Those valves are designed and manufactured by Maekawa Engineering a true engineering company based in Japan. Those valves do exactly what the state, in other words they relief the backing pressured caused by the piston when it moves downwards. Therefore, they minimise the internal crankcase pressure resulting on a free revin engine. We have seen the manufactures achieving the same goal with similar methods on the MX four-stroke engines. Those valves are available in different sizes for several applications and if you want one you may order it through Jetwave.jp
