Abstract: An automatic volume control system for controlling the rate at which fluid, such as paint, is sprayed from spray guns on a mobile vehicle as a function of vehicle speed. The device permits paint lines to be maintained at a uniform thickness independently of the vehicle speed. A tachometer generator generates a voltage proportional to the vehicle road speed which voltage controls the opening of an adjustable hydraulic valve. Hydraulic fluid passing through the hydraulic valve drives a hydraulic generator which in turn drives a spray gun system. The voltage from the tachometer generator thereby causes the hydraulic fluid to drive the hydraulic motor and paint pump at a rate which is proportional to the vehicle road speed. The hydraulic fluid is suitably pumped through the hydraulic valve to the hydraulic motor by a hydraulic pump driven by the power take-off of the vehicle.