Model S684-3 Three-Cell Automated Water Vapor Diffusion Apparatus
A Water Vapor Diffusion Apparatus (WVDA) is an instrument that is used to measure the rate at which water Vapor diffuses through fabrics. The Model S684-3 Automated Water Vapor Diffusion Apparatus (AWVDA) is a multi-cell system that enables an operator to run three separate tests simultaneously under computer control. This model consists of a workstation supporting the test hardware, a data acquisition module, and interface boards that mount in a PC.
The workstation provides space for three Water Vapor Diffusion (WVDC) Cells on laboratory retort stands and three associated auxiliary water reservoirs mounted on top-loading balances. The workstation also provides mounting for the cell water fill reservoirs and the drying columns, flow meters, regulators, and tubing for the dry air supply system.
The system uses a unique combination cell design which may be used to do moisture diffusion tests to the Canadian Government Standards Board (CGSB) Standard or the Van Beest and Wittgen (VBW) method. This cell is similar to the combination cell used in the model 643 manual WVDA, except that the dry air flow through the air-side half-cell is from side to side as opposed to radial.
The cell creates a moisture gradient across the specimen by providing a means for mounting the specimen between a water source and a water sink. The source is water held behind a "wet" membrane, and the sink is dry air flowing behind a "dry" membrane. Moisture diffusion is measured by the computer as a mass loss from the water cavity behind the wet membrane. Moisture diffusion can also be measured manually as a volume loss.
Cell Set Up Positions
When setting up in the CGSB mode, the wet membrane, typically made from Teflon, is above the test specimen and the dry membrane, also made from Teflon, is below. In VBW mode, the dry membrane, typically made from Teflon, is above the test specimen and the wet membrane, made from filter paper, is located below.