[Market-farming] well storage tank?

Willie McKemie mf at austinfarm.org
Sat Jun 2 16:09:33 EDT 2007

On Sat, Jun 02, 2007 at 11:42:51AM -0700, no one wrote:
> The farm I'm managing hit a 10gpm well, and we're looking to drill another to at least double our water.  The well driller we're working with is set on the idea that we'd need a huge storage tank, with 2 wells pumping into the tank, and another bigger pump pumping into our irrigation.  I was wondering if anyone has any experience with such a set-up, and if it has any advantages, drawbacks, etc.  I was thinking we'd just use both wells hooked together with lay-flat, or use them completely seperately in different fields.  Our entire irrigation system this year is drip and wobblers (tiny low pressure over-head), so pressure isn't a huge consideration.  In the future we'd like to use solid set irrigation, but we could also drill more wells.  Thanks in advance for any information..

I assume you're talking about submersible pumps.  Especially if your 
pump is in the well and expensive to service, you should minimize your 
start-stop cycles.  That means a big tank OR matching your supply and 
demand.  If you can just use all the water your pump produces, you need 
no storage tank at all.  You do need to match your pump to both your 
well's capacity AND to your pressure needs.  A pump will operate 
efficiently only over a limited range of maybe 50-100 psi or 100-200 
feet of head.  1 psi, as I recall, is about 2.2 feet of head.  The 
pressure the pump pumps into is your pressure at the surface plus the 
depth to the pumping level.  That's deeper than the static water 
level.  Example: if your static water level is 100' and your expected 
draw down is another 20' and you want 40 psi at the surface, you would 
need a pump that would work efficiently at about 200' of head.  You 
should examine the performance curves for the various pumps available.

I would recommend plumbing your wells together so that either well 
could supply water to any location.  I have a 500 gallon pressure tank 
which spends most of it's time waterlogged; that is, I rarely put in 
more air.  I have miles of buried pvc pipe which act as a buffer; with 
no demand, it takes a pump a minute or so to pump up from the cut on 
pressure to the cut off pressure.  That is, I don't really need a 
pressure tank with the size of my distribution system and a 20gpm pump. 
I have several wells, 20 to 40 gpm.  When we are not irrigating, I 
leave a pressure switch controlled 20gpm pump on for washing and such.  
When we are irrigating, I watch my pressure and try to keep it steady 
at 20-30psi.  If I succeed, I am using all the pump capacity and the 
pump is running full time.  When I need more water, I turn on another 
well and try to increase demand to match.  When I'm irrigating, I try 
to keep using the pump capacity around the clock, moving water 
application locations about twice a day.

Your driller should be able to test your well capacity; your pump 
should have significantly lower capacity so that you don't have to 
worry about sucking air.  That is, put a 10gpm pump in a 20gpm well, 
not a 20gpm pump.

Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
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