WW8583-12 (Watts) | 4 Pressure Reducing Control Valve With Low-Flow Bypass Feature | Class 150This 4 In, Class 150, Watts Pressure Reducing Control Valve With Low Flow By Pass, Model 115 74, is Designed to Automatically Reduce a Fluctuating Higher Inlet Pressure to a Constant Lower Downstream Pressure Regardless of Varying Flow Rates. A Flow Rate Below The Normal Range of The Main Line Pressure Reducing Control Valve is Handled by a Separate, Valve Mounted, Direct Acting Low Flow By Pass Pressure Reducing Valve. Watts WW8583 12