the hub 130 to mount the hub 130 on the shaft 104 two keys 132 insert into apertures in the hub 130 and corresponding recesses in the shaft 104 to prevent relative rotation between the hub 130 and the shaft 104 the keys 132 may be held in place by a weld thus the actuator 300 for the valve 100 turns the shaft 104 approximately 90 u00b0 back and forth in order to move the disc and lever arm assembly 102 between the first and second positions the rotation of the disc and lever arm assembly 102 forces one of the discs 113 115 into contact with a respective one of the valve seats 112 114 depending on whether the disc and lever arm assembly 102 is in the first or second position the ability of the discs 113 115 to pivot about the pin 134 enables the discs 113 115 to compensate for misalignments by permitting the discs 113 115 to squarely contact the valve seats 112 114 regardless of the precise location of the valve seats 112 114 with respect to the disc and lever arm assembly 102 for example the first valve seat 112 may be aligned too far forward such that the disc and lever arm assembly 102 does not complete the entire 90 u00b0 rotation prior to the first disc initially contacting the first valve seat 112 however the disc and lever arm assembly 102 still forces the first disc 113 which pivots about the pin 134 to compensate for the premature contact into mating contact with the first valve seat 112 on the other hand the first disc 113 may pivot about pin 134 in the opposite direction if the first valve seat 112.