The Column (Small Diameter) is a watertight process column made of clear PVC with a capacity of 7.6 liters (2.0 gal). It has an inner diameter of 10.16 cm (4 in) and a height of 93.7 cm (36.9 in).

The column comprises two ports at the top and bottom of the column which can be connected to the process loop or sealed off with a cap. A ruler is affixed to the column to make simple visual measurements of the level of liquid inside the column. Pressure ports allow for the measurement of the pressure at the bottom and at the top of the column. A safety valve is installed at the top of the column to prevent the pressure from exceeding a safe limit. The safety valve starts to open at 240 kPa (35 psi) to relieve excess pressure and is fully open at a pressure of 345 kPa (50 psi).

The column features a bubbler tube to infer the level of fluid in the column and contains a stainless steel baffle plate to reduce water turbulence when it is filled from the bottom. The Column (Small Diameter) can be used to create interacting second-order processes when interconnected to the large diameter column.