Pneumatic internal-diameter measurement device

The invention provides a pneumatic internal-diameter measurement device based on the application of the pneumatic measurement principle. An external mechanical arm equiarm movement mechanism is fixedly connected with the connecting rod of an upper end cover so as to drive a spherical/conical-surface probe to move along the axis direction of a to-be-detected workpiece. Since the to-be-detected workpiece and the spherical/conical-surface probe cannot be ensured to be entirely concentric with each other, a position error exists between the to-be-detected workpiece and the spherical/conical-surface probe. The surface of the spherical/conical-surface probe is firstly in contact with the upper edge of the to-be-detected workpiece. Under the effect between a flexible rod and a spherical/conical-surface, the spherical/conical-surface probe is driven to move at a small amplitude along with the different positions of the to-be-detected workpiece. Therefore, the position error is adjusted and the spherical/conical-surface probe is enabled to smoothly enter the to-be-detected workpiece. The gas is driven to enter the measurement device via a quick-connection plug. Since the upper end cover is compared by the upper end of the to-be-detected workpiece via a sealing gasket to be in sealed cooperation with the to-be-detected workpiece, the gas can only flow away through a circular seam between the spherical/conical-surface probe and the internal diameter of the to-be-detected workpiece.