FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION Domestic storage water heater
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400
030, Maharashtra, India, an Indian Company
INVENTORS
Nadar Vinay Velayueham, Ingle Asha Jayaprakash and Joshi Sachin Sharad, all of Crompton Greaves Ltd , AMPTC, CG Global R&D Centre, Crompton Greaves Ltd., Kanjur (E), Mumbai 400042, Maharashtra, India, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in
which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a domestic storage water heater.
BACKGROUND OF THE INVENTION
Domestic storage water heaters are generally used for heating small quantities of water for personal use like bathing. A domestic storage water heater comprises a totally enclosed storage tank having a cold water inlet, hot water outlet, pressure relief valve and mounting brackets. The storage tank also comprises heater elements provided internally, temperature control device like thermostat and status indicator. The storage capacity of the tank is generally standarised as 6, 10, 15 and 25 litres. All the above capacities of water heaters are generally made of stainless steel. In order to save material cost, they are also made of mild steel of larger thickness and coated with rust resistant material. In the case of 15 litres and 25 litres capacities water heaters, the thickness of a stainless steel tank is 0.63 mm. The storage tank comprises a cylindrical body with a flat top and a flat bottom with a curved corner at the bottom having a radius of 86 mm in the case of a 15 litre capacity storage tank and a radius of 85 mm in the case of a storage tank of 25 litres capacity. All the above capacities of water heaters can generally withstand pressures of 3 to 6 bars. In case there is excess pressure development within the tank, for instance, as a result of excessive heating of water in the tank due to failure of the temperature control device, the storage tank may burst and cause accidents and damage. The life of the tank is also reduced.
OBJECTS OF THE INVENTION
An object of the invention is to provide a domestic storage water heater, which has increased pressure withstanding capability and longer life.

Another object of the invention is to provide a domestic storage water heater, which is cost effective.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a domestic storage water heater comprising a totally enclosed storage tank having a cold water inlet, hot water outlet, pressure relief valve, mounting brackets, heater elements, temperature control device and status indicator, wherein the storage tank has a capacity of 15 litres or 25 litres and is made of mild steel and coated with rust resistant material, the tank comprising a cylindrical body having a thickness of 2 mm and a curved bottom and curved top each having a radius of 245 mm and a curved bottom corner and a curved top corner each of 67 mm radius.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is an elevation of the domestic storage water heater according to an embodiment of the invention; and
Fig 2 is a plan view of the storage water heater of Fig 1.
The water heater 1 as illustrated in Figs 1 and 2 of the accompanying drawings comprises a totally enclosed mild steel cylindrical tank 2 having a cold water inlet 3, a hot water outlet 4, a pressure relief valve 5 and a pair of mounting brackets 6.

Heater elements, temperature control device like thermostat and status indicator of the tank have not been illustrated and described in the specification as such are not necessary for understanding the invention. The storage tank has a 15 or 25 litres capacity and thickness of 2 mm. The tank is formed with a curved bottom 7 and a curved top 8 each having a radius of 245 mm. The tank is also formed with a curved bottom corner 9 and a curved top corner 10 each of 67 mm radius. 11 is the neck of the tank. Because of the curved bottom and curved top of radius 245 mm and curved bottom and top corner radius of 67mm and because of the use of a material thickness of 2 mm, it has been possible to increase the pressure withstanding capability of the storage tank and to reduce the cost of the tank. Mild steel is much cheaper as compared to stainless steel.
Comparative simulation tests were carried out using conventional 15 and 25 litres capacities storage tanks and 15 and 25 capacities storage tanks according to the invention. The conventional storage tanks were made of stainless steel of 0.63 mm. The radius of curvature of the bottom of each of the 15 litres and 25 litres capacities stainless steel storage tanks were 86 mm and 85 mm respectively. The storage tanks of 15 and 25 litres capacities according to the invention were made of mild steel of thickness 2 mm and coated with a rust resistant coating comprising zinc phosphate and solvent less epoxy. The radius of curvature of the curved bottom and curved top of the mild steel tanks were 245 mm. The radius of the curved bottom and curved top corners was 67 mm. A 10 bar pressure was applied on the storage tanks and the results were as under:
1) Conventional 15 litres capacity storage tank

Total deformation of the tank - 64.13 mm
Total stress of the tank - 4514.9 N/mm2
2) Conventional 25 litre capacity storage tank
Total deformation of the tank - 42 mm
Total stress of the tank - 2215.5 N/mm2
3) 15 litres capacity storage tank according to the invention Total deformation of the tank - 0.3 mm Total stress of the tank - 263.2 N/mm2
4) 25 litres capacity storage tank according to the invention Total deformation of the tank - 0.18 mm Total stress of the tank - 218.44 N/mm2
It is evident from the above experimental details that the storage tanks of the invention had very low or negligible deformation. Stress experienced by the tanks of the invention was also very low. Therefore, the tanks of the invention has a high pressure withstanding capability and longer life.

We claim :
1) A domestic storage water heater comprising a totally enclosed storage tank having a cold water inlet, hot water outlet, pressure relief valve, mounting brackets, heater elements, temperature control device and status indicator, wherein the storage tank has a capacity of 15 litres or 25 litres and is made of mild steel and coated with rust resistant material, the tank comprising a cylindrical body having a thickness of 2 mm and a curved bottom and curved top each having a radius of 245 mm and a curved bottom corner and a curved top corner each of 67 mm radius.