Need constructive feedback on surge tank

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Need constructive feedback on surge tank

Postby mynameistory » Tue Aug 22, 2017 10:41 pm

Hi All!

I'm messing around with this idea for a gravity surge/accumulator tank under the gas tank of my 70 Beetle project. Most people just run the feed and return directly from the bottom of the tank using the CB Performance tee, but I'm worried about hiccups at low tide. I used to have a setup with a Carter lift pump in series, but I'm redoing some things to make hardware, plumbing, and wiring simpler.

The nice thing about VW's is that the fuel tank is fairly high, above the steering column and tie rods. I didn't have enough room to mount the gravity tank vertically- it will sit horizontally about an inch under the lowest part of the main gas tank. I'm still using the fuel tee, both as drip feeds. One of the inlets is placed at the top of the surge tank, I'm hoping that it will let any air burp back up into the main tank. The fuel return is plumbed back in here as well. The lines in the picture are for illustration only, they will be trimmed to the right length later.

Please let me know if you have any constructive criticism- I'm mostly concerned whether the pump will work correctly with a fixed inlet. Should I be worried about vibrations possibly loosening/twisting the pump off of the threaded inlet? Other than that, is returning fuel here OK? Any worries about the return fuel facing too much resistance? Temperature concerns (it holds about a quart so I'm less worried about this). The bent lines are 3/8" 304SS with a nice thick 0.035" wall, so I don't think I need to worry about cracks/splits. What else? I want to know if I'm barking up the wrong tree before finishing this.

Thanks for your help- Tory

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Re: Need constructive feedback on surge tank

Postby jsmcortina » Wed Aug 23, 2017 3:48 am

Looks mostly ok, the one thing I would consider is to return the upper outlet to the top of your fuel tank - so any air bubbles are sure to escape.

James
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Re: Need constructive feedback on surge tank

Postby Matt Cramer » Wed Aug 23, 2017 6:33 am

I'd also consider mounting the tank vertically if there's room.
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Re: Need constructive feedback on surge tank

Postby mynameistory » Wed Aug 23, 2017 8:00 pm

Thanks James, I was considering an extra burp line going up to the charcoal canister circuit above the tank. I'll see if I can squeeze one on there.

Matt, I tried going vertical as the tried-and-true method but just couldn't make everything fit. Hope this will work! Thanks again for your help on my new Evo (I was the guy with the goofy registration not working).

Does anyone else think that threading the pump onto a fixed inlet might be a bad idea due to vibration? Or should it work all right?

-Tory
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Re: Need constructive feedback on surge tank

Postby quan3165 » Wed Aug 30, 2017 7:40 pm

I would think the whole assembly vibrates together since the pump looks like it will be mounted pretty solid on the spacer. Some foam between the surge tank body and its adel clamps wouldn't hurt.
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Re: Need constructive feedback on surge tank

Postby mynameistory » Thu Aug 31, 2017 7:26 pm

Thanks quan. I think there's only one way to find out for sure, so I'll give it a shot and monitor how it holds up! Thanks for the review.
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Re: Need constructive feedback on surge tank

Postby jsmcortina » Fri Sep 01, 2017 2:20 am

With a rigid pipe connection between the tank and the pump, you need a rigid mounting between the two. Otherwise the pipe or fittings could fatigue fail.

Better would be a short length of flexible hose and then rubber or foam mountings between the pump and tank.

James
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Re: Need constructive feedback on surge tank

Postby mynameistory » Wed Sep 06, 2017 12:44 am

Yes ideally I would separate the pump and tank with hose instead of a solid tube. I'm trying this out as a means of consolidating- if it begins to fail then I'll look into re-doing it.

My older Walbro pump came with a stiffer, thinner foam sleeve than the one currently wrapped. This might be a better compromise and allow for some damping, but hopefully not too much movement. What do you think?
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Re: Need constructive feedback on surge tank

Postby jsmcortina » Wed Sep 06, 2017 1:13 am

You don't want it to fail at all. Fuel leaks are bad.

James
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Re: Need constructive feedback on surge tank

Postby mynameistory » Wed Sep 06, 2017 1:35 am

jsmcortina wrote:You don't want it to fail at all. Fuel leaks are bad.

James
Yes agree. Thickwall stainless hardlines are replacing all of the braided AN hoses in the car. The car had been sitting too long and all of the liners had dry-rotted, weeping fuel everywhere when I tried to start it up for the first time in a while.

This stuff is beefy-I'm more worried about rattling loose than I am about fatigue cracking (though I understand things are more likely to fail after mile 10,000 than they are after mile 10). I'd still like to try.

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