[compost_tea] Re: Air Required + Measuring

From: Kirk Leonard <kirk_at_oregonatural.com>
Date: Fri, 3 Oct 2003 14:17:24 -0700

A liter of air per minute per gallon of water seems to me like a good
baseline rate, too. Needs to be tested, perhaps at a "tea-up"? Or
"tea-off", whatever. To isolate and test air volume effects all other
variables need to be same... time, place, temp, water, compost, nutrients,
probably same machine using a range of pumps, too. Seems easy to do with a
bunch of bobolators and supplemental pumps. Can be done, by gosh.

I'd like to inject (pun intended) a way to express air/water volume ratio:
cubic feet per minute air/cubic feet water (or metric equivalents?), which
would make Dan's examples, at .18 cfm air/5 gallons (.67 cubic foot),
.18/.67 = .27 a/w ratio, and .53/2.01 = .26 a/w at 15 gallons. Bigger diffs
would make bigger ratio diffs. Reasoning is it makes comparing across
different volumes of both air and water more clear. Does that make sense?

Also, I have a variation on Bob's air volume measuring method to suggest,
having struggled some with it -- How the heck do you keep air out of the bag
in taping it to the tank, and then how do you make sure you keep the air
in on removing it? Boggles me. Didn't work real well.

Here's what I suggest: Using a plastic sheet that will cover the tank and
pipes, cut a hole in a good access spot to tape and seal in a plastic cup
with the bottom cut out. I use small yogurt containers, but any matched pair
(you need two) would work. Cut the sheet to fit on top of the machine and
be sealed with tape all around, leaving enough slack to be able to get your
fingers under the rim of the cup sealed into the sheet. Freeboard air
volume under the sheet is irrelevant in measuring the flow, by the way, so
slack is irrelevant, too. I confirmed that with a bonafide engineer...

Then, get your plastic measuring bag. Kitchen bag, garbage bag, whatever.
If you have an idea how much air flow to expect you can size it accordingly.
A potential problem, as Chris suggested in an earlier post on 32-gallon
garbage containers, is how much the bag really holds. (I got a 19 gallon
bucket recently that will not hold more than 18 gallons... must have been
the mold size, I guess.) I assume a 13 gallon kitchen bag is 13 gallons at
the top edge, could be measured to be sure. If it's taped on the edge, I
assume it's that many gallons when it fills. Keeping the bag with no air in
it, tape seal the top edges together except for a space the size of your
plastic cups. Tape and seal the second plastic cup with bottom cut out into
that slot, keeping air out best you can. Use the top to help.

With the machine filled to water volume, and the top plastic sheet seal in
place, turn it on, let it run and flow a minute or so. Let it puff up and
check your seals. With your timer set, pop the top, put the measuring bag
and cup onto the top seal cup and pinch the two cups together . Time how
long it takes to fill. Voila, you have a volume filled in a given time,
within cup volume presumably, which even I can convert to cfm and an a/w
ratio...

The reason to let the machine run for a minute or so is important. All
pumps I know of have different phases. "Start," "restart" or "intermittent"
and "continuous." Continuous is the one to look for, so you need to let the
pump settle into that phase before you measure, seems to me.

This all could be a lot easier with an air flow meter and top seal (or a
"hood" in air flow measuring parlance) but I haven't found one that measures
down to the kind of volumes we're talking about. Anybody know of one?

Last notes: David and I came up with very different numbers on the little
KIS. He at 1cfm, me at 2.2. Could be a couple reasons for this. One, both
of us are klutzes, or two, more likely, we measured at different hours of
use. Mine was out of the box, zero hours. How many hours were on yours,
Dave? A fact here is the little KIS "pump" is not a pump, it's a blower,
not made for back pressure. It will push less air over time as
it wears out. Lack of pressure capacity also explains why it bogs down in
deeper water. It's a great kit for 4 gallons of tea. If only it were a
little quieter... not my sleeping pal I worry about, but neighbors...

Also, the 5000cc/min Hagen 805-6-7 models may be better for homebuilt 5 gals
tea, hmm? If my math serves me well, that's one liter per minute per
gallon. And as I recall, barometric pressure and atmospheric pressure are
the same thing, relatively speaking. Jeesh I wish these measures were
easier to work with.

-- Kirk

> Date: Thu, 2 Oct 2003 09:48:24 EDT
> From: Lmvine1_at_cs.com
> Subject: Re: Air Required was: Air pump selection & 5 gal brewer
...
> Paul Wagner _at_SFI in NY in personal telecon several months ago said
> 1L/min/gallon is air objective (minimum).
> From my experience this seems about right.

> 28.3L/min = 1CFM
> So for 5 gallons, need 5L/min or .18CFM.
> For 15 gallons 15L/min or .53CFM
> etc

> I think this is a case where more is better, up to a point of course. Dan

Agree. And it'd be nice to know what air/water volumes work best.












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Received on Fri Oct 03 2003 - 22:17:49 EDT

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