Vacuum control valve for vacuum drainage system

A valve for a vacuum drainage system includes a valve body having an interior chamber operatively connectable to a suction device and through an outlet to a vacuum source. A movable member having an aperture is secured within the chamber and movable through points between closed and open positions to adjust the open area of the aperture and the fluid flow through the outlet. The aperture is configured such that during adjustment to increase the effective operational area of the aperture, a rate of change of the effective operational area increases non-linearly in relation to a linear increase in the distance of travel, while providing advantageous and more controllable linear adjustment of the applied vacuum. The aperture can have a trilateral shape including at least one curved side, or comprise a plurality of sub-apertures, and the movable member can comprise a rotary sleeve.