Hookah valves are used to regulate the flow of air in the hookah, and they can be made from different materials, such as metal or plastic. Hookah valves can be adjustable or non-adjustable, and they can also be open or closed. Adjustable hookah valves allow the user to control the amount of air that flows through the hookah, while non-adjustable valves do not. Open hookah valves allow air to flow freely through the hookah, while closed valves block the flow of air.