The tire air valve has a function to let the air in but also out of the tire. Does your tire have a tire pressure that is way too low? Than you can easily put more air in your tire trough the air valve to get the tire pressure on the right point again. Same way when your tire pressure is to high. You can also let the air easily out of the tire trough the air valve. It's only a small part of the tire, but it has a huge value.