Fuel Elbow vs. Plumb El - Vacuum Gauge Up or Down?

The fuel elbows you are describing are indeed very restrictive to the flow of whatever is flowing through it. But it is all relative to the flow needed by the engine. Have you changed the engine? Have you added any restrictions to the fuel flow?

The safest way to deal with the remote fuel restriction gauge, is to use an electric gauge, and leave the fuel where it belongs. Another choice is a gauge isolator. None of the professional racing organizations that I know of allow fuel to enter the passenger area. Do you think they are all crazy, or do you think there is some merit to their rules?

Hi Bob,

No I haven't changed my engine. I just want to be able to switch between fuel filters when one clogs without having to shutdown. No other restrictions than the additional 4 elbows, one T and one 3 way valve I would be inserting. The engine is a 23hp diesel on a sailboat. Do you think I would need to up-size to 3/8"? It requires about 2 gph flow.

The fuel restriction gauge is not remote but sandwiched between the filters. It is all in the rather small engine compartment under the galley sink. I would do the electric sender if I could find one. I'd much rather have my gauge at the nav station. Any ideas?

2 GPH! Cadillac fed a 429 cubic inch engine with a 5/16 fuel line, and ran the engine over 5000 RPM. Your engine should be fine with the smaller line. the digital pressure - vacuum gauges that I am using are sold by Class 1 out of Ocala fl. but they are designed for water pumps. Dwyer is a manufacturer that sells digital pressure-vacuum gauges. they may have something for you. Another option is a latching vacuum gauge, that will show the highest reading after the event has passed. That gauge would be fine in your setup.

Thanks Bob. I already have the latching vacumm gauge but was trying for a remote so I wouldn't have to kneel down to stick my head inside the engine compartment to get a reading.

So you don't think it matters if the sender of the vacuum gauge is against fuel or air? It would work the same in either case?

As long as the internal components of the sender are not harmed, no problem. Remember that there will be limited air in there. Fuel vapors will be there. Check with the sensor manufacturer.

Resistance to FLOW is the determining factor here.You are simply monitoring the vacuuum level,so very little flow is occuring,except during a change of vacuum in the system, and this occurs very gradually, so it will not make a significant difference which type of fitting you use.

The flow that I am refering to is the expansion or contraction of the Bourdon tube inside of the guage when differential pressure changes and the needle moves; very insignificant.

As for position, mount the guage higher than the fuel to prevent fuel from getting into the Bourdon tube.

Hope this is helpful

HTRN

what happens if the fuel gets into the Bourdon Tube?

Nothing, its just a coiled tube that acts as a spring. In instances where we have long runs of tubing oil, water, or fuel I sometimes bleed the air from the line. To me the gauge seems to read more accurate.

Depending on the position of the guage in relation to the fuel supply, you could get an error due to the weight(head) of the fuel above the guage.

If you want to remotely monitor the drop across the filter, then use a differential pressure switch rated for fuel and attach it to an indicator light.

At what pressure do you wish to switch filters?

Carefull selection of the D/P switch will give the desired results.

Cheap and simple.

HTRN

If you end up using a "normal gauge" (mechanical type) that you would find in any hardware store, etc. this will be a Bordon tube design and actually would be much better off if you bled the air from the line instead of having air pockets trapped in the system anyhow. So the answer to one of your primary questions is no the fuel will not harm the "sensor· that is actually a coiled tube much like a spring. If you opt toward an electric sensor, thats a new subject. You will need to be sure the sensor is compatible with fuel, as there will be a diaphragm involved.

I would suggest that you go a couple extra bucks and get a glycerin filled mechanical gauge to accept the pulsations that are normally accosted with a fuel gauge.

Also remember that when sizing your gauge, the most accurate point of measurement is 30-70% of its range. Do not install a gauge in such a way that you are always reading its lowest or highest point.

Something to keep in mind.... I am assuming this is a small diesel engine. You not only need to supply the engine with the fuel required for running, but also to re-circulate to the fuel supply to keep your injectors sufficiently cooled.

If possible go with flexible hose fire rated by USCG with the fittings of your choice. The most common in this case would be the reusable, medium pressure, inverted or JIC connections. This hose is steel braided and has a blue colored exterior jacketing.

Sounds expensive, but not really that bad. You can easily build blocks to get away from a bunch of tee's and nipples that will be nothing but a headache that very rarely goes away until you find a way to eliminate as many unnecessary NPT joints as possible.

If you could provide some sort of detaied drawing or possibly a photo, I'd be happy to access the spares I have avalible to offer a solution with part numbers.

Brass fuel fittings are unually drilled bar stock and suitable for very high pressure and are resistant to vibration caused failure. Water or general plumbing fittings should NEVER be used for any fuel or combustible vapor.

I personally do not recommend using NPT connections in fuel lines of any kind. It is difficult to keep the connections fuel tight without some kind of thread sealant. With hydraulic and fuel lines ,even very tiny slivers of 'teflon tape' can cause complete failure of injectors and float bowl chaek valves. Compression fittings, flare fittings and straight thread 'O' ring sealed hydraulic fittings are best for high integrity applications. These do not use 'thread to thread' contact to effect a seal, but rely on a positive metal-to-metal seal of a precision joint positively held in compression.

NPT threads rely on deformation of threads to seal. The manufacturing tolerances are generous and do not guarantee a tight seal without some kind of sealant. Often the bottoms of the threads are not sealed and fluid leaks through that gap.

One also has to consider vibration and pressure pulsation effects. Copper lines will work harden and fail from fatigue stress if the pressure ocsillations are more than 10-20% of the rated pressure of the tubing. In the application describled, pressure is very low, as are the pulsations, so that will not cause a problem. Vibration is the hidden danger. Copper fuel lines MUST be clamped and restrained to prevent vibration caused flexing. Connections between the engine and metal fuel tubing should be via USCG rated flexible lines. Remember, leaks can develop without warning ,even after long service if inappropriate installation or materials are used. I would use stainless steel tubing and compression fittings in this application--below deck, marine environment, hazardous liguid.

All the fuel line fittings I have seen...fuel valves, electric fuel pumps, fuel filter assys all have NPT connections in and out. How would you suggest I avoid the use of NPT connections? I've always used teflon tape without issue. There is always the secondary filter to trap any teflon particles.

If you are saying never to use general plumbing fittings because they require some sort of sealant, I agree. I use teflon tape. Commercial & residential boilers of both gas and fuel oil are always plumbed with NPT connections with black pipe and usually teflon these days. I'm sure there are conditions more demanding than I am aware of that may require alternative methods but not a small fuel system on a small boat.

Thanks for the advce though.

It's really like most anything. If you apply the sealer or Teflon like you have a clue, then its ok. BUT I'm sure we have all seen screw ups that other people have left behind in the past.

And depending on the situation and the fuel, I would agree with the poster. But in your application on a 20-30 hp sail boat????

Tim,

I'm the poster...what is your question about my application?

My apologies, It should have read I agree with Keith. (And then it probably makes more sense huh?) But in your application with the little sailboat engine I don't think you are going to worry with anything other than your brass NPT connections, etc.

Just be careful and do a good job. The fewer the fittings the better off you'll be.

For a solution to worrying about teflon tape strings being caught in places they might do harm, try this. Use thread sealing paste with teflon instead.

I am very much aware of the discussion given by the guest,I learned so much and I have nothing to suggest what I did is just read the discussion and the suggestions of every one.

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