Abstract:
A method and apparatus for detecting leaks in hollow bodies can be used to detect leaks in recreational vehicles which have standard air vents in their roofs. The apparatus includes a cuff which can be attached to a standard air vent from inside the vehicle. A conduit connects the cuff to an air impeller. The impeller can draw air into the vehicle through the roof vent to increase air pressure within the vehicle. Soapy water or a similar substance is then applied to the outside of the vehicle. Leaks are evidenced by the presence of bubbles in the soapy water, and can then easily be located and repaired. The air impeller can be powered from standard AC power receptacles inside the recreational vehicle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to methods and apparatus for detecting leaks in hollow bodies. The invention has particular application in detecting leaks in the bodies of recreational vehicles. The method includes increasing the air pressure inside the vehicle so that leaks can be located by applying a leak detecting substance, such as soapy water, to the outside of the vehicle, and watching for bubbles which are formed in the soapy water where a leak allows air to emerge. 
     2. Description of the Related Art 
     Recreational vehicles, such as campers and motor homes, are susceptible to water leakage. Water leakage can cause extensive damage to the vehicle, especially if it is permitted to continue for a long time. Water which has entered the vehicle through leaks can collect in spaces behind interior paneling, cabinets and the like. The water can rust, rot and otherwise harm the vehicle and its fittings. 
     Water leaks may be difficult to locate because water can migrate significant distances along the inside surfaces of a vehicle&#39;s shell before the water appears in a visible location. Most interior surfaces in a recreation vehicle are lined or covered with paneling so that it is not possible to easily look for leaks from the inside of the vehicle. Further, it is difficult to recreate the conditions that exist when a vehicle is traveling along a highway while attempting to find leaks. When a vehicle travels at speed certain portions of the vehicle&#39;s exterior experience higher than ambient air pressures. This causes a pressure differential between the vehicle&#39;s interior and exterior which can cause water to be driven into the vehicle. A hole may be large enough to cause a leak when a vehicle is traveling but may be too small to be noticeable from the outside of the vehicle. 
     It is known that leaks in a vehicle may be located by pressurizing the interior of the vehicle. A leak detecting substance such as a mixture of soap and water can then be applied to the exterior of the vehicle to locate leaks. For example, Canadian Patent Application No. 2,106,951 to Hubert provides a fan mounted to a portable frame which can be placed adjacent to a vehicle. A conduit carries air pressurized by the fan into the vehicle. The conduit passes through a pliable, substantially air impervious member. The air impervious member can be used in various ways to seal an opening through which the conduit enters the vehicle. For example, the conduit may enter the vehicle through a window in a door of the vehicle with the air impervious member inside the door. The outer edge of the impervious member may then be placed between the door and the door frame and held in place by closing the door. The interior of the vehicle can then be pressurized by supplying air through the conduit. The Hubert device can be difficult and time consuming to attach properly and the impervious member is prone to becoming damaged. 
     After the interior of the vehicle is pressurized air flows outwardly through any faults in the outer shell of the vehicle. Soapy water or another leak detecting fluid can then be applied on the exterior surface of the vehicle. The presence of a leak is indicated by the formation of bubbles in the soapy water. 
     Schlumbaum, U.S. Pat. No. 3,580,054 discloses apparatus for testing for the presence of leaks in vehicles. The apparatus comprises a portable motor driven suction device which can be placed near a vehicle to be tested. The suction device has a flexible conduit which can be connected to the interior of a vehicle. The suction device can then be turned on. A pressure gauge measures pressure in the interior of the vehicle. If there are leaks in the vehicle then the suction device will be incapable of reducing the pressure inside the vehicle as much as would otherwise be possible. The Schlumbaum device can detect whether or not a vehicle has leaks but is not useful for locating such leaks. 
     There is a need for an effective leak detecting system which can be quickly and reliably attached to different vehicles. 
