The typical water heater includes a tank to contain water to be heated and a jacket is spaced outwardly of the tank to provide an annular cavity therebetween. To insulate the tank, a layer of insulating material, which can take the form of fiber glass or a foam resin material, such as polyurethane foam, is located in the cavity.
When insulating a tank with a foamed resin composition, a liquid resin is introduced into the upper end of the cavity and expands outwardly to fill the cavity and provide an insulating layer. In one method of providing the foamed insulated water heater, as disclosed in U.S. Pat. No. 4,628,184, a bag formed of polyethylene film and having a closed bottom is disposed within the cavity and the liquid resin is introduced into the bag. With this method, the bag contains the liquid resin and prevents the liquid from leaking from the cavity.
In other methods of producing a foam insulated water heater, a dam or closure is positioned at the lower end of the cavity to retain the liquid resin, as it is introduced into the cavity. In accordance with the method of U.S. Pat. No. 4,477,399 an inflatable annular ring is located at the lower end of the cavity, and by introducing gas into the ring, the ring will extend radially to form a dam or closure at the lower end of the cavity. In U.S. Pat. No. 4,372,028, an annular bag is positioned at the lower end of the cavity and the bag is filled with a liquid foamable resin composition. The resin expands outwardly within the bag to provide a collar or dam at the lower end of the cavity.
The use of an inflatable bag is a relatively expensive procedure, particularly if the bag is not removed and is retained in the fully assembled water heater. On the other hand, removal of the bag for reuse is difficult, even if release agents are utilized, because of the tendency of the liquid resin composition to bond firmly to areas that are not adequately coated with the release agent.
It has also been proposed to seal or close off the lower end of the cavity between the tank and the jacket through use of a fiber glass ring. However, a fiber glass ring, if not properly installed, may not provide a positive seal and the pressure of the expanding resin within the cavity may cause the fiber glass ring to shift or migrate during the foaming operation.