Title of Invention

"ELECTRIC WATER HEATER ASSEMBLY"

Abstract

The present invention relates to novel electric water heater assembly (400), as shown in Figure 4 and attached below, wherein, a water storing container (402), along with water flow ports and heater mounting (412) is made of thermoplastic material such as polycarbonate, polypheniloxide or their modified polymers and whole of this assembly (400) is protected from excess inlet water pressure using a Pressure Protection Valve (416).

Full Text

Field of the invention The present invention relates to an electric water heater assembly wherein, a water storing container, along with water pipes and heater mount is made of thermoplastic material, and a pressure protection valve maintains the pressure of water in the water storage container at a preset limit, thereby protecting the electric water heater assembly from excess inlet water pressure. Background The electric water heater assembly is a domestic appliance, which is used to heat up the water for bathing and kitchen purposes. It generally comprises of an outer housing, an inner water storage container and a unit assembly which controls the flow of the water wherein, the said unit assembly provides housing for the Heating element, thermostats, water ports and different valves. The said electric water heater assembly optionally comprises a pressure reducing valve capable of reducing the inlet water pressure from high pressure for protecting the water storage container. US patent 6566484 relates to a complete electric water heater assembly with outer and inner shells made of plastic materials. This invention just describes about two welded plastic shells - one covering the other for thermal insulation. The limitation is that it does not deal with protection required against the excessively high water pressures present in the actual situations. Also there is no description about the limit of pressure the design can withstand and there is no solution provided for such a high pressures in their design. In the said patent, while designing this invention, applicants have not considered the reparability of the component. If the pipe marked 3 in their Figure 1 leaks or clogs and needs replacement - it can not be done. The outer shell will have to be cut open to replace that pipe. In practical usage this product will fail when installed in a high pressure multi storied building or pressure fed Jacuzzi pressure etc. Furthermore it is design of a complete electric water heater assembly and can not be used in variety of outer housing options available to the user. US patent no. 5668922 deals with high capacity storage water heaters with extendable and flexible capacity. This is again a design where the pressure problems are neither discussed nor handled. This design of water heater can again work in an environment of small water head installations. The invention deals with two shells one covering the other for thermal insulation basically. The design of the invention is such that the length of the tubular section can be varied by adding o tubular pieces. The design is basically for floor mounted large capacity boiler type unit which is normally placed in the basement of single or few storied houses and is a complete unit in itself, but again having no protection against high pressures of water supply. US patent No. 5923819 is quite similar to the one referred in US Patent 5668922 and the product design is similar to that. Here the patent claim is for water storage container and not as electric water heater assembly as in above patent. US patent No. 6184509 is about the system of fixing a permanent, non repairable but a leak proof mounting of a heating element on a plastic vessel. Our requirement of fixing a heating element is for a removable type heating element mounting and as such we do not infringe upon this patent in any way. Applicant has filed an Indian Patent Application for the pressure protection valve. (Application No. 1172/DEL/2004 dated 23, June, 2004). Outer Housing The Outer Housing is basically a shell which covers the water storage container and rest of the components. Only Inlet and Outlet water ports and the wire cord for electrical connections come out of this shell. The outer casing also helps in covering the thermal insulation material provided all around the water storage container. This thermal insulation material is used to keep the heated water warm for a long period of time. The Outer Housing is made in various options to suit the aesthetic taste of the customer. The most conventional option is metal housing. In this case a mils steel sheet is rolled to form a tubular center section and its lateral ends are joined by spot welding or riveting. The top and bottom of this tubular section is covered with two end covers made out of deep drawn mild steel sheet only. The top end cover is a closed end cover. The bottom end cover carries an