question: fuel filter vacuum gauge

seattleboatguy said:

What kind of engine do you have, and what is your cruising rpm?

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FL 135 and I cruise at 1800. I also have dual Racor 900's with 30 micron elements and the secondaries on the engine which I believe are 2 micron. I have brand new aluminum tanks and move fuel around between the tanks through a fuel polishing system with a 2 micron element so my particular situation may not be the same as other FL 135s that are in use.

There has been some debate about whether the primaries should be 30 micron or some thing less, but Bob Smith and Steve D'Antonio recommend 30 micron and that's what the PO used so I use those.

I should add that I am no expert on this. Others on this forum are more knowledgable.

Jim
Sent from my iPad using Trawler Forum

MYTraveler said:

That is where the drag needle comes in -- it stay set (until manually reset) at the highest reading the indicator needle reached. Very handy!

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Indeed, a requirement for a remote gauge, in my opinion. I scratch my head when I see an isolated vac. gauges without a drag needle. Won't help with a fast clogging situation but will at least let you know why your engine quit or won't develop full power. With hourly running checks you are good to go.

cappy208 said:

Better to have a gauge to read when running the engine. You have to get all the air out of the line when installing. air is compressable. and alters readings.

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You are forgetting one thing. Remote gauges require a significant amount of tubing. And that air you mention above not only alters readings, it also causes your diesel engine to quit!!! So remote gauges introduce another failure point to allow air into your engine. The only reason I bring this up is that it happened to me. I had gone thru(what I thought was) the entire fuel system and still could not figure out where the air was coming from. I hired it out and he found it. The remote gauge(or its plumbing) had an air leak. Just FYI

Deleted post.

For those that worry about fuel contamination the current issue of PBB has a great article.

Its mostly for the newest engines , but the filtering results effect us all.

Takeaway , use 3 filters in a row to catch the best majority of the gunk.

Nothing it seems will get it all.

As we are forced to use more bio diesel, the filtering problems will continue to increase.

When remote mounting a pressure (or vacuum) gauge at a higher elevation , keep in mind that the reading will be lower than what is at the filter.

The hydrostatic weight of diesel is approximately 0.4 psi/foot of elevation, so if your sensing line is completely filled with diesel, a gauge at you flybridge will show 4 psi of vacuum without the engine running due to a 10 foot rise in elevation.

As mentioned earlier, air in the sensing line can be problematic as well (although the gauge will be more accurate). Bleeding all the air out of the line to ensure consistent readings would be a PITA.

If I was in need of a remote gauge, I'd consider a vacuum sensor at the filter and electronic gauge at the helm.

What about these guys instead of a gauge?

Fuel Fixers - Filter Change Gauges

Drag pointers are really great, but regular ER checks are better. One of my big specs in buying a boat was easy ER access. On the Hatt, you can do an ER check by opening a full sized door and walking in, one door on each end of each engine's ER. If you are merely checking the fuel vacuum, and taking a cursory look, listen and smell, the filters are right by the door. For those ER's accesses by hatch, you can get gauges that mount at a variety of angles, so can accomplish the same thing without diving in.

Just to be a PIA stickler for terminology: I think we are talking inches of mercury here and not psi, The only thing that pushes fuel out of your tank and through the average primary filter is atmospheric pressure, about 14.6 psi. Vacuum is generally measured in inches of mercury -- remember those tall glass mercury barometers from high school chemistry class? A complete vacuum is about 30 in. Hg.

Not mine...I have top feed tanks with anti-siphon valves.

Before my new tanks, my primary fuel filters were even with the fuel when down to 1/3 tanks. So the last 130 gallons or so had to be pulled up through the primaries.

So there is some vacuum created by pull from the lift pump...otherwise it wouln't be needed.

But I think you are correct in saying vacuum is usually measured in inches of mercury...but I guess it depends on the measuring device.

When sensing insufficient fuel flow, I merely turn the lever 180 degrees to change filter.

I can't imagine not having one. I transfer fuel back and forth between tanks through a 2 micron filter to make sure it is clean. With a new filter the gauge reads 2. I change it when it gets up to 10, does not happen very often. On the trip we just took I would open the hatch while underway and check the gauge. It never got over 3. Very reassuring to know when passing 20 or 30 barges a day in a narrow channel that your fuel supply is clean and flowing freely.

Greetings,
Mr. R2G. "...that your fuel supply is clean and flowing freely." Same can be said about bowels...

Unless your lift pump is located before the filter, it is atmospheric pressure that is forcing the fuel through the filters, even with top feed tanks and anti-siphon valves.

I have never seen a vacuum gauge calibrate for psi, although they could exist. There are other calibration units -- kPa and millibars -- and there are gauges that measure both vacuum and pressure. And there are gauges that measure absolute pressure (as if there were no atmospheric pressure) since atmospheric pressure varies slightly from day to day and one location to another.

Most people consider that they walk around under zero pressure, and the gauges most of us use make the same assumption. In fact, although it is a difficult concept to grasp, we are under under pressure from the atmosphere, and many of the phenomenon we experience every day are the result, like fuel going through our primary filters. If your boat were blasted into space, your lift pump would have to be replumbed before the primaries.

