bears against a spring seat 112 encircling the lower half of the stem 74 just above the nut 110 consequently a coil compression spring 114 is trapped within the spring chamber 104 between the seat 112 and the top wall 106 to yieldably bias the poppet valve 58 downwardly toward its closed position of fig4 assisting the coil spring 114 in this respect is a second larger diameter coil compression spring 116 that encircles the spring cup 102 and is trapped between a lower radial flange 118 on the spring cup 102 and an upper transverse wall 120 of the spring housing 92 within which the clearance hole 100 is defined the spring rates of the two springs 114 116 are substantially identical to one another as a consequence of this construction the springs 114 116 are disposed in a series arrangement such that the effective spring rate of the resulting combination is cut in half for a given amount of total opening force this causes the poppet 58 to open twice as far as it otherwise would with only one of the springs 114 or 116 in use the closure 98 at the bottom end of the spring housing 92 has a centrally disposed clearance hole 122 that telescopically receives the lower threaded end of the stem 74 there is complete clearance between the walls of the hole 122 and the threads.