Has anybody tried to refit a scuba tank so that it can be used to pump up kites? Interested to know whether it can be done easily enough.

How about helium, bet that's never been tried.

I'm not an engineer/thermal scientist or anything, but I think filling a bladder with SCUBA tank should be ok regarding condensation.
A kite's empty bladder will contain very little air at ambient temperature, and ambient humidity (i.e. a few litres of air at best).
The SCUBA tank air is dry air (water molecules are filtered out during tank filling to avoid pitting / rusting of the internal tank walls). When the SCUBA tank air expands, it becomes colder than ambient temp due to JT cooling effect. However, as it's dry air, filling an effectively empty bladder, there would be limited water molecules to form condensation as the bladder fills up. Then, as the air pressure in the bladder increases, it will become warmer, and eventually reach ambient, and re-evaporate any tiny amount of condensation that formed. So, in short, I reckon filling with SCUBA tank should be fine. Should be simple enough to rig up a SCUBA tank connector to an inflation hose, even just with some gaffa tape and a few cable ties.

I have not seen it done lately but a guy at my local beach (in Canada), owned a diveshop and he had a regular scuba tank that he used to inflate his kites. Don't recall details of regulator etc but it seemed to work fine.

This would have been 2004 or so. Guess it has not caught on, I would think that unless you were parked very near the beach it would be a heavy tank to carry around.

Brant said..
Not a bad idea. The air going into the kite will be cold so the pressure in the kite will go up as the air in the bladder rises in temp. So be cautious not to over pressurise the kite.
The 1st stage reg pressure of a dive bottle will be around 1MPa, way too much for a kite. It only needs about 50 kPa so you will need to reduce the pressure again.
Approximately 2/3 of the air mass in a kite is just to fill the volume, the remaining 1/3 is needed to bring it up to pressure. Filling the kite with a low pressure pump (like the one for an air mattress) and then using a bail out bottle to bring it up to pressure might be a good option. Make sure to post how you got on.

Brant you seem to have a pretty good grasp of things. The 1st stage reg pressure has been a concern. Do you have a suggestion of what you use to lower the pressure to the kite?

I have a clear plastic 1&1/4 inch flexi pipe that I fix to the exhaust of my hiace which I use to pump up my kite. Works like a charm.

Turn the car on and let it idle.. 40 secs later good to go.

Yeeeehar Kenny

All that extra weight just to save 2 minutes - worth it =Think not!
Pumping up your kite warms and loosens up your back.
You don't run out on the footy field cold without a warm up so why consider a kite session any different.

don't forget to refill tank before going diving