FlyerInOKC

My Feedback: (6)

Leroy, it sounds like a worth while experiment I look forward to reading your findings.

acerc

I can answer that for you Leroy, no, gas cannot be forced through the diaphragm by our normal means of filling. There are three things stopping this, one is the diaphragm is spring loaded, second is there is a metering needle that shuts the fuel off, and last is there are one way flaps that will not operate without the pulse of the vacuum.

John_M_

Well Leroy, the way those gas engine walbro style pumper carb work... the tank is suppose to remain vented to the atmosphere pressure... the pump will pull the fuel from the tank (s)... the fuel should pull from the second tank into the first tank, and balance as the engine draws from the first tank... if you pressurize the tank system, both tanks will be under equal pressure... it won't aid in the transfer of fuel from one tank to the other... you would have to have a completely sealed system and pressurize the second tank only, to push the fuel from one tank to the other... I think what you're are trying to achieve would be the same as a expandable bladder tank with a constant pressure on the carb, not necessary with the gas pumper carbs... with your setup, the second tank should be vented, so as a negative pressure develops in the first tank as the fuel is drawn out, the atmosphere vent on the second tank will allow the two tanks to balance to atmosphere pressure, and as they do, fuel will move from the second tank into the first tank, so they should remain at equel levels as the engine draws fuel.

If you remember those cline regulators used on glow engines... the cline was not a pump, although it resembled the pump section of a walbro carb... with the cline, the tank needed to be under pressure in order for the cline to regulate fuel delivery as the carb sips fuel off the regulator.


***EDIT***

After rereading your post Learoy, Ace answered it... fuel can't move past the pump regulator without the engine running, so it acts as a check valve when static.

But when you fill the tank system as long as you have the second tank vented, there will be hardly any pressure developed during the filling process.. what pressure will exist, will be from the small resistance in the line between the two tanks... the second tank must remain vented while the engine is running.



John M,

acerc

Here is my hand drawing of how I do two tanks, very simple and very effective. I tee off the carb line to a fuel dot, but after the previous conversations about the fill valves I may go back to them.

John_M_

That's it Ace, I believe that's how Leroy has his... both thanks will draw simultaneously... the Great Planes Fill valve, I'll vouch for... that was the last one I used, and like Leroy stated, all it is really, is a manual shuttle valve... keep it clean, which most of us practice with our fuel systems; filters and all, I don't see a problem with the GP model... and with a gas setup, with a vented tank, there isn't enough of a vacuum developed to pull the pintle valve open... if there are any concerns with that, one can always put in a stronger spring in the fueler valve, but then you'll have to hold the fueler fill nipple down while filling the tank, but that shouldn't be an issue unless you need both hands to operate the fuel transfer pump.

***EDIT***

How about using one of these 3 way fuel valves from centralhobbies.... left position would be set to run... middle position would close off the feed from the tank... and the right position for filling the tank... the only unknown does it have a detent ball to key each position.



John M,

Leroy Gardner

Okey, I have been to the 2 cycle shop and they confirmed what Robert just said and yes Robert that drawing is what I have. John M I like what you say about your experience with the fill valves and I'm still going to run the system as it's set up now. In all likely hood I will go to the 3rd fill / drain line just to keep the scale look up there.

Wait a minute, don't all I have to do is Tee a line in what I now have ( removing the fill valve ) and put the dot somewhere out of sight, I can run that line out the fire wall and mount it in the cooling cutout area. That little valve got a lot of press for no more than what it is, sure does make a guy think though.

Leroy

John_M_

Thats what bird was saying all along...

John M,

pilotbum

That's what I'd do. I'm a subscriber to the KISS approach to things and after my multiple experiences with those type of valves I think they just complicate things to a potential point of failure. My hat is off to those who have made them work and had no problems and in all fairness I've only used the Dubro. Sounds like the GP version works better. But it's still mechanical.

Why can't you replace the current valve with a fuel dot in it's preset location?

geoardsog5

My Feedback: (31)

Leroy, for your consideration. Fuel system schematic - close to full scale. The only thing missing, 4-way selector valve and external filler caps. (let's not even go there).
It does require additional plumbing, but should allow you to fill and draw down the tanks, fairly evenly.
I guess my concern, with the fill line tee'd to the carb supply line is: leaky diaphragms on carb, or crack press. set too low. Maybe nothing to worry about - carb problems would show up on start or pre-flight run-up. John R.

