneath the surface of the ground  120 . 
     In accordance with the present invention, the pool  108  is further equipped with a vacuum elimination safety device  10  as represented in FIG. 1, and shown in greater detail in FIG.  2 . The device  10  is designed to vent the suction line  12  to the atmosphere in the event that the outlet  100  becomes blocked or obstructed, such that the suction of the pump  104  is immediately and completely removed. As a result, the vacuum that would otherwise trap the obstruction against the outlet  100  is immediately released, allowing the obstruction to be easily released or removed. In the situation where a young adult or child obstructs the outlet  100 , the person may then swim to safety or be easily assisted by others. The elevation of the pump has no influence on the operation of this vacuum elimination device. 
     FIG. 2 illustrates a suitable construction for the safety device  10 , but not the only construction and design for the device  10  in terms of performing the desired function. The device  10  as illustrated, however, embodies several features that make the device  10  particularly suited for its intended use. As shown in FIG. 2, the device  10  is generally constructed as a prefabricated unit or kit using a cylindrical interior vertical sump pipe  18  having an interior surface  20  and an exterior surface  22  and terminating at two ends, the top end  24  being fluidly interconnected with and perpendicular to suction line  12  at T-shaped saddle connector  28  and the bottom end  26  opening downward opposite the surface of the ground  120 . 
     The T-shaped saddle connector  28  has a downwardly extending cylindrical connection portion  28   a  which receives and connects to the top end  24  of interior vertical sump pipe  18 . Connector  28  has two horizontally extending cylindrical portions  28   b  and  28   c  which connect to pipes or lines  12  when the device  10  is installed into line  12 . The cylindrical portions  28   a ,  28   b  and  28   c  are connected to the saddle T connector  28  with standard PVC adhesive to connect to the pipes or lines. The portions  28   b  and  28   c  extend through and are sealed to the opposed cut outs  50  and  50   a  in the bottom portion  48  of vertical top pipe  42 , as shown in FIG. 2 b , with conventional sealant and adhesive. 
     The interior vertical sump pipe  18  is enclosed in a cylindrical exterior vertical pipe  30  which is a continuation of top pipe  42  via coupling  54  having an interior surface  32  and an exterior surface  34  and terminating at a bottom end  36  and a top end  38 . Although the pipes are standard cylindrical pipes, other shapes such as square pipe could also be used. In lieu of standard cylindrical pipes, the safety relief device  10  could be fabricated as an injection molding or by any other standard manufacturing technique. The interior surface  32  of exterior vertical pipe  30  has a diameter larger than exterior surface  22  of interior vertical sump pipe  18 . The bottom end  36  of exterior vertical pipe  30  and inner surface  92  of cap  90  extend beyond the bottom open end  26  of interior vertical sump pipe  18 . The bottom end  36  of exterior vertical pipe  30  is fitted with the cap  90  to form an enclosed sump. Cap  90  has an inner cylindrical surface  91  that tightly fits on the outer surface of the exterior surface  34  of the exterior vertical pipe  30 . Exterior vertical pipe  30  is sealed by cap  90  through application of conventional adhesive or sealant of the type commonly known in the art at the contact between exterior surface  34  of exterior vertical pipe  30  and inner surface  91  of cap  90 . 
     The top end  38  of exterior vertical pipe  30  is connected to cylindrical coupling  54 . Coupling  54  has an exterior surface  55  and an interior surface  56  having an annular ridge  60  at the longitudinal midpoint of coupling  54 , and terminates at open top end  57  and open bottom end  58 . The interior surface  56  of coupling  54  has a circumference equal to the circumference of exterior surface  34  of exterior vertical pipe  30 . The top end  38  of exterior vertical pipe  30  is fitted into the bottom end  58  of cylindrical coupling  54  so that the top end  38  of exterior vertical pipe  30  abuts annular ridge  60 . Bottom end  58  of coupling  54  is connected to top end  38  of exterior vertical pipe  30  through application of conventional adhesive or sealant of the type commonly known in the art at the contact between exterior surface  34  of exterior vertical pipe  30  and interior surface  56  of coupling  54 . 
