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I always wondered what the actuator in the exhaust air valve for my apartment ventilation was - now I'm pretty sure it's a wax motor! You can use a switch to increase the airflow, but it takes a few seconds to react and opens/closes very slowly and quietly.

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Some of them are a sort of hydraulic one that uses a spring and some fluid to make the spring release slowly. No idea which you would have lol.

The slow closing prevents water hammer, at least in water systems. In air systems it might just prevent a blast of back pressure blowing all the dust out of your vents onto your carpet.

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