Bombard & Zodiac valves
These are a couple of types of valves found on various inflatables. In both cases the valve keeps the air in while you are inflating, but it is the valve cap that creates a proper seal.
The first type has a completely detachable valve body, so be careful not to lose it. To inflate, screw this part into the base and remove the cap. When inflated screw the valve cap in place. These are the type used in the floor of the Bombard Aerotec.
The second, more common, type has a fixed valve body with a spring loaded button in the centre which can be locked down by pushing and turning through 90 degrees. To inflate it should be in the up (or out) position, and to deflate it should be pushed in and locked open to let the air escape.