Abstract:
A spa heater includes a heater element having a single outer wall with indentations near each end for receiving clips for positioning the heater element. The indentations are preferably stamped or formed by some other method which does not weaken the outer wall and the heater element is retained by use of the clips in the indentations. Incorporation of the indentations and the clips allows use of a single thin outer wall thereby reducing cost. The heater element is held and sealed by a combination of O-rings, stepped washers, snap rings clips, and caps. An electrical connection may be made using ring type wire ends residing under the caps or by connecting to posts extending from the ends of the heater element. The heater element is preferably a spiral heater element and a titanium outer wall may be used to resist corrosion and increases heater element life.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to spa heater elements and in particular to a titanium electric spa heater element positioned by a snap ring. 
   Portable spas often use electric spa heaters. Such heaters include heating elements immersed in a flow of sometimes very corrosive liquids, especially when the high levels of chlorine or other chemicals are used to kill algae in the spa or are present do to errors in adding too much chemicals. Known heater element often include welded on fittings. Unfortunately, welding causes the metal close to the welds to be even more susceptible to corrosion. 
   One solution to heater element survival in such corrosive environment is to use a heater element with a titanium outer wall. Such titanium outer wall is highly resistant to corrosion, and provides an excellent heater element life. Unfortunately, titanium is expensive to machine, and the advantages of a titanium heater element are somewhat cancelled if machined fittings are used to attach the titanium heater element to a heater housing. Welding (or fusing) on the titanium fittings also may make the heater element more susceptible to corrosion. 
   U.S. Pat. No. 6,621,985 for “Electric Water Heater,” discloses a water heater with a titanium outer wall and using compression fittings to hold the heater element to the heater housing. While the use of compression fittings is less expensive than machined titanium fittings and welding is avoided, such compression fittings apply an amount of pressure on the titanium outer wall requiring either a thick outer titanium wall, or a second wall under the outer titanium wall to support the outer titanium wall. The &#39;985 patent discloses a second stainless steel wall under the titanium outer wall. Either a thick titanium outer wall, or a double wall, add cost to the heater element. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention addresses the above and other needs by providing a spa heater which includes a heater element having a single outer wall with indentations near each end for receiving clips for positioning the heater element. The indentations are preferably stamped or formed by some other method which does not weaken the outer wall and the heater element is retained by use of the clips in the indentations. Incorporation of the indentations and the clips allows use of a single thin outer wall thereby reducing cost. The heater element is held and sealed by a combination of O-rings, stepped washers, snap rings clips, and caps. An electrical connection may be made using ring type wire ends residing under the caps or by connecting to posts extending from the ends of the heater element. The heater element is preferably a spiral heater element and a titanium outer wall may be used to resist corrosion and increases heater element life. 
   In accordance with one aspect of the invention, there is provided a water heater including a heater housing having a housing wall and a heater element fixed to the housing wall. The heater housing includes a heater housing inlet for allowing a flow of water to enter the heater housing, a heater housing interior for allowing the flow of water to pass through the heater housing, and a heater housing outlet for allowing the flow of water to exit the heater housing. The heater element includes a heating portion residing in the heater housing interior, a first end, and a second end. The heater element further has an outer wall, an electrically conductive wire residing inside the outer wall and electrically insulated from the outer wall, a heat conducting dielectric insulation filling a space between the electrically conductive wire and the outer wall, and indentations circling the outer wall proximal to the ends of the heater element. The outer wall may be a corrosion resistant metal such as titanium, a nickel-chromium alloy sold under the trademark Incoloy® provided by Inco Alloys International in Huntington W. Va., or stainless steel and may be a thin outer wall. Heater element passages reside in heater housing wall and the heater element ends pass through the heater element passages. Stepped seats are formed in the exterior of the heater element passages. O-rings reside in the stepped seats between the indentations in the heater element ends and the heater housing and contain the flow of water in the heater housing interior. Snap rings engage the indentations in the heater element and spacers reside between the O-rings and the snap rings. Caps reside over the snap rings and attach to the housing wall, the snap rings, spacers, and O-rings, are thus sandwiched between the caps and the housing wall. 
   In accordance with one aspect of the invention, there is provided a method for attaching a heater element to a heater housing. The method includes inserting two ends of the heater element through heater element passages in the heater housing from the inside to the outside, sliding O-rings over the heater element ends and into stepped seats in the heater housing, sliding spacers over the heater element ends and on top of the O-rings, positioning snap rings on circular indentations on the heater element ends over the spacers and O-rings, and tightening a cap over the snap rings to retain the heater element ends position through the heater housing. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
       FIG. 1  is a spa including a spa heater according to the present invention. 
       FIG. 2  depicts a side view of the spa heater. 
       FIG. 3  is a cross-sectional view of the spa heater taken along line  3 - 3  of  FIG. 2 . 
