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Old 12-31-2010, 09:57 AM   #1
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Vaccume gages and filters

Hi All, I'm a newbe so i'm not familiar with the protocol here but feel I have some useful information concerning vaccume gages and fuel filters. We all know the gage is normally used to indicate the condition of the element in the primary filter. If you have seen the Racor vaccume gage you notice the scale is color coded green-yellow-red, the implications being obvious. However it is a one size fits all solution and requires a good bit of guess work. The simple reason is because every boat has different supply plumbing and is of different age. Every component ,fitting, hose etc. in the fuel delivery system between the tank supply tube and the fuel lift pump causes a restriction the pump must overcome. The pump can only develop so much vaccume and when there is too much restriction the fuel flow stops. We need to know when our specific fuel system is getting ready to shut down or better yet well befor. The filter elements will cut off fuel flow when the resistance through the element reaches 7" of vaccume. A new element will generally show a 1"-2" vaccume reading on the gage. So when the gage reads 8"-9" the flow will most likely have stopped indicating the element has reached the very end of its life span. For obvious reasons you don't want to go that far. Change the element when the reading is one or two inches lower. All this applies regardless of the micron rating of the element as the gage is simply measuring the results of restriction to flow. I mentioned age befor and it is important because an old lift pump may not be able to develop its maximum rated vaccume and as such fuel flow may stop at a lower point. You end up changing elements earlier or better yet replace the pump. The vaccume can be checked at any RPM but it may be more stable at a speed off of idle. Once you have your specific set of numbers the decision about when to change elements is pretty much cut and dry. After looking at the old elements you can decide if necessary to lengthen or shorten the run time. An easy way to get an idea as to the condition of the elements while under way is to run to full RPM. If the RPM comes up to max then all is good. My choice is to do this at the end of the day. Personally I really dislike having to change an element 1 hour into the days run. It really ruins that second cup of coffee.* The gage used is up to you as they all read the same thing, however try to get one with an easy to read scale. The basic Racor gage is fine but the usual location is poor. Better to buy the Racor adptor that screws into the engine side of the filter body and allows running tubing to wherever you want the gage. The 1/8" plastic tubing used for ice makers an brass fittings work great and are easy to install. Be sure to buy a gage with 1/8" connection to keep things simple. You do need to be careful to make good tight connections as an air leak will shut down the engine rather quickly. Hope this helps. Gotta run but will get to filters next time. Trader
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Old 12-31-2010, 11:11 AM   #2
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Vaccume gages and filters

Why does your gauge show "high"vacuum? Are you sucking fuel uphill or 50 gph while recycling 45 gph? If not, with the right filters, good fuel*and clean tanks on our small trawler motors, an "increasing" vacuum gauge reading points to a fundamental flaw somewhere you better get fixed. My Racor gauges always read 0 -*I do close off the*fuel valves on occasion to check that the gauges are working.

-- Edited by sunchaser on Friday 31st of December 2010 12:13:28 PM
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Old 12-31-2010, 01:18 PM   #3
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RE: Vaccume gages and filters

The vacuum gauges in the fuel lines of low-flow engines like the FL120 never go above "0" unless there is a restriction in the line or the filter element is getting clogged. Everyone I know with a boat with these types of engines and a vacuum gauge changes the filter when the vacuum reading is anything other than "0." The marks and color bands are meaningless in this application--- the only meaningful clue is if the needle isn't on "0." We always change our Racor elements when we change the engine oil, so every 100 to 150 hours. We have had the gauges on our filters for some six or seven years now, and they have never read anything but "0." And yes, we have tested the gauges to make sure they work.
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Old 12-31-2010, 02:04 PM   #4
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RE: Vaccume gages and filters

The vacuum gage on my FL120 read at about 5 or 6 when my engine would shut down. That was on my maiden delivery voyage (and if you think 12 elements are enough for a 500 mile trip, not always).

Since I replaced the lift pump and changed from 2 micron filters to multistage I have never seen over 1. One gage (on the 30 micron Racor) reads 0, one gage reads close to 1 (on the 10 micron Racor) when new.
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Old 01-01-2011, 02:51 PM   #5
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RE: Vaccume gages and filters

The fundamental flaw is a dock side committee passing on flawed information based on a fundamental lack of understanding of the fundamental basic fluid and filter flow dynamics, a fundamental lack of understanding of basic analog gage operational parameters and most embarrassing of all, not being able to understand that if there is O vacuum at the Racor there is O fuel flow. Rearranging facts to fit ones opinion doesn't make the facts incorrect. TRADER
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Old 01-01-2011, 04:47 PM   #6
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RE: Vaccume gages and filters

Quote:
trader wrote:The fundamental flaw is a dock side committee passing on flawed information based on a fundamental lack of understanding of the fundamental basic fluid and filter flow dynamics, a fundamental lack of understanding of basic analog gage operational parameters and most embarrassing of all, not being able to understand that if there is O vacuum at the Racor there is O fuel flow.
Are you the self appointed head of that committee or just wake up and decide to make 2011 the year of the ass?

