Real Dictionary

valve
countable noun: A valve is a device attached to a pipe or a tube which controls the flow of air or liquid through the pipe or tube.
countable noun: A valve is a small piece of tissue in your heart or in a vein which controls the flow of blood and keeps it flowing in one direction only.

valve in American English
either of the halves of a double door or any of the leaves of a folding door
to fit with or make use of a valve or valves
noun: any device for halting or controlling the flow of a liquid, gas, or other material through a passage, pipe, inlet, outlet, etc
transitive verb: to provide with a means of controlling the flow of liquid, gas, etc., by inserting a valve

valve in Automotive Engineering
noun: A valve is a device attached to a pipe or a tube that controls the flow of air or liquid through the pipe or tube.

valve in British English
noun: any device that shuts off, starts, regulates, or controls the flow of a fluid

valve in Mechanical Engineering
noun: A valve is a device that shuts off, starts, or controls the flow of a fluid.