Venting High Pressure Surge? & will in-tank leak under LP pressure?

I have a pretty typical setup planned. Front Mounted fuel cell with Rollover/vent feeding the surge tank in rear with a low pressure pump. My question is has anyone seen issues by not venting the high pressure surge tank loop (venting the surge tank). I assume pressure will be relieved by fuel entering the surge by low pressure loop and returning to the fuel cell which is vented.

I'm using the Aeromotive phantom (in tank) for my High pressure pump in my surge tank which has three openings in/out/vent (see pic) - all three AN06 ORB I believe. Obviously in/out feed rails. I planned to use the third, which labeled vent, to supply the surge from the lift pump. Then I added a top mounted fitting to surge tank to return fuel to LP. I assume this is fine but wondering if anyone has encountered pressure relieving issues?

I did buy a check valve also....I don't recall where I intended to put it inline (I assume prior to the surge to prevent draining - but all fittings are on top). Suggestions there also please.

The last thing I didn't consider when I bought this was whether the phantom might leak. I've seen other's use it and figured it would be a clean install and save space. But I didn't consider whether an in-tank pump (with a gasket seal to the tank) was meant to have fuel under pressure to it. It's only as much pressure as being generated by the Lift pump. Thoughts? I think I saw a GT40 build that had a phantom. I think the second tank fed the first by LP, so it should be the same. Thoughts??

Here's what the surge tank I made and example of the phantom.

looks like I found a partial answer here on the potential for leaking...the answer is yes. SLC with Phantom
I will need to o-ring the studs similarly. I will probably use a sealant on the gasket as well. My fuel is E85 only since I have high compression and 91 octane only in CA .

Anybody know a fuel/ethanol safe sealant? I know Dow 730 but it's $$.

Per further inspection, even though the vent connection is also -06 ORB, the machined opening is smaller, which likely cause fuel to pump into surge at a higher velocity (like nozzle). I'll plug the hole and weld another fitting.

Still don't know why I bought the check valve. I'm pretty sure the lift pumps incorporate a check valve so I don't think its needed on feed side. Maybe return side?

Last question. Does everyone typically upsize they're lift pump return line size? I think I tried to save $$ and stuck with -06 (3/8 hardline) for the feed and the return on the LP side. I only consider it now since I believe that will contribute to a slightly higher pressure in the surge tank and increase chance of phantom leaking past gasket.

Scott,

You definitely don't want the surge tank to become pressurized. That said, I don't think that most people oversize the return from the surge tank. The amount of fuel returned to the swirl pot will be more manageable if you're driving the pump via PWM (i.e., not full blast all of the time) and what type of return you have from the fuel rails; returnless, deadhead return, or flow through return.

I know that one of Allan's high-HP builds was having a lot of problems on the dyno. The issue was that the surge tank was pressurizing so he was told to move the fuel rail return from the surge tank to go directly to the fuel tank which solved the problem. I wouldn't do that unless I had an observed issue.

The manufacturer of my high-pressure fuel pump recommended a check valve after the pump so I have one.

E85 has good power and cooling benefits, but there are several things that you need to consider :

(1)It will corrode your fuel system if you don't have ethanol compatible parts. In particular, the SL-C's aluminum gas tank and your surge tank. I think anything above E10 starts to corrode raw aluminum (http://www.diva-portal.org/smash/get/diva2:720728/FULLTEXT01.pdf. ) Maybe it will become an issue maybe it won't. My surge tank is anodized which helps. I'm considering replacing my fuel tank with a fuel cell, but even then I would need to specify an E85 compatible bladder.

(2)The amount of ethanol in E85 will affect how the engine runs. Ethanol requires more heat to vaporize than gasoline, which can cause cold start problems when the temperature drops below 20 degrees F. To solve this problem, the Federal Government allows up to a 30% gasoline content in E85, which essentially makes it E70. Apparently cranking in cold climates is the primary reason ethanol is blended with any gasoline (i.e., in Brazil pure ethanol is used). I added an ethanol content sensor on the return line to the surge tank and I have a map in the ECU that automatically modifies the tune. I think that this is what OEMs do.

