Steven Shelikoff wrote:

However, Rich recommends that fuel be pushed through due to some
tendency of the filter media to work better in that mode.

I recommend sucking fuel through the primary separator
filters. The much finer secondary filters normally require
pressure feed to assure adequate flow through a reasonable
sized element. The canned type of filter is designed to work
under high pressure and are used very successfully and
safely in that mode by nearly every manufacturer of large
and small engines.

During many years of operating such filters in marine
applications the only time I have see one leak badly was
when the discharge from the filter was closed against the
positive displacement pump serving it. And in that case all
that happened was the rubber sealing ring blew out. Opening
the valve stopped the leak immediately.

... discounting all other aspects at hand such as the pump
emulsifying the fuel before it gets to the filter, why does the filter
media care which side the pump is on? Fuel is being pushed through it
either way, either by the pump with a higher pressure on the inlet or
the atmosphere with a higher pressure on the inlet.

The element cannot possibly know what mechanism is used to
establish fluid flow through the filter. The only thing the
filter sees is rate of flow and as it clogs, differential.
Anyone who claims otherwise is ignoring some other factor or
talking BS.

It does not take much imagination to see that the same flow
and pressure can be applied to a filter housing by gravity,
a pump discharge or a pump suction.

Rick

In article ,
Rick wrote:

The element cannot possibly know what mechanism is used to
establish fluid flow through the filter. The only thing the
filter sees is rate of flow and as it clogs, differential.
Anyone who claims otherwise is ignoring some other factor or
talking BS.

ONLY if you're only looking at the filter.

The casing is a different story. For instance, I don't feel that the
Racor 500's center-screw, edge-seal casing could handle "high" pressure.
It "feels" safer to limit it to the 14.7# maximum vacuum differential.

In addition, the 500's plastic bowl seems quite adequate for up to 15#
suction, but I'm not sure I'd trust it to 15# (or more) pressure.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

On Fri, 09 Jan 2004 07:51:04 GMT, Jere Lull wrote:

In article ,
Rick wrote:

The element cannot possibly know what mechanism is used to
establish fluid flow through the filter. The only thing the
filter sees is rate of flow and as it clogs, differential.
Anyone who claims otherwise is ignoring some other factor or
talking BS.

ONLY if you're only looking at the filter.

We are only looking at the filter, not taking into account the casing,
plumbing, etc.

Steve

In article ,
(Steven Shelikoff) wrote:

On Fri, 09 Jan 2004 07:51:04 GMT, Jere Lull wrote:

In article ,
Rick wrote:

The element cannot possibly know what mechanism is used to
establish fluid flow through the filter. The only thing the
filter sees is rate of flow and as it clogs, differential.
Anyone who claims otherwise is ignoring some other factor or
talking BS.

ONLY if you're only looking at the filter.

We are only looking at the filter, not taking into account the casing,
plumbing, etc.

Steve

I believe that the case is a pretty major component to ignore in a
polishing system. A case designed for partial vacuum may not properly
handle whatever pressure the pump can deliver. If the company says "only
suction", I suspect it wasn't designed for pressure.

Getting back to the filter alone: Since I believe most pumps can "push"
better than they can "pull", we should also consider the maximum
differential the filter can handle before it tears or otherwise breaks
down. Rich mentioned a design limit of 6" vacuum (about 3 psi?) What can
these pumps deliver?

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Jere Lull wrote:

I believe that the case is a pretty major component to ignore in a
polishing system.

You must have missed quite a few posts. The discussion you
entered was about the mechanism for moving a fluid across
the filter element. We were not discussing the entire filter
assembly or its place in the system.

Rick

In article . net,
Rick wrote:

Jere Lull wrote:

I believe that the case is a pretty major component to ignore in a
polishing system.

You must have missed quite a few posts. The discussion you
entered was about the mechanism for moving a fluid across
the filter element. We were not discussing the entire filter
assembly or its place in the system.

Rick

I *had* read the whole thread, and felt that it had lost its way,
talking theoretically about just the filter when a real-life system
includes quite a bit more.

I didn't even mention the 4 or more extra joints that would be probable
problem points if pressurized. The time we got a plugged tank pickup, I
found out that one or more of our joints leaked air into the system.
They don't give us any problem under normal operation. I strongly
suspect that if I pressurized the system, that/those joint(s) would drip
fuel very slowly. While not a safety problem with diesel, it's a mess I
want to avoid. (The first mate is strongly affected by the smell. If she
ain't happy, ain't no one happy!) They're all torqued to spec, so I'd
have to exceed recommended torque(s) to stop the leak(s).

