Rivet gun with a changeable cylinder

A rivet gun comprising:

• a barrel having a bottom side;
• a handle assembly having
• a hydraulic shaft being hollow, mounted on the bottom side of the barrel and communicating with the barrel and having a bottom end;
• a handle mounted under the bottom side of the barrel and around the hydraulic shaft and having a bottom end and an annular shoulder formed on and protruding radially outward from the bottom end;
• a cylinder having
• a top cover mounted on the bottom end of the hydraulic shaft, contacting the annular shoulder and having a top surface, a bottom surface and a central hole defined through the top cover and mounted around the hydraulic shaft, wherein a diameter of the top cover is larger than a diameter of the annular shoulder such that an outer periphery of the top cover protrudes radially out from an outer periphery of the annular shoulder instead of being covered by the annular shoulder;
• a fastener mounted detachably on the bottom end of the hydraulic shaft and abutting the bottom surface of the top cover such that the top cover is sandwiched securely between the annular shoulder of the handle and the fastener;
• an annular body mounted detachably on the bottom surface of the top cover and having a cavity defined in the annular body;
• and
• a bottom seat mounted detachably on the bottom of the annular body;
• and
• a seal ring assembly having a primary seal ring mounted hermetically between the annular shoulder and the top surface of the top cover.