Intermittent AIR Problem

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If you try to open the drain valve when it is frozen you may break the valve or the cord.

If you do get it open and it is broken it won't close again.

If you're lucky and the valve is easy to reach like on my wet tank you can replace the valve.

If it is underneath at the front axle like my dry tank then you have a real problem.

All the above is the reason I drain right after I stop for the day or even during the day before I stop.  I don't ever try to drain when the air is cold and the temp below freezing.

Just the air escaping suddenly and expanding can make the valve freeze open so it pays to drain it slowly or in spurts.