Real world vs rule of thumb - How do you figure GPM & what happens if pump cannot meet demand?

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Boyblue

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We have a 10 GPM pump supplying 2 houses without issue. I'm installing a system to supply one of those two houses but I want to be able to reciprocate by being able to supply next door in a pinch - Although it's just two of us and our peak demand is at most 3-4 GPM.

I believe the rule of thumb is 1 gallon per water outlet/fixture. Between the two houses there are 33 outlets. I estimated the most that could be used a one time is 19 with the maximum likely at 10. I split the difference and decided on 15 GPM.

Then I went shopping and the real world sent me back to Terry Love :) There's a huge difference in price when you talking 15 GPM. So now I'm thinking, a 10 is doing the job now so why reinvent the wheel; or should I consider a 12 GPM?
 

Reach4

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A 15 GPM 1/2 HP pump should cost less than a 10 GPM 1/2 HP pump because it has fewer stages.

With your rather shallow well, IIRC, the 15 was in the sweeter part of the pressure curve, wasn't it?
 

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Yeah well you also have to look at the max pressure the pump can build. A 15 GPM pump will max out at about 73 PSI. So if the water is any deeper in the well than about 25' that pump won't be able to build to 60 PSI for shut off as with a 40/60 switch.

A 10 GPM, 1/2HP will still do 15 GPM, but the pressure will drop to about 30 PSI. And it can still shut off a 40/60 switch as long as the water level in the well is less than about 80'.
 

Reach4

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Yeah well you also have to look at the max pressure the pump can build. A 15 GPM pump will max out at about 73 PSI. So if the water is any deeper in the well than about 25' that pump won't be able to build to 60 PSI for shut off as with a 40/60 switch.

A 10 GPM, 1/2HP will still do 15 GPM, but the pressure will drop to about 30 PSI. And it can still shut off a 40/60 switch as long as the water level in the well is less than about 80'.
In www.terrylove.com/forums/index.php?threads/best-pump-for-hard-water-also-please-review-our-setup-suggest-other-possible-improvements.58913 he is saying that the pump will be lifting 6 or 7 ft. Add another 10 or so to reach the second floor. The well is 20 ft deep per the first post on that thread.

I agree that a 10 GPM would work and still be in the sweet part of the curve. Since he is using a CSV, how does that affect the decision as to whether the 15 GPM or the 10 GPM would be preferred?

I just happened to be looking at one particular document when I posted the 10 and 15 GPM curve tables. Franklin has a 13 GPM 2-wire 1/2 pump which seems worth considering (part number 95201310) which I just saw on sale, and others have 12 GPM 1/2 HP submersible pumps. I am presuming that 230 volts is the preference, although 115 volt versions are readily available.

Goulds 10SB05422C is a 10 GPM that looks interesting.
 
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Reach4

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When using a CSV you want the pump to be able to build a max pressure of at least 10 PSI (23') more than the shut off point of the pressure switch.
So this particular 1/2 HP 15 GPM pump could do that at 30-50 PSI pressure switch, but maybe not at 4o-60. https://terrylove.com/forums/index.php?attachments/huge4-gif.26607/

Here is a chart for a Goulds 10SB05422 "BRUISER" Submersible Pump 10 GPM - 1/2 HP that looks like it should fit 30-50PSI.
huge2.GIF
huge2.GIFhuge4.gif
 
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Boyblue

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Yeah well you also have to look at the max pressure the pump can build. A 15 GPM pump will max out at about 73 PSI. So if the water is any deeper in the well than about 25' that pump won't be able to build to 60 PSI for shut off as with a 40/60 switch.

A 10 GPM, 1/2HP will still do 15 GPM, but the pressure will drop to about 30 PSI. And it can still shut off a 40/60 switch as long as the water level in the well is less than about 80'.

20' that's it the bottom of the well. In that case should I consider that 15gpm pump? Anywhere online you guys reccomend buying this stuff? Where are you seeing these pumps, do I have to go to each manufacturer's site? What about waterpumpsdirect anyone use them?
 

Boyblue

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A 10 GPM pump will be easier to find and I think would be better suited to work with a CSV.

I have to admit, I'm a price shopper. I want the lowest priced good pump I can find - Lowest meaning like the price is 50% more but will last twice as long or...

It cost 50 bucks less but works the same as the others :)

Is longevity more a function of getting the right fit than name brand, or is there a brand that has a reputation of giving value for money?
 

Valveman

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I have to admit, I'm a price shopper. I want the lowest priced good pump I can find - Lowest meaning like the price is 50% more but will last twice as long or...

It cost 50 bucks less but works the same as the others :)

Is longevity more a function of getting the right fit than name brand, or is there a brand that has a reputation of giving value for money?

This has been discussed many times. There is not much difference in quality of pumps these days. Everybody makes them cheap anymore. All the internals are basically the same. You just want a pump with a housing that won't corrode like cast iron. Plastic end bells and suction adapters are OK as long as you don't split them tightening the pipe. The ones people consider the best have Stainless Steel or Brass end bells and suction adapters, but that is about the only difference.

Limiting the number of on/off cycles is the best way to make any pump last longer.
 
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