opening for water pipes and wire cord. Whole of this unit is finished either by some stoving paint or powder paint. The joining edges of center tubular section and end covers are normally covered with a PVC belt to hide the fastening screws. In an alternate option the end covers are made out of ABS plastic. The advantage of using ABS plastic here is that it makes the end covers shock proof and rust proof. The third option used by many manufacturers is to make full outer shell out of some thermoplastic material. In case of full plastic out shell, it is made in two parts only- the back side and the front side. The advantage of making full plastic outer housing is that it makes the whole of the unit rust proof and shock proof. Plus the plastic variant offers a wide variety of design options and a high gloss finish to the product. All the outer housing then carry a set of mounting clamps. The mounting clamps are used to hang the electric water heater assembly on the wall. Water storage container Presently, the Inner Water Storage containers are all made out of metal. The material of this water storage container should be bale to withstand following requirements: • It should be non-corrosive to water and water salts. • It should withstand high water pressures, especially in case of multi storied or pressure pump fed water lines. • It should be non-reactive or low reactive with salts from water deposited on the inside walls of the metal container • It should withstand temperature up to about 100°C. In India, copper is the most widely used material for these water storage containers. Copper is non corrosive to water. But at the same time, it is not a very strong material to be able to withstand the high water pressures of multi storied buildings. It is also reactive to water salts. But still, this is the most popular choice, because of the ease of forming and ease of welding. The second popular material is stainless steel. It is non reactive to water, non reactive to water salts and is also a very strong material. But at the same time it is very difficult to form and extremely hard to weld. The only welding possible in this application is seam welding. Since any other welding takes the stainless steel to a very high temperature and changes the properties of the material, this makes it corrosive to water. In certain percentage cases of seam welding also - the material at times shows bad spots, which rust out in the presence of water and cause the water storage container to leak. In some parts of the world, Vitreous Enameled Water storage containers (Glass Lined water storage containers) are also used. In this process, a thick shell of mild steel is made and it is then vitreous enameled. This shell is required to be very thick because vitreous enameling is done at temperature of approximately 850°C and for the shell to maintain the shape at such high temperature it needs to be very thick. This shell is then required to be coated with at least two coat vitreous enameling process to achieve a non porous layer. The process of vitreous enameling is again a difficult process and it is very hard to control the quality, especially in the inside of the water storage container. Even a small dot of enamel gap or burn can cause it to rust the base metal sheet and start leaking in a short time. The vitreous enameling is a glass layer and hence is very brittle and prone to damage. The impact damaged area will again get rusted very soon causing the water storage container to leak in a short time. But, a good quality vitreous enameled water storage container has the best life compared to above choices. In some cases, galvanized water storage containers are also used. A manganese rod is placed inside these water storage containers to save the galvanizing. This manganese rod needs replacement at a regular interval. If this is not replaced, the water storage container will rust off and start leaking. Unit Assembly The unit assembly is basically a brass plate, which is used to close the mouth of the water storage container. The inlet water pipe and outlet water pipe made out of brass and are welded to this plate. On the other side of these pipes - either copper or Brass pipe are welded to maintain the water level inside the water storage container and to provide a good mixing of cold water coming in. This plate also carries a mounting place for the heating element and thermostats. Certain fuse plugs, drain nuts, pressure release valves etc are also mounted on this unit assembly only. Whole of this unit is made out of either brass or copper parts. Immaterial of the material of the water storage container - this unit assembly is more or less same in all the cases. The electric water heater assembly comes in various storage capacities and mounting variants. Capacity may range from 1 litre to 100 litres. In the mounting options - Vertical, Horizontal and Floor model are the different