A stand-alone control module for use in closed-wound drainage systems is described. The control module transforms a variable high-vacuum source into a constant low-vacuum source. The control module also provides a one-way check valve to prevent return of air to a patient when draining such air from the pleural cavity of the patient. The control module is a water-based control module. It includes a first-suction control chamber for transforming a variable high-vacuum into a constant low-vacuum. The first chamber contains a first column of fluid at a first pre-determined level. The module also includes a second water seal chamber that contains a second column of fluid at a second pre-determined level. The height of the second column of fluid is less than the height of the first column of fluid. Tubes are placed in each chamber that have one end of each tube located below the columns of fluid. The column of fluid within the first chamber acts to regulate the vacuum within the chambers and the column of fluid in the second chamber provides a one-way check valve to prevent air from returning to the patient.