     SUMMARY OF THE INVENTION 
     The invention provides a leak detection method and apparatus. The apparatus comprises an air impeller which can be placed inside a vehicle to draw air into the vehicle. A duct connects the air impeller to an opening in the vehicle, such as a roof vent. One end of the duct has a cuff which seals to a roof vent or other suitable opening. The air pressure inside the vehicle can be raised by drawing air into the vehicle with the impeller. Preferred embodiments of the invention take advantage of the fact that many recreational vehicles have roof vents which are a standard size. This permits the impeller to be readily connected to the roof vent from inside the vehicle. The impeller can then draw air into the interior of the vehicle through the roof vent. Preferred embodiments of the invention provide a cuff which can be attached to the roof vent from inside the vehicle and then attached to the impeller with a flexible conduit. With the conduit detached from the cuff, a person can reach through the cuff to attach the cuff to the roof vent. The cuff may be attached to the roof vent with attachment members which include wide hooks. The hooks can be hooked over the edge of the rim that surrounds standard roof vents as are used on most recreational vehicles sold in North America. The attachment members can then be tightened to secure the cuff against the roof vent. 
     Another aspect of the invention provides a method of locating leaks in a vehicle having an interior, an exterior surface, and an opening, such as a roof vent. The method comprises: placing an air impeller in the vehicle interior and connecting an inlet of the air impeller to the opening in a substantially air tight manner; closing doors and windows of the vehicle; and, operating the air impeller to draw air into the vehicle interior, thereby raising an air pressure in the vehicle interior to permit leaks to be detected by applying a leak detecting fluid to the exterior surface of the vehicle. Operating the impeller preferably comprises plugging the impeller into an alternating current power outlet built into the vehicle. This avoids the need to have any power cords feed into the vehicle through partially open doors or windows. Preferably the air impeller comprises a variable speed motor and operating the air impeller comprises adjusting a speed of the motor to achieve an air pressure differential in the range of 0.3 inches of water and 1.0 inches of water between the interior of the vehicle and the exterior of the vehicle. Leaks can be detected by applying a soap—water mixture to the exterior of the vehicle and watching for the formation of bubbles. Preferably the opening comprises a square roof vent having a rim on at least two sides and connecting the inlet of the air impeller to the opening comprises attaching a cuff to the opening and connecting the cuff to the air impeller. Attaching the cuff to the opening comprises providing at least one attachment member on the cuff, hooking at least one attachment member over the rim and reducing a length of the attachment member so as to draw the cuff against the opening. 
    
    
     Further advantages and aspects of the invention are set out below. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way: 
     FIG. 1 is a partial longitudinal section through a recreational vehicle showing a leak detection apparatus embodying the invention; 
     FIG. 2 is a section through the upper cuff portion of the apparatus attached to a vent in the recreational vehicle as indicated by the section line  2 — 2  of FIG. 1; 
     FIG. 3 is an isometric view of the upper cuff portion; 
     FIG. 4 is a plan view of a turnbuckle used to attach the upper cuff to a roof vent; 
     FIG. 5 is an isometric view of the impeller thereof; 
     FIG. 6 is an isometric view of the conduit thereof; 
     FIG. 7 illustrates the use of a bridge to attach a cuff to a roof vent; and, 
     FIG. 8 illustrates a bridge which may be used with the invention. 
    
    
     LIST OF REFERENCE NUMERALS USED IN THE DRAWINGS 
       10  recreational vehicle 
       12  air vent 
       14  roof of recreational vehicle 
       15  opening in air vent 
       16  vent cover 
       18  crank (for opening or closing vent cover) 
       20  rim 
       22  apparatus 
       24  impeller unit 
       26  cuff 
       28  conduit 
       30  attachment members 
       32  hooks 
       34  hooks 
       36  holes 
       38  cross member 
       40  top portion of cuff  26   
       42  edge of cuff  26   
       44  sealing material 
       46  aperture in lower portion of cuff  26   
       47  chains 
       47 A snap links 
       48  lower portion of cuff  26   
       50  L-shaped slots 
       52  ring (on conduit  28 ) 
       54  pins 
       56  impeller housing 
       58  impeller 
       59  vents 
       60  impeller motor 
       61  motor speed control 
       62  connector (on impeller unit  24 ) 
       64  ring (on conduit  28 ) 
       66  power cord 
       68  electrical socket 
       70  pressure gauge 
       72  tube 
       74  through fitting 
       76  tube 
       79  walls of bridge 
       80  bridge 
       82  bridge end members 
     DETAILED DESCRIPTION 
     The preferred embodiments of this invention take advantage of the fact that many recreational vehicles incorporate roof vents having standard sizes. FIG. 1 shows a portion of a typical recreational vehicle  10  which has a standard sized square air vent  12  located in its roof  14 . Air vent  12  is typically dimensioned to fit into a hole 14 inches square in roof  14 . Air vent  12  has an opening  15  which is most typically 12 inches square. A screen (not shown) is usually provided in the opening  15  to keep flying insects from entering vehicle  10 . Such screens are almost always readily removable from inside vehicle  10 . 
