It SEEMS to me, residual and pitot pressure are related as memorialized by Bernoulli in the 1730's. One needs other details, such as friction pressure loss, elevation change, pipe diameter...etc. But residual pressure is the pressure experienced by the fluid, minus the velocity pressure. Without taking the time right now to go through the details myself, I would look to Bernoulli's equation, solving for your pitot pressure from the velocity pressure term. Enough difference in the potential energy term (elevation difference) will make your anomaly happen, but not in the flats of America's heartland it won't .
Happy New Year, Scot Deal Excelsior Risk & Fire Engineering gms: +420 606 872 129 “Human freedom is not in our ability to make decisions. It’s in our ability to put ourselves in an environment that will lead to better outcomes.” - Dan Ariely On Wed, Jan 2, 2019 at 6:20 PM Skyler Bilbo <[email protected]> wrote: > I apologize if this has been discussed already, but I would like to clear > my own mind, if nothing else. > > I can't recall a hydrant flow test, that I performed, where my pitot > pressure has been higher than the residual pressure on the test hydrant. I > have received two tests in the last year from city water departments where > this has been the case. I can't make sense of the physics. This *should* > not be possible, correct? > > I can dream up a scenario where it would happen, but essentially, the flow > test would have to be taken backwards, where the test and flow hydrants are > flipped, and someone is using a decent amount of water, either past the > test hydrant, or between the test hydrant and flow hydrant... It seems like > if this happens (if your pitot reading is higher than your residual > pressure), you should flip the flow and test hydrants and repeat the test. > Am I thinking about this correctly? Has anyone else had this issue, and is > it addressed in NFPA anywhere (perhaps it should be, if it isn't)? Of > course, one of the gauges could be bad as well (which is probably just as > likely, if not more so, than the hydrants being flipped). > > > Thanks for any help with this, > Skyler Bilbo > _______________________________________________ > Sprinklerforum mailing list > [email protected] > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org >
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