Ok I’m "getting the T-shirt" as Tugly says.

Racor PS 120 3/8" installed on my Excursion several months back, only a couple 1000 miles on it.

From the install date I had air entering the bowl from the inlet, small drops that dance around the incoming fuel. As the fuel level in the tank drops the bubbles increase.

Determined to rid myself of these bubbles I rerouted my fuel line from the OEM pre pump hard line back about 2' on the frame rail so the fuel line made no turns or transitions, 5/16 OD factory hard line to 5/16" hose then onto a 3/8" barb fitting at the left side of the Racor. At the same time I removed the sender from the tank again for the 5th time (long story) and reconfirmed all connections in the tank were good, pressure tested the entire system to 60 psi with air, no leaks.

Still bubbles in the Racor. Not enough to fill the bowl but enough to make we think WTF. I decided the transition from the factory steel tube to the rubber and back was a problem so I dropped the tank once more and ran straight 3/8” hose from the pickup to the Racor inlet. Then again I ran straight hose from the Racor outlet to the pump inlet. Same story…


I am not sure what the deal is or if there even is a “deal”.

I am pondering two things to resolve these issues once and for all.

1. Move the pump into the tank into a tank bottom mounted tray.
2. Add a centrifugal fuel pump to the supply line and install a dip tube on the racor to within 1.5” of the bottom of the PS-120. Then tap the housing for a 1/8” vent line to effectively turn the PS-120 into a surge tank.

But then I found an article that contradicts my understanding of the fuel system as I know it.

See I don’t think there should be any bubbles there and I would agree there might be a problem with my install but I can’t find it. All connections are double FI clamped with adequate coverage of the nipple they are attached to. The way it stands now there is one hose between the Racor and the pickup then a short 4” ish piece of stainless tube attached with a Swagelok 3/8” compression union. This fitting is submerged below ½ of a tank so it shouldn’t really even matter.

Anyway, give this a read and tell me what you think.

https://www.parker.com/literature/Ra...iesel_Fuel.pdf

 

When I installed the Racor PS120 I removed the hard supply line altogether and ran 3/8 diesel fuel rated line. In addition, I put diesel friendly sealant on the threads for the barbs screwed into the Racor and double clamped the fuel line with fuel injector style clamps instead of standard worm clamps.

I see you have done a lot of the same things though. Perhaps there is a small leak where the barb is screwed into the Racor inlet? It is hard to tell from the video, but the inlet should be the lower of the two ports on the Racor, is yours set up like that?

I have zero air getting into the fuel system with the way I set it up.

 

The "wtf" is just basic physics.

Diesel fuel contains about 10% dissolved air.

When the fuel is in a container like your tank you can not see it because it is dissolved in the fuel, when you put it under pressure and pump it , it remains dissolved. However when you then plump it into that glass bowled chamber there is a pressure change due to the change is diameter. That allows the bubbles to come out of the solution and why you see them.

It is exactly like opening a carbonated beverage and pouring it on a glass and watching the bubbles magically come from the bottom of the glass where all you see is liquid. Obviously there is no "air leak" at the bottom of your glass

 

A few things come to mind. I went 3/8" fittings to the pump, used double 45's for elbows, made sure they were full-ported, and definitely double-clamped the hose to the pickup. I need to see if I still get micro-bubbles, but I can say for sure I don't have air-in-fuel symptoms.

 

Sous, Yes my setup sounds just like yours. Straight shot single hose to the lower inlet on the left.

Camo, Agreed however my personal experience in the diesel engine field tells me I should be able to eliminate the bubbles. I commonly use a piece of clear hose for troubleshooting the machines I work on. If I saw the bubbles like I am seeing I would try and rectify the problem We don't use clear housings so it's very likely I am just seeing the bubbles pop out of suspension when entering the larger chamber of the PS-120.

My centrifugal supply pump would solve the whole problem (if there is one) by slightly pressurizing the PS-120 then bleeding any air out the orfice while the stand pipe would prevent any floating bubbles from entering the outlet.

Tugly, The fittings are straight 3/8" full port sealed with gasolia and then painted over with liquid electrical tape. The bubbles have to be entrained air...

 

If you run a section of clear fuel line the same diameter as your other fuel line before the chamber I bet you will not see any bubbles passing through the clear line.

The clear line would show bubbles that are present from a leaking fitting but because the line is the same diameter ( and pressure ) the dissolved air will remain dissolved until it enters the larger diameter chamber.

