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A flush valve is provided for opening and closing a drain connecting a toilet bowl to a waste holding tank maintained at a partial vacuum. The flush valve is located external to the drain and comprises a pinch or nip mechanism surrounding a flexible section of the drain and an electro-mechanically o

A flush valve is provided for opening and closing a drain connecting a toilet bowl to a waste holding tank maintained at a partial vacuum. The flush valve is located external to the drain and comprises a pinch or nip mechanism surrounding a flexible section of the drain and an electro-mechanically operated actuator for moving the pinch mechanism to close the drain by pinching it shut or to open the drain by pulling it apart. The actuator includes a motor for moving a piston in opposite directions, and a cylinder having one end connected to the pinch mechanism and another end containing an enclosure. The piston is retained and reciprocable a limited distance within the enclosure, and a spring is interposed within the enclosure to provide biasing means between the piston and the cylinder. The spring has sufficient stiffness relative to the force needed to shut the flexible drain section, in the absence of an obstruction, so that the flexible drain section may be fully closed without compression of the spring by the piston. However, when the flexible drain section is nipped shut, or if an obstruction is encountered, the spring will be compressed within the enclosure by the piston, causing operation of a switch to deactivate the motor and prevent motor stalling and damage to the valve. A manually operable shut-off flush valve also is provided, comprising a plate slidable through a coupling in the drain line to bring an opening in the plate in or out of registration with the drain line to open or close it, respectively.

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A flow control assembly for controlling flow through a drain from a toilet bowl to a waste tank maintained at a partial vacuum, the control assembly comprising: (a) a flexible drain section connected in line in the drain; (b) a nip mechanism movably connected to said drain section for nipping said f

A flow control assembly for controlling flow through a drain from a toilet bowl to a waste tank maintained at a partial vacuum, the control assembly comprising: (a) a flexible drain section connected in line in the drain; (b) a nip mechanism movably connected to said drain section for nipping said flexible drain section shut to stop flow and for dilating said drain section open to enable flow; (c) a drive motor having an output shaft selectively driven in opposite directions by said drive motor, and control means for starting and stopping said drive motor; and (d) linkage means connecting said output shaft to said nip mechanism for nipping said flexible drain section shut on shaft motion in one direction and for dilating said flexible drain section open on shaft motion in the opposite direction, said linkage means including lost motion means for permitting motion of said output shaft over a limited range of travel without opening or shutting of said nip mechanism, resilient biasing means connected with said lost motion means for preventing operation of said lost motion means until said linkage means encounters a predetermined level of force resisting motion of said nip mechanism, said biasing means having sufficient stiffness relative to the force needed to shut said flexible drain section in the absence of an obstruction that said drain section is nipped fully to the shut condition without operation of said lost motion means, application of force beyond that necessary to fully shut said flexible drain section overcoming said biasing means to enable operation of said lost motion means, and stop means actuated by said lost motion means and operably connected to said control means for stopping said motor when said linkage means applies a predetermined level of force to said nip mechanism and said lost motion means has travelled a predetermined distance.