An apparatus includes a valve body defining a chamber located on an axis. The fuel processor of the present invention efficiently maintains an internal vacuum by balancing the surface area of the air intake with the atomized airfuel combination output. Each key of a pair of keys is individually actuatable. Two retaining members extend from an inner surface of said rose and two engaging members extend from said mounting plate. The invention pertains to a 1,4-benzothiazepine-1-oxide derivative represented by general formula I or a pharmaceutically acceptable salt thereof, and a pharmaceutical composition containing the same I.