A microminiature valve includes a crystalline substrate having a flow via and a raised valve seat structure. The valve seat structure has a planar bearing surface. The inner edge of the bearing surface defines an orifice to the flow via. The flow via has a varying cross sectional area and is narrowest...http://www.google.com.au/patents/US5333831?utm_source=gb-gplus-sharePatent US5333831 - High performance micromachined valve orifice and seat
