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Subject: Re: [worldcruising] Diesel problems
truelove39@XXX.XXX
Date: Thu Aug 09 2001 - 22:13:32 EDT
Thanks for the attempt at a lesson, Robert, but let me assure you that in my
30+ years as a marine engineer, I learned a bit about the subject matter. [g]
So, permit me to return the favor:
Gauges on fuel filters are almost always compound gauges; they read vacuum in
inches of mercury and pressure in pounds per square inch, on the same dial,
with a zero point (0 PSI/0 in. Hg.) between. Gauges reading in inches of
water are not suitable for this service. Typically, a gauge on a primary
filter will show a vacuum with the engine running, assuming the supply tanks
are below the pump. A "normal" reading with a clean filter is about 3 inches;
a reading above approximately 8 inches is an indication that the filter
should be changed. Only in a situation where the filters are below the tank
(such as a day tank) and/or where there is a pump ahead of the filters would
such a gauge show a positive pressure with the engine running. Which is why I
asked the question.
Insofar as guessing, by the gradations, what the gauge is measuring; you
don't have to. Quality gauges are always marked as to the units of measure.
Regards,
John
In a message dated 8/9/2001 8:35:38 PM Eastern Daylight Time,
roberthepler@XXX.XXX writes:
> PSI and inches are not comparable units...
>
> PSI is a self-supporting (complete) unit, whereas inches requires another
> bit of information: namely the density of the fluid being used to determine
> the "Inches". Mercury being the most common, IMHO. One atmosphere is
> 14.7+/- psi and (about) 30" of mercury. so 3 psi would be equal to
> 3/14.7*30=6" of Hg
>
> Of course, what this really boils down to is how many gradations show onthe
> face of the gauge. Are there 30? then it's inches of Hg. Are there 14?
> Probably psi... ;-)
>
> -Rob
"Thinking is the hardest work there is, which is the probable reason so few
engage in it." - Henry Ford
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