Would this cause high fuel vacuum

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well, i'm not a Diesel engine guy, but I am a hydraulic guy and deal with pressure, flow, pipe, tubing and hose every day. your 1/2" copper tubing has an inside area of .1492"sq. Your 3/8" hose has an inside area of .1908"sq. so your new hose is actually larger than your old tubing. Start looking somewhere else. Some of the earlier comments may hold the answer. Possibly a kink in the hose, debris stuck in the hose, a barb fitting issue, etc.
PS, I pulled this info from the Womack Fluid Power Data handbook. Its a publication that all fluid power engineers carry with them at all times. Saves a ton of work on a calculator.
Good luck
John
 
start with 1/2 inch hose, hose barb hole 3/8 inch hole..... ??
start with 3/8 inch hose, how barb hole 1/4...??
 
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Couple questions
Did you replace all of the hose? Before the Racor and after? Was the hose properly rated for vacuum? Stiffer sidewall?

The fact that you have normal readings with no filter and then high vacuum with a filter (assuming you have ruled out the filter) could imply that when suction is applied with no filter the hose is keeping shape. When the filter is installed the additional restriction causes slightly higher vacuum after the Racor. This may be just the difference to collapse a hose and then further increase vacuum to very high levels. Could also happen if you have a near kink.
 
KnotYet said:
Well close, a typical 3/8" hose barb for petroleum use has an ID of 0.30".
Click to expand...

Yup, close. Each time a hose barb is involved, the the flow rate is decreased.
It would be better if he started out with 1/2 inch hose and the 1/2 barbs.

Alas, I too am confused, when he removes the Racor the filter he does not have any vacuum. Maybe the hose is collapsing under vacuum.
 
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OldDan1943 said:
Yup, close. Each time a hose barb is involved, the the flow rate is decreased.
It would be better if he started out with 1/2 inch hose and the 1/2 barbs.

Alas, I too am confused, when he removes the Racor the filter he does not have any vacuum. Maybe the hose is collapsing under vacuum.
Click to expand...

The first part could be right at the barb connections the hose insides may have been scraped, partial blockage.
Your second part, removing filter was well answered with the cumulative effect causing the vacuum reading as in caused by filter and???
 
I have decided to pull all the 3/8 and put the 1/2 copper back. With the push lock fittings in 3/8 hose there is a restriction. I will still need hose so that to will go to 1/2. I plan to do the swap this week after work. I will share my results when its is done.
 
The symptoms sure point to the filter elements. I assume you used new elements but where did they come from? Were they factory Racor elements and were the bags they arrived in hermetically sealed. Are you certain the elements were not bootleg? or imposters?

pete
 
The filters are OEM Racors. Tonight I began the not so fun process of installing the copper line. The chase is not much bigger than the pipe. The battle begins by crawling into the port side hatch in the lazerette. Then taking the coiled copper and in a few feet taking all the bends out so I will with effort go in. I am guessing I am about half way through. My arms finally gave out for the night.
 
"If I remove the elements there is no vacuum at all. I have 30 micron filters in now with 12hg."


Two additional thoughts (assuming the gauge is correct)
Are you sure the elements are actually 30 microns? Try a new set.
Are you sure the elements aren't waterlogged ?


Restrictions do add up as mentioned but mostly towards the limits of flow for a given system and you are not near that yet. In that regard, I would look for a bad piece of hose or a mis-made fitting however you have already said that there is no vacuum when there are no filter elements in place.
 
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I am just finishing up installing all new 1/2 ID fuel lines. What a MF it was getting the coiled copper through the chase. The only hose I have left is the one from the filters to the lift pump which has an SAE fitting that I need to change. As for filters I have now tried six OEM Racor filters @ $10 ea. so I am very sure it is not a filter issue. The Racor set which cost a boat buck is also brand new. I will let you know the results after I get it running this weekend.
 
I'm in the 'it can't be the hose vs. tube diameter' camp. I've used 3/8" diameter hose on on up to 450 HP engines.

Was the high vacuum recorded at idle?

For clean elements, there should be no change in vacuum regardless of micron rating.

Too late now but I would have run a separate fuel source to the tandem Racor to rule out the hose/tube. If it were a hose diameter issue, removing the elements would have no effect.

When installing hose on barbs, it's possible to shave off a sliver of hose which can act like a check valve. However, the filter elements would have no effect on this, so still a bit of a mystery. I'm leaning toward a defective or contaminated Racor housing, or valve, since you said it occurs with either of the two housings on line, right?
 
Okay, he is returning the system to "pre trouble" condition.
Let us all wait for the results.
I forgot, did he rebuild the Racor filter bodies too? That is something to consider for at least one side of the duel filter set up.
As I recall, he did not have the vacuum problem before he started changing out the fuel line?

We are starting to run out of suggestions.
The only other suggestion include something (crud) in the fuel pick up? Blow it backward into the tank??? Or perhaps swap the supply tank?
Someone has suggested to borrow or buy a 'known' vacuum gauge?
 
Even at the engine producing 100HP at cruise (about what my twin Perkins use at 9 SMPH between them), and even allowing for a fuel return of say 50% (i.e. as much going back return as is used) the flow rate will be about 5 gallons per hour. This is a peanuts flow rate, so it should not be the hose diameter. If you take the filter out and the rate drops to zero, then the issue is within the racor bowl. Please remember that there was a series of racor filters produced that required a spacer, and if you got some of these and did not install the required neoprene spacer, it could be the problem.
 
