or as a pilot control stage of servo valves used in anti lock braking systems a method of producing a sealed cavity with a residual gas pressure therein which may have applications other than valve manufacture is also disclosed application_number US 56699790 A description the sectional view of fig1 shows the arrangement of the individual layers of the valve however for reasons of clarity the thickness of the individual layers is greatly exaggerated microvalve 1 features a first wafer 3 which serves as the carrier layer a second overlying layer 5 bonded to layer 3 and a third layer 7 bonded to second layer 5 onto topmost layer 7 a cover layer 9 is joined by e g bonding or some other method suited to the particular material comprising the cover layer into lowermost layer 3 one forms a recess 11 the overlying second layer 5 is so structured that a first channel 13 is created whose bottom 15 forms a portion of the cover of recess 11 into the overlying third layer 7 a second channel 17 was created whose bottom opens into the first channel 13 second channel 17 surrounds a region which forms a valve plate 19 the valve plate is connected with a region 21 of second wafer 5 which is surrounded by first channel 13 the dimensions of the first and second channels are so selected that valve plate 19 projects beyond the region.