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

In article . net,
Rick wrote:

Jere Lull wrote:

I believe that the case is a pretty major component to ignore in a
polishing system.

You must have missed quite a few posts. The discussion you
entered was about the mechanism for moving a fluid across
the filter element. We were not discussing the entire filter
assembly or its place in the system.

Rick

I *had* read the whole thread, and felt that it had lost its way,
talking theoretically about just the filter when a real-life system
includes quite a bit more.

I didn't even mention the 4 or more extra joints that would be probable
problem points if pressurized. The time we got a plugged tank pickup, I
found out that one or more of our joints leaked air into the system.
They don't give us any problem under normal operation. I strongly
suspect that if I pressurized the system, that/those joint(s) would drip
fuel very slowly. While not a safety problem with diesel, it's a mess I
want to avoid. (The first mate is strongly affected by the smell. If she
ain't happy, ain't no one happy!) They're all torqued to spec, so I'd
have to exceed recommended torque(s) to stop the leak(s).

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Jere Lull wrote:

I believe that the case is a pretty major component to ignore in a
polishing system.

You must have missed quite a few posts. The discussion you
entered was about the mechanism for moving a fluid across
the filter element. We were not discussing the entire filter
assembly or its place in the system.

Rick

On Sat, 10 Jan 2004 05:40:18 GMT, Jere Lull wrote:

In article ,
(Steven Shelikoff) wrote:

On Fri, 09 Jan 2004 07:51:04 GMT, Jere Lull wrote:

In article ,
Rick wrote:

The element cannot possibly know what mechanism is used to
establish fluid flow through the filter. The only thing the
filter sees is rate of flow and as it clogs, differential.
Anyone who claims otherwise is ignoring some other factor or
talking BS.

ONLY if you're only looking at the filter.

We are only looking at the filter, not taking into account the casing,
plumbing, etc.

Steve

I believe that the case is a pretty major component to ignore in a
polishing system. A case designed for partial vacuum may not properly
handle whatever pressure the pump can deliver. If the company says "only
suction", I suspect it wasn't designed for pressure.

When looking at the entire fuel polishing system, we're not ignoring the
case. When looking strictly at the difference in the performance of the
filter media, by definition we are ignoring the case. My question is
why does it matter strictly to the performance of the filter media
whether fuel is being pushed through by a pump or pushed through by
atmospheric pressure?

Getting back to the filter alone: Since I believe most pumps can "push"
better than they can "pull", we should also consider the maximum
differential the filter can handle before it tears or otherwise breaks
down. Rich mentioned a design limit of 6" vacuum (about 3 psi?) What can
these pumps deliver?

Typical of the pumps used in this application is the Walbro 6802. I
don't see the spec on vacuum for it on the web but it delivers 7 psi
pressure so the vacuum is probably somewhat less. I do have the manual
on the boat, but I'm not going down there anytime soom. In application,
I haven't measured more than about 5 psi of vacuum before I changed
elements. The Racors have no problem with 7 psi vacuum or pressure.

Steve

Steven Shelikoff wrote:


...filter media, by definition we are ignoring the case. My question is
why does it matter strictly to the performance of the filter media
whether fuel is being pushed through by a pump or pushed through by
atmospheric pressure?

It's often a function of system and pump design. For e.g., when
using a centrifugal pump (or liquid ring, and sometimes vane), the
inlet is typically sized larger than the outlet. The result is
higher fluid velocity on the outlet side versus the 'suction'
side. Higher velocity, higher impact pressure, often resulting in
better particulate retention.

Additionally, all pump curves I've seen are, to some degree, more
dependent on suction head than discharge head, and cavitation
becomes an issue (i.e. efficiency drops more rapidly for loss of
head on the suction side than for increase in head on the
discharge side). Thus, when the filter begins to clog, you not
only lose flowrate due to loop pressure drop increasing, you lose
pump *efficiency* as well, exacerbating the problem. The result
is, typically, less allowable filter loading before the system
performance is affected, so more frequent filter changes.

Whether this is an issue with the Racors or not, I have no idea,
not being familiar with them. But if you want maximum system
efficiency, maximum filter loading capacity, and longest interval
between changeouts, discharge filtration is the way to go.

Or...just use more *wind*, and all this diesel stuff is moot :-)

Keith Hughes