# vacuum gauge with Racor filter



## flechenbones (Oct 2, 2009)

Does anyone use this vacuum gauge to indicate when it is time to change the fuel filter?
Fuel Fixers Inc. : R2D2 -T - HANDLE WITH RESETTABLE FILTER CHANGE GAUGE [R2D2] - $89.50

It has some nice features and I'm considering getting it. However, I'm not sure it will be as easy to read as a more traditional vacuum gauge (below) so I thought I would see if anyone had first hand experience with it.
LED lighting, soundproof, Sailor's Solutions Inc.


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## RichH (Jul 10, 2000)

Those links you posted are faulty.

Fuel flow capacity through such a filter is obtained from the "flow vs. ∆P" charting as found on the Racor Division - Parker website. Look for your specific filter cartridge model number and its 'flow vs. ∆P" chart (where "∆P" = differential pressure/vacuum) - this chart is for CLEAN filters, not loaded with debris. The 'capacity chart will have both vacuum and pressure values. Essentially ALL filters are so rated and applied.

First you need to determine the theoretical Fuel Consumption of your engine at WOT (wide open throttle) from your engine manual, etc. .... then add 25+% to that value. Determine the MAXIMUM suction lift from your (new) lift pump in inches of mercury (Hg.) vacuum - this will be the suction pressure that the lift pump 'stalls' or can deliver NO flow as when a filter is completely 'choked' .... should be in the max. range of 5 or 6 inches of Hg. vacuum; such values are usually obtained from each engine's 'shop maintenance/rebuild manuals'.

The important thing is that you should be IMMEDIATELY changing out the filter(s) when the MAXIMUM lift pump value reaches ***75% of the maximum value of the lift pump*** as indicated on the vacuum gage. Example: (5" Hg. X .75)= 3.75" Hg. vacuum on the gage. as the rate of the debris deposition on the filter is 'exponential' because once a filter starts to become plugged it will begin to remove finer and finer, or smaller and smaller µM sized particles ... and the filter will then *very soon* 'choke' with these smaller particles AND the suction pressure of the lift pump will soon be 'overwhelmed' - all resulting quickly in NO FLOW.

*When to change a filter as indicated on a vacuum gage*: at 75% of the value at which the lift pumps maximum 'draw value' (pump 'stalls') .... typically 5-6" hg. 'times' 75% = 3.75" to 4.5" hg. vacuum on the gage. 
-------------------------
Vacuum motive filtration is Extremely inefficient: 1. because the lift pump cannot draw more than about 5-6" hg. vacuum. 2. the particles will be more or less IN the filter media rather than on the surface. 
Boat builders prefer vacuum motive fuel filtration because its the cheapest and least labor intensive method to do the job (translation: cheap and dirty); plus, if you develop an air leak in the fuel system, the system rapidly and 'automatically' shuts down and doesnt fill the bilge (and surrounding water) with oil thus preventing serious EPA, etc. fines.

Commercial maritime fuel installations are usually PRESSURE motive fuel systems. Such Racors are usually designed for a maximum of 30 - 60 psig 'filter media burst pressure'. As you will see from the 'flow capacity curves' the higher the differential pressue across sthe filter - the higher the flow. Simply look at the specific fuel filters "flow vs. ∆P" curve and note that the 'flow capacity' at higher PRESSURE is vastly more in quantity (flow rate) than in vacuum motive flow .... It means that if you installed a 12 vdc PRESSURE pump on the tank or between the tank and the racors, the filter would have 10X - 20X the 'crud capacity', simply because its operating at a higher PRESSURE. Of course, the fuel delivery system now has to be 'bomb-proof' against leaks, cannot use cheapey 'compression fittings', etc. and should have 'double flared' stainless tubing instead of copper.

The 'compromise' is to install a 12vdc diesel compatible pump (automotive stuff) on the tank or between the thank and the racor, etc. filters so that when a filter is 'plugged' when run solely by the lift pump .... instead of shutting down the engine, changing a filter when underway, etc.; then, simply switch on the 12 vdc pressure pump .... and use the built-in capacity that is still available in the filter media when supplied by PRESSURE from the 12 vdc pump. BTW ... a 12 vdc pump so arranged will take out 99% of the 'bother' when 'bleeding' a fuel system. In this 'redundant' configuration the 12vdc is only ON when you need to 'bleed' or in an emergency (to get more FLOW out of a filter that became blocked while in 'vacuum' motive service) ..... thus enabling one to simply 'motor-on' for a short time until its SAFE to change out a plugging filter.


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## Gene T (May 23, 2006)

Vacuum gauges are great for diagnosing a problem. I prefer having them mounted near the engine gauges. Scenario is like this. Engine starts to run crappy, look at vacuum gauge. If vacuum is higher than normal you have a plugged filter, if not then something else. i.e. over heating. I have a dual Racor setup with a gauge between them in the new(er) boat. 

In my experience filters don't get dirty over time. They get plugged all at once from some crap that comes loose in the tank. I have run for years without having to change any filters. Then I eventually just change them because it seems like a good idea.

Gene


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## MacGyverRI (Nov 14, 2007)

When a diesel engine loses high end/max RPM, that's when the filter flow is very restricted and needs immediate changing. There's no need to waste money on that fuel gizmo, just watch the RPM's. An "air cleaner restriction gauge" tapped into the intake manifold on the other hand is very useful. You can get those at any heavy truck dealer.

OTOH, Preventative Maintanence is another story, change the filters in the spring or spring and fall if you cruise a lot yr. round and most filters will be fine for the duration. 


I've been working on heavy diesels (and everything else...) since 1973 and have seen many gadgets that are useless...


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## flechenbones (Oct 2, 2009)

The links are fixed now.

