Gas sampling valve:

For samples that exist as gases under normal conditions, a gas sampling valve, shown in Figure, is used for sample injection.

Figure:  Gas sampling valve

As carrier gas passes by the valve on the way to the column, a sample could be filling the sample loop. While the actuator is turned the carrier gas stream is redirected by the sample loop and sweeps the sample within the column. The loop itself might have a volume as low as one quarter of milliliter or as large as 10 milliliters. A choice of loop size is made to be compatible along with the analyst's experimental requirements.