VP44 return line question

[QuietWyatt]

Hi there, First time posting, but i have been reading posts for a while now, really appreciate all the help this forum has given me in doing a 1998.5, 5 speed, 24V Cummins swap into my 1976 Chevy 3/4 ton.  

 

I am now working on the building a fuel tank, I'm halfway done building it.  I just was about to drill holes, and I've run into a question i have on where I'm going to run the return line from the VP44, and also from the Fass 95g lift pump i have installed. 

 

This picture represents where I would like my fuel tank to be, its 65" wide, 32" tall, and 6" deep

 

I have scrapped the idea of using the factory Chevy saddle tanks, as i want under the flat deck tool boxes and those take up valuable real estate. 

 

My question is where the return line should be going into the tank from,  I know the VP44 is a very sensitive girl, and i don't want to disrupt it in causing premature failure.  My plan was to plum the return line into the bottom of the tank, thus creating less aeration when the fuel returns.  But since the tank is so tall, after calculations, the return line will have to overcome about 0.866 PSI of head pressure from the fuel (if the tank is full), which isn't a lot, but it seems the return line should be 0 PSI.   

My other option is running the return line up and dropping in from the top of the tank, but i will still be overcoming 2.5 ft of head, which equates to the same 0.866 PSI (all the time, rather than getting smaller as the tank drops).  

My other option is running to the top of the tank, and then having a pipe inside the tank, bringing the fuel too near the bottom, but if I'm thinking correctly, that would cause similar head pressure acting on the outlet of the return fuel, as the first option.

 

I haven't found a lot of information around the internet of people running a MAIN tank from the bed like i have, i have seen a lot of AUX tanks in the bed, which either pump, or gravity feed into the main tank, which is in between frame rails or what have you. 

What i have gathered is a lot of people are running an auxiliary tank, that gravity feeds into their main tank. They have reported, that when the AUX tank is full, you cannot open the main tank cap, as the fuel will pour out.  if this is true, then their return line would be running into the main tank, and overcoming a similar head pressure like i am describing. 

 

Any and all input would be greatly appreciated at this point, because i want to get the fuel tank built, and sealed up.

 

Thanks so much!

Wyatt

I Should've mentioned it in the first post, 

But even though i don't want to do this, i am slightly open to running a small main tank in between the frame, that this tank feeds to, and i run everything off of that.  I would like to keep it simple and run only this tank ideally, but if that's what i have to do, then I'm open to making something work. 

[Tractorman]

I think your return fuel back pressure concern is valid, but it may not be a problem at all.  The real problem is that there is no place I know of to get the information as what is the maximum fuel return pressure allowed.   I would give Blue Chip Diesel a call - they may have some information for you.  Or, call a VP44 fuel injection pump rebuilder.

 

- John

 

 

[Dieselfuture]

Cool project. My personal opinion is you're over thinking it, nothing wrong with that better to over think then under 2.31 ft = 1psi factory is in the basket so when tank is full there's some pressure but not as much as you'll have. The advice @Tractorman gave is probably the best, contact someone that actually builds them. As for fass some return it to filler neck with an adapter some like me, returns to bottom of basket. I like the idea of returning to bottom so it doesn't foam up as much. But then again those that return it to filler neck have no issues ether. More importantly is how you suck it out of tank and where. 

[QuietWyatt]

Hey, thanks so much for the replys @Tractorman @Dieselfuture, i really hope i am overthinking it.  Great idea to call some people and ask, when i do that i will report back my findings.  

Really appreciate the replys!

[LorenS]

Neither the lift nor the injection pump care how high the tank is. If you return to the top, the dip tube is a good idea as it allows the fuel going down the dip tube to help pull return fuel up to the tank top (like a siphon). For the same reason, you can come out the top of the tank with supply fuel and the pump knows no difference (once the 'siphon' has started).

 

What I don't know, is if the return at the back of the head cares that the tank is above head. I would think not, until the day there's a leak somewhere and the whole tank is drained empty, either onto the ground or into your head followed by the oil pan, and it streams out the breather. Of course that'd either be a big leak, or a little leak and a lot of time.

Edited February 3, 2021 by LorenS

[IBMobile]

 

How about the filler neck?  That's where the Fuel Boss pump dumps the extra fuel. 

[wil440]

4 hours ago, IBMobile said:

 

How about the filler neck?  That's where the Fuel Boss pump dumps the extra fuel. 

