Final answer:
A vapor recovery cap is used on a vent riser to prevent vapor escape or entry, which operates once pressure or vacuum conditions exceed certain limits. Venturi tubes exploit pressure differences through constriction, leading to entrainment, which is also the principle behind gas distribution between two flasks, one of which is evacuated.
Step-by-step explanation:
A vapor recovery cap is installed on the vent riser to prevent vapors from escaping or entering the system, unless a pressure or vacuum condition exists that exceeds the design opening pressure or vacuum limit of the cap. Devices similar to vapor recovery caps, such as Venturi tubes, are used to manage fluids and gases. A Venturi constriction refers to a section of a tube that is narrower than the rest, which can cause a pressure change facilitating fluid or gas movement. It is commonly used in devices like carburetors and aspirators because it utilizes the entrainment principle. This principle is also evident when two flasks are connected, one containing a vacuum. Upon opening a valve between them, the gas will evenly distribute due to the pressure difference.