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

On Sat, 10 Jan 2004 12:53:52 -0700, Keith Hughes
wrote:

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.

Sounds like we have to limit this further. Ok, I'll limit it to the
typical filter, like a Racor fuel filter, with a typical pump, like the
Walbro, with the pump either before or after the Racor attached to it by
at least a few feet of hose and in both cases, a 3 psi difference
between the outlet and inlet. How would you explain a difference in the
performance of the filter media between the pump pushing or pulling the
fuel?

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.

Basically, the above is saying that the pump can push better than it cal
pull. That I agree with. But if it can pull well enough to maintain
enough pressure differential across the filter up to the point where you
would want to change the filter anyway, it becomes a non-issue.
Especially if you're not as worried about filter element replacement
costs as you are about other aspects of the system such as polishing
ability and safety.

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.

And if I want maximum life out of the pump (it's always seeing clean
fuel), filtration capability (the pump isn't emulsifying the fuel just
before it gets to the filter) and safety (a leak will shut the system
down rather than pump fuel into the bilge) then I'd go the other way.

You pick the parameters you want to maximize and go with it.

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

Yup.

Steve

Steven Shelikoff wrote:

Sounds like we have to limit this further. Ok, I'll limit it to the
typical filter, like a Racor fuel filter, with a typical pump, like the
Walbro, with the pump either before or after the Racor attached to it by
at least a few feet of hose and in both cases, a 3 psi difference
between the outlet and inlet. How would you explain a difference in the
performance of the filter media between the pump pushing or pulling the
fuel?

I did not claim there *is* a difference. As long as the DP is the
same, and fluid velocity is the same, there should be no
appreciable difference. I mean, if you continue to "limit this
further" such that all pneumatic parameters are identical,
operating in a steady state condition, then of course there's no
difference between suction and pressure filtration. There can't
be, QED.

The point I was making is that in real world applications,
parameters will not be identical, and the system is not steady
state. So you have to factor in the overall system design (pump
curves, filter cartridge design, flow rates, velocities, etc.) to
determine if there may be an impact, since the filter does *not*
operate independently of the overall system. For your basic
'rock-n-alligator' filters, I would not expect any differences.

And if I want maximum life out of the pump

You put a strainer in front of it.

You pick the parameters you want to maximize and go with it.

So true...

Keith Hughes

On Sat, 10 Jan 2004 16:29:32 -0700, Keith Hughes
wrote:

Steven Shelikoff wrote:

Sounds like we have to limit this further. Ok, I'll limit it to the
typical filter, like a Racor fuel filter, with a typical pump, like the
Walbro, with the pump either before or after the Racor attached to it by
at least a few feet of hose and in both cases, a 3 psi difference
between the outlet and inlet. How would you explain a difference in the
performance of the filter media between the pump pushing or pulling the
fuel?

I did not claim there *is* a difference. As long as the DP is the
same, and fluid velocity is the same, there should be no
appreciable difference. I mean, if you continue to "limit this
further" such that all pneumatic parameters are identical,
operating in a steady state condition, then of course there's no
difference between suction and pressure filtration. There can't
be, QED.

Exactly my point. I don't see how there could be a difference between
pushing and pulling "all else being equal". But Rich keeps saying there
is a difference and that the difference is unexplainable and is just
waiting for a doctoral thesis in filterology to explain it.

The point I was making is that in real world applications,
parameters will not be identical, and the system is not steady
state. So you have to factor in the overall system design (pump
curves, filter cartridge design, flow rates, velocities, etc.) to
determine if there may be an impact, since the filter does *not*
operate independently of the overall system. For your basic
'rock-n-alligator' filters, I would not expect any differences.

And if I want maximum life out of the pump

You put a strainer in front of it.

The pump already comes with a strainer. But it's a royal PITA to
replace and really only gets out the largest of crud. For a "strainer"
to be effective, it's just another filtration stage and we're back to
sucking fuel through a filter rather than pushing it through.

You pick the parameters you want to maximize and go with it.

So true...

Steve