first bore 24 is formed in the neck 18 and a second bore 26 is formed in the boss 22 both bores being in axial alignment along a diameter of passage 16 the bore 26 is closed at its lower end by a plug 28 an annular seating surface 30 surrounds the flow passage 16 the valve closure assembly 14 is formed by a disk member 32 defining a sealing surface 34 profiled to be received in the annular seating surface 30 an annular groove 36 in the surface 34 receives an o ring 38 and wiper seal 40 therein the o ring 38 is preferably made of conventional resilient materials such as rubber or polymeric material while the wiper seal 40 is a thin metallic member such as stainless steel an upper valve stem 42 is received in the first bore 24 of the body while a lower stem 44 is received in the second bore 26 the valve stems 42 and 44 are axially aligned extending into the flow passage 16 along a diameter thereof the upper valve stem 42 is mounted by a packing ring 46 a bushing 48 a packing 50 which preferably is layered with fireproof materials and a bearing 52 while the lower valve stem 44 is mounted by a bearing 54 a packing 56 also including fireproof material and a thrust washer 58 the upper end of the upper valve stem 42 extends beyond the.