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CaptnWil is back from the wilds. Since he started all this business about
using a Walbro pump for diesel polishing, he feels a responsibility to
respond.
1. There are two Walbro pumps and one does have an max output of 7 psi.
That is the one to use. Remember that 7 psi is a little over 14-inches of
mercury, pressure drop across filter elements are normally stated in inches
of mercury. Any filter element, and certainly the GCF element, should be
changed long before the pressure across it reaches 10-inches.
2. The Walbro pump is a CG approved diesel fuel pump. It is meant to
replace existing fuel pumps on marine engines. That means that it is rated
for continuous duty -- it can run all the time without over-heating or
wearing out motor brushes -- it has no brushes. It is very hard to find
continuous duty 12-volt pumps. I have been unable to locate any except the
Walbro. I have talked to manufacturers of "continuous duty" 12-volt pumps
and they all reply that the motors are brush type motors which will wear out
in 50 to 100 hours of operation, and the brushes can not be replaced. That
duty cycle is unacceptable for this service.
3. There is a great advantage of the Walbro design in that it is "pass
thru." That means that your normal diaphragm-engine-operated lift pump can
pull fuel through the Walbro if it were to fail. This allows the system to
be designed so that fuel polishing can go on while underway -- see
CaptnWil's drawings on the TW web site. It also means that you have a
back-up for your standard lift pump.
4. The full benefit of diesel polishing can only be obtained by long
periods of system operation. Mine operated at least 48-hours every week
when at the dock and continuously while the engine ran. The fuel stayed
"just like new" without any additives of any kind. Bottom samples of the
tanks came up clean all the time.
5. The initial clean-up of the system took pumping for 176 hours and
changing some Racor filter elements. After that the pressure drop across
the filter never registered on the vacuum gauge even when a GCF was put in
series with the Racor. There was some pressure drop across these filters,
but never more than the positive head from the bottom feed fuel tank. If
you get clean, dry fuel, and it stays "just like new" with a diesel
polishing system, the filter will last a very long time without any increase
in pressure drop across it. After all, that is what diesel polishing is all
about.
6. The Walbro is a quiet little worker and you can almost tell how much
pressure drop it is encountering by its sound.
7. Any pump that gets the job done will make a diesel polishing system
successful, but the little Walbro has proven it is a sure winner.
CaptnWil
----- Original Message -----
From: "AKAMA" <>
Sent: Thursday, February 01, 2001 4:37 AM
Subject: TWL: Bumble Bees Can't Fly (about fuel pumps)
> Hi,
>
> We are in the process of designing an integrated fuel
> polishing/transfer/priming system for AKAMA. It will be along the lines
of
> what has already been written, so I'll spare you all the details.
>
> We received the following information from a huge, reputable pump vendor,
> "The Walbro pump is an excellent priming pump but not suitable for fuel
> polishing because max discharge pressure is only 7 psi. It may work on a
> clean filter, but will quit as the filter starts to get dirty. A gear pump
> would be a better choice. However, neither are (sic) flow through and
should
> be on a tee/valve. We have DC gear pump 1gpm and up."
>
> Now, nearly everyone is using the Walbro pump as far as we know. We'd
like
> to hear from those of you who are using it as to whether you have noticed
> that the pump is a bit anaemic for the use, as has been suggested by the
> pump vendor. We only want to build this once!
>
> Maurice & Louise-Ann Nunas
> M/V AKAMA
> Pier 2, Ponggol Marina
> Singapore
>
>
>
>
