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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