A regulator is a piece of scuba equipment that reduces the high pressure of air in a scuba air tank to a pressure level that is usable by the diver. It delivers air to the diver only during inhalation. The modern scuba regulator is a very simple and reliable device with only a few moving parts. Regulators have two stages: a first stage that attaches to the scuba tank, and a second stage that has a mouthpiece. Air under high-pressure from the scuba tank is reduced sequentially in each stage. The first stage reduces the high tank pressure to an intermediate pressure of 100 to 150 psi above the surrounding water pressure. The second stage reduces the intermediate pressure to that needed for comfortable breathing.