UGears Pneumatic Engine.

Be a part of the once great era of steam with just a breath of air. The Pneumatic Engine is a small but fully functional example of a steam engine, except it uses air pressure instead of steam to set it in motion. Use an ordinary inflated balloon and watch the pistons and gears chug along just like the locomotive engines of yesteryear. The model comes with a built-in air pressure gauge and two compartments for storage and spare parts.

This model is 162mm (length) by 78mm (width) by 100mm (height). There are 81 pieces that can be assembles in around 2 hours without glue.