options. For each capacity and model, the water storage container and unit assembly design - varies. Most of the inner copper water storage containers are made in 3 piece format. Figure la shows a typical 3 piece inner copper water storage container 100. A rectangle sheet 102 is rolled and welded at the ends to form a cylindrical pipe. The top and bottom of this cylinder is covered with hemispherical deep drawn covers 104 and 106. The three pieces 102, 104 and 106 are welded together to form a water storage container. Weld lines 108 can be seen in Figure la. In the case of stainless steel water storage container and in few cases of copper water storage containers also - two halves 110 and 112 of a water storage container are deep drawn and welded together (as shown in Figure lb). The welding process in the case of copper is gas torch welding using a filler material. In the case of stainless steel, seam welding is used. Long time back Argon TIG welding has been tried in stainless steel case, but did not prove successful since the starting and intermittent spark in this process caused the stainless steel surface to achieve very high temperatures, which changed the corrosion resistant property of the metal. In the case of seam welding also, in small percentage cases, the non uniformity of alloy composition or thickness variation or voltage variation during the weld process - causes similar bad spots, resulting in changing the corrosion resistant property of the metal. Such water storage containers corrode out after some time causing the water storage container to leak. As shown in Figure 2, an opening is made on one end of the water storage container 200 and a flange 202 is fixed on its neck 204 for fixing the unit assembly on the water storage container 200. This neck 204 at the flange 202 is the weakest part of the water storage container 200. To fix this flange 202, a hole is cut on the water storage container 200 as shown in Figure 2. Then a collar 206 is drawn out of this hole, which is then heated to make it soft. The flange 202 is placed around this collar 206 and the collar 206 is hammered to wrap the inner edge of the flange 202 as shown in Figure 2. The softening and hammering of the collar 206 makes the material very weak and in most of the cases - the water storage container 200 gives away from this neck 204 only. In the present design, applicant have molded the water storage container in two parts and welded it at single seam without using of foreign material or filler. In the present design, the concept of flange all together has been eliminated and has provided the provisions of the pipe assembly and heater mounting on the solid water storage container only. This resulted in removing the weakest part of the water storage container. Pressure reducing valve (PRV): Presently PRV 300 is being used in high pressure installations as described in Figure 3. In this construction- there is a flexible rubber seal 302. When the outlet pressure Po acts on the surface area Sr of the rubber seal 302, a force of Po x Sr is created upwards. This rubber seal 302 is connected to a stopper 304 as shown in Figure 3. The stopper 304 works on the Port A to control the flow of the fluid to the storage container. The input force at Port A is inlet pressure Pi x Surface area of Port A Sa. There is also a controlling force Fs of a spring 306 - which is unused to preset the maximum limit for Po. Here, the Port A closes when Po x Sr > (Pi x Sa) + Fs Here, since Sr is many times more than Sa - the Po is equivalently reduced from Pi. The force Fs just acts as the preset level. As Pi increase - the Po also increase in same proportion as Sr: Sa. The outlet of this valve 300 is connected to the inlet of the water storage container. When the water is drawn from the said water storage container by opening the stop cock at the outlet of the water storage container - the pressure Po falls. Thus opening the Port A and letting the flow in to the water storage container - till the pressure reaches Po preset limit again. The drawback in this valve 300 is that - the outlet pressure Po is directly proportional to inlet pressure Pi. If the Pi goes too high - the Po also goes to a proportional higher pressure and thus damaging the water storage container. Novelty As on date, no one thought of using thermoplastic material in an electric water heater assembly because the water storage container is subjected to TEMPERATURE, PRESSURE and WATER EROSION characteristics. As far as temperature and water erosion are concerned, above mentioned thermoplastics can fulfill the requirements - but when the question of pressure comes- a thermoplastic vessel can not withstand high pressures at high temperatures. That is why no one thought and has used thermoplastic as material for electric water heater assembly. Applicant has designed a pressure protection valve which will ensure that the pressure in the vessel