Air operated bottle jack issue

[scrwright]

Bought a cheap-ish 20t air/hydraulic jack off ebay which has been working fine for a while but yesterday the air side of things packed up. Manually cranking it still works okay and the air pump side works but doesn't lift it. It had fallen over in the garage so I am assuming (hoping) it may just be air in it and it needs bleeding out. Any ideas how you do this? And if the manual pump works okay will it be just air in the air pump side?

For info it is one of these (although not the selller I bought from)
http://www.ebay.co.uk/itm/20-Tonne-Air-Bottle-Jack...