You could, or you could calc the time based on velocity equals acceleration times time. Instead of the comb you could look for a rock. Better yet 2 rocks, as an old timer replied off forum, he measured from the start of the splash to the end of the splash to get the average velocity.
-----Original Message----- From: Tom Duross [mailto:[email protected]] Sent: Sunday, June 27, 2010 7:37 PM To: [email protected]; [email protected] Subject: RE: Accuracy of Hydrant Flow Test Using Pitot Diffuser OK, so now we add a stopwatch and pocket comb to the flow test kit? Thanks Ron, very interesting and informative. Here is something else about flow tests I think is interesting, and might come in handy sometime for someone willing to trudge through this: say you're bidding a 4- story Comfort Inn and you need to know the water at least close enough to know 1 res head per room or 2, but all you got on you is the tapped cap w/ gage, the wrench, a 25' tape, and your comb- could you do it? Say static is 60 psi, get a decent stream going, and walk out and drop your comb across from where you think the middle of the splash is. Shut it down. Measure from the hydrant to the comb--- 16'. Measure from the the ground to the center of the butt--- 4'. The time of flight of a droplet straight down from 4' is half a second. The time of flight of a droplet shot straight out from the same height is also half a second (knowing this is the other key to applying velocity pressure correctly in calcs). If the water went 16 feet in .5 sec the velocity is 32 ft/sec x .03 ft^2= about 1 ft^3/sec, about 450 GPM, x .8 for the butt, about 360 GPM. So you got 60 and... dang it! I glanced at the residual when I was shutting down but forgot to remember it. No prob! The velocity head h=v^2/2g is 45 ft x.433= 20 psi----oh yea, the residual gage read 40 psi. _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.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)
