referring now to the drawings , a double throw thermally responsive valve assembly 10 of this invention has a two part generally cylindrical valve body comprising a first valve part 14 and a second valve part 74 . the first valve body part 14 as shown in fig2 and 3 has a first , a second and a third port 16 , 18 and 20 which are generally perpendicular to the body part 14 . the three ports 16 , 18 , and 20 each have central bores 22 , 24 and 26 respectively which run the entire length of the ports and respective external nipple portions 23 , 25 and 27 . first valve part 14 and ports 16 , 18 and 20 are preferably made from one piece of material such as glass filled nylon . ports 16 , 18 and 20 are typically connected with tubing ( not shown ) which run between valve 10 and the vacuum or vent sources and control functions which the valve operates . the disposition of ports 16 , 18 and 20 are conveniently parallel and adjacent to one another yielding a valve which is compact in size . central bores 22 , 24 and 26 all connect with a central cavity 28 within first valve part 14 . bores 24 and 26 lead directly into cavity 28 whereas bore 22 leads into a connecting passage 30 which in turn leads into cavity 28 . the outlet of connecting passage 30 into cavity 28 functions as the upper or first valve seat 32 for valve assembly 10 to be discussed further below . anchored within cavity 28 as by press fitting is a bushing 34 having a central hub 46 depending therefrom and having an axially extending bore 36 running through bushing 34 comprising a large diameter portion 38 and a smaller diameter portion 40 . in addition to axially extending bore 36 bushing 34 has a laterally extending bore 42 positioned in hub 46 in communication with bore 36 preferably adjacent to central bore 26 and perpendicular to axially extending bore 36 which provides a passage between port 18 and port 20 . the passage extends from port 18 to cavity 28 through large diameter portion 38 and laterally extending bore 42 to cavity 28 and to port 20 . the small diameter portion 40 serves to maintain proper alignment of a transfer pin 44 to be discussed below . bushing 34 may be made from glass filled nylon similar to the material for first valve part 14 . in accordance with this invention a lower or second valve seat 48 is formed where the large diameter portion 38 of axially extending bore 36 opens into the upper portion of central cavity 28 as shown in fig2 and 3 . positioned between first valve seat 32 and second valve seat 48 is a stopper 50 as viewed in fig2 and 3 with preferably a first conical portion 52 and a second conical portion 54 with a circular flange piece 56 positioned between portions 52 and 54 . stopper 50 may conveniently be formed from a single piece of material such as rubber . the two conical portions 52 and 54 may have an acute included angle such as sixty degrees so that the two external ends 58 and 60 have diameters smaller than those of valve seats 32 and 48 while the internal ends 62 and 64 have diameters larger than valve seats 32 and 48 . the purpose of conical shaped portions 52 and 54 of stopper 50 is to allow them to reliably seal the valve seats . a coil spring 66 as shown in fig2 and 3 at one end fits over tubular portion 68 at the opening of connecting passage 30 into cavity 28 and at the other end rests on flange piece 56 of stopper 50 . spring 66 serves to bias stopper 50 toward second valve seat 48 . the spring has a predetermined spring constant which is compatible with the snap - force of a bimetallic member 72 to be discussed further below . a second valve body part is generally indicated by numeral 74 and is shown to comprise a cup - shaped member adapted to be sealingly secured to first body part 14 . more particularly second body part 74 comprises a member of thermally conductive material such as brass having a preferably hollow threaded stud 76 and a shallow central cavity 70 with a flat bottom 96 which serves as a seat for reception of a wave spring washer 78 , bimetallic member 72 and first body part 14 . body part 74 has a hexagonal shaped portion 80 enabling the valve assembly 10 to readily be inserted in a threaded hole and also a relatively thin wall 82 extending upwardly from the hexagonal shaped portion 80 . a shoulder 84 is formed at the junction of wall 82 with the remainder of portion 80 and against which a first circular projection 86 of body part 14 bears when the two body parts are assembled . a sealing gasket 88 ( e . g . an o - ring ) is disposed in a notched portion 90 of body part 14 and is compressed when side wall 82 is rolled over to sealingly secure the two valve portions together to form valve body 12 . bimetallic member 72 is preferably a dish - shaped element having one layer of metal of a low thermal coefficient of expansion and another layer of metal of a somewhat higher thermal coefficient of expansion . the outer peripheral edge of bimetallic member 72 is secured between wave spring 78 and a second smaller circular projection 92 at the bottom edge of body part 14 as shown in fig2 and 3 . also a recess 94 is provided adjacent projection 92 in body part 14 to allow clearance for member 72 . upon reaching a predetermined temperature bimetallic member 72 will snap between a first position as shown in fig2 and a second position as shown in fig3 . a transfer pin 44 extends through axial bore 36 with one end in contact with stopper 50 and the other end resting on bimetallic member 72 . the length of pin 44 , the distance between valve seats , and the distance the bimetallic member 72 snaps are coordinated such that when bimetallic member 72 is in the first position stopper 50 biased by coil spring 66 will seal the second valve seat 48 and when the member snaps to the second position , pin 44 will force stopper 50 to seal first valve seat 32 . the alignment of pin 44 is controlled by the smaller diameter portion 40 of axial bore 36 in which the size of the bore is just large enough to slidingly receive the pin . the pin may be made from any suitable material such as low carbon steel . valve assembly 10 is particularly adapted to be threaded into an object , such as an automotive engine block or the like , to transfer heat from the engine block to bimetallic member 72 so as to heat the member in response to a corresponding temperature increase of the engine block . upon cooling of the engine block , the member will be maintained at approximately the temperature of the engine . when valve assembly 10 is installed in an engine , disc member 72 is in the first position as shown in fig2 when the engine is cold thus providing that stopper 50 seals second valve seat 48 . this condition allows for passage between ports 16 and 18 . as the engine heats up , heat is conducted in body part 74 so as to heat member 72 . as member 72 exceeds a predetermined temperature it snaps over - center to a second position which seals the first valve seat 32 . this condition allows for passage between ports 18 and 20 . in a typical automotive emission control system , the snap temperature of disc member 72 is below a mean operating temperature to which the valve may be subjected . the temperature override beyond the valve switching temperature will cause the disc member 72 to continue to creep after snapping thereby exerting more force on the stopper 50 . in order to avoid compression set of the elastomeric valve material and overstressing of the disc member , wave spring 78 is employed to adsorb some of the force by deflecting at a predetermined force level . although the present invention has been shown and illustrated in terms of a specific preferred embodiment , it will be apparent that changes and modifications are possible without departing from the spirit and scope of the inventions as defined in the appended claims . for example , stopper 50 may be in a spherical shape such as a rubber ball and work to seal the valve seats as required .