I started thinking about it after having spent the last few weeks replacing just about everything in the fuel system after having difficulty consistently isolating the problem. Plus, the current filters I use are quite expensive, which made me start to consider ways to only replace them when needed (instead of after some arbitrary length of time). The Racor turbine series seems to be a better system with cheaper filters.

If the red area begins at 10 hg, it sounds like that would be too late according to the numbers suggested by Rich.


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## RichH (Jul 10, 2000)

MacGyverRI said:


> When a diesel engine loses high end/max RPM, that's when the filter flow is very restricted and needs immediate changing. There's no need to waste money on that fuel gizmo, just watch the RPM's.


Well how does this make any sense at all .... why would one allow a fuel filter to become plugged and only to realize at the moment that the fuel supply is ALREADY starving/happening by loss of engine rpm. Loss of engine rpm means that the fuel filter system is plugged and needs immediate attention. With a gage, or better - a differential pressure/vacuum switch wired to an alarm and set to 80% of max. vacuum as needed by the lift pump, will clearly show that the filter need changing **** in the immediate FUTURE**** and 'not immediately'. Why wait until the engine is 'stumbling' during a severe seastate, passiing through busy channel/inlet, etc. to find out that the engine rpm is dropping and you need to do something aboit it *right now" ????? Monitoring a gage, etc. is much 'safer'.


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## RichH (Jul 10, 2000)

flechenbones said:


> The links are fixed now.
> 
> If the red area begins at 10 hg, it sounds like that would be too late according to the numbers suggested by Rich.


 It all depends on the mechanical strength of the lift pump and how much it can 'suck' when 'deadheaded' (totally blocked flow).


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## Gene T (May 23, 2006)

I would point out that fuel starvation can come from other things than a plugged filter. I have personally had a collapsed fuel line - the inner part of the hose collapsed plugging the line when vacuum was applied. This was not visible from looking at the hose. I also had a problem with a piece of crud that plugged the pick up tube in the tank. That was intermittent, it would drift away once the vacuum was gone only to get sucked back and replug it at some point. A vacuum gauge can identify a fuel flow problem. However these types of problems can be identified by installing a simple outboard fuel bulb before the filters.

Gene


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## MacGyverRI (Nov 14, 2007)

RichH said:


> Well how does this make any sense at all .... why would one allow a fuel filter to become plugged and only to realize at the moment that the fuel supply is ALREADY starving/happening by loss of engine rpm.
> .


Why do some people wait until they're almost dead before they will go see a Dr.?? same people, same logic. It's sad, but people do it daily....


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## RichH (Jul 10, 2000)

Gene T said:


> However these types of problems can be identified by installing a simple outboard fuel bulb before the filters.
> 
> Gene


ABYC, as well as most insurance carriers, prohibits 'fuel bulbs' on internal space fuel systems .... because the are very prone to leakage and they are not 'fire proof' to any time based rating.


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## flechenbones (Oct 2, 2009)

RichH said:


> It all depends on the mechanical strength of the lift pump and how much it can 'suck' when 'deadheaded' (totally blocked flow).


I may be incompetent, but I can't seem to find that information. This is the lift pump.
Facet Cylindrical Solid State Electric Fuel Pump - 476459E - Discount Yacht Supplies, Vetus Nautical Accessories, Scandvik Parts, Garmin Marine Electronics


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## RichH (Jul 10, 2000)

Not a problem
"1 - 8 psi" ... use the 8 psi as the deadheaded ("0" flow or max.) pressure. 

8 psi = 16" of hg. pressure or vacuum. 

Nice pump.


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## rikhall (Feb 7, 2008)

MacGyverRI said:


> There's no need to waste money on that fuel gizmo, just watch the RPM's.


I have had problems with restricted filters three times and none of them was reflected in low RPMs. I am baffled as to why not, but such was the case. I lost speed with the same RPMs. Made no sense at all.

Rik


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## RichH (Jul 10, 2000)

rikhall said:


> I have had problems with restricted filters three times and none of them was reflected in low RPMs. I am baffled as to why not, but such was the case. I lost speed with the same RPMs. Made no sense at all.
> 
> Rik


Assuming that you have a diesel engine, several things could have occurred. 
1. most particles in diesel fuel are 'deformable' and can 'extrude' though filters under increasing differential pressure/vacuum across a filter ... the filters may have 'unloaded', yet retained the correct µM rating for 'hard' particles.
2. It takes 'work' (differential pressure across a filter) to filter and you may have had sufficient flow capacity at the lower rpm demand, but not the higher rpm demand due to the 'partial' plugging of the filter(s). Thats why my usual recommendation is to change at about 75% of maximum vacuum/pressure ON THE GAGE (75% of what the lift pump can 'suck' at maximum) when 'tested' with the engine running at wide open throttle (WOT) .... ensure you have enough 'dirt capacity' still left in the filter or to discover WHEN to change it. Its easy to determing max. vac./pressure output of the lift pump... simply close the tank valve and watch the gage for its maximum reading. Then you know to quickly change the filter(s) when the gage gets to 75% of that max. lift pump value. ;-)


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## flechenbones (Oct 2, 2009)

Thanks Rich. I guess that means that the red "change filter" indicator on the R2D2 guage beginning at 10 hg is fine considering you think that it should be changed by 12 hg.


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## RichH (Jul 10, 2000)

All depends on the 'deadhead pressure' of the pump, then I recommend the changeout @ 75% of max. If max. is 10" then change out @ 7.5"; if max is 8" then change at 6", etc. etc. All depends on the pump.


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## flechenbones (Oct 2, 2009)

Understood. I arrived at 12" hg by 75% of 16" hg.


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