Easy ... called 'block and bypass' :

You need two tees & four valves.
A valve on EITHER side of each filter will allow switching out the
filter while under vacuum ... and without leaking all over the place.

How to run a parallel filter set with block and bypass: Run both
filters ON-LINE (active) .... as you will get ~3 times the life as with
running one to clogging then switching to the other 1+1 = 2.
If you run BOTH then the deposition of debris will tend to be more ON
the surface of the filter media than IN the filter media as with flow
to one. Monitor the performance with gages and when the vacuum
indication begins to move significantly, then shut the bypass and
change one, then run full open while chaning the other and then put it
back on line = 2 on line --- simply run with a momentary high
differential pressure on one as your continue to run on the other.
Best is to use wired differential pressure (vacuum) switches across
each filter wired to an alarm. You can set the 'trip' pressure that the
pressure activates the alarm.
Pressure feed is vastly better than vacuum feed with respect to
filtration .... significantly extendes the service life of filters -
has to do with the way that the particles are captured ... pressure
feed tends to deposit the debris ON the surface (using dirt to filter
dirt) while vacuum feed draws the particles deep into the filter media
hence plugging it faster. If you use stainless tube with double flared
connections then consider a pressure feed system. Boat manufacturers
being cheap use soft copper tube with compression fittings ... that
usuallly loosen with vibration and age. Also copper is CONTRAINDICATED
for use with (long term storage) diesel fuel --- promotes
decomposition.
:-) .


In article .com,
Skip Gundlach wrote:

As I work my way back from the bow (the bulkhead forward of the
saloon), being almost finished in there, my thoughts turn to what's
ahead (or behind/astern, as you prefer).

I succeeded in buying a second Racor on eBay, and two mounted 2-way
valves at a flea market, but would prefer to not have to reinvent the
wheel, as I'm sure there are many here who have done it already.

I considered an already-built dual system, a standard Racor part
number, but it was prohibitively expensive. Theirs, of course, has a
single valve which controls all functions, and a vacuum guage.

Can anyone point me to how to make two separate filters set up in
parallel with the least amount of fuss about it?

Thanks.

L8R

Skip

Morgan 461 #2
SV Flying Pig KI4MPC
http://tinyurl.com/p7rb4 - NOTE:new URL! The vessel as Tehamana, as we
bought her

"Believe me, my young friend, there is *nothing*-absolutely
nothing-half so much worth doing as simply messing,
messing-about-in-boats; messing about in boats-or *with* boats.
In or out of 'em, it doesn't matter. Nothing seems really to matter,
that's the charm of it.
Whether you get away, or whether you don't; whether you arrive at your
destination or whether you reach somewhere else, or whether you never
get anywhere at all, you're always busy, and you never do anything in
particular; and when you've done it there's always something else to
do, and you can do it if you like, but you'd much better not."