Another question about Fire Hydrant Flow
Another question about Fire Hydrant Flow
(OP)
I had posted a question about Fire Hydrant Flow a little while ago but I have another design question. Let me refresh my first post. I have a subdivision that is being designed by a local architect and land developer. The subdivision is small of only 11 homes with no expansion and it will be a culdesac road. From the city, they want the fire hydrant at the end of the road on the culdesac and have told me that my main line in the subdivision will be a 6", which I find annoying. Anyway, their flow test on their 8" maiin was conducted at the top of the road gave me a static pressure of 30 psi and residual pressure of 20 psi at 660 gpm. They did not give me a pitot pressure drop measurement but I can usually estimate that unknown. I have a 50' positive head pressure from the top to the bottom of the road due to elevation changes, which helps in my pressure issues.
However, I ran through my calculations and modeled the flow. The problem is that I am getting mix results. State requirements of residual pressure of 20 psi and 500 gpm at the fire hydrant cannot be met. I have hand calculated a pressure of 13 psi at the fire hydrant which will not meet the state requirements. Does not this pressure on the city's main that we will be tapping into seem a little low? I have usually seen 70-100 PSI on main loop systems. If it is low, what are some good approaches to getting the system pressure boosted without or minimal cost to my client?
Thanks in advance for the feedback.
However, I ran through my calculations and modeled the flow. The problem is that I am getting mix results. State requirements of residual pressure of 20 psi and 500 gpm at the fire hydrant cannot be met. I have hand calculated a pressure of 13 psi at the fire hydrant which will not meet the state requirements. Does not this pressure on the city's main that we will be tapping into seem a little low? I have usually seen 70-100 PSI on main loop systems. If it is low, what are some good approaches to getting the system pressure boosted without or minimal cost to my client?
Thanks in advance for the feedback.





RE: Another question about Fire Hydrant Flow
You might be able to get around the fire flow requirment if you have sufficient residual pressure without the 500 gpm fire flow. If the local fire department has water trucks that they fill to achieve sufficient water pressure you may be able to get away with a color-coded fire hydrant that indicates that the fire department cannot connect their hoses directly to it.
If that option is not available to you then it could well be that your 11 lot subdivision is not feasible.
RE: Another question about Fire Hydrant Flow
RE: Another question about Fire Hydrant Flow
What if the developer provides fire sprinklers for the homes in accordance with NFPA 13D in the subdivision. Will the AHJ reduce some of the fire flow demands?
RE: Another question about Fire Hydrant Flow
RE: Another question about Fire Hydrant Flow
Thanks for all the post they have been very helpful.