Objects have been washed of undesirable coatings and debris by directing a high pressure stream of heated liquid against the surface of the object.
Surface cleaning systems in use today spray a heated cleaning liquid onto the surface to be cleaned and the spent liquid and debris is vacuumed away from the surface. U.S. Pat. No. 4,940,082 granted Jul. 10, 1990 to James R. Roden for "Cleaning System" discloses a system in which exhaust gases from an internal combustion engine are passed through a heat exchanger to heat the cleaning liquid. The engine, of course, drives a pump to pressurize the cleaning liquid and a blower to create the vacuum.
U.S. Pat. No. 5,033,264 granted Jul. 23, 1991 to Richard E. Cabral for "Compact Cogeneration System" discloses the idea of placing a catalytic converter inside the exhaust gas heat exchanger and utilizing the heat given off by the converter to further heat the cleaning liquid.
The combination of the Roden system with the Cabral heat exchanger is capable of heating the cleaning liquid to temperatures which are adequate for cleaning fabrics and carpets; 180.degree. F. to 200.degree. F. However, for more difficult cleaning tasks, say removing oil, grease and grime from a concrete surface, it is highly desirable to heat the cleaning liquid to higher temperatures. This is particularly true when cleaning the surface with an appliance like that disclosed in U.S. Pat. No. 5,711,051 granted Jan. 27, 1998 to Michael J. Roden for "Hard Surface Cleaning Appliance". That apparatus relies on the force of the cleaning liquid sprayed onto the surface to loosen the debris.