Abstract: A water heater for use in a carpet cleaning system has a pair of inner copper tubes which are press fit into outer copper sleeves. Each tube/sleeve combination defines a heating chamber. A hollow tubular bridge extends perpendicularly between and in fluid communication with the heating chambers. A heating element extends coaxially into each heating chamber. A small annular clearance extends between each heating element and inner tube. High pressure fluid enters one of the heating units through an inlet/outlet port and circulates through the bridge to the other heating unit for additional heating. An electronic thermostat is mounted to the exterior surface of each outer sleeve at a desired location to detect the temperature of the fluid by monitoring the temperature of the exterior surface of the heating unit.

Abstract: A cavity in a heat-resistant structure, eg. of ferrous metal, is filled by fitting it with refractory brickwork. Instead of securing the brickwork with conventional cement, a flowable aluminous slag is produced in contact with the brickwork by exothermic reaction of a composition containing metallic aluminium and an oxidizing agent, preferably ferric oxide. The reaction, which may take place wholly or partially within the jointing space or spaces, is at such a temperature that the slag in said spaces is at least at a bond-forming temperature. Additives, eg. refractory particles, a flux, potassium nitrate or ferrous metal may be incorporated in the reaction mixture for control purposes subject to considerations described.