Hi Rio Owner,
Yes, Screamer has it right.
If you sailed with the vent plug (your "air valve") completely removed, then your board could have taken on a significant amount of water.
As Screamer suggests, put the board in a warm place or out in the sun.
Use some paper toweling as a "wick" to pull the water from the board.
When you see no more water at the base of the vent plug hole (where you can see a bit
of the core foam) and your paper towel wick comes out dry, you will have done all you can do.
For summer use, I would put the vent plug back in, tighten it, and leave it tightened for the summer.
Next winter, store your board in a warm dry place, with the vent plug removed completely.
If you want to "accelerate" the drying process, use the ambient outside temperature.
In the morning when things are heating up, remove the vent plug and use the paper towel wick. As the temps come up, the inside of your board will heat up and push the moisture up to the vent hole and onto your wick.
As soon as you get the hottest part of the day, and things start to cool down, put the vent plug back in tightly. This will lower the pressure inside your board's core and pull more moisture up near the vent plug.
In the morning, as things are heating up, remove the plug and use the wick.
Repeat this process until you see no more wetness at the bottom of the plug hole or on your wicks.
Mostly, once dried out, you can install the plug and leave it in unless you are going to change altitude by more than 1000 meters or going to air ship your board in the cargo hold of an airliner.
Only other time you need to open the plug is when the seasons change, and then you only need to open it (away from the water) long enough to let the pressure inside equaliize with the ambient outside pressure/temperature.
Hope this helps,