Differential Pressure Probe

Model 861

Waddell has combined several well-known fundamentals to provide an extended range differential pressure probe.


The impact (upstream) pressure enters a series of orifices that are designed with a profile similar to a bell mouth. The bell mouth shape not only minimizes the entrance losses but also minimizes the effect of skewed flow (sometimes called yaw).


The twin entering and discharge transport tubes are oversized to reduce internal pressure resistance. The discharge holes are located at the point of maximum negative pressure. The twin tube concept magnifies the normal velocity pressure signal.


This expanded signal will permit sensing lower flow rates than normal Pitot tube based devices. We define this expanded signal as a sense signal and use this term in our performance charts.


The 861 averaging differential pressure probe is made of stainless steel, with brass fittings (outside of the air stream).


Features and Benefits



  • Supply Air Dampers

  • VAV Fume Hood Exhausts

  • Zone / Floor Control Dampers



  • Simple, Rugged Design

  • Accurate through a Wide Velocity Range

  • Repetitive Output



861 Product Bulletin