Auto drains are used to replace the manual drains that are normally standard equipment on compressor tanks.
In order to keep free water from accumulating inside the receiver, this manual drain should be opened at least once a day to allow the tank to drain all water completely.
Depending on the size of your compressor and the length of time that your compressor runs each day, it might be necessary to drain water more frequently than that. Better to drain it too often than not enough.
The required daily ritual of manually draining a compressor tank is often overlooked by routine maintenance creating the situation discussed on the pages referring to water and water problems here.
An electric auto drain will contain a 2 ported, 2 position valve that incorporates a timer that can be set both for the frequency of operation, and for the length of time (the duration) that the auto drain valve is actuated, to effectively and automatically rid the compressor tank of water that is generated by the compressing of air.
The electric auto-drain comes complete with a wire and plug to allow it to be powered from a standard 120 VAC outlet. The auto drain can also be hardwired into a control system that could monitor the functioning of the auto drain automatically.
The existing manual drain is screwed out, and the auto drain is screwed into the same port. You may need a close nipple to connect the in port of the auto drain to the drain port of the compressor.
There will be a timer knob, usually calibrated for hours and/or days on which you set the frequency of operation of the auto drain. Once a day? Perhaps twice a shift?
There will be another dial or knob to allow the setting of the duration of the drain cycle, this one calibrated in seconds and/or minutes. This adjusts the length of time that the drain is open and voiding water and mist from the receiver.
The use of the receiver auto-drain will mean that the compressor tank gets drained of free water often enough to solve problems, and without a maintenance person having to remember to do so.
When you're setting up your auto drain, time how long it takes to drain the reservoir using the existing manual valve, and after the compressor has run for a shift.
When draining is complete, water should be gone and there may a be a slight mist still exiting the drain; but at this point it's mostly compressed air venting. Set the auto drain to run that same length of time, and for one cycle each shift.
You don't want the valve to auto-drain the receiver for too long a duration, as after the water is voided, all you're doing is wasting expensive compressed air.
The use of an air filter auto-drain will ensure that the filter bowl is drained as necessary, without operator intervention, with long-term positive effects on the downstream compressed air components that the filter precedes.