A mechanically-controlled vacuum throttle for a continuous dense phase pneumatic conveying system and related method is provided. The system includes a pneumatic conveyance line, a particulate material insertion assembly, a positive displacement blower, a transport fluid intake assembly, and a vacuum throttling assembly. The vacuum throttling assembly is configured to control the flow of air mass density into the blower and through the conveyance line. A portion of the vacuum throttling assembly is tied in to the conveyance line pressure downstream of the blower and adjusts the air mass density flow depending on the downstream pressure. Preferably, the vacuum throttling assembly includes an obstruction element and an opening collar, where the obstruction element is moveable relative to the opening collar and the air mass density flow is adjusted depending on the amount of movement of the obstruction element relative to the opening collar.