If the level of fuel in the tank in service is higher than the filter then there is a positive static head. If the lift pump is at or below the level of the filter then there is a positive static head at the pump as well. When the engine is running there will be a slight pressure differential created by the filter element and friction in the fuel lines but in most cases it is not enough to move a bourdon tube gauge off the peg unless the element is very dirty.

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Old 01-01-2011, 06:33 PM   #7
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RE: Vaccume gages and filters

The racor gage reads 0-30,*It would be nice to have one that reads 0-10.** I have not seen any like that.
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Old 01-01-2011, 07:18 PM   #8
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RE: Vaccume gages and filters

Quote:
RickB wrote:


trader wrote:The fundamental flaw is a dock side committee passing on flawed information based on a fundamental lack of understanding of the fundamental basic fluid and filter flow dynamics, a fundamental lack of understanding of basic analog gage operational parameters and most embarrassing of all, not being able to understand that if there is O vacuum at the Racor there is O fuel flow.
Are you the self appointed head of that committee or just wake up and decide to make 2011 the year of the ass?

If the level of fuel in the tank in service is higher than the filter then there is a positive static head. If the lift pump is at or below the level of the filter then there is a positive static head at the pump as well. When the engine is running there will be a slight pressure differential created by the filter element and friction in the fuel lines but in most cases it is not enough to move a bourdon tube gauge off the peg unless the element is very dirty.

*

Rick,

Well "fundamentally" said!

El Sea/ L.C.

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Old 01-01-2011, 08:24 PM   #9
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Old 01-01-2011, 10:20 PM   #10
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RE: Vaccume gages and filters

Dear Trader

Welcome to the Forum. You have joined an elite crowd. Someof us actually have boats, unlike other Forums where landlubbers opine regularly. Some of us in fact have an educational and experience background where fluid dynamics are a way of life. Personally I am on this Forum to escape the drudgery of work issues such as shear thinning, apparent vs actual viscosity*and Pascals. For fear that some person much smarter than me is lurking nearby, I try not to let too much of my ammo show.

My situation is as RickB suggested, with Racors* positioned* below my nominal fuel tank level. I indeed have static positive pressure at the Racor gauge, approximately* 1.5 whopping psi.

Tell us about your boat, we'd love to hear more.
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Old 01-02-2011, 05:28 AM   #11
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RE: Vaccume gages and filters

To me the problems are ,

1. there is only one filter so it will have to be changed , rather than a lever simply thrown.

2. its in the engine room, do you really want to be down there bouncing off a dead engine attempting to change the element , fill the filter and perhaps bleed the engine?

3. Hose , even USCG fuel hose is cheap , I would get a pair of whatever your favorite filters are , and a pair of lever operated fuel OK ball valves and move it OUT of the engine spaces to a spot you can see them, drain them and as required replace the elements .
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Old 01-02-2011, 06:21 AM   #12
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RE: Vaccume gages and filters

Carl

Your reading is identical to mine with engines running.

Unless you have old dirty tanks and a history of clogging filters, I'd ignore the need for a second filter as FF suggests - nice to have though. Moving the filters outside the*ER is not necessary as FF suggests and seems silly for a 2 gph Lehman or a*75 gph MAN for that matter. I'd be curious to know how many have their primary filters removed from the ER space - very few I betcha. As for the hoses, yes use the right stuff if you are not already.
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Old 01-02-2011, 08:48 AM   #13
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RE: Vaccume gages and filters

Last time*I checked, Nordhavns have their fuel filters in the ER.
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Old 01-02-2011, 12:43 PM   #14
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RE: Vaccume gages and filters

With low or no vacuum the needle will point to ~05:00 which is where yours is. That's where vacuum guages rest.
With the engine running and clean filters that's where you want to see it or as close as possible.
As the filter plugs, the vacuum rises, the needle will rotate counterclockwise.

Aside from adding filters and such, one easy and inexpensive improvement that could be made is to get a guage with a telltale, second needle, which will stay at the highest point of vacuum reached while running. That way you can check later, after the engine is shutdown, to get a warning of filter clogging. You do not need to look at the guage while running. The guage you have now, without the telltale, must be observed while running to get a reading.
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Old 01-02-2011, 02:05 PM   #15
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RE: Vaccume gages and filters

Quote:
trader wrote:

The fundamental flaw is a dock side committee passing on flawed information based on a fundamental lack of understanding of the fundamental basic fluid and filter flow most embarrassing of all, not being able to understand that if there is O vacuum at the Racor there is O fuel flow. Rearranging facts to fit ones opinion doesn't make the facts incorrect.


