Abstract: A system for spraying fluids at variable flow rate using pulse width modulation utilizing a circuit including a reservoir, pump, spray nozzle, pulse width modulated valve. While no spray issues from a nozzle, the fluid circuit is closed with the reservoir as the initial and end point of the circuit. While no spray issues from a nozzle, the fluid flow through a heated nozzle functions as a heat sink. While spray issues from a nozzle, the circuit contains a means to maintain a specific fluid pressure. While no spray issues from a nozzle, the circuit pressure is much lower than the spray pressure allowing reduced energy consumption and lessening wear on the pump and motor. This system may be incorporated into a selective catalytic reduction (SCR) system for controlling NOX emissions from diesel engines using a urea-water solution as a fluid.