Large Model Association Forum

Speaking to Dave, he uses GAZ gas cylinders for air tanks.

I was thinking the same but would need a 4mm festo connector on them instead of a nipple.

Has anyone done this before with festo fittings?

Mike.

Mike,
I have a spare Gaz cylinder on my patio the heater has broken

made Phil Clark a carbon fibre air tank, with ally ends, this had a festo fitted, just drilled and tapped, and in it went, it was for his marauder, now living in america

What pressure do these tanks get used up to?

Found some large air tanks with 4 mm festo from eurokit retracts.

They are 750ml each so not sure how many I will need. maybe run 2 or 3?

Mike.

Here is the carbon/aluminium tank Alan made me for the B-26 last year.......4ltrs in capacity

Reason for the large capacity was the size of air rams being used......25mm x 200mm travel on the mains!!, plus 2 conventional rams on the nose leg & 2 more on the nose gear doors.

Capacity is everything on retract installations. It's utterly pointless expecting small bottle at high pressure to work well as for every cycle, you get a large pressure drop. MUCH better to fit as much capacity as you can so you have a good head of pressure doing the work, and you get minimal pressure drop per cycle. Depends on the size of the rams on the legs as well, but if you have 750ml bottles, I'd go with at least 4, especially as their weight is negligable and you have acres of space inside the fuselage.

Phil

....& before anyone say the tank is unsafe with 'glued' on ends (Hysol 9462), there is an M4 'tie bar' running end to end that is screweed into a lug in the cente of each end cap, so you actually screw the ends on & glue at the same time. The tank was repeatedly pressure test to 100psi outside the model, and was also left in direct sunlight fully pressurised to get the tank nice & hot so increasing the internal pressure further.

Phil

The reason I was asking what pressure these are used to was so that I could advise how to test safely if you were making your own. At 100psi air they are like a small exposion waiting to happen with more than half a ton on the end of a 4" diamter. The safe way to test is to fill it with water then if you do not have a small liquid pump you can use air for the final pressure. This way if it fails the only stored energy is in the very small volume of air used, as the water does not compress (much).

Here is a test being carried out by an enterprising individual who has inflated a 2 litre PET bottle to 7bar (100psi) with a car foot pump!


His test is here if you wan to read it http://letsmakerobots.com/node/3048..its part way down the page.


Regards, Andy

Hi Phil,

Ok mate, will probably go with 4 or 5 then as they are quite big cylinders etc and they are retracting alot of weight on the mains.

What PSI do you run your systems at?

Cheers,

Mike.

and Phil tested it the safest way i know, him in Durham, me in Manchester worked though, and very well too

Mike altham wrote:Hi Phil,

Ok mate, will probably go with 4 or 5 then as they are quite big cylinders etc and they are retracting alot of weight on the mains.

What PSI do you run your systems at?

Cheers,

Mike.

Generally between 80 and 100psi....if it needs more than that then you have geometry issue in the units and/or too heavy struts/wheels, so more pressure is unlikely to help.

Phil