Fimco sprayers are designed to spray a large variety of Agricultural and Lawn & Garden chemicals diluted in water.  The pumps do not pressurize the tank, but actually draw the solution from the tank and pressurize the sprayer's plumbing system.

High-Flo Gold Series pumps used on Fimco sprayers are "demand" pumps that only run when there is an open outlet for the spray.  When the lever on the handgun is squeezed to spray, the pressure in the plumbing drops and the pump will run.  When the lever is released, a pressure switch located on the pump head senses the pressure increase and shuts the pump off.  The pressure switches are preset at the factory and are different for each of the three different sized pumps.  Some Fimco sprayers are equipped with a pressure gauge and bypass valve.  On these units, the pressure at the spray tip can be regulated by opening or closing the bypass valve.  Opening the valve reduces the pressure by diverting some or all of the spray back into the tank.  Highest pressure is achieved by having the bypass completely closed.