Venting Membrane Switches: How is it Done?

Venting: 

When a key is depressed in a membrane switch, air pressure within the switch cavity increases. In order for the switch to close properly, air within
a switch cavity must be displaced, equalizing the internal pressure. This is usually only a problem in switches that are environmentally sealed. There are two standard venting methods that can solve this issue:

Internal Venting: 

Narrow channels between key location cutouts are cut into the spacer layer, permitting the air from one location to move elsewhere when that key is pressed. Note, however, that these air channels never exit to the outside of the membrane switch, preventing the risk of contamination since the switch remains sealed.

External Venting: 

As in internal venting, narrow channels that have been cut into the spacer layer connect each key location. These channels then exit through the sides, rear, or internal cut-outs of the membrane switch. This design allows pressure within the switch cavities to be equalized with the surrounding atmosphere, thus allowing switch closure at any atmospheric pressure. Because external venting increases the risk of contamination, it is only recommended when the membrane switch is exposed to rapid or extreme atmospheric pressure fluctuation and will generally not come into contact with a harsh environment.

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