     Vent  14  has a tilting cover  16  for covering opening  15 . Cover  16  can typically be opened or closed by turning a crank  18 . Cover  16  swings upwardly when it is opened. Air vent  12  generally has an upwardly projecting rim  20  When cover  16  is closed it rests against rim  20 , which is typically coated with a rubber layer to provide a seal. It would be awkward to attach to vent  12  apparatus for forcing air into vent  12  from outside of vehicle  10  (as is shown by Hubert in Canadian patent application No. 2,106,951) because cover  16  opens outwardly. The Hubert device would also require an operator to climb onto the roof of a recreational vehicle to attach apparatus for forcing air into vent  12 . This would place the operator at risk and also risk damaging the roof of the recreational vehicle. 
     Apparatus  22  attaches to the inside of a suitable opening, such as an air vent  12  as shown best in FIG.  2 . Apparatus  22  comprises an impeller unit  24  which draws air into vehicle  10 . In the preferred embodiment of the invention, apparatus  22  comprises a cuff  26  adapted to attach to and seal against vent  12  and a reinforced conduit  28  which connects cuff  26  to impeller unit  24 . Conduit  28  is fashioned of an airtight flexible material which is reinforced sufficiently so that it does not collapse in use. Conduit  28  is preferably of an “accordion” style to allow for easy storage and flexible length and shape. Conduit  28  may comprise, for example, cotton impregnated with neoprene rubber and reinforced with a wire helix. Conduit  28  has sufficient diameter to permit air to easily flow into vehicle  10 . It has been found that a conduit  28   14  inches in diameter provides good results. When impeller unit  24  is operating the interior of vehicle  10  may be pressurized by closing all openings such as windows and doors which would permit air to escape from vehicle  10 . If there are large holes where air can leak out of vehicle  10  then such holes should be plugged, for example with a damp rag. It will likely not be possible, nor is it necessary, to make vehicle  10  completely airtight. Cover  16  of air vent  12  should be open. 
     Impeller unit  24  may be coupled to vent  12  as shown in FIGS. 1 and 2. In the illustrated embodiment, a ceiling vent to conduit adapter or “cuff”  26  is attached to vent  12  with attachment members  30 . Members  30  are adapted to be secured to rim  20  of vent  12 . Attachment members  30 , preferably comprise turnbuckles or other tightening means which permit cuff  26  to be drawn upwardly until it seals around the periphery of vent  12 . 
     Preferably, each attachment member  30  has a wide upper hook  32 . Hooks  32  can be hooked over rim  20  as shown. Hooks  32  should have a significant width so that they do not apply enough pressure to damage rim  20 . Preferably two diametrically opposed attachment members  30  are used to secure cuff  26  to vent  12 . In the illustrated embodiment, each attachment member  30  has a lower hook  34  which can engage an aperture  36  on a cross member  38  in cuff  26 . 
     As best seen in FIG. 2, cuff  26  has a top portion  40  having an upper edge  42  shaped to fit around vent  12  and faced with a sealing material  44 . Sealing material  44  is preferably a non-scratching durable compliant material such as a closed cell foam. When attachment members  30  are tightened then cuff  26  is drawn against vent  12  and sealing material  44  seals against vent  12  and/or portions of roof  14  surrounding vent  12 . 