The above was obviously written by someone with minimal experience with boats and marine powerplants. I can think of no other explanation unless the fact that our two FL120s run just great with the Racor vacuum gauges on top of the filters sitting on zero is a fantasy and we are in fact sitting in our slip with dead engines instead of cruising through the islands. I also have to assume that the identical experience of everyone I know with an FL120-powered boat and vacuum gauges is also a fantasy.
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Old 01-03-2011, 04:52 AM   #16
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RE: Vaccume gages and filters

"and I have run up the coast with her with no problem, "

Its NOT the "no problem" runs a fuel filtering system is designed or located for.

Its the sound of silence that a good system is designed to prevent , or at worst cure.
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Old 01-03-2011, 05:29 AM   #17
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RE: Vaccume gages and filters

Slightly off topic, but stimulated by the pic of the big red engine (120 Lehman, same as mine) in the original post, when I went to check the engine levels and top up as required before heading out last weekend, I noticed a drip from the port end of the oil cooler/heat exchanger, and when I fired her up, two jets of water squirted out from the end join. Needless to say that kiboshed our new year short cruise to watch the fireworks etc.
I presume the gasket has gone in that end, but what are we likely to find when the diesel mechanic pulls it apart. I am preparing myself for the worst - possibly a new unit - as it looks rather corroded round that end, even tho it is bonded through attachment to the engine - or so I thought. I think the zincs were done when the main engine heat exchanger above it was re-conditioned ~ 2 yrs ago. How often should these zincs be changed....? I guess that would be a time thing, rather than an engine hours thing..?
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Old 01-03-2011, 06:40 AM   #18
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RE: Vaccume gages and filters

Quote:
Peter B wrote:

Slightly off topic, but stimulated by the pic of the big red engine (120 Lehman, same as mine) in the original post, when I went to check the engine levels and top up as required before heading out last weekend, I noticed a drip from the port end of the oil cooler/heat exchanger, and when I fired her up, two jets of water squirted out from the end join. Needless to say that kiboshed our new year short cruise to watch the fireworks etc.
I presume the gasket has gone in that end, but what are we likely to find when the diesel mechanic pulls it apart. I am preparing myself for the worst - possibly a new unit - as it looks rather corroded round that end, even tho it is bonded through attachment to the engine - or so I thought. I think the zincs were done when the main engine heat exchanger above it was re-conditioned ~ 2 yrs ago. How often should these zincs be changed....? I guess that would be a time thing, rather than an engine hours thing..?

If you are talking about the engines heat exchanger, replacing the end gaskets and cleaning up the end plates will probably stop the leak.

If one of the oil coolers is leaking I think I would get a new one. There is one for your engine for 79. dollars on Ebay.* Type in Ford Lehman 120 and it will appear the seller is FredWerner, I have purchased an exhaust elbow from him and he is an honest seller.

If you open the main heatexchanger it is a good time to flush it out, The zinc should be changed at least once a year.

These engines are easy to maintain.* Hope that helps
*
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Old 01-03-2011, 07:26 AM   #19
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RE: Vaccume gages and filters

Quote:
Peter B wrote:

Slightly off topic, but stimulated by the pic of the big red engine (120 Lehman, same as mine) in the original post, when I went to check the engine levels and top up as required before heading out last weekend, I noticed a drip from the port end of the oil cooler/heat exchanger, and when I fired her up, two jets of water squirted out from the end join. Needless to say that kiboshed our new year short cruise to watch the fireworks etc.
I presume the gasket has gone in that end, but what are we likely to find when the diesel mechanic pulls it apart. I am preparing myself for the worst - possibly a new unit - as it looks rather corroded round that end, even tho it is bonded through attachment to the engine - or so I thought. I think the zincs were done when the main engine heat exchanger above it was re-conditioned ~ 2 yrs ago. How often should these zincs be changed....? I guess that would be a time thing, rather than an engine hours thing..?
Peter, transmission coolers have soldered end caps (no gaskets). I have had one resoldered at a radiator shop. It lasted about 3 months and then started leaking again. The lead in the solder gets eaten away just like a zinc. Removing the end cap, cleaning both surfaces and resoldering is the only way to get a good seal. Unfortunately it takes real skill to resolder it without disturbing the solder on the internal tube bundle. Buy a new one as a used one will give you no idea of the life expectancy of the solder.

Ted

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Old 01-03-2011, 11:53 AM   #20
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RE: Vaccume gages and filters

...and folks, I think FF was talking about putting the GAUGE outside of the engine room....not the whole filter assembly.
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