Do you know where that spacer is or goes? Or is that another call to the Racor tech.
 
Good thought. But, I think the lack of that spacer would cause the filter to be bypassed, allowing it to flow unrestricted (and unfiltered) by the racor primary filter. It is hard for me to see how the absence of the spacer would increase vacuum.

Something isn't adding up in this picture. I'd want that vacuum confirmed to exist with the filter in by another gauge -- and confirmed to be absent by another gauge. Gauges are relatively cheap.

After that was done, if the problem really did occur with the filter present, but not with it absent, I'd dig deeply into that filter.

In my mind, the way something like this happens, if the symptoms are confirmed, is that the filter sits to high and its top rim blocks the fuel outlet into the filter element, or the filter sits too low and blocks the discharge, or there is some debris or something else preventing it from sitting correctly and one or the other is being blocked by the top or bottom of the element. Or, maybe in some way I can't presently imagine, the filter element is impacting the water float.

Maybe there are two of those spacers, when one is needed, or one of those spacers when none is needed?
 
Where exactly are you measuring the vacuum, and with what gauge?

If filter, no filter is what stimulates the problem, then I would be focused on the filter body and how you are measuring. Those filters are somehow blocking flow way beyond the effects of filtration. Also consider that you are not measuring what you think you are measuring.
 
I agree with Steve D´Antonio. There is no way that the length and diameter of the fuel line are causing this problem.

The problem has to be some specific blockage that only manifests itself when there is a filter cartridge in the housing.

Unfortunately it looks like the PO is wasting effort re-running the fuel line.

I suggest a second vacuum gage on the tank side of the Racors - that way you would have positive indication of whether the problem is in the fuel line or in the Racor setup.

Nick
 
Unclematt said:
Do you know where that spacer is or goes? Or is that another call to the Racor tech.
Click to expand...
The spacer goes under the filter. If it was not used, then the fuel would bypass the filter and there would be no high vacuum, however if it was used, and put on top of the filter rather than underneath the filter, it would occlude the fuel flow.
 
Here is what the issue was. The inline fuel pump used for bleeding was my restriction. It is a big 125 gph pump. I plumbed up a bypass and all is well. That was quite the education I know my fuel system intimately now which is a good thing.
 
That doesn't sound quite right.

The lifter pump is downstream of the racor, between the racor and the engine?

The vacuum was measured at the racor?

If this was the case, the pump couldn't have caused the vacuum by being a restriction, right? If that was the case the vacuum would be measured between this pump and the engine lifter (or injector) pump.

It is possible the electric lifter caused the vacuum at the racor, but not because it, itself, was a restriction. The way it would have caused the vacuum is because the electric pump was trying to pull fuel through the filter faster than the fuel or upstream plumbing could deliver it.

This could be, for example, a relative restriction in the racor, the fees from the tank, or the tank vent. And, since the removal of the rqcor filter element relieved the vacuum, it remains a consistent suspect.

I wouldn't expect a 500gph rqcor, properly configured, and with a relatively clean element, to act as a restriction when fed by a 125gph pump.

I don't think two lifters in series can develop nearly the same flow as in parallel. But, even if this electric lifter and the subsequent engine lifter weren in parallel, I'd expect the racor would be okay.

I think you lowered vacuum by lowering demand. And, that's fine, actually, but gets at someone's earlier question about how the engine is performing.

If you've got no vacuum at the slip...but fuel starve underwaynor at high throttle due to a construction proximal to the racor, you've still got a problem to solve.

Happy hunting!
 
Gkesden:
I suspect that the bleeding pump is located between the fuel tank and the Racors (as it is on my boat). In this way, the lift pump was trying to suck the fuel through the non-operating bleeding pump and it is difficult to pass fluid through this pump if it is not turning.

My boat also has a bypass valve plumbed in parallel with the bleed pump.

What still does not make sense is the claim that removing the Racor filter cartridge reduced the vacuum to zero. Perhaps this was a mistaken observation.

I am very happy that the OP reached a definite solution and especially that he shared this with us. One more piece of knowledge to help us keep things working!

Nick
 
The bleeder pump should have an internal strainer/screen that is partially clogged. Find a diagram and clean it
 
The electric pump is back at the fuel tanks and is only used to bleed the system. The mechanical lift pump is on the engine and it to is new. By adding the bypass the problem 100% disappeared.
 
Sounds good to me.

Many bleed pumps have near zero resistance to fuel flow when off, so checking that it doesn't have a clogged filter or some other problem might be a good idea, especially if the problem is new vs newly observed (something changed).

But, there are plenty of pumps, often times transfer pumps the filter. ed pumps, that do have resistance to flow.

Still don't understand the apparent red herring with removing the filter.
 
Priming pumps are typically mounted between tank and primary filter, that's the only way they would supply fuel to the filter. So that part makes sense.

Some electric lift pumps have an actual pleated paper element, the cylindrical Facet is one. Most have a screen; worth checking. Most are fully capable of being installed in line and present little if any resistance when not running.

But, as others have noted, how would removing the elements from the Racor have an affect on the resistance of the pump?
 
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