can be set to not go beyond 10 to 20 psi - which is normally sufficient for an electric water heater assembly. Once the pressure is controlled inside the water storage container and a thermoplastic material is selected which can withstand the normal operating temperatures of the electric water heater assembly - a thermoplastic water storage container becomes a feasible option. Object of present invention The main object of the present invention is to design an electric water heater assembly having non-corrosive water storage container for storage of water. Another object of the present is to design an electric water heater assembly having water storage container made up of thermoplastic polymers selected from a group consisting of polycarbonate, polypheniloxide or their modified compositions, hereby making the water storage container corrosion proof and rust proof. Another object of the present invention is to have an electric water heater assembly without any flange thereby removing the weakest component of the water storage container. Another object of the present invention is to have an electric water heater assembly, which can be installed at any location with any pressure in the water supply lines, making it suitable for multistoried building and pressure pump fed water supply also. Another object of the present invention is to have an electric water heater assembly, which would cost lesser than copper or stainless steel models. Another object of the present invention is to have a faster process of production. Another object of this present invention is to develop an electric water heater assembly which can be mounted in any outer casing or shell namely metal shell, plastic shell or the combination thereof. Another object of this invention is to improve the thermal insulation of the electric water heater assembly, thereby reducing the energy consumption required. Brief description of accompanying drawings: Figure 1 shows design of a water storage container of a conventional electric water heater assembly. Figure 2 shows details of fixing flange in the water storage container of the conventional electrical water heater assemlby. Figure 3 shows older design of Pressure reducing valve Figure 4 shows cross sectional view of an electric water heater assembly of the present invention. Figure 5 shows cross sectional view of the Pressure Protection Valve. Figure 6 shows Inlet and Outlet Pipe design. Figure 7 shows Bottom mounting side layout in new design. In reference to figure 4, wherein 402 water storage container 404 water inlet pipe, 406 water outlet pipe, 408 thermostat pipe, 410 auto cut pipe, 412 heating element mounting, 414 heating element, 416 pressure protection valve, and 418 pressure release valve The description given below is for illustration only and should not be construed to limit the scope of the invention Detailed description of the invention Accordingly the present invention provides an electric water heater assembly 400 having a water storage container 402, a water inlet pipe 404 for supplying water into the water storage container 402 and a water outlet pipe 406 for discharging water from the water storage container 402. The electric water heater assembly 400 further includes one or more heating elements 414 disposed in the water storage container 402 and a heating element mounting 412 for mounting the heating element 414 in the water storage container 402. A thermostat is inserted into the water storage container 402 through a thermostat pipe 408, an auto cut thermostat and an auto cut pipe 410 for mounting the auto cut thermostat is disposed in the water storage container 402. In addition a pressure release valve 418 is connected to the water outlet pipe 406 for releasing the excess pressure above a preset limit inside the water storage container 402. The water storage container 402 is made of a thermoplastic material. The inlet pipe 404 that is provided with a pressure protection valve 416 is connected to the water storage container 402. The pressure protection valve 416 controls the pressure Po of the water that is entering the water storage container 402 to a maximum preset limit. The pressure protection valve 416 includes an inlet 504, an outlet 502, a stopper 304 for controlling the flow of water from the inlet 504 to the outlet 502. The stopper 304 restricts the flow of water when the pressure Po at the outlet 502 reaches the maximum preset limit, irrespective of the pressure Pi at the inlet 504, thereby maintaining a constant outlet pressure Po. The water storage container 402 is made up of suitable thermoplastic material like polycarbonate, polypheniloxide or their modified alloys. The water storage container 402 is designed to have a thickness of 1 mm to 6 mm, preferably 2.5 mm to 3.5 mm, depending on the water carrying capacity of the model. In one embodiment, the water storage container 402 is surrounded by an outer casing