The Model HD400 is a 4 Gallon Backpack Sprayer w/Piston Pump & Santoprene Cup - The HD400 Backpacks are very popular with landscape professionals and organic farmers. It han an internal mechanical agitator that does an excellent job of keeping powdered chemicals, such as kaolin clay organic insecticides, in suspension. Can be right or left hand operated. Tested for over 1,500 hours of continuous operation.