Rick Morel wrote:
Well, you didn't have a watermaker either, so you
were trying to conserve a lot. I measured what we
used at home for showers one time, and was really
surprised. Something like 20+ gallons each even
with the low flow shower head. I could easily see
us using 30-50 GPD with the two of us, and more
with guests.


No. Well actually yes we did have a watermaker. Of course we could
have run it 24/7 and made 40 GPD, but the whole idea is it "costs"
energy to run. Over about 8 to 10 GPD it would have overdrawn the
solar "bank". Add in it was fairly noisy.

That noise is the worst problem in my estimation.
I don't mind paying to run the genset or the
watermaker, I just don't want to hear it or feel it.

"Navy" showers are the way to go. Wet, push the button on the shower
head to turn it off. Soap, push the button and rinse. We used about a
gallon. Okay, sometimes 2 gallons :-)

We'll give it a try. I can see how it works, but
won't know if it will work for us until we're
actually doing it. Right now, the marina we're in
has nice hot showers available, so guess where we
go to shower on mornings we sleep on the boat.


You have to have enough pressure to reverse the
natural osmosis.

Basically, its pre-filtering, pressure across the
membrane, and flow on the "dirty" side of the
membrane to keep the "debris" moving along so as
not to clog the membrane.

Well, I was trying to be succinct.

Watermakers 101 (maybe we should change the subject line!):

Not a real lot of system type info out there, but some neat equations
and stuff. Yep, pressure is a function of molecular weight,
dissociation and solute concentration, and in the case of salt the
"osmotically effective" concentration of solute. All that to determine
the osmotic pressure of seawater is approx 460 PSI and that it takes a
higher pressure than that for it all to work. Note "higher", not a
specific pressure.

Right. Although for a given effective size of
membrane, you get more purified water out of it
the higher the pressure is above the natural
osmotic pressure. This works right up to the
point where the membrane ruptures at which point
you get a lot more water, but its not purified ;-)

All the talk about reducing pressure for brackish water, etc., is not
due to the process directly, but to the second requirment. To properly
wash off stuff from the membrane. Some sources say 5% of the water
should go through, others, specifically membrane manufacturers, say
something else. One says a range of 10% to 20%. As an aside and real
world observation, PUR said for the 40E it didn't matter - they said
run in in the lake or canal (fresh), in the bay (brackish) or in the
ocean (salt). And we did, with no damage or noticable increase or drop
in product water output. Guess it was "made" to operate at the
percentages encountered under all those conditions.

Sooooo... One has to supply the proper volume of water per time unit
at the proper pressure for a given size membrane/pressure vessel. Make
that within a low to high range for both. That says a piston or
plunger pump of X volume per stroke, operating at Y strokes per minute
to supply that volume. So nice that water is incompressible :-) Force
required to the piston/plunger = PSI required / area of
piston/plunger. Strokes per minute = volume required / volume per
stroke.
Next is some way to regulate the brine flow out of the pressure vessel
to maintain that pressure at that volume. Apparently the most used
method is an orifice or needle valve. Adjust it to "bleed off" the
brine at such a rate to maintain pressure from the properly sized
pump. Another way I ran across is a pressure regulator. This on one
that had an engine driven pump. The reason was that the pump output
would vary with engine RPM. Even so the engine had to be run within
certain RPM ranges.

These are the basics. Obviously, the pressure
regulator approach is better given a variable flow
source.

So now to my "ideal" 3 GPH, 12V watermaker. Research pumps. Maybe do
some experimentation with a plain old pressure washer pump. Noticed
Walmart has a cheap 1,600 PSI 3.8 GPM pressure washer. Little bitty
thing. Must have a small motor. No, I'm not advocating turning it into
a watermaker pump. Probably would turn to rust in weeks, if not days.

Don't count on it. The pump in my pressure washer
has a bronze housing, and 316 stainless balls and
springs.

Let's see. At 10% that would yield .38 GPM, or a
little over 1 gal/3 minutes, so if mated with the
appropriate membrane it would be a 20GPH system.
Didn't you tell me not to get a 25GPH system?? ;-)

Just shows high pressure water pumps are no big deal. Come to think of
it, I've seen some really neat little plunger pumps around here. Back
to the good old oil industry.

3 GPH output should take 20 GPH, .33 GPM at 15% product water. Subject
to adjustment.

15% might be a little high, but not much. Maybe
figure 10%. There you go again. We got the same
number by different methods. Must be right ;-)

Build a pump from scratch? Why not. I've got a metal lathe and other
stuff in the shop. Have built stuff that operated at 10,000 PSI. Have
built steam engines and very small, less than 1 CI, model diesel
engines. Got a geared down wheelchair motor that'll run all day on 12V
at 5 to 15 AMPS.

Sounds like neat projects. My cousin Mark built a
minature four cylinder steam or compressed air
engine complete with cam and valve train in the
engineering shop at WSU while I was there. The
total displacement was about .2 CI.

BTW, the high pressure pump on my airless sprayer
is a kind of neat design. It basically has a
spring loaded inlet valve, an spring loaded outlet
valve, a liquid chamber, and a piston that
intrudes into the liquid chamber. It is low flow
rate, but puts out 2000PSI and will pump almost
anything you want to run through it. You can
adjust the pressure as well. The valves are ~$25
each, and the liquid chamber is milled aluminum.
Really a pretty neat design all in all, and
practically indestructible.

Oops. Sorry to use this group for a napkin!!!

Rick

You can do it! But you will have to buy the
membrane and filter housings. Remember that if
you are going to pressurize the whole thing the
pre-filter housings have to be stout as well. Of
course, I don't know why you would do that... ;-)

Don W.