@Doug. I don't think it is the absolute accuracy that is important here but the ability to 'see' the before and after differences in vacuum (however it is measured). As noted, all our boats idiosyncrasies have to be figured out individually. But being able to have a warning about fuel filter condition is very helpful to avoid embarrassing situations.

Vacuum gauges are usually in mm of mercury (Hg). Pressure gauges can be calibrated to read "gauge pressure", pressure above atmospheric, or "absolute pressure", includes atmospheric pressure.

My vacuum gage registers a vacuum as the filter element becomes dirty because the fuel pump has to draw the fuel thru the filter element. It's some thing I check regularly while underway along with the engine condition and shaft stuffing gland leak off. Seems to be a prudent procedure on a single engine trawler.
I'm very familiar with vacuum measured by a mercury column as was used on steam turbine driven Navy ships The column was scaled from 30" down to 20" with the other 20" of mercury in a reservoir.

cappy208 said:

@Doug. I don't think it is the absolute accuracy that is important here but the ability to 'see' the before and after differences in vacuum (however it is measured). As noted, all our boats idiosyncrasies have to be figured out individually. But being able to have a warning about fuel filter condition is very helpful to avoid embarrassing situations.

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You are absolutely right. I warned at the beginning that I was just being a PITA!

I just bought a liquid filled on Amazon for under $10 , free freight.

JDCAVE said:

I should add that I am no expert on this. Others on this forum are more knowledgable.

Jim
Sent from my iPad using Trawler Forum

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Not that I'm aware of (but I do know your skills sets a bit JD) unless you count the now banished RickB. Count me as another 30 micron primary guy.

Doug H said:

You are absolutely right. I warned at the beginning that I was just being a PITA!

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If we were blasted off into space in our boats, there would be a lot more than just the gauges that would need to be recalibrated

sunchaser said:

Not that I'm aware of (but I do know your skills sets a bit JD) unless you count the now banished RickB. Count me as another 30 micron primary guy.

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Ditto

oscar said:

Is there an electronic "read it on the bridge" version?

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Maretron FPM100 module with a vacuum transducer PT-V-0-1BAR-01. Then it would be on a NMEA2000 bus.

Doug H said:

Unless your lift pump is located before the filter, it is atmospheric pressure that is forcing the fuel through the filters, even with top feed tanks and anti-siphon valves.

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The lift pump pulls it thru the filter. "Lift" pump.

Doug has it correctly, on all counts. The reference to vacuum "psi" was getting to me also but I let it pass. The reason youz guyz need vacuum gauges is because you have those junky Racor filters. Davcos are designed to show when the filter needs changed. Super simple, even a truck driver cant mess it up. And filters are WAY cheaper and more available.

I can't tell you guys how many of those Racor vac gauges fail. I've replaced a bunch of them. Unscrew the thing and in your hand it reads 10"Hg. Great. Others read zero and you close off filter suction valve and the stupid thing still reads zero even as engine starts to starve.

Another one got an internal leak, air loaded the engine, then it stalled while the 90 footer was maneuvering in a current. He did hit with some damage. I redesigned his system so it had the gauges tee'd into the filter outlet line... with an isolation valve!! And got a commercial grade gauge.

If you guys want vac gauges, get something commercial quality, better yet, fluid filled. Not sure where Racor sources theirs, but the number of failures is off the chart.

Never had any failures with the Racor brand, but I really like the Designated Engineer stuff.

Davcos are designed to show when the filter needs changed. Super simple, even a truck driver cant mess it up.

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I don't think the Davco's have the same water separation capacity the Racors or Fleetguards do, thus they are very rare on boats.

Wrong. They have a better water seperation system and more water storage capacity. The have a provision for a water in fuel indicator switch, fuel heater (electrical or engine coolant), and they dont pretend to be "turbine centrifugal" or anything stupid like that. Just good dependable filter units that are used on lots of commercial boats.

kulas44 said:

Wrong. They have a better water seperation system and more water storage capacity. The have a provision for a water in fuel indicator switch, fuel heater (electrical or engine coolant), and they dont pretend to be "turbine centrifugal" or anything stupid like that. Just good dependable filter units that are used on lots of commercial boats.

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Interesting, I thought they got out of the marine market when they discontinued the SeaPro line. They don't seem to have "marine" listed as an application for any of their current filter systems, not that you couldn't use one.

Greetings,
Re: Post #44...(from and off site friend-read expert)

Unless your lift pump is located before the filter, it is atmospheric pressure that is forcing the fuel through the filters, even with top feed tanks and anti-siphon valves."

Not necessarily. As long as the fuel level is above the pump and/or filter the the suction head is positive and fuel will flow through the filter without the pump. Even in a vacuum ... as is amply demonstrated by the ancient technology used to remove dead steam (condensate) from the bottom (hotwell) of the condenser of a steam plant, which normally operates at a vacuum of around 28 to 29"HG which is pretty darned high vacuum. It works because you always keep a couple feet of water above the pump impeller level.