     Top end  57  of coupling  54  is connected to the bottom end of vertical top pipe  42 . Vertical top pipe  42  is cylindrical, has interior surface  44  and exterior surface  46 , and terminates at open bottom end  48  and open top end  52 . Bottom end  48  of vertical top pipe  42  has a cylindrical cut out  50  as illustrated in FIG. 2 a  of a diameter equivalent to the diameter of exterior surface  16  of suction line  12 . Cut out  50  allows pipe  28   b  and  28   c  to be carried through vertical top pipe  42  being sealed thereto with application of conventional adhesive or sealant of the type commonly known in the art at the contact between  28   b  and  28   c  and  4     2 .    
     Bottom end  48  of vertical top pipe  42  is connected to top end  57  of coupling  54  as shown in FIG. 2 b . Bottom end  48  of vertical top pipe  42  is fitted into the top end  57  of cylindrical coupling  54  so that bottom end  48  of vertical top pipe  42  abuts annular ridge  60 . Top end  57  of coupling  54  is connected to bottom end  48  of vertical top pipe  42  through application of conventional adhesive or sealant of the type commonly known in the art at the contact between exterior surface  46  of vertical top pipe  42  and interior surface  56  of coupling  54 . 
     The top end  52  of vertical top pipe  42  extends beyond the connection  28  between interior vertical sump pipe  18  and suction line  12  to an elevation equivalent to ground surface  120 . The top end  52  of vertical top pipe  42  is open and fitted with a cap  62  by coupling  76  that allows ventilation of safety device  10  to the atmosphere but protects against blockage or obstruction. 
     FIGS. 3 and 3 a  show a preferred embodiment for the connection between the suction line  12  and the safety device  10  of FIG.  2 . In this embodiment, a hole  51  is provided through the exterior surface  16  of suction line  12 , from which water W flowing through line  12  can ingress and egress. Suction line  12  is fed through cut-outs  50  and  50   a  in vertical top pipe  42  so that hole  51  is enclosed within top pipe  42 . The exterior surface  16  of suction line  12  is mated and sealed to the PVC weldment  49  of top pipe  42  that surround hole  51 . The contact between suction line  12  and the weldment  49  of vertical top pipe  42  is sealed together with application of conventional adhesive or sealant commonly known in the art. 
     In FIG. 3 a  the saddle shaped connector  28  described in FIG. 2 is shown. Here, connector  28  has a lower cylindrical portion  202  and an open semi-cylindrical upper portion  204  extending in an orthogonal direction to portion  202 . Upper portion  204  has an inner surface  206  and an outer surface  208 . Likewise, lower portion  202  has an inside surface  210  and an outside surface  212 . 
     The connection between vertical top pipe  42 , cylindrical coupling  54 , and exterior vertical pipe  30  shown in FIG. 3 is identical to that described above for FIGS. 2 and 2 b.    
     FIG. 3 b  shows another embodiment for the connection between the suction line  12  and the safety device  10  of FIG.  2 . In this embodiment, a T-shaped coupling  12   a  is connected to pipe  12   b  and suction line  12  is connected to the T-shaped coupling  12   a , from which water W flowing through line  12  can ingress and egress. Pipe  12   b  extends through cut-out or hole  50  in vertical top pipe  42  and ends at  12   c . The exterior surface of pipe  12   b  is mated and sealed to the PVC weldment  49  of top pipe  42  that surrounds pipe  12   b . The end of pipe  12   b  is connected to an elbow  12   d  that is also connected to pipe  18 . The contact between line  12   b  and the weldment  49  of vertical top pipe  42  is sealed together with application of conventional adhesive or sealant commonly known in the art. 
     After suction pipe  12   b  is fed through cut-out or hole  50  of top vertical pipe  42 , elbow  12   d  is inserted up the interior of top pipe  42 . Using an adhesive or sealant of a type commonly known in the art, the elbow  12   d  is connected matingly to the exterior surface of pipe  12   b  and pipe  18 . The line  12  is generally perpendicular to the pipe  12   b.    
