dual pump, residential fire sprinkler: thoughts?


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Old 03-17-08, 06:51 PM
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dual pump, residential fire sprinkler: thoughts?

Looking for some experienced thoughts.

Current setup is a 1/2hp shallow well system - the well is spring fed, likely less than 25ft deep. There is always plenty of water. Recently I upgraded from a 20gallon to a 33gallon diaphragm pressure tank. In the future I hope to install a residential anti-burn-my-house-down sprinkler system. Of importance is the need for low power consumption (house should use solar power one day).

I was thinking of installing 2 1/2hp pumps in parallel, independent pressure switches, one set with a cut-in pressure a bit lower than the other. One 1/2hp pump is sufficient to handle normal everyday load. If a high load comes on to the system the idea is that the pressure would drop below cutin of the first pump and the second pump would kick in. I'd install check valves on both pump outlets.

Is this a standard approach? The pipe to the well looks to be a 1 1/4" ID pipe. Would this be problematic or no different really than hooking up a 1hp pump (instead of 2 1/2hp pumps)?

I have a lot of research still to do on the sprinkler components and configuration itself, I'm most concerned at this point at the basic feasibility of the system - starting at one of the primary points, the pumping system.

Any thoughts appreciated.
 
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Old 03-18-08, 08:41 AM
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First of all. as with any sprinkler system, you need to know what the requirements are going to be. You'll need to know how many heads are required, how much water each head will use, what size pipe is needed (so you don't lose all of your pressure to friction and elevation losses). Once you have your system requirements, then a pump can be properly sized to supply the needed water and pressure.
It is very difficult to design a system around the pump first.
Ron
 
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Old 03-19-08, 06:46 AM
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Pumpman: Thanks, that makes perfect sense. I have an idea of the number of heads, but not pipe size, etc. I haven't gone to that detail. I wasn't clear enough in my first post. What I'm looking for is whether or not the idea of multiple pumps pulling from one supply pipe is something that is standard practice or out to lunch. I could size the second pump to whatever is appropriate after system design. After checking it looks like the pipe from the well is only 1" ID. I'm worried that this might be too thin a "straw" to draw from.
 
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Old 03-19-08, 07:34 AM
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Pumps should not share the same suction line. One pump will always starve the other.
Not only that, but if the suction line leaks, both pumps are "dead in the water".
Ron
 
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Old 03-19-08, 09:05 AM
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Thanks for the advice. Understood that I'd have to look at a second suction line - aka. a lot of digging to do. Thanks.
 
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Old 03-19-08, 10:25 AM
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What if the pressure switch of the second pump was hooked to a relay that cut power to the first pump when the lower cut-in pressure was hit? So one suction line, 2 pumps, one 1/2 hp for normal use a second large hp one (if necessary) but only one pump is running at a time - therefore no starvation and only 1 suction line needed?

What would be the best approach for connecting the one suction line to both pumps? Would a check valve be best on the output of both pumps or on the input?
 
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Old 04-04-08, 10:47 AM
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Originally Posted by dmacneil
I have an idea of the number of heads, but not pipe size, etc. What I'm looking for is whether or not the idea of multiple pumps pulling from one supply pipe is something that is standard practice or out to lunch. I could size the second pump to whatever is appropriate after system design. After checking it looks like the pipe from the well is only 1" ID. I'm worried that this might be too thin a "straw" to draw from.

Residential sprinkler system design is covered under NFPA 13D. You can go to nfpa.org and view all of their codes online for free. Heres the link for NFPA 13D

http://www.nfpa.org/aboutthecodes/Ab...asp?DocNum=13D

At the bottom of the page click "View the 1007 Edition of this document.

You can not print or save them, only view. You get what you pay for...

The number of design sprinklers is a maximum of 2. They generally flow 15-18 gpm at a pressure of 7 psi.

Good luck, Fire sprinklers save lives.
Jack Fairchild, CFPS
 
 

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