Pressure Independent (PI) Valves are designed to deliver the proper flow to the coil over any operating load regardless of system pressure fluctuations that occur in a typical system with multiple control valves and interactive circuits. This eliminates coil overflow which reduces low Delta-T problems and reduces pumping cost. Coil underflow is also eliminated which can result in poor comfort control. PI valves are always Dynamically balanced and never need to be adjusted regardless of changes to the system.
Mechanical PI valve series PIQCV models consists of a differential pressure regulator in series with a 2-way control valve. The control valve is throttled to match the flow command of the control signal. As system pressures change, the differential pressure regulator moves in response to keep the flow stable. When differential pressure increases the regulator opening is reduced. When differential pressure decreases the regulator opening is increased. This allows for the constant pressure differential across the ball of the valve and constant flow.
Electronic PI valve series ePIV and Energy Valve models consists of an integrated in-line ultrasonic flow meter in series with a 2-way control valve. True Flow readings are sourced from the flow meter and are also used by the actuator logic to deliver pressure independent flow to the coil. The valves use the available differential pressure across the valve and the actuator throttles to any position needed to obtain the flow setting, just like VAV box actuator behavior. Under light load conditions low flow settings can be achieved with as little as 1 psid across the valve. True Flow readings can be read with a handheld tool or computer software.