       FIG. 4  is a side view of a heater element according to the present invention. 
       FIG. 4A  is a cross-sectional view of the heater element taken along line  4 A- 4 A of  FIG. 4 . 
       FIG. 4B  is a cross-sectional view of the heater element taken along line  4 B- 4 B of  FIG. 4 . 
       FIG. 5  is a cross-sectional view of a heater element passage in a heater housing wall showing an end of the heater element passing through the housing wall, an O-ring for sealing the heater element passage, a spacer to position the O-ring, a snap ring for retaining the spacer, and a cap attached to the housing wall for retaining the heater element, all according to the present invention 
       FIG. 6A  is a front view of the cap. 
       FIG. 6B  is a rear view of the cap. 
       FIG. 6C  is a bottom view of the cap. 
       FIG. 7A  is a side view of the spacer. 
       FIG. 7B  is a rear view of the spacer. 
       FIG. 8A  is a side view of the snap ring. 
       FIG. 8B  is a front view of the snap ring. 
       FIG. 9A  is a side view of a ring type wire end usable to connect electrical wiring to the heater element. 
       FIG. 9B  is a front view of the ring type wire end. 
       FIG. 10  is a method for connecting the heater element to the heater housing according to the present invention. 
       FIG. 11  contains the composition of Incoloy 800 alloy and Incoloy 825 alloy. 
   

   Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
   A spa  10  is shown in  FIG. 1 . The spa  10  includes drains  12   a  and  12   b.  The drains  12   a,    12   b  are in fluid communication with a pump  14  through first lines  16   a  and  16   b  carrying flows  17   a  and  17   b  respectively, through a filter  13  and to the pump  14 . A spa heater/controller  18  is in fluid communication with the pump  14  through a second line  20  carrying second flow  21 . A spa-side control  11  is electrically connected to the spa heater/control  18  by control wires  11   a  for controlling the spa  10 , or may be wirelessly connected to the spa heater/controller  18 . The heater/controller  18  is in fluid communication with at least one jet  22  through line  24  carrying a third flow  25 . Water  26  is thereby circulated, filtered, and heated. 
   A side view of a spa heater  40  element of the heater/controller  18  is shown in  FIG. 2  and a cross-sectional view of the spa heater  40  taken along line  3 - 3  of  FIG. 2  is shown in  FIG. 3 . The heater  40  has a heater inlet  40   a  for allowing a flow of water to enter the heater  40 , and heater outlet  40   b  for allowing the flow of water to exit the heater  40 , and a heater interior  40   c  for allowing the flow of water to pass through the heater  40 . One or two heater elements  50  (also see  FIG. 4 ) reside in the spa heater  40  and are electrically connected to electrical power through a heater manifold cover  44 . The manifold cover  44  mounts to a side of the heater housing  42 , preferably on a cover ridge  46  which resides in a cover groove  47  in the manifold cover  44 . A cover O-ring  48  resides inside the cover groove  46  to seal the cover  44  to the heater housing  42 . The manifold cover  44  including the heater element(s)  50  is preferably secured to the heater manifold  42  by 10 machine screws to create a heater assembly. Each heater element  50  is held to the manifold cover  44  by caps  60  (also see  FIGS. 5 , and  6 A- 6 C). Sensor wells  47  extend into the heater housing  42  for temperature probes to allow closed loop control of spa water temperature. 
   The heater element  50  is shown in  FIG. 4 , a cross-sectional view of the heater element  50  taken along line  4 A- 4 A of  FIG. 4  is shown in  FIG. 4A , and a cross-sectional view of the heater element  50  taken along line  4 B- 4 B of  FIG. 4  is shown in  FIG. 4B . The heater element  50  includes a single outer wall  57  encasing an electrically conductive wire  59  surrounded by an insulating material  58 . The outer wall  57  is preferably between at least approximately 0.015 inches thick and is more preferably between approximately 0.020 and approximately 0.030 inches thick and most preferably between approximately 0.028 and approximately 0.030 inches thick. The insulating material  58  is, for example, a dielectric insulation such as magnesium oxide or other suitable dielectric medium disposed around the electrically conductive wire  59  to permit transfer of heat from the electrically conductive wire  59  to the outer wall  57 , while providing electrical insulation between the electrically conductive wire  59  and the outer wall  57 . The outer wall  57  is preferably a corrosion resistant metal such as titanium, a nickel-chromium alloy sold under the trademark Incoloy®, or stainless steel and may be a thin outer wall. Preferred Incoloy® alloys are Incoloy 880 alloy and Incoloy 825 alloy and the like. The composition of Incoloy 880 alloy and Incoloy 825 alloy are contained in  FIG. 11 . 
