The VFS-24 is an economical solution on a first cost basis and from an energy basis. Since the diffuser is self powered and self contained there are no accessory products needed.

No maintenance contracts are needed. Compare the first time cost to that of a VAV system with electric or pneumatic controls. You will find that VARI-FLOW^TM diffusers provide more zone control for less money.

The VFS-24 uses a unique sleeve type damper to vary the diffuser outlet area in response to the thermal element's call for more or less air. (See sketch) This moving sleeve solves the basic problem inherent to the earlier types of thermally actuated diffusers which used disk, plate or multiple diffusion blades dampers. Thermal diffusers are designed to make use of the temperature sensitive characteristic of the thermal mechanical pressure applied to the shaft of the element. The temperature operating curve of the element is stable at a constant mechanical pressure. If the pressure on the element were to vary in operation, the temperature operating band would also vary.

The force needed to move a sliding sleeve damper is not affected by changes in system air pressure on the sleeve. As a result, the air pressure merely tries to expand the cylinder---a virtual impossibility. On the other hand, a disk or plate trying to close against the velocity and static pressure in the diffuser neck is subject to widely varying forces on the relatively large surface of the disk face.

This problem is magnified due to the design of the linkage which is used to amplify the small movement of the thermal element shaft into a greater movement of the throttling disk.

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