Stuffing device

In the immediate vicinity of the air seal, there is a very large pressure gradient between the inside and the outside. This is because the external air is at a pressure of 1 atmosphere, and the internal air is at a pressure of 12 atmospheres, and the distance over which this pressure change occurs, that is the axial thickness of the seal, is very short compared with the length of the duct. Naturally this very large pressure gradient results in very large buoyancy forces in the cable tending to push it back out of the seal. In order to overcome this force, and push the cable into the duct through the seal, the apparatus usually includes some form of traction that can grip and motivate the cable. Typically, two rubberised tracks grip the cable between them, and rotate together in such a way as to drive the cable through the seal and into the pressurised chamber.