US Patent 8032979 Heat exchanger

A heat exchanger for use with a carpet cleaning system having combined exhaust gases of an internal combustion engine and other hot exhaust gases expelled from a vacuum pump as a single input to a heat exchanger for heating the carpet cleaning fluid. A heat exchanger control system permits constant control of a stream of cleaning fluid both while the cleaning fluid is flowing through the heat exchanger and while the cleaning fluid is stagnant within the heat exchanger, without the potential overheat condition of the portion of cleaning fluid stagnant in the heat exchanger known in prior art devices that required a constant flow of the cleaning fluid.