The Hivac XFR3 from the 1950s
As part of the precautions against airborne dirt which Hivac have adopted at their new Ruislip valve factory, the atmospheric pressure in the air-conditioned assembly shop is kept above normal to ensure that no dust can enter from outside. The same principle is used on some of the individual assembly benches, which are enclosed and have glass shields in front to prevent any moisture from the assemblers' breath from condensing on the electrode components.
The hospital-like nature of the factory is further enhanced by polished wood-block floors, a self-supporting roof structure to avoid dirt-collecting stanchions and girders, and white nylon overalls and head scarves for the girl operatives. All supplies of electricity, gas, water and vacuum are piped into the main shop from a specially constructed basement so that contaminating oil fumes and dust-harbouring pipes and wires are eliminated.
The factory is mainly concerned with manufacturing subminiature valves, and the precautions are particularly necessary when work is being done on special quality types in this category.