Series S116, S1116 Pressure Relief, Sustaining or Backpressure Control Valve is designed to permit flow when upstream pressure is above the adjustable setpoint of the control pilot, and throttle toward closed when upstream pressure falls below the adjustable setpoint. When the valve is installed off the main line on the branch of a tee, it serves as a Pressure Relief Control Valve. It is normally closed, and quickly opens when upstream pressure exceeds the pilot setting, relieving excess pressure. When valve installed in line connecting two distribution zones, the valve acts as a Pressure Sustaining Control Valve. When pressure in the upstream zone falls below the pilot setting, the valve modulates toward a closed position, sustaining pressure in the upstream zone. When the valve is installed in line on the discharge of a pump, it acts as Backpressure Control Valve. When pump discharge pressure falls below the pilot setting, the valve modulates toward a closed position, increasing backpressure against the pump.