A Boston valve is a two-way valve typically used to inflate items such as a kayak or other inflatable boats, inflatable bed or air mattress. The valve allows air to be pumped in yet not escape by means of a flap.
The bottom opening of the valve should first be screwed on to the kayak. The top valve is opened and used to pump air inside the desired object. Once the boat or mattress is filled with the correct amount of air, the upper valve is then closed. Air can be released from the object by unscrewing the bottom or base valve.