Utilisation des cannes dérivées du tube de pitot pour l'étude des débits dans les conduites

Ingénieur E.S.E., Ingénieur des Services Techniques, chargé des Etudes et Réalisations au Service des Eaux de la Direction des Services Industriels et Commerciaux, Préfecture de Paris.

Résumé

1. The author states the problem as having to determine a simple instrument capable of being introduced without difficulty and at little cost at any point in the pipes constituting the Paris Prefecture's water distribution loop system. His choice fell on a cylindrical tube derived from the Pitot tube, featuring two dynamic pressure tappings and no static pressure hole in order to increase the differential pressure. 2. On calibrating this probe in an infinite medium in the French Navy's hull testing tank, it was found that the conventional formula Q = K D2 Ha relating discharge to average velocity Vm gave two values of the exponent a, both of which were dose to 1/2, and that the discontinuity invariably occurred at a velocity in the neighbourhood of 1 m/sec. 3. The author decided to always measure the velocity in the centre Vo in order to reduce the margin of uncertainty to a minimum. He made measurements on a large number of pipes with widely varying velocity distribution curves in order to determine the maximum probable variation range of coefficient v = mean velocity/central velocity 4. The author was then able to plot a graph consisting of a family of straight lines on a double logarithmic scale, the spacing of which was related to pipe diameter by a parabolic law. 5. The author then goes on to show successive applications of the probe in the Paris Prefecture's water distribution system, including one probe permanently installed in a 1.5 m diameter pipe. 6. Finally, the author argues in favour of the use of these probes for investigation and supervisory purposes and not as precision instruments-as a means of establishing basic requirements for operation ensuring optimum running economy, combined with satisfactory service to the consumer.