Cylinder device for constant-pressure tank

The utility model relates to a cylinder device for a constant pressure tank for the operation of well cementing for extracting petroleum or natural gas. The utility model comprises a constant pressure container, and is characterized in that the utility model also comprises a pretension sealing device, a sealing ensuring device and a sealing cover, wherein, the pretension sealing device can ensure that the pressure of the constant pressure container is constant and the constant pressure container is sealed; the pretension sealing device comprises a cylinder body in which a piston, an elastic piece which acts on the piston, and a cylinder cover are arranged. The sealing ensuring device comprises a pin shaft, wherein, one end of which is provided with a spherical pin post movably connected with the piston, and the other end of which is provided with a universal joint connected with the constant pressure container. The sealing cover arranged at the lower part of the pin shaft is overlapped to be pressed at an upper port of the constant pressure container. The device leads the constant pressure tank to reliably ensure that constant pressure which is required is produced. The utility model fundamentally eliminates the problem that because a gas bladder is aged, gas leaks from the constant pressure tank. Because the manufacturing cost of the device is low and the usage is reliable, the utility model can be popularized and used for mining on land, which improves the collecting quality of an oil gas well and greatly increases economic benefits.