     FIGS. 3 c  shows another embodiment for the connection between the suction line  12  and the safety device  10  of FIG.  2 . In this embodiment, a T-shaped coupling  12   a  is connected to pipe  12   b  and suction line  12  is connected to the T-shaped coupling  12   a , from which water W flowing through line  12  can ingress and egress. In this embodiment, a hole  51 ′ is provided through the exterior surface of pipe  12   e , from which water W flowing through line  12  can ingress and egress. Pipe  12   e  is fed through cut-outs  50 ′ and  50   a ′ in vertical top pipe  42  so that hole  51 ′ is enclosed within top pipe  42 . The exterior surface  16  of pipe  12   e  is mated and sealed to the PVC weldment  49  of top pipe  42  that surround hole  51 ′. The contact between pipe  12   e  and the weldment  49  of vertical top pipe  42  is sealed together with application of conventional adhesive or sealant commonly known in the art. A standard cap  12 d is secured to the end of line  12   e  with adhesive. The line  12  is generally perpendicular to the line  12   e.    
     The embodiments of FIGS. 3 b  and  3   c  allow connection of the safety device to drain lines of varying sizes. This can be accomplished by varying the sizes of the two connections on the T-shaped connector  12   a  that connect to the drain line  12 . 
     FIG. 4 details cap  62  and coupling  76 . Cap  62  has a top surface  68 , a bottom surface  70 , an outer side surface  72 , and an inner side surface  74  of a larger diameter than the coupling  76  and exterior surface  46  of vertical top pipe  42 . Cap  62  is vented with a plurality of apertures  64  extending longitudinally across and through the top  68  of cap  62  and forming a grate  66 , as shown in FIG.  6 . Coupling  76  has an exterior surface  80  and an interior surface  78  having an annular ridge  82  at the longitudinal midpoint of coupling  76 , and terminates at open bottom end  84  and open top end  86 . Top end  86  has a plurality of apertures or slots  88 . The interior surface  78  of coupling  76  has a circumference equal to the circumference of exterior surface  46  of vertical top pipe  42 . Cap  62  is fitted to top end  86  of coupling  76  through application of conventional adhesive or sealant of the type commonly known in the art at the contact between exterior surface  80  of coupling  76  and inner edge  74  of cap  62 . Fitting cap  62  to coupling  76  allows apertures or slots  64  to align to apertures or slots  88  in the top end  86  of coupling  76 , thereby venting vertical top pipe  42  to the atmosphere when fitted together as shown in FIG.  5 . 
     The top end  52  of vertical top pipe  42  is fitted into the bottom end  84  of cylindrical coupling  76  so that the top end  52  of vertical top pipe  42  abuts annular ridge  82 . Bottom end  84  of coupling  76  is connected to top end  52  of vertical top pipe  42  through application of conventional adhesive or sealant of the type commonly known in the art at the contact between exterior surface  46  of vertical top pipe  42  and interior surface  78  of coupling  76 . 
     An alternative embodiment of the present invention is shown in FIGS. 7 and 8 wherein cap  62   a  has a plurality of radial flanges  74   a ,  74   b ,  74   c , and  74   d  extending from inner surface  74 , as shown in FIG. 7 that act as spacers between cap  62  and top end  52  of vertical top pipe  42  when cap  62  is fitted on vertical top pipe  42  as shown in FIG.  7 . The flow of air through this alternative embodiment is detailed in FIG.  7 . 
