ASTM D3796-09(2016)

5.1 The Type S pitot tube (Fig. 1) is often used to measure the velocity of flowing gas streams in industrial smokestacks and ducts. Before a Type S pitot tube is used for this purpose, its coefficients must be determined by calibration against a standard pitot tube 1.1 This practice covers the determination of Type S pitot tube coefficients in the gas velocity range from 305 to 1524 m/min or 5.08 to 25.4 m/s (1000 to 5000 ft/min). The method applies both to the calibration of isolated Type S pitot tubes (see 5.1), and pitobe assemblies.

1.2 This practice outlines procedures for obtaining Type S pitot tube coefficients by calibration at a single-velocity setting near the midpoint of the normal working range. Type S pitot coefficients obtained by this method will generally be valid to within ±3 % over the normal working range. If a more precise correlation between Type S pitot tube coefficient and velocity is desired, multivelocity calibration technique (Annex A1) should be used. The calibration coefficients determined for the Type S pitot tube by this practice do not apply in field use when the flow is nonaxial to the face of the tube.

1.3 This practice may be used for the calibration of thermal anemometers for gas velocities in excess of 3 m/s (10 ft/s).

1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.