and heat insulating material is filled in the space between the outer casing and the water storage container 402. At the (bottom) mounting side, it is designed to have a thickness of 5mm to 6mm to provide the mechanical mountings such as the water inlet pipe 404, the water outlet pipe 406, the thermostat pipe 408 and the heating element mounting 412. This thickness of the selected material imparts required strength to the water storage container 402 to withstand the normal requirement of temperature and pressure. A thermostat of the electric water heater assembly 400 is normally set to cut off the heating once the water is heated up to 70°C. The selected material is capable of withstanding operating temperature of 140°C. The selected material is non reactive to water and hence makes the electric water heater assembly 400 rust proof and corrosion proof. The selected material has no electrical conductivity and as such makes the electric water heater assembly 400 shock proof also. Thermal conductivity of thermoplastic is also very low and thus, the water heated inside the water storage container 402 will remain hot for a longer time, thereby covering all the requirement aspects of an electric water heater assembly 400. Water inlet pipe 404 - where the cold water supply is connected - is also designed to be made out of similar thermoplastic material as used above (Figure 6). We have designed a wall thickness of 6mm for the water inlet pipe 404, since the water inlet pipe 404 is to carry strong threading arrangement 600 at one end, where the water inlet is provided to be connected. The other end of the water inlet pipe 404 has a rectangular flange 602, which is used to mount the water inlet pipe 404 on the water storage container 402 using a rubber gasket. This pipe 404 can easily be removed and replaced in the need of repairs. Water outlet pipe 406 - is similar to the water inlet pipe 404 as explained above with just one additional feature. This pipe 406 also carries a Pressure release valve 418 (as shown in Figure 4). The pressure release valve 418 is used to release any excess pressure buildup above the present limit inside the water storage container 402. This pressure release valve 418 is a simple spring countered port valve calibrated to release pressure above the preset limit. This pressure preset limit in the water storage container 402 is in the range of 10 psi to 90 psi, preferably about 40 to 75 psi. Thermostat pipe 408 - every electric water heater assembly is required to carry a thermostat which should cutoff the electricity after the water is heated to the preset temperature. This thermostat needs to sense the temperature of the electric water heater assembly accurately, so the thermostat needs to be placed inside the water through a pipe dipping in the water. A leak proof mounting is required for the purpose. Auto cut Pipe 410 - for mounting an auto cut thermostat. The auto cut thermostat is a re-settable type protection thermostat which cuts off the electricity at a preset temperature and needs to be manually switched back for operation. A similar pipe as described above is required for this also. The ideal position of mounting this autocut pipe 410 is at the top of the water storage container 402. Cases happen when the water level goes below the minimum level. Cases also happen when the user switches on the power before completing the installation and filling in the water. Cases also happen when thermostat fails and water temperature rises above the maximum set of limits. In all the cases, the top portion of the water storage container 402 gets heated first. If the Auto cut 410 is placed at the top - it will sense the heat at the right time and cut off the power before any damage is done. The purpose of Auto cut 410 is to prevent all these cases only and the proper position is at the top of the water storage container 402 only. But in old type of fittings, because of flange and plate construction concept, Auto cut is fitted at the bottom plate only. Heating element mounting 412 - is the place to fix the heating element 414. Because of the bigger cross section area, this mounting 412 faces the maximum force and also carries the maximum heat. The heating element mounting 412 needs to be very strong to keep it leak proof. In one aspect of the present invention, a three-stud mounting acts as the heating element mounting 412 in order to accommodate the standard heating element flange. Pressure Protection Valve 416 - This valve 416 has been designed to control the pressure of water inside the water storage container 402 to a preset maximum level. If the Inlet pressure Pi of water is less than the preset level, it will allow water to pass as it is. If the inlet pressure Pi raises above the preset level - this valve 416 closes down the input of the water moment and the pressure inside the water storage container 402 rises above the preset level. Whatever