That particular news release was for a new 3" series. The 2540 has
always been rated for .4 gpm but driving them at max output takes a lot
of extra detail in the design work and you have to push 4.5 gpm of
seawater through them. Keeping the product under .3 gpm is a lot safer
and more energy efficient.

I am using a pair of SW30-2540's to get 800 gpd using an engine driven
Cat 271. I gave up on trying to drive the pump with an electric motor.
It takes 2 HP to push 3.5 gpm at 850 PSI. That takes 125 amps. I
would rather let the alternator charge the batteries for an hour while I
make 35 gallons of fresh water on a separate pump.

Installing an engine drive is slightly more expensive than electric but
when you add in the larger alternator and bigger battery bank it is
actually a lot cheaper. The downside is that you are limited by the
engine RPM but with careful choice of pulley ratios you can get maximum
water output at the same time the alternator reaches its peak and still
have a reasonable cruising speed. I balanced my system atan engine RPM
of 2200. The pump will be turning 1750 and the alternator 4200. That
will give me a decent cruising speed and maximum output of water and
amps. Idling at 1600 RPM I will get 75% output and still load the
engine nicely to reduce cylinder glazing and keep the carbon blown out. .

wrote:

The standard sw30-2540 watermaker 2.5x40 membrane has been improved by
Dow and now rated at 700 gpd (29 gph) up from the old 540 ppd (22
gph). still same 800 psi.
http://www.dow.com/liquidseps/news/20030928a.htm

I'm researching building one (there was a good article in the Good Old
Boat mag Jan 2003 issue . Now I'm wondering about pumps and 120 vac hp
needed for the 700 rating as the higher permeate rating will reduce
the flow across the membrane and increase the clogging from the
reduced flow - dirty membranes being the biggest problem with under
sized raw water flow from small pumps and low hp.





--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
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