Thats where mines going when it gets a bit warmer/drier outside, already made the piece just got to get on fitting it

[Mopar1973Man]

 

First of return pressure isn't a concern. The restriction is NOT the plumbing but the VP44. Look at the photo the return is the left side while supply is the right side. No matter what you do for the plumbing this restriction will always be in the pump and will not flow any more. My max fuel temp in the summer with temps between 110 to 115*F outside barely makes 130 to 140*F fuel temp for me. Still running fully stock return lines. The key for me is I do NOT draw from the basket where all the heat fuel is coming back to. I pull from the front side of the tank on a separate draw straw. For all you drawing from the sender basket remember the return from the rear of the heat is heating the fuel to near coolant temperatures and then return to the sender basket to be sent back to the VP44 preheated. Again where I draw away from the heated fuel and get cooler pump temperatures.

 

 

 

 

Edited February 3, 2021 by Mopar1973Man

[wil440]

1 hour ago, Mopar1973Man said:

First of return pressure isn't a concern. The restriction is NOT the plumbing but the VP44

I have done a lot of testing on my system and any restriction in the return raises the overall fuel pressure, I ran a new fuel line from the tee at the back of the head to the filler neck, when I restricted this with a hose clamp fuel pressure rose and by a lot.

I get around 8 to 10 psi at idle and 25 to 28 ish at  2k +, restrict the return hose and I could blow the glass out of my pressure gauge and it is plumbed into the inlet passage of the fuel filter, 25psi at idle with the hose partially closed.

I don't use the steel lines down the frame anymore or the standard filter

The above is just my observations of my truck and FTR 8 to 10 at idle on my truck is returning a huge amount of fuel back to tank 

[Mopar1973Man]

1 minute ago, wil440 said:

I get around 8 to 10 psi at idle and 25 to 28 ish at  2k +, restrict the return hose and I could blow the glass out of my pressure gauge and it is plumbed into the inlet passage of the fuel filter, 25psi at idle with the hose partially closed.

 

You 2k RPM pressure is TOO HIGH! The whole problem pressure go up with RPM. The return system is not designed for 20+ PSI inlet pressure. Hence why your fighting this. Then again you not going to gain anything on the return being there is no way to open the passage from the VP44 return port internally. Above 30 PSI you at risk fro blowing out the front seal which does happen quite a bit. 

 

Mine is fairly steady at 15 to 17 PSI over from idle to 3k RPM. So my return line is not over pressurized and fuel temps remain low. Mine has been like this for years. Like I know my pressure regulator spring is getting weak my pressure have been slipping slightly down in the loaded area. I'll be ordering a AirDog 17 PSI spring.

[dripley]

1 hour ago, Mopar1973Man said:

 

You 2k RPM pressure is TOO HIGH! The whole problem pressure go up with RPM. The return system is not designed for 20+ PSI inlet pressure. Hence why your fighting this. Then again you not going to gain anything on the return being there is no way to open the passage from the VP44 return port internally. Above 30 PSI you at risk fro blowing out the front seal which does happen quite a bit. 

 

Mine is fairly steady at 15 to 17 PSI over from idle to 3k RPM. So my return line is not over pressurized and fuel temps remain low. Mine has been like this for years. Like I know my pressure regulator spring is getting weak my pressure have been slipping slightly down in the loaded area. I'll be ordering a AirDog 17 PSI spring.

If younhave the 165 pump head it should have a pressure regulator on it you can adjust. Or is that on filter base. Cant remember now.

[wil440]

1 hour ago, Mopar1973Man said:

 

You 2k RPM pressure is TOO HIGH! The whole problem pressure go up with RPM. The return system is not designed for 20+ PSI inlet pressure. Hence why your fighting this. Then again you not going to gain anything on the return being there is no way to open the passage from the VP44 return port internally. Above 30 PSI you at risk fro blowing out the front seal which does happen quite a bit. 

 

Mine is fairly steady at 15 to 17 PSI over from idle to 3k RPM. So my return line is not over pressurized and fuel temps remain low. Mine has been like this for years. Like I know my pressure regulator spring is getting weak my pressure have been slipping slightly down in the loaded area. I'll be ordering a AirDog 17 PSI spring.

My return lines are not what came with the truck and my lift pump is mechanical so I'm happy with my pressures, all I'm trying to say is return lines DO have an impact on fuel pressure but hey what do I know