high be the input water pressure, the pressure inside the water storage container 402 is never allowed to go above the preset level, as an effect of the input water pressure. Applicant has filed an Indian patent application 1172/DEL/2004 dated 23, June, 2004 claiming for the pressure protection valve 416. The working of this valve 416 can be understood with figure no. 5. In this Valve 416, the stopper 304 closes Port A 500 once the outlet pressure Po at the outlet 502 of the pressure protection valve 416 reaches the maximum preset limit. The Port A 500 remains closed till the pressure at outlet 502 is Po, irrespective of the Inlet Pressure Pi at the inlet 504 of the pressure protection valve 416. It means that the outlet pressure is blocked to a maximum level of preset Po-irrespective of the amount Pi is above preset Po. Only in case Pi is lower than the preset Po value - the Port A 500 will remain open - thus keeping the outlet pressure Po to a level below the preset limit. In this case, the Port A 500 closes when (Pi x Sa) + (Po x Sr) > Fs In this case, when Port A 500 is closed - whatever is further increase in Pi - the condition remains the same and Port A 500 remains closed only. So, the pressure inside the water storage container 402 never goes above Preset Po limit and hence saves the water storage container 402 from any damage. In an embodiment of the invention, the water storage container 402 is a thermoplastic material, preferably made of poly-carbonate, polypheniloxide or their modified alloys to withstand working temperature up to 100°C. The novelty of the present invention is the use of thermoplastic water storage container 402 coupled with a pressure protection valve 416 to maintain the inlet water pressure in the water storage container 402. Another embodiment of the present invention is to provide an electric water heater assembly 400, which can overcome the difficulties when it is subjected to varying TEMPERATURE, PRESSURE and WATER EROSION conditions. In another embodiment, applicant have designed the pressure protection valve 416, which will ensure that the pressure in the water storage container 402 can be set to not go beyond 10 to 20 psi - which is normally sufficient for an electric water heater assembly 400. Now, once the input flow of water is blocked - the increase in pressure due to heating of water would be small only and can be easily controlled by the pressure release valve 418, prebuilt in the electric water heater assembly 400. Since this additional pressure buildup is only due to the expansion of the limited water inside the water storage container 402 - the pressure buildup is very small. Even if the pressure rises due to abnormal heating - a very small bleed of pressure from the pressure release valve 418 will always keep the pressure under control. In another embodiment of the invention, the thickness of the polycarbonate water storage container 402 used is in the range of 1.0 mm to 6.0 mm depending on the capacity of the water storage container 402. The water storage container 402 can withstand water pressure even above 100 psi, at the working temperature. In the present electric water heater assembly 400 - the water storage container 402 carries a 6 inches wide opening at one end with a flange mounted on the opening. Then a unit assembly, which carries the inlet and outlet pipes 404 and 406, the heating element 414, thermostat pipe 408 etc - mounted on a brass plate 700 (as shown in Figure 7) of app. 6 inches plate - is fastened on the mouth of the water storage container 402 using a rubber gasket. This joint is the weakest joint of the electric water heater assembly 400. Firstly, because of the process of creating this opening and flange and secondly, because of the rubber gasket sealing. Most of the leakage cases happen at this joint only. I have designed not to provide such a big opening. Instead I am providing 4 small openings - one opening 702 for the heating element 414, one opening 704 for thermostat pipe 408, one opening 706 for the water inlet pipe 404 and one opening 708 for the water outlet pipe 406. In the case of 6 inch opening, the force on the joint is huge because of huge surface area. In my design - the force on Inlet Outlet and thermostat joints is extremely small and on Element joint also it is a small fraction only. This is how I have improved on the weakest part. Pressure withstanding data Example 1 Stainless steel being a good tensile material, can withstand very high pressures. A stainless steel water storage container made out of 0.6 mm thick sheet is tested for pressure leak test and found to withstand the pressures at 100 psi. The same experiment is repeated for a stainless steel water storage container with the mouth opening is sealed properly; it withstood pressures in excess of 200 psi also. Example 2 In another set of experiment, a water storage container made out of copper having 0.7 mm