I am building a small robot having pneumatic system. I am using 12v car tyre inflator as my compressor.But i didn't find any 3ltr to 6ltr standardrd air tank. Can i convert my old 3ltr lpg tank into air tank
According to one of many resources regarding pressure in propane tanks,
a tank with 20 pounds of gas at 70°F has a pressure of 145 psi, at 90°F would have 180 psi, at 105°F would have 235 psi, and at 130°F would have 315 psi.
Those numbers convert to 21°C / 10 bar, 32.2°C / 12.4 bar, 40.5°C / 16.2 bar and 54.4° / 21.7 bar respectively. Quite substantial numbers for "ordinary" use as an air storage tank. My commercially produced tank of approximately the same size has a red-zone on the gauge at the 150 psi level.
One aspect of using a propane tank is the inherent danger of the fuel within. Exhaust the tank through ordinary use or similarly safe manner. Remove the valve and fill the tank with water. This will cause any remaining fuel vapors to be displaced, rendering the tank safe(r).
Have you checked the tanks used for gases for blowing up party balloons - they are smaller : about 30cm long and 15cm dia.
They may be a better option as they are probably lighter than the one you are looking at - weight must be a consideration for you.
I have kept one for something I am planning that is why I have the size...
Another possibilty is to check out the Nitrous tanks used in tuning cars ...
Or, even, some of the compressed air tanks used for vehicle brakes,
Or possibly the smaller divers air tanks...