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Re: [Shop-talk] OT: Well Water Pressure Tanks

To: Shop Talk List <shop-talk@autox.team.net>
Subject: Re: [Shop-talk] OT: Well Water Pressure Tanks
From: Wayne <wmc_st@xxiii.com>
Date: Fri, 15 Apr 2011 16:48:30 -0400
On 4/15/2011 4:14 PM, Douglas Braun wrote:
> Isn't there a huge variation in requirements depending on how deep the well 
>is?

Indirectly related to depth.  Deep well submersible pumps are fairly 
large, 1/2 - 3 HP typically depending on the depth.  Cycling them on and 
off rapidly is bad for pump longevity and your electric bill.  Even the 
smallest of pumps are supposed to be run for a minute or so, then off 
for several.  Two minutes run time is even better.  20 - 35% duty cycle 
sounds typical;  if you run for a minute and are off for two or three or 
more, that's good.

My pump puts out 11.5 gal/min.  The undersized 20 gal (total volume) 
tank has about 5 - 6 gallons "draw down" per cycle (30% of total volume 
seems typical draw down.)  That would have it run for about 30 seconds, 
then maybe 1 - 2 minutes off with a continuous draw.  Now the diaphragm 
is leaking and it runs for 15 seconds to supply about 2.8 gallons, and 
is probably only off 45 seconds in between.

Some places try to baes tank size on house demand;  this is totally 
wrong from what I can figure out.  You need to know pump delivery 
volume, and get a tank that allows 1 - 2 minute run times.  The bigger 
the pump HP, the longer the suggested run time (thus the indirect 
relation I mentioned -- deeper wells require larger pumps, and longer runs.)

Oh -- how did I recognize my tank had failed?  Air surges and bubbles in 
the water.  Then I realized I could hear the thing buzzing through the 
plumbing and a loud "click" of the pressure switch in the basement. 
About a month ago I noticed I could open a faucet or flush and hear it 
instantly kick on, then run for only 15 seconds or so.

-Wayne
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