Petrol tank plumbing

[ARC]

Hi Guys , 

 

Bit of a daft question but how do you all gauge when you petrol tank is full when filling.  On previous models I've always been able to see the tank via a top hatch so no probs. Current model is a PT 19 large scale with no access on top . 

With a three line tank (carb, vent & filler) i cannot see how fuel will rise back up anywhere to indicate full. 

 

Any ideas on this ?

[Ron Gray]

If you have a vent pipe then the fuel will come out of that when full!

[Geoff S]

On my petrol models the tank has, like yours, 3 pipes.  Obviously one to the carb, the others come from the top of the tank and loop upwards before exiting out of the bottom for access.  I link them together to seal the tank to prevent leaks and smell.  I just one of them as a filler and the other spills out once the tank is full.  I leave them both open when flying, though I once forgot to unlink them with no problem except the tank changed shape a bit ?

 

Geoff

[ARC]

thanks Ron. Will it stiil do this if i have a loop in the vent line ?

 

[ARC]

1 minute ago, Geoff S said:

On my petrol models the tank has, like yours, 3 pipes.  Obviously one to the carb, the others come from the top of the tank and loop upwards before exiting out of the bottom for access.  I link them together to seal the tank to prevent leaks and smell.  I just one of them as a filler and the other spills out once the tank is full.  I leave them both open when flying, though I once forgot to unlink them with no problem except the tank changed shape a bit ?

 

Geoff

thanks Geoff . My filler will be attached to a remote filler bolted to the fus , so in theory the full tank will spill fuel out of the vent line even with a loop in it ?

[Geoff S]

I assume so.  The surplus has to go somewhere and the vent is the only route.

 

Geoff

[ARC]

thanks both for advise 

[Ron Gray]

Yes, even with loops it will spill out from the vent, all of my gassers are setup that way.

[Andrew Calcutt]

When it pours out of the exhaust it’s full!

[Alan Gorham_]

But not all (most) petrol engines use exhaust pressure, so a full tank won't vent to the exhaust.

[Engine Doctor]

Sorry misread post . Comment deleted 

Edited July 21, 2021 by Engine Doctor

[cymaz]

You could do a two vent set up if you want.

Have a Tee fitting in the carb line with the end as the fill. The vent / line at the top of the tank to show when it’s full.

This works fine with a pumped carb, like a Walbro 

Edited August 1, 2021 by cymaz

[stu knowles]

22 hours ago, cymaz said:

You could do a two vent set up if you want.

Have a Tee fitting in the carb line with the end as the fill. The vent / line at the top of the tank to show when it’s full.

This works fine with a pumped carb, like a Walbro 

I have used this set up but if the plug comes out or leaks air the engine stops.  Since then I have avoided any potential interruptions between clunk and carb

[John Minchell]

How do you empty the tank if you haven't run it dry when the clunk is direct plumbed to the carb? 

The filler only pipe stops just past the bung and the vent to the top of the tank.

Does a second clunk need to be fitted just for emptying?

[Ron Gray]

If I have a 3 pipe tank the filler has a downturn to the bottom of the tank. If yours terminates at the bung then put the ‘plane on its nose to empty it. I also use 2 pipe systems with a 2 way valve on the carb feed, this means you drain from the clunk. 

[Engine Doctor]

On 04/08/2021 at 18:52, John Minchell said:

How do you empty the tank if you haven't run it dry when the clunk is direct plumbed to the carb? 

The filler only pipe stops just past the bung and the vent to the top of the tank.

Does a second clunk need to be fitted just for emptying?

Simple . Set one of the pipes in a three pipe set up as a fill and drain pipe. I bend the   fill /drain pipe so that it points to a corner of a square tank  or bottom of a round one with short length of fuel tubing to  allow it to lay flat. Make sure it doesn't interfere with the clunk.  Never fit any filling  or filtering device into a fuel to engine  supply tube. Sods law states that "if it can leak air it will " A sintered filter clunk is the best option for a glow engine or a composite/ felt filter for a petrol engine . An appropriate filter should always be fitted as its amazing how debris finds its way into a tank. A sintered or felt/ composite filter will prevent any debris getting into fuel line and wont blocks easily or degrade like a mesh type.

Edited August 7, 2021 by Engine Doctor

[Ron Gray]

3 hours ago, Engine Doctor said:

Never fit any filling  or filtering device into a fuel to engine  supply tube.

Not sure I agree with this! All of my petrol (apart from my Lasers) setups have in-line filters fitted to the carb feed lines, never had an air leak problem. Similarly quite a few of my glow setups have 2 way fillers, again, no problems but I do make sure they are kept clean. I do not fit in-line filters to my glow setups.
My glow and petrol fuel cans all have filters (clunks) on the fuel pickup lines inside the cans.

Edited August 7, 2021 by Ron Gray

[John Minchell]

Thanks chaps - three pipe set up and I have a new felt covered clunk (petrol) for the carb feed line and will make the filler pipe able to empty as well with a  short length at the front of the tank and close it off for flight use just leaving the breather line open.

[Frank Skilbeck]

Don't forget to block the breather line when the model is in the car or it will stink if you are using normal pump petrol.

[John Minchell]

Good point Frank - and with two tugs in the car.......................the stink would be twice as bad!

I feel a turning session on the lathe coming up for two nice knurled edge ally pipe bungs.

[Ron Gray]

Or, as some would suggest, use Aspen instead!

[cymaz]

Just started using Aspen fuel. There was no needle changes made. The engine ran cleaner with only 5-6 spots of oil to clean. I used 32:1 as per engine instructions.

[John Minchell]

I can put up with the petrol smell due to the ridiculous price of Aspen fuel.

Between 4 and 6 times the price of supermarket pump petrol looking at ebay & local Aspen stockists.

[cymaz]

Granted..not cheap £20 for 5 liters. With the ethanol % doubling soon, I’m not sure how this will affect the carb diaphragm and other parts.

[Jason Channing]

Use Esso Supreme+99 as there's no ethanol in it,