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Aircraft Retract Tanks for backup ballast systems - Help required with retract tank

R/C Submarine modelers

Postby Slats » Wed Dec 17, 2003 7:28 pm

I understand a few people are using RC aircraft retract tanks in "hybrid" ballast systems that typically use Skip's setup of a tee valve and reversible pump. I too am interested in using an aircraft retract tank as opposed to a propel tank. Whilst I am aware that a propel tank can be pumped up with a bicycle pump, I am aware that a retract bottle will hold more air from a bicycle pump than a standard copper propel bottle.

Can anyone out their provide me with info on:
If I want to use this system - what do I need to buy?
What is the "plumbing arrangement" for using a retract bottle? That is, how you charge it, how you release the air etc. Do retract bottles come with a separate charge and release valve?
Where do you locate the retract bottle on board?

Also, what size retract bottles are you using and how many blows do you get from it? Can you release the air using a servo linkage like with the propel systems?
Anything else I need to know about using retracts?

Many thanks

Edited By Slats on 1071705685
John Slater

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Postby Bob the Builder » Wed Dec 17, 2003 8:13 pm

I tried it. Didn't like it.

The air retract system can be charged with a bicycle pump... true, but I didn't get very many vent / blow cycles out of it. Liquid gas will give you way more bang for the buck, and it takes up far less room. It also took me about 10 minutes to charge with Robart pump.

The air retract bottle has more volume than a propel tank, but holds gaseous air, whereas the Propel tank is holding liquid gas and has actually more volume than the former.

My initial setup used a 12V Clippard solenoid to blow the tank. Worked fine, and the compressed air didn't corrode the valve like Propel will. I was using the big 16oz? bottle (biggest I could find) and it gave me about four cycles worth of air. Another route is the standard Robart valve that you can actuate with a servo.

I guess if you're after a "clean" system, air would be the way to go, but only if you've got the room for it. Propel takes up a lot less room inside a sub.

The air retract bottle has more volume than a propel tank, but holds gaseous air, whereas the Propel tank is holding liquid gas and has actually more volume than the former.

Just my two cents worth.
Bob Martin,
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Postby toneburst » Fri Dec 19, 2003 3:38 am

Hi Slats,

I have Robart equipment installed in my U47. Check for info. I have kit #188VR with one extra airtank #191 added tot the bow-section of the U. My ballasttanks are two bicycle tubes added to the saddletanks.
I do have the Robart air-pump, capable of getting the 750CC of air in the tanks to about 7.5 bar. It takes some time to reach this pressure, so I plan to take my filled 25Liter compressor with me (has 8 bar pressure). My ballasttanks take up about 600cc, so this gives me about 8-9 full loads to go(theoretically). Still experimenting with a 'pressure release valve' to prevent my U47 from blowing apart in case the air-valve gets stuck in open position.
You might take a look at my website ( and spec. picture at ). Very detailed/big pics, so it might take a while to load.
Hope this helps...

Jos (Netherlands)
Bailed out aircrew please report here......
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