Scuba Regulator

Why a regulator is needed

A full scuba tank holds gas at around 200 bar (3,000 psi) or more. Your lungs need it at exactly the pressure of the water around you, which might be 1 bar at the surface or 4 bar at 30 m. The regulator bridges that gap. Its design, the demand valve, was developed for diving by Jacques-Yves Cousteau and engineer Émile Gagnan in 1943 and made modern scuba possible.

The first stage

The first stage screws or clamps onto the tank valve. It reduces tank pressure to an intermediate pressure, usually around 9 to 10 bar (130 to 145 psi) above the surrounding water pressure. Because it is referenced to the water, intermediate pressure rises as you descend, so the second stage always gets enough gas.

First stages come in two main designs. Piston first stages are simple and robust. Diaphragm first stages seal the internal parts away from the water, which helps in cold or dirty water. Most modern first stages are balanced, meaning their performance stays steady as tank pressure falls.

The first stage has several ports: low-pressure ports for hoses to the second stages and the BCD inflator, and high-pressure ports for the pressure gauge or a transmitter for an air-integrated dive computer.

The second stage

The second stage is the part in your mouth. When you inhale, you lower the pressure inside its case. A flexible diaphragm moves inward and pushes a lever that opens a valve, letting gas flow at the surrounding pressure. When you stop inhaling, the valve closes. When you exhale, the breath leaves through a one-way exhaust valve, making the bubbles you see.

Most second stages have a purge button, which pushes the diaphragm in by hand to clear water or to start gas flowing. Many also have a breathing-resistance knob and a venturi switch to stop free-flow at the surface.

The alternate air source

Every recreational diver carries a second source of gas for a buddy who runs out. The most common is an octopus, a spare second stage on a longer hose, often brightly coloured and worn in the triangle between your chin and the lower corners of your ribcage. Other options are an alternate second stage built into the BCD inflator, or a fully separate small tank called a pony bottle. Where you keep your alternate air source is one of the things your buddy checks during a buddy check.

Yoke and DIN

Regulators attach to the tank in one of two ways. A yoke (also called A-clamp or INT) fits over the tank valve and is tightened with a screw. It's common in many warm-water resorts. A DIN fitting screws into the valve, trapping the O-ring, and is common in Europe and in technical diving. Adapters exist to fit a DIN regulator to a yoke valve or the reverse.

Care and servicing

Rinse the regulator in fresh water after each dive with the dust cap in place, and never press the purge button while rinsing an unpressurised regulator, which can let water into the first stage. Let it dry out of the sun. Regulators should be serviced by a trained technician on the schedule the manufacturer sets, often every one to two years. Signs it needs attention include free-flowing, hard breathing, wet breathing or a changing intermediate pressure.

Frequently asked questions