An interesting sidelight of building our own 3″ diffusion pumps is that as we built ever larger vacuum equipment, larger pumps were required. Motivated by our success with the 3″ pump, we gradually built a series of larger pumps going up one size at a time to 10″ diameter.
Critical point drying was invented by Tom Anderson and described in his fine paper in 1952. He was a bit ahead of his time as the widespread use of the technique was not until the arrival of the SEM in about 1970.
I became involved in critical point drying when Dr. Gennaro of New York University asked if I could make him a unit.. He sent me a copy of Tom's original paper and we visited Tom's lab for a demonstration.
With Tom's dryer, the chamber opening and closing involved a high pressure threaded seal. Fortunately, he had working with him a man big enough to be a NHL defensive end who manhandled a three foot wrench to seal and unseal the chamber.