(3)Ethanol contains 40% less BTUs per gallon so you'll need 40% more fuel to obtain the same power level. Not a problem, but you need to take this extra volume into account when sizing your fuel system.

Venting surge tank - The surge tank by design is suppose to always be full of fuel so trying to extract any air out of the top seems pretty futile to me. If anything it increases the risk of fuel leaks if the air/fuel separator fails. In a typical installation application for the Phantom there's almost always air right below that plate so it would work well. I've also never seen this done.

Using vent port as surge tank supply - I think this is fine specially if you're concerned about over pressurizing. The reduced port opening would add a little restriction to limit flow possibly. Yes velocity will be higher but flow will be same or reduced.

Surge tank in/out line sizing - Oversizing return line back to tank can't hurt but it really shouldn't matter as long as you're using a proper lift pump to feed the surge tank. Lift pumps max out at only a few PSI, Holley Red will max at 7 PSI for example, that is plenty safe. I'm having a hard time imagining even a high pressure pump being able to build all that much pressure since the loop is pretty free flowing. I would say you can safely ignore what may be happening with the primary pump(s), they may or may not be circulating fuel but they will never add any fuel to the surge tank, only subtract so they can't add any pressure. The expansion rate of heated fuel is negligible. I will say all this depends on a properly functioning fuel system. If the lift pump is picking up a lot of air that could very well cause pressurization issues as heated air expands quickly. I can tell you from personal experience my SLC was venting a ton of fumes during twisty road driving before I sorted out the tank pick up issues. At one point I had to pull over and inspect since I smelled so much gas.

Check valve - I would just toss this, it's just another potential failure point in the fuel system, it's only usefulness is right after the primary pump for quick startups. The surge tank is always full so primary pump has all the fuel it needs (as you said the ports are on top so there will be no significant drain back). The lift pump should be pretty close to tank anyway so worst case you got a little air after the lift pump that will quickly be purged out.

Leaking from bolts - A little surprised to see this was an issue for one of the owners. All the major fuel cell companies use nylon washers to seal that interface with no additional sealant or rubber o-ring. I have noticed they tend to use bolts with large heads and nuts plates on the inside so there's a lot more surface contact going on.

x2 ^

The vent from my swirl pot (GT40 lingo for surge tank) is the fuel return line to the main tanks. The exit port is located near the top of the tank, with the standing pressure in the tank pushing the excess fuel (or air) back to the supply tank (which is properly vented) or into the high pressure EFI pump. 7k miles on it, no issues.

Thanks for the feedback!!

Because of the reshaped combustion chamber on my heads, I knew from the beginning I'd have to run E85. All the parts I sourced should be E85 safe (filters/E85 stainless hose etc). I'm having the surge tank hard anodized since it's aluminum. I have an ethanol content sensor as well....will likely be running the Haltech Nexus ECU/PCU with that. Luckily I don't have the cold weather issues in SoCal. I think cars put away for the winter have more issues because the E85 takes on a lot of water. Also converting to E85 from gas can have a cleaning affect that loosens buildup in the system...but not a problem here.

It is a return system. I figured I would be safer then sorry and just go ahead and plump the return line to 1/2" hardline, so I already bought a -08 weld on bunge. Only another $40 for peace of mind. That will also free up the -06 bunge for the return on the high pressure side. I'll plug the vent. Regarding the "lift" pump itself, I think I went off a recommendation from Fran to use a Walbro GSL392. It's 255 LPH but as I look at it doesn't appear to be specifically a low pressure pump, so probably best I increased the return.

Good point on the check valve as potential source of failure. It's also too small to put after my primary pump. Into the unused parts bin.

Leaking Bolts yeah I was surprised too, but there's probably not to many dummies like me putting these on surge tanks. I'll add o-rings to be safe and probably some of this sealant that's not $100 a tube. Permatex. I'll just have to give it a shot. Been to long to return anything. I think it'll be ok.