turning now to the drawings , there is shown in fig1 a pressure cooker 16 particularly well adapted for use in microwave ovens . the pressure cooker has a housing including a bowl - shaped container 18 open at its top for receiving food , and a cover 20 in the shape of a dome and adapted for sealing engagement with container 18 to close the pressure cooker and enable maintenance of a positive pressure inside the housing . container 18 and cover 20 preferably are formed of a thermoset polyester resin , or other material permeable to microwave energy . formed as an integral part of container 18 are a plurality of feet 22 for supporting the container with respect to a counter or the floor of the microwave oven , not shown . handles 24 and 26 are provided on opposite sides of the container near its top . near the periphery of cover 20 is a cut - out 28 for accommodating a pressure relief safety valve which extends through the cover . a flat landing 30 is formed at the center of cover 20 , and supports a pressure indicator and release assembly including a plastic stem or poppet valve 32 and a silicone plug or grommet 34 supporting the stem and contained in an opening through cover 20 . a stand 36 , extending upwardly from landing 30 , supports a pressure control valve 38 . extended radially outward from landing 30 , in opposite directions , are first and second wings 40 and 42 , formed as part of cover 20 and enabling convenient manual rotation of the cover with respect to container 18 , about a vertical axis . a steel locking ring 44 , permanently mounted to cover 20 , secures the cover and container in their sealing engagement as is later explained . as seen in fig2 locking ring 44 is provided with a rectangular notch 46 . a rise 48 in cover 20 , of a size and shape similar to notch 46 , fits snugly within the notch to ensure a proper angular alignment of ring 44 with cover 20 prior to its permanent attachment . first and second markers 50 and 52 , each formed as a raised portion on cover 20 , indicate whether the cover , relative to container 18 , is in its open unlocked or locked angular position . more particularly , first and second handle markers 54 and 56 are provided on handles 24 and 26 , respectively . the alignment of second marker 50 with either handle marker indicates that the pressure cooker is properly locked , while the alignment of marker 52 with either handle marker indicates the closed , but unlocked position . a pressure relief safety valve 58 extends through cover 20 to provide fluid communication between the interior and exterior of the pressure cooker , by means of a pressure relief orifice 60 through the valve . fig3 shows the bottom or inside surface 74 of cover 20 , to reveal six latching members 62 forming a part of locking ring 44 and extended radially inward from the remainder of the ring at the bottom thereof . a pressure release opening 64 contains grommet 34 and poppet valve 32 during use of the pressure cooker , but these components are readily removed from opening 64 for cleaning or inspection . near opening 64 is a smaller pressure control opening 66 , likewise extended through the cover . a plurality of relief elements or raised portions are formed into cover 20 proximate openings 64 and 66 , including five relatively short relief elements 68 , and a pair of parallel spaced apart ribs 70 and 72 extended from the cover periphery to a point near the pressure release opening . these relief elements prevent relatively large , flat and pliable food items , for example leaves of lettuce or cabbage , from lying against the cover inside surface 74 to block or otherwise interfere with openings 64 and 66 . a rim 76 of cover 20 is specially shaped to accommodate an annular gasket used to seal the cover and container 18 . formed near rim 76 is a boss 78 through which is formed valve opening 80 for containing safety valve 58 . in fig4 a portion of container 18 is shown in top view with cover 20 removed , in order to show an upper rim 82 of the container , and part of an annular gasket 84 which fits into a groove 86 formed in upper rim 82 and into a corresponding groove in the cover to effect a positive fluid seal between container 18 and cover 20 when the pressure cooker is locked . a sealing ridge 87 in groove 8 cooperates with gasket 84 to seal the housing . also shown at 88 is one of six container latching members , each of which extends radially outward from upper rim 82 , and is adapted for an interlocking engagement with one of latching members 62 of locking ring 44 . like latching members 62 , container latching members 88 span approximately 30 ° of angular rotation , and are spaced apart from each other approximately 30 °. as seen from fig4 and 5 , a closure projection 90 extends radially inwardly from the inside surface 92 of container 18 . the closure projection spans most of the container height , but is particularly useful in that it provides an inclined camming surface 94 which extends upwardly at an angle of approximately 45 °, and a horizontal retaining or crimping surface 96 adjacent the upper end of the camming surface . a substantially identical second closure projection , not shown , extends radially inwardly from inside surface 92 opposite closure projection 90 , i . e . angularly spaced apart 180 °. safety valve 58 , shown as removed from valve opening 80 in fig6 has a cylindrical body 98 of a nominal diameter , for example 0 . 