Averaging Pitot Tubes
Pitot Tubes produce an averaged differential pressure (DP) signal proportional to the square of the flow rate.
The DP output is normally piped to a Differential Pressure transmitter in order to generate an electrical signal proportional to the flow rate. For certain applications, the DP transmitter can be directly mounted via an integral 3-valve manifold.Sensors are designed to span the process pipe diameter and comprises four basic components:
Outer impact tube - One piece construction
Internal averaging tube
Low pressure chamber
The outer impact tube has a number of pressure sensing holes facing upstream which are positioned at equal annular points in accordance with a log-linear distribution. The “total pressures” developed at each upstream hole by the impact of the flowing medium are firstly averaged within the outer impact tube and then to a second order (and more accurately) averaged within the internal averaging tube. This pressure is represented at the head as the high pressure component of the DP output. The low pressure component is generated from a single sensing hole located on the downstream side of the outer impact tube. For bi-directional flow measurement, tubes can be supplied with the same number of downstream ports as upstream.