     Another embodiment of the present invention is shown in FIG. 9, wherein suction line  12  is separated into two segments  12   a  and  12   b . First segment  12   a  of suction line  12  runs from outlet  100  into exterior vertical pipe  30 . First segment  12   a  of suction line  12  is extended through a cylindrical cut out or hole  53  in exterior vertical pipe  30  and directed downward inside vertical pipe  30 , either through bending, molding, use of an elbow joint, or some other well-known method in the art, with the open end of first segment  12   a  of suction line  12  opening downward at a point  12   c  near the bottom end  36  of exterior vertical pipe  30 . Conventional sealant is used to seal around hole  53 . Second segment  12   b  of suction line  12  runs from exterior vertical pipe  30  to pump  104 , with second segment  12   b  of suction line  12  extending into exterior vertical pipe  30  through a cylindrical cut out or hole  53   a  of vertical top pipe  42  in the identical manner as the open end of first segment  12   a  of suction line  12 , the open end of second segment  12   b  of suction line  12  likewise opening downward at a point  12   d  near the bottom end  36  of exterior vertical pipe  30 . Conventional sealant is used to seal around hole  53   a . As shown in FIG. 9, interior vertical sump pipe  18  is not used. In this alternative embodiment, the diameter of interior surface  32  of exterior vertical pipe  30  is greater than two times the diameter of suction lines  12   a  and  12   b.    
     According to the any of the embodiments described above, vertical top pipe  42 , coupling  54 , and exterior vertical pipe  30  act as a sump when safety device  10  is installed in the suction line  12 . The configuration of the present invention allows water W to be drawn by gravity through outlet  100  into suction line  12  and into the safety device  10 . The safety device  10  creates a vented sump whereby water W from suction line  12  is drawn through interior vertical sump pipe  18  and into exterior vertical pipe  30 , rising to a level which is substantially equivalent in elevation to water level  118  in pool  108 . 
     Referring to FIGS. 2 and 9, during normal operation, water W is drawn out of the safety device  10  through suction line  12  by pump  104 . The flow of water W through suction line  12  initially draws water up from interior vertical sump pipe  18  or pipes  12   a  and  12   b , dropping the level of water in exterior vertical pipe below the pool water level  137 . A gravity-created static hydraulic head, equal and opposite to the force drawing the water up vertical pipe  18  or pipe  12 b into suction line  12 , is thereby formed within the safety device  10 . The hydraulic head corresponds to the difference between the pool water level  118  and the water level in interior vertical pipe  18  or pipes  12   a  and  12   b . If the safety device  10  has the proper dimensions, then during normal operation suction line  12  remains unvented to the atmosphere by the safety device  10 , enabling pool  108  and its recirculation system to operate completely as designed and intended. 
     When a blockage or obstruction of outlet  100  occurs sufficient to cause the vacuum level within the suction line  12  to exceed the hydraulic head created by gravity in the safety device  10 , pump  104  evacuates the water W out of the safety device  10  and draws air from the cap  62  down through vertical top pipe  42 , further down through exterior vertical pipe  30 , and then up through the interior vertical sump pipe  18  or suction line  12   b  into suction line  12 . This causes the loss of suction, thereby eliminating the vacuum within suction line  12  and at outlet  100 . 
     If the obstruction or blockage of outlet  100  is sufficiently brief, it is foreseeable gravity flow would return and that pump  104  could regain its prime and continue to operate normally. Where the obstruction or blockage is complete, however, such as when a person is trapped at outlet  100 , there will be a complete loss of flow of water at pump  104 . This will cause a complete loss of vacuum within suction line  12 , allowing the person to be released or pull free from the suction and swim free by themselves or with the help of others or to prevent disembowelment due to even momentary entrapment. Due to the proximity of the invention to the outlet and the designed short distance between the typical interior operating water level in pipe  34  and bottom end  26  of pipe  30 , the time delay for suction relief in the main drain is very short (may be less than a second) thus providing significantly greater protection against disembowelment. 
     It is important to note that the response time of safety device  10  is not dependent on the capacity of recirculating pump  104 . High capacity pumps are often used in large commercial pools and under normal operating conditions, generate a stronger vacuum more rapidly than lower capacity pumps. The device of the present invention, however, limits the suction head of pump  104  to a maximum suction head designed into the safety device equal to the gravity-created hydraulic head in safety device  10 , regardless of the capacity of pump  104 . The benefits of the safety device  10  are equally appreciated under virtually all swimming pool recirculating system sizes and configurations. 
