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I am coordinating a flow test with a contractor.
NFPA 291 Section 4.4.6 states "To obtain satisfactory test results of theoretical calculation of expected flows or rated capacities, sufficient discharge should be achieved to cause a drop in pressure at the residual hydrant of at least 10 percent. In water supply systems where additional municipal pumps increase the flow and pressure as additional test hydrants are opened, it might be necessary to declare an artificial drop in the static pressure of 10 percent to create a theoretical water supply curve." The contractor did not achieve the 10% pressure drop and asked if the "artificial pressure drop" option is a possibility here. I do not see anywhere in NFPA 291 or elsewhere explaining how to do this. Any recommendations on what to advise the contractor / how to even calculate the artificial pressure drop? Thanks in advance. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
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In a recent project, I asked for hydrant flow test results from the civil engineer, and I received Boundary Conditions instead.
Is there a way of using this information to validate hydraulic calculations? An example of Boundary Conditions given to us: Demand = 18.54 gpm (1.17 L/s), HGL = 463'-11" (141.41 m), Pressure = 64.1 psi (442 kPa). Thanks! Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe Can a hydrant flow test (for the purposes of a fire sprinkler design) be conducted using a single hydrant?
If so, how is this actually done? Is it recommended? Thanks in advance. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe During a recent site visit, I conducted a 2-hydrant flow test with the assistance of a city engineer and the fire department.
The static pressure measured at one hydrant was 84 psi, and then I proceeded 650 feet downhill to the actual flow hydrant, where the pitot pressure was recorded as 70 psi. A question arises due to the city's reluctance to test additional fire hydrants. My boss believes that testing more than one outlet is necessary to achieve a residual pressure drop. However, the city claims that their water distribution system is looped and, therefore, does not anticipate any pressure drop. As a result, we are unable to calculate consistent numbers on a graph. Additionally, we have come across information suggesting that there should be a 15 to 25% drop from static to residual pressure. Is this a compliant approach? Should we be opening up more than one outlet on the flowing hydrant? Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe Most cities require fire flow tests before design and calculation of a sprinkler system, but I have dealt with a few cities that instead use a water modeling system to calculate the pressure and flow at certain locations.
What is the reason for this? Are there benefits or downsides to one or the other? Is one more accurate? Thanks in advance - appreciate the input. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe When conducting flow tests and the desired flow (gpm) for the test is not obtained via a single 2-1/2" fire hydrant outlet, should additional flow be achieved by opening an additional 2-1/2" outlet on that SAME fire hydrant, or should a single 2-1/2" outlet be opened on an ADDITIONAL fire hydrant?
So for multiple 2-1/2" outlets opening and flowing, should this be done:
I have heard people say that (A) is correct and (B) is incorrect, and vise versa. Thank you. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe I'm quite familiar with conducting hydrant flow tests, NFPA 291, and have read articles such at the Sprinkler Age article from Feb. 2018. And I know the residual hydrant should be between the hydrant(s) to be flowed and the large source mains for the area.
But in terms of a specific project site (especially if the underground is well-gridded), would you chose the hydrant closest to your project to be the static/residual hydrant, or would you select the flowing hydrant to be closest to your project (and adjusting the static/residual for any elevation difference)? Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe When we run hydrant flow tests, we usually use both 2-1/2" side-outlets of a typical dry fire hydrant. We hook up one, threaded, swivel 45-elbow on each side to divert water in a direction that won't destroy anything.
What is the appropriate Coefficient of Discharge when measuring the pitot on the centerline of the elbow? Traditionally flowing straight out of the side outlet of a hydrant, NFPA 291 gives three Coefficients (0.90, 0.80, and 0.70) based on how the outlet projects into the barrel. NFPA 291 also states that a coefficient of 0.85 is suggested for stream straighteners, unless the coefficient of the tube is known. Is there a known Coefficient for a single 45-degree elbow? Any help is greatly appreciated. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe Fire hydrant flow test question - is the pitot the same as the residual pressure on a water flow test from a fire hydrant?
Is it possible to know the residual pressure and 'chart out' the flow of the fire hydrant, or is there a way to determine the flow with only the static and residual pressures? Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe |
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