thick sheet is tested for pressure leak test. Since, copper being a soft metal it starts ballooning and deshaping at about 100 psi. Example 3 The same experiment is repeated for a water storage container made of polycarbonate having a wall thickness of 2.5 mm of the material. It is found to withstand a pressure of about 100 psi water temperature of 70°C without showing any deformation. Example 4 The same experiment is repeated for a water storage container made of polycarbonate having a wall thickness of 5 mm of the material. It is found to withstand a pressure of about 250 psi at room temperature. In another experiment, a water storage container made of polycarbonate having a wall thickness of 5 mm of the material is tested for hot water pressure withstanding property it is found to withstand a pressure of about 125 psi at water temperature of 70°C without showing any deformation. Example 5 The same experiment is repeated for a water storage container made of polypheniloxide having a wall thickness of 2.5 mm of the material. It is found to withstand a pressure of about 180 psi at room temperature. In another experiment a water storage container made of polypheniloxide having a wall thickness of 2.5 mm of the material is tested for hot water pressure withstanding property it is found to withstand a pressure of about 100 psi at water temperature of 70oC without showing any deformation. Advantages of present invention 1. Copper is reactive to water and water salts. Stainless steel is also corrosive to water. In both the cases - a scale is formed inside the water storage container. Plastic has no reaction with water or water salts - so no corrosion and no scaling takes place in our product. 2. Copper water storage containers are Unit assembly in nickel and chrome plated to protect them from erosion. This chrome plating forms poisonous chromates. Stainless Steel also has 18 % Nickel and 8 % Chromium - which again may produce poisonous salts. Plastic is safe. The material we are proposing to use - poly phenylene oxide (PPO) - also has anti bacterial properties. So even if the water is stored in this water storage container for a longer time - it would be still safe from medical point of view. 3. Plastic has much lower thermal conductivity in comparison to both the metals. So heat loss is much lower - hence better efficiency and energy saving is there. 4. Both the metals are conductive to electric current. Plastic is not. Hence our product is shock proof as well. 5. Both the metals do corrode with salts of the water. Especially in case of hard water areas - the problem is very fast. Plastic has no reaction. So our design has a much longer life and is hard water suitable also. 6. Every electric water heater assembly is fitted with a safety device - called Auto cut. It should cut off the electric supply in case of excessive temperature. The ideal position of fixing of the device is at the top of the water storage container. The construction constraints do not allow such fixing in metal water storage container cases. We have designed our water storage container to position this auto cut at the top of water storage container only. 7. The only weakness - plastic has in comparison to metals - is the strength. The ability to withstand high pressures. The material we have selected for our design allows our product to withstand high temperatures as well as high pressures. Furthermore, we have designed our product to carry more effective controls for both the situations. The proper positioning of auto cut gives a better control for both the situations. The proper positioning of auto cut gives a better control of temperature and pressure protection valve helps to control the pressure to a preset limit only. 8. Above all - our product is much cheaper in cost in comparison to metal versions. Cost reduction is as high as 30 to 40 % 9. Since our design is injection molded - each piece retains uniform dimensional specifications. Whereas the metal fabrication includes lots of manual forming. Because of this only the rate of production is also very high in our product. 10. The net weight of the product is also much less in our design. 11. The raw material used here can be easily recycled. I Claim: 1. An electric water heater assembly (400) comprising: a. a water storage container (402), b. a water inlet pipe (404) for supplying water into the water storage container (402), c. a water outlet pipe (406) for discharging water from the water storage container (402), d. one or more heating elements (414) disposed in the water storage container (402), e. a heating element mounting (412) for mounting the heating element (414) in the water storage container (402), f. a thermostat inserted into the water storage container (402) through a thermostat pipe (408), g. an auto cut thermostat disposed in the water storage container (402), h. an auto cut pipe (410) for mounting the auto cut thermostat