     To secure cuff  26  to vent  12 , the screen (if present) is removed from opening  15 . In some cases it may be necessary to remove some trim around vent  12  and/or to remove crank  18  in order to remove the screen. Upper hooks  32  are then hooked over rim  20  on either side of opening  15 . Then cuff  26  is placed against vent  12  and the lower hook  34  of each attachment member  30  is secured in one of apertures  36 . This can be done by reaching up through the aperture  48  at the bottom of cuff  26 . The operator can then reach through cuff  26  and tighten attachment members  30  so that cuff  26  is secured around vent  12  in a sufficiently air tight manner. The ease with which cuff  26  may be affixed to vent  12  from inside vehicle  10  provides significant advantages over those prior systems which require an operator to stand on the roof of a vehicle  10  in order to affix an attachment to the outside of the roof vent. 
     Some recreational vehicles have much thicker roofs than others. If roof  14  is very thick then lower hooks  34  might not reach holes  36 . In this case an extender is needed. In the embodiment of FIG. 3, pieces of chain  47  are attached to cross member  38 . Chain pieces  47  are preferably detachable from cross member  38 . For example, chains  47  may be connected to cross member  38  by snap links  47 A. If hooks  34  cannot reach holes  36  then they can be hooked into a link of one of chains  47 . 
     Cuff  26  has a lower portion  48  to which conduit  28  may be detachably affixed. In the illustrated embodiment, lower portion  48  is cylindrical and has L-shaped slots  50  spaced around its lower edge. Conduit  28  has a ring  52  which is dimensioned to fit snugly around lower portion  48  of cuff  26 . Pins  54  project radially inwardly from ring  52 . Conduit  28  can be attached to cuff  26  by sliding ring  52  over lower portion  48  until pins  54  engage in slots  50  and then rotating ring  52  to fully engage pins  54  in slots  50  so that ring  52  is removably affixed to cuff  26 . 
     Impeller unit  24  comprises a suitable housing  56  containing an impeller  58  driven by a motor  60 . Impeller  58  is of a type which can deliver a high volume of air at low pressure. Vents  59  in housing  56  deliver air from impeller  58  into the interior of vehicle  10 . Impeller  58  is preferably also compact so that impeller unit  24  can be made small enough to be easily carried into a vehicle  10 . Impeller unit  24  is preferably capable of delivering about 1500 to 2000 cubic feet of air per minute at zero static pressure differential at maximum output. It has been found that a backward curved AC impeller capable of delivering about 1850 cubic feet of air per minute at 0 static pressure differential and capable of delivering about 1500 cubic feet of air per minute through a static pressure differential of 0.6 inches of water column works well for leak testing a wide variety of recreational vehicles. Some such impellers are very compact, being less than 15 inches in diameter. Impeller  58  can preferably deliver in excess of 1500 cubic feet per minute against a pressure differential of 0.3 inches of water column and in excess of 1250 cubic feet per minute against a pressure differential of 1 inches of water column. 
     Impeller  58  is preferably incapable of developing sufficient air pressure within vehicle  10  to create any risk of structural damage to vehicle  10 . Preferably impeller  58  is incapable of delivering any air flow against pressure differentials in excess of 1.7 inches of water column. 
     Motor  60  is preferably a variable speed motor. The pressure within vehicle  10  can then be adjusted to an optimum value by adjusting the speed of motor  60 . A motor speed control  61  is provided on impeller unit  24  for this purpose. 
     Conduit  28  is most preferably detachable from impeller unit  24 . In the illustrated embodiment, impeller  24  has a cylindrical connector  62  to which a ring  64  on conduit  28  can be detachably affixed. Connector  62  has several L-shaped slots  50  which receive pins  54  which project radially inwardly from ring  64 . Ring  64  attaches to connector  62  in the same way that ring  52  attaches to lower portion  48 . 
