The downstream portion of the class tube is 1.8 m long. The nozzle was precision machined from aluminum stock, with a contraction ratio of 4.77. At both the inlet and outlet, the nozzle merges seamlessly with the glass tube segments. The lower end of the glass tube connects with the supply tank outlet, through a rapid opening pneumatically-operated valve, and a diaphragm assembly. The diaphragm, made from thin mylar sheet, is to improve sealing between the two volumes.
Evacuation is accomplished by a bank of vacuum pumps, one roughing, and two high vacuum pumps.
Our initial target is to operate at 10-4 bar, but still higher vacuum is possible if so desired. At the top of the T-junction, we can see the drop generator, a mechanism that allows the highly reproducible introduction of a liquid droplet into the evacuated system. This initiates an experimental run. The automatic sequence is triggered by the droplet's arrival to a desired location in the test section, as sensed by interrupting a large beam directed into a photodiode. The resulting signal triggers, with some specified delay, the valve opening mechanism, and with another specified delay the optical imaging system.