Fuel Vacuum Issue

[Dartanyon]

Howdy! I'd appreciate any thoughts on a couple of options ...

First, the background: A new to us Norseman 447 with a 2011 Yanmar 4JH4-TE (Turbo) with 582 hours. New fuel lines in 2011. Racor 900 series primary / 10 micron filter. Pick up about 4' lower than the filter give or take 10%.

I was changing the fuel filter over the weekend, and decided to add a vacuum gauge to the Racor to get a better view into filter condition, and potential fuel system problems. I fired her up at the dock, and in idle was pulling 6" of vacuum with a new filter. I thought that was high, so I re-check my installation, and switched fuel tanks to make sure there wasn't any potential blockage to the pick up. Fired it up again still 6" vacuum. Start tracing back the fuel line looking for kinks and realize that a pump that was added to allow fuel polishing is permanently in-line. This seems like the most likely culprit since the lift pump is having to suck fuel through it.

Now, I surmise that the RIGHT answer is to plumb that pump on to it's own branch, and leave the primary line unencumbered. (Tell me if you'd do something different.) However, in the mean time, while I'm gathering the bits to make that happen, and preparing myself mentally for the diesel I'm bound to get all over the place, and the air in the lines ...

What temporary solution do you think would cause the least ill effects?

1 - Run it at high (er) vacuum, as it has been run for the last 5 years (and 580 hours). -OR-
2 - Run with that fuel transfer pump "on" and putting positive pressure on the system.

The pump is very small, has absolutely no markings, moves maybe a 1/3 gallon a minute through the Racor when the loop is closed back to the tank. I assume relatively low PSI, but that's an assumption.

Of course the solution to the temporary problem, might be don't do anything temporary and fix it right, which I accept, but don't like

Thanks

[jamhass]

On our older Volvo, our priming-polishing pump is on a branch, and with clean filters we draw 0 vacuum. My suggestion is replumb it correctly.

[Scot McPherson]

As answered by yourself and by jamhass, the right thing to do is to branch it off. That really shouldn't take much time or expense. You just need two Ts (one for the fuel and one for the fuel return), hose clamps, and perhaps a couple feet of fuel line. The amount of work should be less than an hour.


To answer your specific question about what to do in the interim until you get to it?


Nothing, the fuel lift pump may be working a little harder, but I don't think it will hurt it short term, I think it's more of the longer you leave it that way, the shorter the pump's life will be.


I do recommend just spending the less than $50 to do it right.


Now having said that, and it's just something to think about. The more "things" you put on a fuel line, the more resistance the fuel line will create. There comes a point where you want to increase the ID of your fuel lines to relieve that added resistance. Just a 1/16th of an inch should do it. The reason is, those T's have a smaller ID than the hoses, and when you add more things that reduce the ID, the overall vacuum needed to draw a proper volume of fluid increases. Adding more valves and T's or even just male to male host connectors and they start to act like baffles.

[Cheechako]

I had one boat with a fuel pump in line rather than branched. I didn't have a vacuum gauge on that boat but had no problems. But, I'm in the camp of bypassing the electric pump. Just a 3 way valve prior to the pump, T after, ought to do it right?

[David M]

A pump not running with fuel flowing through it is going to create resistance. Put in a bypass.

[Dartanyon]

Of course, you're all right, it should be, and will be repaired properly by sending the pump to it's own loop. I was thinking of doing 2 three way valves, one on either end of the pump loop, to completely isolate it. It's probably unnecessary, and might even being flying in the face of keeping it more simple than using a valve and a T.

My hesitation only really comes for the location of the pump under the galley cabinets, from the sole I can either see it, or touch it, but not both, and it just looks like it's going to lead to diesel in the bilge, there's room for a couple of diapers underneath it, but no catch vessel of any consequence.

I suppose I could close the tank valve, use the pump itself to move as much fuel out the bottom of the racor as possible then remove the fuel line from the filter terminate it in a jug in the bilge and hope for the best.

Thanks all!

[Lepke]

I have Detroits, each with an electric inline pump (normally off) and have zero vacuum with a new 2 micron filter in a Racor. But my electric pumps are rated 35 gallons an hour. Many small electrics are rated under 10 and could be more restrictive.
Also, vacuum gauge needs to be directly after the filter. If too close to the pump, it will be showing suction vacuum.

[DeepFrz]

Four feet of head will give you about 3.5 inches Hg.

Are there screens on the bottom of your pickup tubes? If there are they could account for the added vacuum and if there are the only good place for them is the garbage can.

[boatbod]

Some pumps aren't a problem with flow through, others are. The only thing you can do is bypass/remove the pump and try it again. If the problem persists, you might look for a clog somewhere in the lines or inside the filter itself. Racor 500 have an aluminum ball inside the turbine assy that I've seen get clogged with sludge.