Abstract: The overcharge prevention device is installed in a solvent processing plant in a vacuum evaporator of a heat exchanger. It assures that the level of the cleaning solution in the vacuum evaporator cannot randomly rise when a feed valve malfunctions. A float body of an overcharge valve extending into the vacuum evaporator exerts a pressure through a double-arm lever and a valve plunger upon a ball valve and a valve seat in normal operation and holds the overcharge valve in a closed position. As the level of the cleaning solution undesirably rises, the buoyant action of the cleaning solution acts on the float body, causing the pressure on the valve seat to diminish, and the overcharge valve opens. This permits air to enter into the vacuum evaporator through the overcharge valve. The generated vacuum collapses and the suction force employed to ingest the cleaning solution disappears.