Process engineering design relies on a host of mechanical devices that enable transport phenomena to take place under controlled conditions.  These devices include pipes, valves, pumps, chemical reactors, heat exchangers, packed columns, etc.   Mass, energy, and momentum transfer will also be essential phenomena in nano-process engineering, particularly at the interface between micro and nanodevices.   Control valves are one of the most fundamental components.   In this paper we explore the design of a silicon cantilever valve for fluid transport control at the molecular level (32.5-55 nm in length).  We utilize design elements that can be synthesized with existing or emerging chemical methods.  Thus, the valve is constructed with functionalized silicon surfaces, single-wall carbon nanotubes, and organic monolayers.  While Molecular Mechanics design limitations were overcome with help from classical engineering approximations, non-linear effects, such as nanotube crimping (for an in-line valve design), are accounted for through full-physics atomistic simulations. Optimal design geometries and operating deflection ranges have been estimated for a device containing over 75,000 atoms.