6.5 Regulated Return for Dummies

[JayTheCPA]

Lets skip the part of why I want to build a regulated return and simply focus on that I want to do it.

Goal: Need help with fitting sizes (ex: ID hose sizes, etc) and likely locations for the new parts.

Presumptions:
> OE fuel filter manager (FFM).
> Feed the Beast (FTB) mod with 3/8" fuel supply line from the OE FFM to IP inlet.
> Am considering a simple bleed-off valve that also dual functions as a check valve.


Am considering placing a 'T' for the bleed-off immediately after the FFM rather than at the IP inlet. Rationale is to have this part easily accessible and not buried under the intake manifold.


Questions:
> Where is a good location to tap into the return?
> What ID size is the return line?
> Aside from pulling off the intake manifold to find the return line, where does it route so that I can find it?
> What are most likely fittings I will need? So far am thinking just two 'T' fittings. One 3/8 ID 'T' for the supply side and whatever size ID for the return line; am I missing something?
> Should I add a check valve to the return line just to make sure the bleed-off fuel does not back-feed to the IP's outlet side?

If anybody has links to specific parts, please post them for consideration

 

[Will L.]

The return line is 1/4". Back when I was in go fast mode, and used a huge pump, I tried tying into the return line, but it restricted the flow coming out the pump and would cause stuttering. I suggest assemble your regulator system first, and run the return line back to the tank just through the fuel cap access to start. Include your one way in it, as they add restriction and will affect your settings. Once your good with it running, then try tying into the factory return. After a few attempts, I ran a new 1/2" supply line via sump fitting to the liftpump and used the factory pickup tube as the return. Loosing the sock of corse...

If your after the draft effect, that's out of my league.

 

[WarWagon]

Return line 'metal' is run under the intake passenger side of the engine and crosses over to the driver side via hose near the FFM.

Will's return line suggestion 'return to the cap area' has one major flaw that needs clarification as to why the next step is using the factory pickup as a return: draining the fuel system overnight and having to purge the air aka burn the starter down. GM has the return line submerged in fuel for a reason. This is so the system doesn't siphon all the fuel back to the tank overnight past the leaky fuel pump check valves leaving your IP full of compressible air.

Just remember both the pickup and return need to be submerged in fuel in the fuel tank when you are done.

Note any 'pressure' in the return line can blow the 1/8" return hoses off the injectors. Usually under the turbo for the most fire risk and real PIA factor to put back on. Use the clamps on the injector return lines for your project for extra safety.

 

[JayTheCPA]

Good inputs!


Am starting to lean toward returning the bleed-off fuel at the lift pump inlet (in my case at the LP pre-filter's inlet). Rational is:
> bleed-off fuel is post FFM, so it already has max filtration in case anybody is still using the OE tank filter.
> suction on the intake side of the lift pump might aid in pulling the bleed-off fuel through.
> for those whom use a LP pre-filter, the bleed-off fuel will likely have a higher temperature than the tank fuel and possibly reduce the opportunity of fuel gelling.

Only down side I am seeing to this is bleeding out the air after initial installation.


Thoughts?

 

[WarWagon]

'returning the bleed-off fuel at the lift pump inlet'

You didn't suggest this but for this thought experiment. If you tie this return into the factory return line then put that side of the return system to the pump inlet: This puts the return system under a vacuum... Any air leaks including the constant bubble stream from some 'good' injectors... go to pump inlet from return line.

Now if you just by pass the pump with the return regulator say from the IP inlet area to the pump intake with a separate 3rd line - the air is still the #1 concern. Use some clear line on a rotary vane pump and look at how it churns diesel into a stream of fuel and small bubbles. Not theory - just watching the bubble output of a carter roller vane fuel cooled motor pump. I suggest it's just vaporized diesel and @Will L. can explain what lighter part of the ULSD fuel mix is evaporating while pumping. Maybe it's like a soda being shook up?

It's not that hard to drop the fuel tank to put a different pickup and return in including sump it, the sock needs to go, and you need Leroy's bomb proof fuel level sensor that even I can't kill. @Burning oil put this fuel level sensor on your website...

 

[Burning oil]

Why would you want to do that?!!


Just kidding Im to lazy and my brain is to tired today to digest your ?.

Not sure if its what you would want or work for what your doing, but when I ran WVO I tapped into the hard line union on the frame under driver door (just forward of LP). I have the perfect fittings for the return line (similar to my LP bypass fittings) if you need a couple?

@WarWagon Im working on a new improved FSU.

 

[Will L.]

Good catch WarWagon. Doing it that way could allow it to draft air after sitting just a while. I was thinking back to tank just for temp testing on set up day, and doing the return to tank, so he could test it without modification, then tie in afterwards.

