The oil bubbler is filled approximately two-thirds full with oil. The oil level should be above the inner inlet pipe and below the side outlet. The oil bubbler is inserted into an NS 14/23 ground joint (sleeve).

To avoid overpressure when heating up the reaction vessel or when working under inert conditions, the oil bubbler is fitted in the reactor lid. Any resulting pressure or gas can escape via the opening of the oil bubbler, while the ambient air cannot enter the reaction vessel through the oil filled in. The oil bubbler can also be used to visualize the gas flow in the reactor vessel.