Mechanics (in certain types of pump) a hollow chamber, closed with a valve, which is moved to and fro inside a cylinder in the manner of a piston (now historical).
Origin
Late 18th century.
Definition of working box in US English:
working box
noun
Mechanics (in certain types of pump) a hollow chamber, closed with a valve, which is moved to and fro inside a cylinder in the manner of a piston (now historical).