25 inches . at the top of valve 58 is a radially outwardly extended flange 100 . an indicator ring 102 is formed in the valve near its longitudinal center . approximately midway between ring 102 and flange 100 is an annular raised portion 104 designed to frictionally secure valve 58 within valve opening 80 . pressure relief orifice 60 , formed longitudinally through the valve , has a diameter of 1 / 8 inch . fig7 shows safety valve 58 contained within valve opening 80 of cover 20 and crimped between boss 78 and closure projection 90 . flange 100 rests within a radially enlarged portion on a ledge of the opening . the remainder of opening 80 has a diameter substantially the same as the valve nominal diameter . as a result , raised portion 104 is elastically compressed and thus frictionally maintains valve 58 within opening 80 . indicator ring 102 lies just below the bottom or inside surface of boss 78 . when a user , having inspected or cleaned safety valve 58 , re - inserts the valve into opening 80 , ring 102 emerges from the bottom of the opening to indicate that the valve has been properly inserted . also seen in fig7 is the manner in which each latching member 62 of locking ring 44 interlocks with an associated one of container latching members 88 to secure the sealing engagement of the container and cover . six container latching members , each spanning approximately 30 ° arc , are symmetrically arranged about upper rim 82 . similarly , latching members 62 are symmetrically arranged on locking ring 44 . the latching members are so arranged , that when cover 20 is placed upon container 18 with first marker 50 aligned with either handle marker , each latching member 62 descends between an associated pair of container latching members 88 , to a point below the associated pair . rotation of cover 20 , relative to container 18 toward the locking position , moves each of latching members 62 into an interlocking engagement with one of its associated container latching members 88 , namely the one to its clockwise side as viewed in fig2 . thus , with cover 20 in the locking position , six interlocking pairs are formed , each pair including a latching member 62 and a container latching member 88 . with the cover and container locked together , gasket 84 , responsive to a positive pressure inside the housing , elastically deforms to provide a fluid tight seal between the cover and container . more particularly , an annular sealing ridge 105 is formed in a groove 107 in rim 76 , radially aligned with ridge 87 . the free ends of generally c - shaped gasket 84 are directed radially inward as shown in fig7 each end associated with one of ridges 87 and 105 . a positive pressure inside the housing urges the annular end portions of gasket 84 away from one another , pinning each against its associated sealing ridge to form the required seal . to enhance the seal , each of ridges 87 and 105 has opposite , inclined side walls converging to a sealing edge . because each sealing edge is relatively sharp , its associated end portion is bent around it , responsive to positive pressure , in a wrapping engagement to improve the seal . the edges are not so sharp , however , as to cause any damage to gasket 84 . as cover 20 is rotated into its locking position , safety valve 58 is crimped to close off the fluid path provided by orifice 60 . this crimping or closure of valve 58 is illustrated in fig8 a - 8c . fig8 a shows the position of safety valve 58 -- including a valve portion 106 of the valve extending into pressure cooker 16 -- relative to closure projection 90 after some movement of cover 20 toward its locking position . in fig8 b , as the cover is further rotated toward its locking position , valve portion 106 is carried into contact with camming surface 94 of the closure projection and is bent . finally , with cover 20 completely locked , boss 78 has been carried rightward beyond the majority of retaining surface 96 , leaving valve portion 106 trailing and held between the boss and retaining surface , crimped sufficiently to close the fluid passage otherwise provided by the valve orifice . it can be appreciated that a substantially identical locking sequence would occur between valve 58 and the other closure projection . should cover 20 initially be improperly positioned on container 18 , safety valve 58 would not encounter either closure projection during locking . hence , pressure relief orifice 60 would remain open , preventing a positive pressure build - up following such improper closure . safety valve 58 also can protect an operator who attempts , improperly , to open the pressure cooker before positive pressure has subsided . from considering fig8 a - 8c