<p>My experience with glow engine models is that the tanks are made to be opened and resealed; the user needs to be able to replace the tubing inside the tank (which deteriorates over time due to methanol and nitromethane exposure) as well as in some cases change the length of the flexible &quot;clunk&quot; pickup tube to optimize for tank position and type of flight regime (trainer, sport, aerobatic, or pattern?).</p>
<p>Additionally, this appears to be a metal cap, so it should be capable of handling enough tightening torque to slightly compress whatever seal is inside the cap.  When the tank pressurizes (assuming you're running pressure), the tank pressure will slightly push the cap away from the tank body; there needs to be enough compression on the seal to stay sealed in this state.</p>
<p>Prompted by comments and the edited question: tank pressure, also sometimes broken down to &quot;muffler pressure&quot; or &quot;crankcase pressure&quot; is a method of pressurizing a model fuel tank to ensure high G maneuvers (tight loops, for instance) don't starve the engine for fuel exactly when you need power the most.  By pressurizing the tank (typically to only 0.1 bar or so) the tank pressure can force fuel up some distance, even against, say, 20 G.  For trainers, it's unneeded; for most sport aircraft, very optional, but for aerobatic or pattern flying it's almost a necessity (last time I flew a lot, pattern models were starting to use actual fuel pumps for this).</p>

CC BY-SA 4.0
2022-06-28T03:35:10.547Z
Hey, thanks! Yes, It's a metal cap. I am going to put liquid fuel in it. By pressure, I believe you were talking about gaseous fuel? What do you mean by "running pressure"?
Atharva
CC BY-SA 4.0
2022-06-28T04:13:24.537Z
Hey, I have also added an EDIT. Please have a look. Thanks!
Atharva
CC BY-SA 4.0
2022-07-18T16:22:08.163Z
_Whatever seal is inside the cap_. This seal may have deteriorated as well, and is no longer seating correctly. The seal may have also fallen out and gone unnoticed. Note teflon tape is a _bad idea_ in this case
Brydon Gibson
CC BY-SA 4.0
2022-06-27T15:55:46.793Z
2022-06-28T11:08:47.313Z
2022-06-28T11:08:47.313Z
Zeiss Ikon
<p><br />
I am using a RC Fuel tank which looks like: <br />
<a href="https://i.sstatic.net/XhU9i.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/XhU9i.png" alt="enter image description here" /></a></p>
<p>Is there anything special about the cap?
The problem is I opened the cap. Should it never be opened?
There are a few drops that leak in intervals when I put it back from the circled region.<br />
<a href="https://i.sstatic.net/9Js08.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9Js08.png" alt="enter image description here" /></a></p>
<p>Should I buy a new one? Or should I just tighten the cap hard enough or put some seal on the lid?</p>
<p><strong>EDIT1:</strong> On a website selling the fuel tank the following is stated:
&quot;High quality and durable shatter proof tank of 1000ml. This fuel tank has 3 openings. One for fuel, another for fuel refill and another for compression from muffler.&quot;
What is meant by &quot;for compression from muffler&quot;?</p>
<p>Thanks</p>

<aircraft><fuel>
RC Airplane Fuel Tank Issue
Atharva
# RC Airplane Fuel Tank Issue

(Asked by: username_0 on 2022-06-27)

I am using a RC Fuel tank which looks like:   
[![enter image description here](https://i.sstatic.net/XhU9i.png)](https://i.sstatic.net/XhU9i.png)

Is there anything special about the cap?
The problem is I opened the cap. Should it never be opened?
There are a few drops that leak in intervals when I put it back from the circled region.  
[![enter image description here](https://i.sstatic.net/9Js08.png)](https://i.sstatic.net/9Js08.png)

Should I buy a new one? Or should I just tighten the cap hard enough or put some seal on the lid?

**EDIT1:** On a website selling the fuel tank the following is stated:
"High quality and durable shatter proof tank of 1000ml. This fuel tank has 3 openings. One for fuel, another for fuel refill and another for compression from muffler."
What is meant by "for compression from muffler"?

Thanks

**Tags:** aircraft, fuel


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## 1 answers

### Answer by username_1 on 2022-06-27. Score: 3 | Accepted answer

My experience with glow engine models is that the tanks are made to be opened and resealed; the user needs to be able to replace the tubing inside the tank (which deteriorates over time due to methanol and nitromethane exposure) as well as in some cases change the length of the flexible "clunk" pickup tube to optimize for tank position and type of flight regime (trainer, sport, aerobatic, or pattern?).

Additionally, this appears to be a metal cap, so it should be capable of handling enough tightening torque to slightly compress whatever seal is inside the cap. When the tank pressurizes (assuming you're running pressure), the tank pressure will slightly push the cap away from the tank body; there needs to be enough compression on the seal to stay sealed in this state.

Prompted by comments and the edited question: tank pressure, also sometimes broken down to "muffler pressure" or "crankcase pressure" is a method of pressurizing a model fuel tank to ensure high G maneuvers (tight loops, for instance) don't starve the engine for fuel exactly when you need power the most. By pressurizing the tank (typically to only 0.1 bar or so) the tank pressure can force fuel up some distance, even against, say, 20 G. For trainers, it's unneeded; for most sport aircraft, very optional, but for aerobatic or pattern flying it's almost a necessity (last time I flew a lot, pattern models were starting to use actual fuel pumps for this).

> **Comments:**
> **username_0**: Hey, thanks! Yes, It's a metal cap. I am going to put liquid fuel in it. By pressure, I believe you were talking about gaseous fuel? What do you mean by "running pressure"?  
> **username_0**: Hey, I have also added an EDIT. Please have a look. Thanks!  
> **username_2**: _Whatever seal is inside the cap_. This seal may have deteriorated as well, and is no longer seating correctly. The seal may have also fallen out and gone unnoticed. Note teflon tape is a _bad idea_ in this case  

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