Returning back just before the LP it wouldn't give the same effect, so I would skip the return through fuel cap idea, I was picturing you returning through the tank.

To bleed out the trapped air making the loop, just hook a drain hose to the FFM bleeder and catch it in a Jerry can. Hook up a jumper to let the LP run a while with the engine off. If you can't get rid of the air after 5 gallons, you'll need to reconfigure the run.

 

[Will L.]

On returning the fuel pre-LP but not hitting the tank, and related to the "air" on return side from the injectors Warwagon spoke about:

We think of diesel fuel like it's a straight weight of liquid, it is not. Almost all fuel you are buying has a cut of biofuel, methanol, ethanol in it. Just like he mentioned shaking up a soda bottle you get the bubble effect from the lighter grade of the fuel that is in your diesel fuel. You can see this with this experiment, if you're brave enough to ruin your wife work girlfriends blender. Fill it up 100% so no air is in there , Turn it on and watch the bubbles.
Diesel fuel, even without the added alcohol, will aerate from turbulence. That is where the bubbles come from when going through the injectors, no outside air is infiltrating your injectors.

Having the return line link into The inlet side of the LP in a feedback loop has the potential to aerate the fuel. That is probably why I was assuming you were returning all the way to the tank, is to eliminate the aerated fuel.

The higher the flashpoint of any fuel, the easier it is to aerate. This is also what happens when fuel is pulled into a vacuum, and part of why when I suggest a fuel pressure gauge having a vacuum reading.

The reason the clear fuel line coming out of the IP is suggested is quick, and easy diagnostic with little outlay and ease of install. However, The next step in diagnostic if you cannot find the source of the leak, is to replace the fuel line going from the FFM to the IP. If no bubbles exist before the IP but do exist after the IP, rebuilding the IP is the fix. I don't normally suggest replacing all of the fuel line with the clear, because it does not last as long as the good stuff. 5 years is about it. However if you're going to do a feedback loop, without a settling tank, I think you should do it all and clear.

If @Burning oil or anyone finds any clear line rated sae30r9- PLEASE share the info- that would be what I would replace all my fuel lines with, and would suggest the same for all diesels.

 

[ak diesel driver]

On oil burning appliances it's pretty common to use what's called a tiger loop which IIRC takes out any air. It eliminates most of the return line.

 

[Burning oil]

If @Burning oil or anyone finds any clear line rated sae30r9- PLEASE share the info- that would be what I would replace all my fuel lines with, and would suggest the same for all diesels.

I run Tygon on my injector return hoses. I have some in stock too. Not sure what all sizes it can be had in. Any chainsaw type shop will have the smaller stuff for injectors.

 

[JayTheCPA]

I think Leroy answered the curiosity item with the bio return at post LP without any notation of adverse effects.


AK, de-aerator (TigerLoop) looks interesting. Anybody know of an automotive / OTR application?


WW, No, the Bleed-Off return fuel and IP / injector return fuel are no longer mixing (per earlier comments from Will).

The bleed-off point remains between the FFM and IP and the question is now where to put the bleed-off return fuel.

If any air creation is going to occur when the fuel passes through the LP pre-filter, LP, and FFM, it is going to happen even without the bleed-off, so we all are living with it. At worst the bleed-off will / should loop any bubbles and do nothing new in terms of their existence.



For recap / level setting, here is the current theory and a textual schematic:

> Fuel from the tank is via the OE line and goes from (optional) LP pre-filter, to LP, to FFM, to bleed-off valve.
> The bleed-off valve diverts fuel away from the IP (as necessary) to maintain a max of X psi going to the IP. At this point there are now two fuel pathways: IP and Bleed-off.

IP fuel:
> Fuel going to the IP continues along the OE routing to the IP, then injectors and / or return lines. No change here. Any air entering the IP return fuel via the injectors will travel to the tank.

Bleed-off fuel:
> Bleed-off fuel does *not* mix with the IP fuel and returns at point Y. Any air generation at the LP pre-filter, LP, or FFM might loop.


So far we have three candidates for Point Y:
> The tank via a new port. This adds complexity to the install but allows for any bubbles to percolate off per original design.
> somewhere in the fuel supply line. This reduces complexity of the installation but allows for any bubbles to remain / loop in the line until it passes over to the IP fuel supply. Nothing new here.
> the tank fill or breather tube. This reduces complexity of the installation, but allows for air to enter the fuel just upstream of the IP if the bleed-off valve does not do a good job of sealing while closed and not running the motor.


Am still leaning toward Point Y somewhere in the fuel supply line. Rationale:
> theoretically, any bubbles created by the LP pre-filter, LP, or FFM are likely going to flow over to the IP (am using the theory that the bubbles will follow along with the larger quantity of liquid and the flow to the IP is the larger quantity).
> this is along the lines of original GM design and is *not* introducing anything new.


