"One Way" valve. Few years ago LEGO used to build what I would call a "Pneumatic diode" Its particularity is to separate blowed air from sucked air. On its middle connection air can be blowed or sucked. Right connection blowing air. Left connection sucking air. This piece was use cause of an old different LEGO pneumatic system. Old pump doesn' t only blowing air, it's also sucking it. This old pump is connect to a "pneumatic diode" that separate the two different air. The pneumatic switch select wich kind of air is connected to the single-acting air cylinder. Thus activing the cylinder by blowing or sucking. Know that Air-tank would be useless in a such circuit.(If you are a viking you could talk about it on lugnet....) What a shame LEGO used to build this pneumatic piece. Using pneumatic circuits I decide to build my own « one way » valve. This piece would be the half part of the pneumatic diode. In «one way » valve air can circulate only from top to back HOW TO BUILD It's an easy to build piece but you have to sacrify a present LEGO 48mm pump. 48mm pump has a «one way »valve build at bottom of the piece.We will use it. You need : a : any plastic piece that will fit the splited pump b : the 48 mm pneumatic pump c : 4mm tube, LEGO ones (for example yellow tubes in Mindstorm kit) are good d :a small 1x1 LEGO bricks attached to a ring (space or legoland piece) PAY ATTENTION HOW LONG YOU CUT THE CYLINDER, bigger is the "one-way- valve" more it could act as a air tank too. Well this is time to split and pierce the pump. Watch the d piece fit the pierced pump. Split the d piece to obtain a simple ring and cut LEGO tube c to 1,5 cm long. Just assemble and glue the 4 new pieces. Know that it won' t work with 48mm pneumatic cylinder or old pump. I haven't tested it with small 32mm pump but I think it would work. chrismaker@noos.fr