Center pneumatic positioning device

A center air-actuated positioning apparatus is for positioning a pipe welder on the hole of a pipe element. The positioning apparatus comprises a cylinder, an shaft sleeve which is fixed on the cylinder after one end is sleeved on the cylinder brace, an elastic fixing letter which is sleeved movably on the cylinder brace which projects from he cylinder, and a rotarily fixed nut sleeve which limits the elastic fixing letter to the cylinder brace, wherein the shaft sleeve which bites the two ends of the elastic fixing letter and the lateral sides form cone portions respectively to facilitate the two ends of the elastic fixing letter to position on the center of the hole of a pipe element after being squeezed and expending radially when the cylinder brace and the nut sleeve shrink relative to the shaft sleeve, thereby realizing the center positioning of the pipe welder which is arranged on the cylinder seat on the center of the hole of a pipe element. The utility model provides a center air-actuated positioning apparatus which is convenient to operate and has high positioning accuracy and good reliability.