Pitot tube

Pitot tube flow meter

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Presentation

The Deltafluid Pitot tube is an averaging sensor for use on pipes, ducts or chimneys. Differential pressure created across the tube has the standard square root relationship to flow rate, making a simple, removable sensor for installation or retrofit on flowlines of any size.

The principle of the Pitot tube consists in direct measurement of the dynamic pressure of the fluid (or impact pressure) that is to say the difference between the total pressure and the static pressure. The tube is mounted across the pipe diameter, with a number of impact pressure sensing ports on the upstream face.

Liquid and gas flows produce an impact pressure. The Pitot tube averages this pressure across the pipe diameter, to take account of any profile irregularities and to be less sensitive to the deformation of the velocity profile.

Downstream there is a single pressure sensing port; the precision engineered profile at this reference pressure position ensures a stable separation for flow vortices, giving a stable flow calibration factor over a wide flow turndown.

Each Pitot tube is designed to span the process pipe diameter and comprises four basic components :

- Outer impact tube as a one-piece construction
- Internal averaging tube
- Low pressure chamber
- Head

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 Pressure developed at each upstream hole by the impact of the flowing medium are firstly averaged within the outer diameter tube and then to a second order and more accurately averaged within the internal averaging tube.

This Total Pressure consisting of static pressure and dynamic pressure of the fluid 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.