It has been quiet on he support desk lately so I have been working on an
automatic flush system for the watermaker. I have breadboarded a simple
little circuit made from a 555 timer, a few transistors and some relays.

When the system shuts down or the flush button is pressed it turns on
the pressure relief solenoid and the fresh water supply solenoid just
downstream of the pre filters. The high pressure pump turns on and the
boost pump turns off. It pumps through the membranes for a set period
of time then shuts down the HP pump and closes the pressure relief
solenoid. The fresh water then back flushes the pre filters for about
15 seconds and the second solenoid closes. (For the negative thinkers
out there, there ARE manual valves just in case and the fresh water goes
through a charcoal filter to remove any chlorine.)

The question is, how long should the flush stage be set for? The high
pressure piping and pressure vessels hold a little less than 2 gallons
and the HP pump is operating at about 3.7 GPM. To displace the sea
water in the system would take about 40 seconds but is that enough?
If it stays on to long I waste fresh water but if to short I don't get
complete flushing.

The time will be adjustable +/- 20% by a trimmer pot but I need to
figure out where the center is.

BTW, The watermaker companies want upwards of $1,000 for this option.
The high pressure stainless solenoid does cost $150+ (I found mine on
eBay for $25) but everything else is under $15.00 total.

BTBTW, the total cost for this engine driven 800 GPD fully automatic
watermaker with stainless Cat pump has ended up right at $2,675.00.
(Gloat Gloat) :-)

--
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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