in the systems and the processes. In 1971, Gary Minkin developed an aqueous based parts washer for degreasing automobile parts. The Minkin breakthrough used the force of hydraulic impact pressure to significantly improve the cleaning power of the aqueous parts washer. Cleaning methods Beside high mechanical energy, higher cleaning temperatures are one of the most effective methods of improving the cleaning results in a parts washer. In general, a 10 to 15 °F (5 to 8 °C) rise doubles the chemical reaction of the detergent. The increased chemical reaction between the greases and oils and the detergent delivers faster cleaning cycles and cleaner parts. Additionally, all greases and oils exhibit a lower viscosity at higher temperatures. Cleaning solution temperatures of and above softens or melts most oils and greases causing them to flow like water so they are easily removed resulting in faster cleaning, better results and cleaner parts. Many parts washers are not capable of maintaining this operating temperature due to the lack of amply heating systems. Additionally, careful design is required of the pumping system so it can pull in and deliver cleaning solution at temperatures that approach boiling in the parts washer. All centrifugal pumps require a net positive suction head (NPSHr) in order to be able to pump solution. As the temperature of the solution approaches the NPSHr, the pump stops pumping because the cleaning solution flashes to steam in the pump intake. Careful design of the pump is required to minimize NPSHr and allow pumping of high temperature cleaning solution. A typical parts washer is aqueous based but there are some types that use solvent. Solvent-based Ben Palmer invented a solvent style parts washer in 1954. The parts washer was a success from the start, and he decided in the early 1960s not to sell his machine, but to lease it to the customer and service it by removing and replenishing the used solvent. Since the early 1990s there has been a significant shift towards aqueous based systems due to the environmental and safety hazards associated with solvent systems. A solvent style parts washer is filled with several gallons of solvent that is stored in a settling pan at the bottom of the washer. A small flame-tight electric liquid pump is immersed in the solvent and skims clean solvent from near the top of the settling tank, and pumps it at low pressure through a