Bridgman seal

A Bridgman seal, invented by and named after Percy Williams Bridgman, can be used to seal a pressure chamber and compress its contents to high pressures (up to 40,000 MPa), without the seal leaking and releasing the pressure
A cylindrical driving piston is mounted within a cylindrical channel that is closed at its far end. This piston presses against a hard steel ring, followed by a softer steel ring, and then a ring of more viscous or elastic material such as rubber, copper or soap stone, all within the channel. These three intermediate stages provide an inner cylinder, and the third stage bears on a specially shaped final steel piston that applies the force to pressurise material held at the end of the outer, enclosing channel. The final piston consists of a wider portion that fills the main channel, and a narrower cylindrical extension that leads back through the inner channel formed by the three ring-shaped intermediate stages, ending within the hard steel ring without making direct contact with the driving piston. This arrangement ensures that higher pressures create tighter seals that resist any leakage from the material at the end, since the pressure within the last and softest ring is greater than that in the material at the end.