For a better illustration and official description, this information is taken from the original patent application.

1,095,759. Crank-case ventilating. SMITHS INDUSTRIES Ltd. Dec. 7, 1964, No.49776/64. Heading F1B.

In a valve mechanism for ventilating a crankcase to an induction manifold or carburetter a diaphragm 21 acts on spring-loaded valve 30 to restrict gas flow through port 14 as crank-case pressure falls. Valve 18 is loaded so as to be closed when the engine is inoperative and when the engine is running is drawn by the suction in pipe 15 away from port 14. Crank-case gases are drawn through pipe 7 and port 14 into pipe 15. As crank-case pressure on diaphragm 21 falls valve 30 moves downwardly against spring 9 until valve 30 enters port 14 causing the pressure on diaphragm 21 to rise until valve 30 occupies an equilibrium position thereby maintaining crank-case pressure constant.