in a reverse sequence , it is understood that unlocking cover 20 involves moving boss 78 and valve 58 leftward as viewed in these figures . the arcuate dimensions of latching members 62 and cover latching members 88 are selected such that they remain at least partially interlocked even with valve portion 106 free of camming surface 94 as pictured in fig8 a . valve 58 is made of a silicone with sufficient elastic memory properties to rapidly restore the valve to its normal configuration . a silicone with a durometer of about 50 has been found satisfactory . as a result , steam and vapor quickly escape through orifice 60 , depleting the positive pressure . fig9 shows stand 36 extended from flat landing 30 . running through the stand and through the remainder of cover 20 is a pressure control orifice 108 . pressure control valve 38 includes an annular metal core 110 surrounded by a polymer casing 112 . a nodule 114 is formed in the casing , and normally rests inside pressure control orifice 108 as pressure control valve 38 is supported by stand 36 . a sufficient build - up of positive pressure in the pressure cooker , however , forces control valve 38 to temporarily rise , permitting escape of steam and vapor . the weight of control valve 38 is selected to permit the escape of steam and vapor whenever the pressure inside the pressure cooker exceeds a predetermined level , for example ten pounds per square inch . casing 112 protects stand 36 from any damage from the impact of valve 38 as it falls upon the stand and vibrates against it . fig1 shows the pressure relief assembly including grommet 34 and poppet valve 32 housed in pressure release opening 64 of the cover . a central bore 116 through the grommet has a flared portion 118 at the bottom to receive an enlarged base 120 of pressure indicator poppet valve 32 . valve 32 has an enlarged top portion 122 which maintains the valve within grommet 34 . grommet 34 has a nominal diameter of 0 . 625 inches , with radially outwardly extended upper and lower flanges 124 and 126 , respectively . release opening 64 , in turn , has a first radially enlarged portion at the cover outside surface to accommodate flange 124 , and a second radially enlarged portion 130 at inside surface 74 to accommodate flange 126 . an annular boundary 132 between enlarged portion 130 and the medial part of opening 64 is inclined , radially outward and upwardly ( longitudinally ) away from inside surface 74 . as a result , flange 126 is bent upwardly responsive to positive pressure , as shown in fig1 . also in response to positive pressure , base 120 becomes seated in flared portion 118 of bore 116 , raising enlarged top 122 above grommet 34 , to provide to the user a visual indication of a positive pressure inside the pressure cooker . due to the incline of border or boundary 132 , grommet 34 is prevented from a premature ejection . at the same time , should there be a severe rise in positive pressure due to a malfunction of pressure control valve 38 , grommet 34 , and valve 32 are forced upwardly out of pressure release opening 64 . in practice , the normal desired internal pressure is ten pounds per square inch , and the grommet is fashioned to exit the pressure relief opening when the internal pressure exceeds twenty pounds per square inch . thus is disclosed a pressure cooker particularly well suited for use in microwave ovens . the grommet 34 acts as a safety valve and is released in the event of excessive pressure . by contrast , the poppet valve rises responsive to even slight positive pressure to indicate its presence . the steel locking ring and polyester resin latching members provide a convenient and secure seal between the cover and container , yet also permit the cover and container to be constructed of microwave permeable material . the safety valve , in an inexpensive , simple and reliable manner , prevents positive pressure build - up unless the cover is properly locked against the container , and further allows rapid escape of steam and vapor in the event of an attempt to unlock and remove the cover before positive pressure has subsided .
a pressure cooker for use in microwave ovens includes a microwave permeable bowl shaped container , a microwave permeable dome cover , and a steel locking ring permanently attached to the cover for maintaining the container and cover in fluid - tight seal during use . a safety valve , formed of flexible tubing , encounters a projection of the container and is deformed into a closed configuration responsive to movement of the cover , relative to the container , toward a locking position . a pressure regulator valve , consisting of a metal core surrounded by an elastically deformable casing , is positioned over a pressure control opening in the cover to maintain a selected operating pressure level in the pressure cooker . a pressure indicator and relief assembly , contained in a pressure release opening through the cover , indicates positive pressure in the chamber and is ejected in the event of an abnormally high pressure inside the housing .