The differential pressure is below the minimum needed to activate the AutoFlow piston. It is fully extended and acts as a fixed orifice with a Cv of .71 times design flow (2-32 range) or .45 times design flow (5-60 range). The ATC is controlling the GPM in this zone.

AutoFlow piston now responds to changes in differential pressure by repositioning the variable side orifices to maintain design flow ±five percent. At approximately 50 percent of control range, the consolidated side port now handles all flow through the variable orifice. The Cv is variable in this range and is a function of piston position.

Now fully retracted, only the AutoFlow piston’s end port is exposed. The regulator functions as a fixed orifice and will react to increased pressure differential with increased flow in accordance with the formula: GPM = Cv &P. Fixed Cv of the valve is now 18 times design flow (2-32 range) and 13 times design flow (5-60 range). A 25 percent “over range” (32 psi to 40 psi) increases the flow by only 12 percent!