Reference Professor Pat Brock's "Fire Protection Hydraulics and Water Supply Analysis" as an excellent text on performing these tests.
In general, I prefer not to use large orifices (e.g. steamer connections). Any voids (air bubbles, etc.) and highly turbulent flow from those openings will be difficult to obtain an accurate velocity pressure reading from, regardless of the experience and skill of the inspector/tester. An appropriate distance from the connection is necessary to obtain a good reading. I have found it difficult to hand hold steady the pitot knife on large openings such as a steamer connection. I recommend that these not be used when the data obtained is going to be used for design purposes. In addition, the law of small numbers applies. If the small velocity numbers you reported were indeed accurate (I suspect they are not) one would want to use a gauge on the pitot of appropriate scale. Gauges generally are most accurate when the expected reading is in the middle of the scale. A good inspector/tester should use an appropriate scale gauge. If the inspector/tester really expected to see a velocity of 6, then a 0-12 (more likely, a 0-25, or 0-50) gauge would produce a more accurate reading versus a 0-100 or worse, a 0-300 scale gauge. (In fact, one reason to suspect the 4-6 velocity numbers you reported is that they were most likely read or interpreted from a gauge that had a 0-100 PSI scale. Trying to read numbers at either end of the scale with erratic void filled flow is dubious, at best.) I would recommend the test be repeated using the appropriate method in the Brock text and I would recommend the smaller butts be measured and used. Byron -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Richard Lindner Sent: Tuesday, June 23, 2009 3:25 PM To: sprinklerforum Subject: Hydrant Flow test results Have a question regarding hydrant flow tests. We have received a report where the contractor flow a single 2 1/2" outlet and gave us static, residual, pitot and calculated flow. He then performed another test using the 4 1/2" outlet on the hydrant, again giving us values. Plotting the graph, is there supposed to be a correlation between the testing of the 2 1/2" versus the 4 1/2" or are they supposed to be used separately. For example, when graphing the 2 1/2" outlet, the 4 1/2" outlet info should be hitting this line or not?? Also, is a pitot reading of a range of 4 to say 8 on a 4 1/2" outlet valid data? We're not sure how to use this info. Richard _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
