Page 295 - Mechanical Engineer's Data Handbook

ENGINEERING MEASUREMENTS 283

/ Nozzle meter

The flow formula is as for the Venturi meter.

h m

- ~______

7.7 Velocity measurement

7.7. I Pitot-static tube

The Pitot-static tube consists of two concentric tubes, large pipes or ducts, traversing gear is used and an
the central one with an open end pointing upstream of average value of velocity calculated.
the fluid flow and the other closed at the end but with
small holes drilled at right angles to the direction of Fluid velocity V= P2p1)
flow. The central tube pressure is equal to the static
pressure plus the ‘velocity pressure’, whereas the outer
tube pressure is the static pressure only.
A manometer or other differential pressure measur-
ing device measures the pressure difference between
the tubes which is equal to the ‘velocity pressure’. For