Date: Sun, 28 Jun 2009 13:39:17 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Fuel Filter "Update" Results
In-Reply-To: <C66CF77A.88F2%dave.arthur@nscc.ca>
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At 09:33 AM 6/28/2009, Dave Arthur wrote:
>So, is it fair to say that a noisy FP may be caused by the pump delivering
>too much volume?
I'd prefer to say that it's *caused* by inlet restrictions, but could
be *relieved* by slowing down the pump. Purely semantics.
>Does the list have any advice on what resistance to use or
>what wattage has been used to 'slow' down the pump?
What's required first is the working draw (amperage) of the specific
pump, from which you can calculate its effective resistance while
running. From that point a starting figure for the resistance to
drop the output by some percentage is easily calculated using methods
illustrated in the electrical primer that I started a while
back. This would then be adjusted by experiment. Heating elements
from a toaster are a convenient source of nichrome ribbon resistance
wire as well as a heat-proof matrix to support it on. The ribbon
would have to be welded, brazed or mechanically swaged/clamped -- you
can't solder to it. If someone wants to actually do this and has
trouble with the calculations I'll be happy to help.
Another possibility would be using largish diodes (I'm guessing that
the pump draws something like five amps) in series to provide about
0.6v drop per diode, if the required drop lends itself to that
interval. This would have less effect on pump startup, which could
conceivably be a problem using resistors. However diodes this size
may not be readily available, and you can't simply parallel smaller
diodes directly without adding a series resistance to each parallel
diode string. Also, any diode array should probably have a single
diode in reverse across the whole array, to eliminate the diodes
being punched through by voltage spikes when the pump is shut
off. The pump is a highly inductive load, so it will generate quite
a spike when the relay opens.
Once this is done the first time, it should generalize somewhat to
other pumps, though individual tweaking would still be required.
And of course the whole thing assumes that you're dealing with a pump
with excess delivery, or are willing to reduce delivery below the
spec and take on responsibility for any problems that arise from that.
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'89 Po' White Star "Scamp"