TonyBuilder

My Feedback: (11)

Leroy, doing the side saddle tank and using a T inline to the carb is in my opinion the best setup. I use the sure fire T and filter and a fuel dot, can't beat that setup, simple and it works.

TB

pilotbum

How do you fill tank 2?

geoardsog5

My Feedback: (31)

t\Good question. Overflow from Tank 1.

TonyBuilder

My Feedback: (11)

This all sounds complicated for a simple setup


TB

pilotbum

But that's also a vent. So what makes it go into tank 2 and prevents it from venting out the vent? I'm only asking because this is the way I've thought of doing this but what I drew up needed more lines for filling/defuling.

acerc

Actually the tank with the vent will drain first.

rt3232

My Feedback: (6)

You T the fill line and have a second clunk on each fill line (no filter on the clunks)

I am not a fan of the crap trap in the fuse, I like it ware I can get to it to back flush/clean it.

But that is just me

Cheers Bob T

John_M_

That's probably correct, I've never run with a two tank setup.. but that does make sense, since air can't enter the first tank without the second tank being empty... its a clever idea, I'll have to find a way of utilizing it in a project.


John M,

geoardsog5

My Feedback: (31)

Pilotbum, i'm probably worrying about nothing. the simplest thing to do would be to tee the fill line into the carb supply line, between tanks 1 and 2. If the carb acts up, you will probably know it on start - up. John R.

Leroy Gardner

John R you might want to consider another design, even if there was a 2 nd tank filler it's a disaster waiting to happen. There is nothing wrong with my fuel system, the filler was the only issue.

Leroy

Leroy Gardner

It appears some like it simple others like it complicated, I like it to work while being simple and less likely ever be a problem. If you use Tygon fuel lines they will get hard, internal ones first so what ever you do make it serviceable and simple all at the same time, that's what I'm doing. I'm ready to run the engine tomorrow, possible snow tonight and I'd like the temp to be in the high 40's at the least come mid day, will see.

When I test run / break in my engines I use everything that's going in the plane to do it, those trays are setup as they are in the plane, I did mount the fuel tanks on top so I can monitor fuel flows in and out of the two tanks. After 5 tanks or so I will put the fill / defuel line Teed where the present fuel filler is and see how well you can defuel the tanks without it sucking air through the carb. line. For me there are still unknowns, this is my first twin tank system, who knows, I may need a selector valve John_M_, glad you posted it.

Leroy

pilotbum

FYI, when I had problems with the filler valves they were not immediate. They came on over time. So in your test runs they probably won't be a problem.

You probably already knew that but thought I'd say it anyway...

John_M_

There's not a lot of info posted on it, so I guess one needs to call to get more info on it... it is a 3 way ball valve; takes 3/32"-1/8" inch ID fuel line... its not very big either... as long as the quality is good and it has a detent ball, then it should be reliable... I have a use for one and may investigate it further.

Tettra 3-Way Fuel Valve # TET4321

http://www.centralhobbies.com/Fuel/fittings.htm


John M,

FlyerInOKC

My Feedback: (6)

When installing two or more tanks I have a vent line (or pressure line to the muffler) and a fuel exit line on the first tank going to the vent line of the second tank. The fuel exit line on the second tank goes to the fueler and the fueler is connected to the carb. I like a filter between the fueler and the carb.The second tank will draw fuel from the first tank as it empties. When the second tank is filled the vent acts as an overflow and fills the first tank.

Leroy Gardner

John_M_ Central Hobbies has a lot of nice looking stuff, I didn't even know they made all those small valves.

Mike the OKC guy, a nitro pressure system will work different than a gas system and I'm not much into nitro any more and they do have their limits because of their poor suction hence the exhaust pressure needs.

TonyBuilder

My Feedback: (11)

I have found this to be the best Tee and filter combo, I use this on all my sidesaddle tanks with a fuel dot.



http://www.jlproducts.net/ProductQuikFire.html

TB