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Old 11-07-2012, 06:14 PM   #16
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multiple sump pumps on generator issues


great post...big issue...the avg above ground pool holds about 10000 gals you got some real water issues...wow..good luck keep us posted..

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Old 11-08-2012, 01:14 AM   #17
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multiple sump pumps on generator issues


I think this can be done much more cheaply than $3k. If you can find a good deal on a used 3-phase generator and the pump, then you can probably get by without a VFD. Using a wye-delta starter (also called a reduced voltage starter) will help you get the pump running on a generator that might be marginally sized to power it. That does not give you variable speed, but it does save you $500-700 on a VFD. If you can get by with a 3HP pump, then everything becomes cheaper: a 5kW single phase generator, a $350 VFD, and a cheaper pump. You could even get a 5HP pump and run it on the smaller VFD and generator, as long as you don't turn it up past the current limit. Using a valve on the pump discharge line will let you regulate the flow rate to keep the current down (paradoxically, blocking the discharge reduces pump current).
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Old 11-08-2012, 07:31 AM   #18
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multiple sump pumps on generator issues


Are we making this subject overly complicated because we are trying to juggle three independently addressable questions at the same time?

1. The generator can't sustain all four pumps for a prolonged time necessitating riding shotgun over and varying the speed of the fourth.
2. The generator can't start the fourth pump. (or is it unable to start the third pump after two are running?)
3. After peak flood conditions pass, the pumps empty out the pit so fast that they run dry for awhile.

The third question is addressed by having a larger and deeper pit.

Quote:
Originally Posted by pod View Post
Also there is a problem with too big a pump since it can pump down the pit and run dry until the pit refills----it is a strange situation where there are thousands of gallons of water under the floor but I can only take off so much at a time.
Normally we don't worry about the thousands of gallons of water saturating the soil under the floor. All we care is that none of those gallons comes up above floor level.

By the way, as a point of information only and, if you insist, you can get rid of some of those thousands of gallons under the floor by installing a (or another) perimeter drain system 18 inches deeper than your current perimeter drain system (and 5 feet in from, or 5 feed outside and away from, the foundation wall*) and a new sump pump pit for that new system with 25 gallons of water capacity below that level (and not partially occupied by rocks) . Because the water table outside during dry season is probably higher than this new deep system, you will be running one sump pump in that new deep pit all year long.

You will need to keep the current drain system and sump pump pit in operation also. During peak flood conditions, some water will make it above floor level before the space freed up by the removal of some of those thousands of gallons from under the floor can absorb new water. How much depends on the porosity of the soil under the basement floor.

* You may not dig the new deeper system up against the foundation because you will undermine the footings.
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Last edited by AllanJ; 11-09-2012 at 09:41 AM.
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Old 11-08-2012, 02:14 PM   #19
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multiple sump pumps on generator issues


AllanJ: I oversimplified my situation for puposes of space and time BUT I actually years ago dug a 13-15 foot trench around three sides of my house (not all at once of course) and placed 2 feet of crushed stone then 12 inch heavy duty perforated pipe and then more crushed stone and then a tar paper cover and then refilled the trench. Which is to say that I have a contiguous u-shaped 12" perforated pipe conduit surrounding my house at the 12 foot level (which is below the foundation) or so. There is a stand pipe at one end of the system which permits me to drop a pump (or two if stacked) into the conduit level. This is one of the four pumps I referred to. It is the 5000 gph pump. So, actually I was pumping from the inside (a pit in the floor with two pumps) and the outside (also two pumps) simultaneously.

I left this out because I wanted to keep it simple for discussion purposes and I hope no one feels snookered by the ommision. It was just too much to get into a new forum discussion when I had no credibility.

I had intended to place the trash pump (15,000 GPH) in the standpipe and control the level that way. The trash pump would not prime (a separate issue). I was not able to assess the level of water in the stand pipe since the pumps and hoses obscured the view but they pumped water at what appeared to be full bore until the floor was just wetted and for a bit afterward.

I have to go to work now but thought I would expose the full system at this time since I think you are on to something. I think the two level access is a bonus and will be happy to discuss further later on. That is why I placed the deep piping system in the first place, an intuition that it would permit high volume pumping in crises. Since it is a piped system encased in crushed stone I figured that erosion would not be a problem. I hope that is corrent.
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Old 11-08-2012, 11:29 PM   #20
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multiple sump pumps on generator issues


mpoulton: I just have to say that you impress me greatly with the breadth of your knowledge and your flexibility in understanding that there are many solutions to a problem. I think you think like an engineer and I mean that as a great compliment.

I'm going to be away for a few days and wanted to acknowledge the posts to this topic. I'll be back and will, I'm sure, have some new or different thoughts about my situation. I greatly enjoy having many different recommendations to think about, each of which raises some new topic that is related to the others but new nonetheless.
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Old 11-09-2012, 02:07 AM   #21
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multiple sump pumps on generator issues


Well thanks! Glad I could help.
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Old 11-09-2012, 10:46 AM   #22
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Quote:
Originally Posted by Leslie508 View Post
I am not very knowledgeable about motors but is ther some way to "soft start" a pump (have it come up to power gradually).
That's one of the main features of using s VFD. In addition to variable speed, they always soft-start the motor (at an adjustable rate). The peak current is no more than the maximum operating current. There are other ways to soft-start motors without a VFD too, like wye-delta starters.

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