Most of these units use a gas engine to power the pump and a diesel-fueled 12V burner to heat the water; no need to plug them in to get the heated pressurized water needed to handle the toughest, oily, dirty jobs. There are small and portable models, as well as larger skid units that can be mounted in a truck, van or trailer. Some units feature generators, instead of 12V burners for better life-cycle maintenance. Versatile, tough, powerful, these can handle the widest variety of cleaning jobs.