[compost_tea] Re: Re: Re: Flow rate for air pumps

From: Kirk Leonard <kirkleon_at_open.org>
Date: Sat, 19 Feb 2005 12:32:32 -0800
Whoo ya, some fun happening here.  Hopefully there is something useful too.

Dave, both Bob and my air volume numbers accommodate water depth, I believe.
I'd be willing to bet he put a bitti pump boost into the larger tank to get
to the same actual air volume.  He may have a new fancy way of measuring
that but I have a simpler and more reliable one than the one he originally
suggested for measuring air volume through the tank, I think.  Anyway,
"backpressure" is included.

For those who want another number, water pressure is 1 psi per 27.71 inches
of depth.  So I've been informed, anyway, whatever volume. I haven't ever
tried to measure it. I also believe that's at any elevation, gravity being
pretty much constant.  That's backpressure on the pump.  It wears out
blowers and "spa pumps" relatively quickly because they aren't designed to
deal with it.  (How many six foot deep spas have you been in?:)

A pump won't put any air into water at 28 inches if it doesn't have more
than 1 psi capacity.  Discovered that trying to use a little KIS blower in a
deeper tank.  Kinda funny, actually.  Hit the switch and get basically an
electrical echo, no air.  Eeek -- shut that thing off before it burns up!

The actual volume of air through water increases as pump pressure capacity
increases.  True diaphragm or piston pumps are pretty steady to 50 plus
feet, certainly steady at compost tea depths.  Linear pumps run out of uumph
relatively shallowly, but they're good for depths to 3-4 feet.  Air pump
makers should provide a table that tells you what volumes to expect at
different water depths, so you shouldn't need to measure it.

And DO is DO.  No amount of air pumping (short of a pressure chamber) will
cause it to rise above atmospheric and temperature conditions.  The added
air in making aerated compost teas is "free" air for the critters, available
for dissolved oxygen below the surface, also useful for stirring the water
and extracting organisms.  Natural physics control DO, no doubt about it.

Kirk


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Received on Sat Feb 19 2005 - 18:14:56 EST

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