For unsaturated flow and transport studies, a negative pressure is maintained at the lower end of the soil column.  To keep the negative pressure constant, a vacuum regulator is needed. The regulator, available from SMS, gives precise control of the negative pressure (vacuum level).

The regulator has two outlets: one is connected to the vacuum source and the other is connected to the chamber in which the negative pressure has to be kept constant (i.e. a vacuum chamber or an effluent collection bottle). By turning the control knob of the regulator, one can adjust the regulated vacuum to within 1 cm of the desired level.

A 5 micron air filter is recommended between the regulated vacuum and the regulator.

Because the negative pressure used for flow and contaminant transport studies is nearly always between 0 and -0.5 bar (-7.5 psi or -50 kPa), a relatively low cost vacuum pump may be used.