in the water storage container (402), and i. a pressure release valve (418) connected to the water outlet pipe (406) for releasing the excess pressure above a preset limit inside the water storage container (402), characterized in that said water storage container (402) is made of a thermoplastic material, said inlet pipe (404) that is provided with a pressure protection valve (416) is connected to said water storage container (402), said pressure protection valve (416) controls the pressure Po of water entering said water storage container (402) to a maximum preset limit, said pressure protection valve (416) comprises an inlet (504), an outlet (502), a stopper (304) for controlling the flow of water from the inlet (504) to the outlet (502), wherein the stopper (304) restricts the flow of water when the pressure Po at the outlet (502) reaches the maximum preset limit, irrespective of the pressure Pi at the inlet (504), thereby maintaining a constant outlet pressure Po. 2. The electric water heater assembly (400) as claimed in claim 1, wherein the water storage container (402) is surrounded by an outer casing. 3. The electric water heater assembly (400) as claimed in claim 2, wherein heat insulating material is filled in the space between the outer casing and the water storage container (402). 4. The electric water heater assembly (400) as claimed in claim 1, wherein the thermoplastic material is selected from a group consisting of polycarbonate, polypheniloxide or their modified compositions. 5. The electric water heater assembly (400) as claimed in claim 1, wherein the wall thickness of the water storage container (402) is in the range of about 1.00 mm to 6.0 mm, preferably about 2.5 to 3.5 mm. 6. The electric water heater assembly (400) as claimed in claim 1, wherein the water inlet pipe (404) is made up of a thermoplastic material having wall thickness of about 6 mm. 7. The electric water heater assembly (400) as claimed in claim 1, wherein one end of the water inlet pipe (404) is connected to the pressure protection valve (416) through a threading arrangement (600) and other end, having a rectangular section 602, is attached to the water storage container (402) using a rubber gasket. 8. The electric water heater assembly (400) as claimed in claim 1, wherein the water outlet pipe (406) is made up of thermoplastic material, and wherein one end of the water outlet pipe (406) has a rectangular section, which is attached to the water storage container (402) through a rubber gasket and the other end of the water outlet pipe (406) is connected to a delivery pipe. 9. The electric water heater assembly (400) as claimed in claim 1, wherein the water outlet pipe (406) is connected to a pressure release valve (418) for releasing excess pressure above a maximum preset limit inside the water storage container (402). 10. The electric water heater assembly (400) as claimed in claim 1, wherein the pressure release valve (418) comprises a spring countered port valve calibrated to release pressure above the maximum preset limit. 11. The electric water heater assembly (400) as claimed in claim 10, wherein the maximum preset limit of pressure Po is in the range of 10 psi to 90 psi, preferably about 40 to 75 psi. 12. The electric water heater assembly (400) as claimed in claim 1, wherein the auto cut pipe (410) is placed at the top of the water storage container (402). 13. The electric water heater assembly (400) as claimed in claim 1, wherein the heating element (414) is mounted inside the water storage container (402) by means of a heating element mounting (412), which is a three-stud mounting element. 14. The electric water heater assembly (400) as claimed in claim 1, wherein the stopper (304) closes a port A (500) to restrict the flow of water from the inlet (504) to the outlet (502), when the pressure Po at the outlet (502) reaches the maximum preset limit. 15. An electric water heater assembly (400) substantially as herein described and illustrated in the figures of the accompanying drawings.

Documents:

1171-DEL-2004-Abstract-(04-08-2008).pdf

1171-del-2004-abstract-(07-07-2008).pdf

1171-DEL-2004-Claims-(04-08-2008).pdf

1171-del-2004-claims-(07-07-2008).pdf

1171-DEL-2004-Correspondence-Others-(04-08-2008).pdf

1171-del-2004-correspondence-others-(07-07-2008).pdf

1171-DEL-2004-Description (Complete)-(04-08-2008).pdf

1171-del-2004-description (complete)-(07-07-2008).pdf

1171-DEL-2004-Drawings-(04-08-2008).pdf

1171-del-2004-drawings-(07-07-2008).pdf

1171-del-2004-form-1-(07-07-2008).pdf

1171-del-2004-form-13-(04-08-2008).pdf

1171-DEL-2004-Form-2-(04-08-2008).pdf

1171-del-2004-form-2-(07-07-2008).pdf

1171-del-2004-form-26-(07-07-2008).pdf

1171-del-2004-form-3-(07-07-2008).pdf

1171-DEL-2004-Form-5-(04-08-2008).pdf

1171-del-2004-form-5-(07-07-2008).pdf

1171-del-2004-others-document-(07-07-2008).pdf

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