This easy-to-use flowtester/diffuser provides consistent accuracy for large water flows. Each flowtester features a lightweight barrel with NST swivel fitting and diffuser. Barrels include a gauge and a replaceable pitot tube that is correctly positioned in the stream of water. Reading flow rate in gpm is as simple as reading gauge pressure and selecting the corresponding flow rate from the tables provided.
The stream from a large hydrant outlet of 4 to 4-1/2" contains voids; meaning that the entire stream of water is not solid. For this reason, standard circular orifice flow formulas alone will not provide accurate results with 4 and 4-1/2" inch hydrant barrels. The table provided with each steamer nozzle flowtester/diffuser shows flow calculations and factory-recommended correction factors for hydrants with industry standard 0.90 nozzle coefficients.
If you have hydrants with nozzle coefficients other than 0.90, we can provide custom tables at no charge; contact USABlueBook for more details.