ffutures | Steam!!!!?

I picked up something in a charity shop that is either a steam engine or a compressed air engine - not entirely sure which. It has a biggish cylinder (over 1" wide), slide valve, inlets and outlets that look to be designed for 3/16" or similar tubing. It turns by hand but I think it needs to be cleaned and lubricated at least, not sure what else needs doing. My guess is it's intended for compressed air and was originally used to run a sewing machine or something, but I could be completely wrong. No manufacturer's logo or anything.

Anyway, I paid 15 quid for it - I have some friends who are very into steam and have first refusal if they're interested, if not I'll either keep it as an ornament or sell it on eBay, if I can find out more about it.