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Using Domestic Water Booster Pumps in Sprinkler Calculations

Using Domestic Water Booster Pumps in Sprinkler Calculations

I don't know if this is something the forum can help with, or if I need the EoR to weigh in. Between writing my third RFI and playing phone tag with the EoR and GC I am now behind schedule on my permit drawings, and if I cant figure something out soon it could impact the project schedule. So I figured I would ask here to see if anyone could offer advice.

I am currently working on a college project that has a private domestic loop on campus. The new building that I am designing the sprinkler system for will have a supply line from the city main entering, a quadruplex (primary) and triplex (secondary) Vertical Multi Stage Domestic Water Booster Pump Skids, and associated valving, backflow, etc. This will all be installed by the plumber, and the sprinkler system will tap off the discharge manifold with its own backflow.

I have all of the product information and pipe routing from the plumber to consider in my calculations. The big hangup I have is the pump curve. Rather than a curve it is an area, and there is no data sub 500gpm so I am not certain what boost to use for my light hazard and 4 residential head calculations per NFPA 13. I have reached out to the EoR, but the response was to only consider the secondary booster pump, and to use the top of the area as the curve, the lack of data below 500gpm was not addressed.

My main concern is the Min. Flow of 150gpm designated on the performance curve of the individual pump. Would the pump activate at a low flow, like a light hazard calculation reduced to 900sqft? That is only 90gpm plus losses. The sequencing from the product sumbittal says the lead pump starts on a 5 second delay after a 5psi drop below set pressure so it sounds like it would regardless of flow.

My second concern is would I just use the pump curve for an individual pump for these lower flow calculations? If the lead pump never exceeds it BOP then the lag pump will never start. I can use the performance "curve" (top of the area) per the EoRs direction for the standpipe calculation. (750gpm for two standpipes)

My third concern, and unrelated to the pump performance, is there is no bypass from pump suction to pump discharge even though the city water supply is of some value for fire suppression.

Does anyone have experience with these kinds of pumps? Even if all you can do is help me come up with more pointed questions for the EoR, they don't seem to understand what I am trying to get at.


RE: Using Domestic Water Booster Pumps in Sprinkler Calculations

Will you post an underground/ site utility layout.

Where is the pump in relation to the riser?

Any existing buildings have this set up?

Does not sound good in many ways

RE: Using Domestic Water Booster Pumps in Sprinkler Calculations

Those are probably similar pumps to what the municipal pumping station has, so you likely use them every day, we just don't think of it that way. The EOR should have a model they can provide. They should be able to provide something like pressure at maximum daily demand. Use that as static. Then they should provide pressure at max daily demand + fire flow (assuming there are hydrants downstream of this setup). That would be your residual flow and pressure values. At that point, you should be good to go on calcs.

Travis Mack
MFP Design, LLC
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RE: Using Domestic Water Booster Pumps in Sprinkler Calculations

How do you know when the pump might actually turn on?

And if it does not turn on, where is your water supply?

RE: Using Domestic Water Booster Pumps in Sprinkler Calculations

Spoke with the EoR and now I have a good understanding of the design philosophy. What the two AHJs and insurance company agreed on is that everything from the discharge manifold upstream could be thought of as an offsite municipal pumping station where the FP and domestic water would traditionally be supplied by DI underground mains. Just in this case the pump station happens to be in the basement so FP and domestic water just tap off the discharge manifold. This was the reasoning the EoR gave for the lack of a bypass.

Still waiting on the data from the EoR like TravisMack mentioned in his post, hopefully I get it soon.

cdafd, I also am still not 100% on this design. At least if something goes wrong I will have a paper trail showing that I was instructed by the EoR on how to I was to proceed, and that the EoR developed this working with two AHJs and the owners insurer. I don't like to pass the buck like this, but I just don't have the experience on something like this.


RE: Using Domestic Water Booster Pumps in Sprinkler Calculations

I will say that this situation is not common, but also not rare either. I've run into it a few times. Provided they have done the proper modeling, they should be able to provide you with that information I stated above. Depending on how the schedule goes, you may want to try to get a true hydrant flow test before you fab or install pipe. That will eliminate all questions in your mind. But, the schedule may not provide for that.

Travis Mack
MFP Design, LLC
"Follow" us at

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