I was asked recently for a specific project how much flow the owner should anticipate coming from a building's main drain.
There's just a few factors that play into exactly how much water to expect. Is the drain serving as the main drain for a system? Is it only serving an inspector's test? Is the drain off a 1-inch pipe, or 2-inch? How much pressure is on the system?
These aren't often difficult to answer if you're familiar with the job, but each of these answers plays a role in determining how much water will come out of an open orifice.
This week I've simplified a few of these parameters to come up with a quick inspector's test and drain calculator for fire sprinkler systems.
With it, you can estimate the amount of flow that will come from an inspector's test (use the k-factor option) or from a drain (diameter option). For our international audience I have incorporated real units from the get-go this time. It's a free tool that's now live on the site, here.
Give it a spin and let me know what you think in the comments here.
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Thanks & have a great week!
11/7/2019 12:49:52 pm
This is a great tool and illustrates why it's best for the main drain to extend outdoors. It's a lot of water! It's difficult for a floor drain to handle such a large flow.
Khaja Rafiuddin Ahmed
11/13/2019 10:15:52 pm
It is always recommended to bring the test line outside the building, it's highly impossible for a 4" floor drain to handle this flow.
This is a great tool, but I think that it could use some further info. I recently used this tool to estimate how much water that would be coming from our main drain tests for a large project I am designing. The issue that I find is that this gives you the total flow as if it were a 2" diameter hole in the pipe. It does not take into the account the valves fittings and pipe that you need to run over to the drain, which can reduce the flow exponentially. I came across this when asked a what the flow will be out of our test and drain, and our in house FPE was on a job site. I put the system pressure in as it asked and filled out all the other info and it gave me a total of 1500 gpm, as we have a 150 psi pump on the project. The plumber freaked out and said that they have never seen that much flow from a sprinkler drain. When my FPE got back into the office we did the calc his way and come up with around 750 GPM, worst case. Your math work perfect if you do the calc so that the "System Pressure" takes in account of all the loss though the pipe, fittings and valves, but if you just put your actual system pressure in, I don't believe this provides an accurate flow. Love what you do, keep it up!
12/3/2019 11:46:22 am
This is really outstanding feedback.
12/3/2019 12:18:09 pm
Yes, ideally it would be nice to be able to add the total feet of pipe over to the drain, maybe a total of fittings and possibly a pull down to show the loss though the testing device, Whether that be a ball valve or a AGF test and drain.
Comments are closed.
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Joe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About