   The heater element  50  further includes indentations  54  having a depth D in the outer wall  57  proximal to the first end  52   a  and the second end  52   b  of the heater element  50 . The indentations  54  preferably circle the ends  52   a  and  52   b  and preferably have sharp corners  54   a  to help retain the clip  66  (see  FIGS. 5 ,  8 A, and  8   b ) in the indentation  54 . A spiral heating portion  51  of the heater element  50  resides inside the heater housing  42  and heats a flow of water through the heater  40 . The indentations  54  are preferably stamped indentations made by a stamping die and have an indentation depth D and an indentation width W. The indentation depth D is preferably between approximately 0.004 inches and approximately 0.008 inches, and the indentation depth D is more preferably approximately 0.008 inches and the indentation width W is preferably between 0.044 and 0.048 inches. The indentations may be made by any process which pushes the thin wall inward and does not remove metal from the outer wall  57 , thereby facilitating the use of a thin outer wall. The depth D of the indentations  54  is preferably selected to allow the clips  66  (see  FIGS. 8A and 8   b ) to loosely reside in the indentations without putting radial pressure on the outer wall  57  also facilitating the use of a thin outer wall. 
   A cross-sectional view of a heater element passage in the heater housing  42  wall showing an end  52  of the heater element  40  passing through the heater housing  42  wall, an O-ring  62  for sealing the heater element passage, a spacer  64  for positioning the O-ring  62 , a snap ring  66  for retaining the spacer  64 , and the cap  60  attached to the housing wall for retaining the heater element  40 , all according to the present invention, are shown taken along line  5 - 5  of  FIG. 3  in  FIG. 5 . The O-ring  62  and spacer  64  reside in a stepped seat  45  formed in the manifold cover  44  of the heater housing  42 . The stepped seat  45  preferably includes a smaller diameter first step  45   a  and a larger diameter second step  45   b.  The O-ring  62  (or other sealing element) rests against the first step  45   a  and the spacer  64  rests against the second step  45   b  and includes a smaller diameter portion  64   a  extending past the second step  45   b  and pushes the O-ring  62  inward. The snap ring  66  engages the indentation  54  (see  FIG. 4 ) to position the snap ring  66  on the heater element end  52 . The cap  60  is preferably attached to the heater housing  42  by three screws  70  but may be attached by a different number of screws or other fastener. The O-ring  62 , spacer  64 , and snap ring  66  are thus sandwiched between the stepped seat  45  and the cap  60 . 
   The cooperation of the snap ring  66  with the indentation  54  results in a low level of force on the outer wall  57  (see  FIG. 4A ) and allows a thin outer wall to be used without, for example, a second wall under the thin wall to provide strength, with resulting cost savings. 
   A front view of the cap  60  is shown in  FIG. 6A , a rear view of the cap  60  is shown in  FIG. 6B , and a bottom view of the cap  60  is shown in  FIG. 6C . The cap  60  includes three arms  76   a,    76   b,  and  76   c  extending radially from a center passage  78 . The center passage  78  is sized to slide over the heater element end  52 . Each of the three arms includes a passage  74  of the screws  70  (see  FIG. 5 ) which attached the cap  60  to the heater housing  42 . The cap  60  further includes a round contact surface  80  for pressing against the spacer  64 , and a recessed surface  81  inside the round contact surface  80  for capturing the snap ring  66 , and preferably a ring type wire end  72 . Bosses  68  are formed on the interior of the heater housing  42  for the screws  70 . 
   A side view of the spacer  64  is shown in  FIG. 7A  and a rear view of the spacer  64  is shown in  FIG.7B . The spacer  64  is round and has a single step  84  which cooperates with the stepped seat  45  in the heater housing  42 . 
   A side view of the snap ring  66  is shown in  FIG. 8A  and a front view of the snap ring  66  is shown in  FIG. 8B . The snap ring  66  is a common snap ring sized to engage the indentation  54  in the heater element end  52  (see  FIG. 4 ) without applying more than slight force to the outer wall  57  (see  FIG. 4A ), and may loosely reside in the indentations and apply no force to the outer wall  57 . 
   A side view of a ring type wire end  72  usable to connect electrical wiring to the heater element  50  is shown in  FIG. 9A , and a front view of the ring type wire end  72  is shown in  FIG. 9B . The ring type wire end  72  is a common wire end sized to slip over the outer wall  57  and is available from most electrical supply stores. 
     FIG. 10  is a method for connecting the heater element to the heater housing according to the present invention. The method includes inserting two ends of the heater element through heater element passages in the heater housing from the inside to the outside at step  100 , sliding O-rings over the heater element ends and into stepped seats in the heater housing at step  102 , sliding spacers over the heater element ends and on top of the O-rings at step  104 , positioning snap rings on circular indentations on the heater element ends over the spacers and O-rings at step  106 , and tightening a cap over the snap rings to retain the heater element ends positioned through the heater housing at step  108 . 
   While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.