 

I had a ton of bubbles in my Racor when I first put it in. After much hair pulling and cursing of the diesel gods, I found it to be a significant blockage in the outlet fitting coming from tank, due to a piece of plastic debris. Once I cleaned that out, all was fine; not a single bubble since.
Now, I have a different setup than most. I cut a 3" diameter hole in the bottom of my tank ( right at the center) and installed a bottom feed sump bowl. ( A small aluminum cup-sized bowl bolted to the bottom of the tank.) This has a 3/8" barbed fitting on it, and directly feeds the Racor from there, with a 3/8" fuel hose. I completely bypassed the in tank pickup and quick connect fittings, etc.. I also rerouted the return line in the tank, to one back corner, to get the return fuel away from the bowl. Sort of a half-a-hutch mod.
I had underestimated the amount of fuzzy plastic chip debris that cutting the hole with a dremel had generated, and a left over chip was lodged in that 3/8" fitting, blocking most of fuel flow.

 

I think you are right.

The truck ran flawlessly on a recent 700 mile trip in the 100* heat.

I really wanted this out there to get a group consensus on the possible issue.

Side note:
Is it possible to have the foot too close to the floor of the tank?

 

Couple of thoughts and questions...

1. The presence of dissolved air can become obvious when the liquid is in the kind of pressure change conditions as described by pirate444_camo and carguy3j... it's just physics.

2. If your bubbles are coming from #1 above, then you have nothing to worry about because this is on the suction side of your pump, and any air bubbles will disappear again (collapse only, not redissolve into the fuel) on the discharge of your pump once the fuel is forced into a much higher pressure condition... IF the bubbles are from the physics issue in #1 above.

3. Are you certain that you used adequate diesel-rated pipe dope to completely seal your barb connections into the PS120 head?

4. Are you sure that you have a solid seal between the clear housing and the PS120 head?

5. With the ridged teeth around the perimeter of your pickup foot, as long as you don't have the foot pressed HARD down onto the tank bottom (to the point where the screen is pressed against the bottom), there should be more than enough open area between the teeth and the tank bottom to be equal to or greater than the open area of your pickup tube. In other words... maybe... but only if the foot is shoved down hard against the tank bottom... just touching the bottom should not be a problem unless you have trash in there sealing around the openings between the foot's teeth.

 

I really think the foot to floor clearance could cause an increased suction on the line, which would have a severe negative pressure effect on the entire hose/ps-120. I have measured all this several times due to loosing the abiltiy to draw down as much fuel as before. Several times I have taken the tank back down to investigate and have found a new cause each time. I have always measured to apply some "pressure" to the foot on the floor. I really mean if the measurement was 17 xx/XX inches I made sure it was -by 1/16 to 1/8". I might try the other way as the fuel sender has died recently when reading around half tank so down it again it will come.

Now with the 120 installed I will remove the screen from the foot altogether as I don't need it in there I would rather those particles make it to the 120 where they can be removed.

I would really like to put in some sort of baffle to keep the pickup flooded, with the excursion tank there is allot of room for sloshing. I might try to build something that accomplishes that. A sump is out, I don't want to have to modify the skid plate/tank. I have though about just strapping the bottom of a oil jug to the pickup tube. Anything to keep the fuel from running from the pickup.

I never had any of these problems with my 2 other superdutys.

 

I have a word of caution on taking this approach. If or when your pickup foot crumbles, it WILL plug your pickup tube with plastic crap. I KNOW it will because I've had to live through it myself.

To avoid this issue altogether, you'll need to extend the hard tube down to (almost to) to bottom of the tank, but make sure it doesn't contact the bottom to avoid rubbing-related wear on the tank liner.

In my Excursion, I did the H&H mod and removed the screen, and ended up years later having to replace the pickup foot and I went ahead and left the screen in place. It's only like 1/8" mesh anyway, just small enough to prevent plugging you pickup tube, and will not create any resistance to your pump picking up the fuel.

 

A blocked vent on the tank could contribute here. Placing the fuel under stronger than normal negative pressure before the pump will allow more of the dissolved gasses to emerge. Explains carguys experience too, as the plastic blockage increased negative pressure on the fuel before the pump.

Pull off the "gas" cap to allow unrestricted tank venting and see if the bubbles go away.

 

F250___ I got the foot t-shirt when I dropped the tank on time #3 I think. New foot installed but you are right on with your caution.

aawlberninf350 Great point on the cap. I have not thought about the cap. Thinking about it now is the cap even vented, I think there is some sort of rollover vent on the top of the tank?

 

Since we do not have an Evaporative Emissions System ( as gas vehicle would), these tanks are not sealed. There is one vent tube at each end of the tank, and the fill tube has its own 3rd vent. I think its highly unlikely that all 3 would be plugged up, unless the truck had been submerged in deep mud. ( or spiders..... Mazda issues recall because spiders invade fuel tank causing fire risk.)

 

I agree that it would be very unlikely, easy enough to test though.