     A new and significant advantage of the present invention, seen in view of the above, is that existing swimming pool recirculating systems can be simply and readily retrofitted with the present invention through installation of the safety device  10  into suction line  12 . This allows the benefits of the present invention to be realized without redesigning or reconstructing an existing recirculating system, performing any structural work on an existing swimming pool at great expense, or even draining and retrofitting the swimming pool. The existing configuration and flow characteristics of a swimming pool recirculating system can also be preserved. 
     According to the present invention, the safety device  10  may be prefabricated with the dimensions  128 ,  129 ,  130 ,  131 ,  132 ,  133 ,  134  and  135  set according to the size of the drain line  12 . Also, the internal dimensions of safety device  10  may be prefabricated to limit suction at the swimming pool main drain to 2.2 PSI (or 4.5″ Hg). Further, the head dimension  131  may be sized to allow the pump to withdraw water from the pool by gravity under normal circumstances when there is no blockage of the drain. Accordingly, the safety device  10  will rely solely on the forces of gravity for its operation, needing no adjustment, electricity, magnetism, or moving mechanical parts, and be relatively maintenance-free. 
     For example, a preferred embodiment for a two (2) inch drain would have the following dimensions: two inch diameters for PVC pipe connectors  28   b  and  28   c ; six inches for the distance  128  between a water level mark  137  on pipe  42  and the top  68  of cap  62 ; four feet six inches for the total length  130  of the safety device  10 ; three feet and nine and one-half inches for the distance  131  between the bottom end  26  of interior vertical sump pipe  18  to the water level mark  137  on pipe  42 ; and one foot and five inches for the distance  133  between a horizontal midpoint of suction line  12  and the top  68  of cap  62 . Also, in this embodiment the exterior vertical pipe  30  would be three inch PVC pipe and the interior vertical sump pipe  18  could be two inch PVC pipe. With these preset dimensions, the safety device  10  could easily and quickly be installed in any pool having a two inch drain line by positioning the pool water level mark  137  at the same elevation at the normal pool water level W. 
     It is understood that the pool water level W varies between normal operating limits. This slight variance does not adversely affect operation of the pool safety device  10 . The above dimensions may vary for a pool have having a smaller or larger drain line diameter. Since the drain line diameter is generally determined by the pump and pool size, kits can be prefabricated for common drain line sizes. 
     The present invention may be implemented by installing the safety device  10  into suction line  12  at some point between the outlet  100  and the pump  104 . Such installation will most conveniently occur near the edge of the swimming pool deck  114  at a point where the suction line  12  is buried near the surface of the ground  120 , thereby minimizing necessary excavation. 
     The key to installation is the position of the safety device  10  relative to the water level W in the pool  108 . Since the dimensions  130 ,  131 ,  132 ,  133 ,  134  and  135  are already determined according to standard engineering calculations, the only variable for installation is positioning the safety device  10  relative to the water level W. One way to accomplish this is with a label  136  that includes the water level mark  137  around the pipe  42  and the words “POOL WATER LEVEL” on the pipe  42 . An important criteria is that the top of pipe  42  is positioned so that there is a sufficient head of water in the vertically disposed pipes to allow normal flow through the drain line  12  without sucking all of the water out of the safety device  12  except when the swimming pool drain is blocked. 
     Should the safety device  10  be installed incorrectly (too high) then the maximum suction available at outlet  100  would be lower than the designed safety limit. Should it be installed too low then swimming pool water W would run out of the vent cap  62  and its installation would not be acceptable and the pool would drain down below its designed operating water level. In either case, safety device  10  would still safely control the maximum suction at outlet  100  to within its designed limit. 
     While the present invention has been described in terms of the preferred embodiments described above, it is apparent that one skilled in the art could adopt other forms. Accordingly, the scope of the invention is to be limited only by the following claims and their equivalents.