A positive displacement piston flowmeter (10) for measuring air flow comprising a hollow flowtube (12) preferably arranged in a vertical orientation, having a movable piston (14) disposed in the flowtube (12) for movement betweeen a starting position, preferably at the bottom end (16) of the piston stroke, and an elevated position at the top end (24) of the piston stroke. The piston (14) is reciprocated by means of a pressure relief control valve assembly (25) by means of a flexible string, which causes the piston (14) to automatically close the valve assembly for automatic operation on reaching the bottom end (16) of the piston stroke and to reverse direction.
展开▼