Thoughts?

 

[ak diesel driver]

I have one on my genset and no return to tank

 

[Will L.]

I've seen them in use, but not on mobile platforms. My understanding is there is a modified one as part of a fuel pump for high perf diesels, but I haven't used one.

 

[WarWagon]

Complexity for a decision is an excuse in this Rube Goldberg thing you already want to do. Why start compromising this system on the drawing board by reusing aerated fuel? You want to assume you get less bubbles - by why deal with bubbles on the inlet side of the pump at all? You can't assume the second pumping of the same fuel isn't going to churn more bubbles out of that fuel. So now you have input bubbles plus the normal amount the pump introduces.

It's bad enough that the small bubbles may not make it out of the fuel in the tank before getting sucked up again. the OEM tank has a fuel cup for low fuel situations and grades. This puts the return close to the pickup increasing the chances of bubbles being sucked back in. It also generally warms the area rather than the entire tank of fuel - good for gelling, but, bad for PMD cooling.

Hot fuel - we can go off the rails here. You are running the pump on hot fuel perhaps increasing it's temperature. I suggest hot fuel would allow more bubbles to form during pumping. However this may be a cooler running system overall as the pump isn't stalled at max pressure. Wait, most regulated pumps just return the fuel to their own inlet so what's the point of the remote regulator again when you feed it back to the inlet?

Keep in mind the OEM lift pump is a plunger pump that isn't known for the bubble stream of rotary vane lift pumps. (I can't comment on gerorator pumps as I never looked that close at the output of one.) Then the fuel gets pumped and aerated a second time by the IP vane pump and in the case of the DB2 excess pressure is put back into the IP inlet.

Biodiesel is not the same as ULSD. I caution one to keep this in mind and do not assume tests or experiences on either fuel translate to the other. ULSD works fine on brass and on our fuel tanks, but, Biodiesel turns brass green and eats the lining off the early 1990's era tanks. Does ULSD bubble more than B100 in a rotary vane pump? What about B20, B5 etc? Cutting wet B99 with ULSD will rain the water out of it in the FFM and tank.

This said I am assuming you want an improvement with this design when it's all said and done. Not saying AirDog, but, the name and the gimmick is less air in your fuel.

 

[JayTheCPA]

This said I am assuming you want an improvement with this design when it's all said and done.

More like a tweak on the OE design to address what we know are weaknesses.

Am not sold that there is anything we can do about either the LP pre-filter (or OE tank sock), LP, or FFM creating bubbles as part of normal operation. Even if this is the case, we are all living with it and I am just not seeing anybody experiencing negative issues. Also not really sold that bubbles from these elements are an issue otherwise we would have tackled it a *long* time ago . . . Yes, these elements can introduce air by way of a leak, but when this happens the motor reacts and we fix the leak.


Did follow-up with the shop last night regarding our discussion and the owner (Master ASE) is leaning toward dumping the bleed-off return fuel into the tank mostly from a 'just-cause' and 'what-if' a leak at the FFM occurs approach. Even if a leak at the FFM happens, the IP is still likely going to ingest air anyway, but at least some of it might route back to the tank if the bleed-off dumps there.

Definitely not the end of the world to add the extra line back to the tank as it is only money for those of us who pay for the wrenching . . .

Aside, respectfully disagree about complexity avoidance as an excuse. Generally, complexity adds more opportunity for failure in a system (ex: more moving parts, etc) which decreases its durability / reliability, so a personal goal remains to KISS. And, Yes, I get it that a regulated system adds complexity, yet at the same time I want to minimize the opportunities for failure from longer lines, more parts touched during install, etc

 

[Will L.]

The return to tank is definately a better idea IMO, like I mentioned, I just assumed that's where you were going with it. Fuel pumps push- they are not good vacuums & the more vacuum induced to fuel causes it to aerate more. Always put fuel pumps as close to the tank as possible. As much as I H8 in tank pumps- it is the best theoretically.
If you are going to add a line anyways, leave the tiny return line alone. Use the current supply line as the new bleed off return line, removing the sock. Install a new sump supply line that is 1/2" out, through the upgraded LP, and don't reduce until you are at the IP. As in get a threaded king nipple (barb fitting) that is 3/8 thread and 1/2" hose.
Install a quality spin on 20-30 micron spin on pre lp, then sequential spin on filters that take it down to 5 micron.

If it is so cold where you live that you need a preheater, put a separate on right after the tank so both pumps and all filters get the benifit. The water separator works best after a heater and lift pump but before final filtering.
The oil industry btw heat ful to 195f to drop out water... That's the name of the seperation tank or line "the 195 tank".

The stock FFM is a relatively good design, but if you are spending the $ to make a good upgrade then do it right from the beginning IMO.