Twin City Fan is pleased to introduce The PiezometerRing Airflow Measuring System, now available as anaccessory for our housed and plenum fans. The systemconsists of a Piezometer ring mounted at the throat and astatic pressure tap mounted on the face of the inlet cone.A differential pressure transducer and digital display canalso be provided. Based on Twin City Fan laboratory tests,the system was determined to be accurate within +/-5%.

How it WorksThe System is based on the principle of a flow nozzle. The inlet cone of the fan is used as the flow nozzle, andthe flow can be calculated by measuring the static pressuredrop through the inlet cone.

The pressure drop is measured from the tap located onthe face of the inlet cone to the piezometer ring in thethroat. The inlet tap is connected to the high-pressure sideof the transducer and the piezometer ring is connected tothe low-pressure side (see diagram at right).

DemonstrationShown below is a Twin City Fan model 165 BCV fitted with a Piezometer Ring Airflow Measuring System, operatingat 1100 RPM. With an unobstructed inlet, the digital display indicates the fan is producing 1713 CFM, which closelymatches rated performance (see photo A). After placing an obstruction in the inlet, the airflow is reduced to 1597CFM (see photo B).

Piezometer Ring (Airflow Measuring System)

A. Fan operating withunobstructed inletproduces 1713 CFM

B. Fan operatingwith obstructed inletproduces 1597 CFM

Inlet Tap mounted on face

of inlet cone

Piezometer Ringmounted on throat

of inlet cone