Homemade Miniature-compressor

Hello, this is a project I've been working at, it's a miniature reciprocating compressor made out of some cooper pipes as cylinders and connecting rods made of acrylic. I used epoxic glue for casting the pistons and a 9 volt drill and an abrasive file to machine them. A good way to cast the pistons can be found here

https://www.instructables.com/id/SWGD4M3FABRWWS9/

Crankshaft is made with a pulley and other parts of an old cassete player, and motor was taken from a broken 3 volt electric screwdriver
As me, you can get the one way valves from coffee bags, which aren't hard to find but it's pretty hard to prepare and drink all the coffee to get them empty ( because of this, maybe you will get some non sleeping nights) .
I still have to get two more check valves for finishing this project , but two were enough for building a big part of the compressor. The reason why I need four check valves is explained in the scheme. I hope in next months I get the parts needed, so i can finally present you this thing finished.

This was my first instructable (well, actually my first slideshow), so please comment.