     Impeller unit  24  is preferably powered by standard AC power provided through a power cord  66 . Power cord  66  can be plugged into a power socket  68  inside vehicle  10 . Most recreational vehicles have interior power sockets  68  capable of providing electrical power to operate impeller unit  24 . This is advantageous because it does not require any door or window of the vehicle to be left ajar to pass a power cord into vehicle  10 . It also does not require feeding a power cord into vehicle  10  through opening  15  as would otherwise be necessary. Leaving a door or window ajar would likely prevent the development of the necessary pressure differential between the interior and the exterior of vehicle  10 . Power sockets  68  are typically built into recreational vehicles and draw electrical current from an external supply delivered through a power cord (not shown) which delivers power to recreational vehicle  10  through a power receptacle (not shown) on the exterior of vehicle  10 . In some cases, the electrical power at sockets  68  can also be provided by a power generator in recreational vehicle  10 . 
     A differential pressure gauge  70  is preferably provided to indicate the difference in air pressure between the interior of vehicle  10  and the exterior of vehicle  10 . Pressure gauge  70  may be mounted on impeller unit  24  for convenience. A tube  72  extends from pressure gauge  70  to an interior side of a bulkhead fitting  74  on cuff  26 . Another tube  76  extends from an exterior side of bulkhead fitting  74  to a location on the exterior of vehicle  26  where it can sense the ambient exterior air pressure. The pressure in the interior of recreational vehicle  10  is sensed at differential pressure gauge  70 . 
     When apparatus  22  has been assembled as described above and impeller  58  is turned on then air is drawn into vehicle  10  and the air pressure within vehicle  10  rises. Motor speed control  61  can be used to adjust the air pressure within vehicle  10  to a desired value. The difference in the air pressure between the outside and inside of vehicle  10  should be small enough so as not to damage vehicle  10 . A pressure difference of less than about {fraction (1/28)} lb./square inch or less (1 inch of water column) is typically sufficient for leak detection purposes. The air pressure differential between the inside and outside of vehicle  10  is preferably maintained in the range of 0.3 to 1.0 inches of water column and is most preferably somewhere in the range of 0.3 inches of water column to 0.8 inches of water column. 
     While a desired pressure is maintained inside vehicle  10 , the operator(s) can apply a plain soap/water mixture or another suitable leak detecting liquid to the exterior of vehicle  10 . Where a soap water mixture is used it is preferable to use about 1 part of soap to 40 parts of water. The formation of bubbles in the soap/water mixture indicates air flow from a leak. This allows the leak to be easily located. The leak may then be mended. 
     The subject apparatus and method thus provide for a portable apparatus and method of detecting leaks. While most recreational vehicles have a standard size of roof vent  12 , cuffs  26  may be provided to accommodate different sizes and/or shapes of vent. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of the invention without departing from the spirit or scope thereof. For example, the particular manner in which cuff  26  is attached to vent  12  may be varied. All that is necessary is that there be some way to detachably attach cuff  26  to provide a seal around vent  12 . It is highly preferable that conduit  28  be detachable from both cuff  26  and impeller unit  24 . Having an easily detachable conduit makes apparatus  22  easier to move around and install. Conduit  28  could be permanently attached to impeller unit  24  and the apparatus could still be used. Conduit  28  could be permanently attached to cuff  26  and apparatus  22  could still be used if a hatch were provided to allow access to members  30  or if some means were provided to manipulate members  30  from outside of cuff  26 . 
     One type of air vent, which is sold under the trademark FANTASTIC FAN VENT™, fits into a standard sized roof opening but provides a smaller through hole  15  than usual. Cuff  26  can still be used with such roof vents by bridging the roof vent with a flat-bottomed U-shaped bridge  80  and hooking hooks  32  over the edges of the upwardly extending walls  79  on either side of bridge  80 , as shown in FIG.  7 . Bridge  80  may have members  82  at either end. Members  82  distribute forces on bridge  80  along the sides of a vent  12 . 
     While it is highly convenient for impeller unit  24  to be powered by standard AC electrical power provided through an electrical socket inside vehicle  10 , other power sources could be used. 
     Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.