Abstract: An agricultural sprayer of the injection type has a charging circuit for generating a pressurized circulating flow of fluid additive. This is supplied to the inlet of a metering pump of the variable stroke piston type. This allows the pump to operate at optimum volumetric efficiency throughout a wide range of pump speeds, for agricultural chemicals of all common viscosities and at all temperatures normally encountered. The speed of the metering pump can thus be controlled to control the amount of chemical injected into the water being sprayed.