Select the Right Scuba Regulator First Stage

Diaphragm and Piston First Stages

Piston-type first stages are easier to make and have a simpler design than the diaphragm type. This may help to improve reliability. They need more careful maintenance because some of the internal moving parts are exposed to water and contaminants in the water.

With the piston-type first stage, the piston is rigid and acts directly on the seat of the valve. When the pressure in the medium pressure drops because the diver has used gas from a second stage valve, the piston lifts off the valve seat and slides towards the medium pressure chamber. This brings high pressure gas into the medium pressure chamber until the pressure in the chamber has risen enough to push the piston back onto the seat and close the valve.

Diaphragm-type first stages are more complex and have more components than the piston type. They have an environmentally sealed design, and are thus particularly suited to cold water divers and those working in water containing a high degree of suspended particles, silt, or other contaminating materials.

The diaphragm is a flexible cover to the medium-pressure chamber. When the diver consumes gas from a medium-pressure second stage, the pressure falls in the medium-pressure chamber and the diaphragm collapses inwards pushing against the valve lifter. This opens the valve letting high-pressure gas pass the valve seat into the medium-pressure chamber. When the pressure in the medium-pressure chambers rises, the diaphragm inflates outwards reducing the force on the valve lifter, letting the spring behind the valve close it.

Balanced & Unbalanced Scuba Regulators

An unbalanced regulator is one in which extra pressure must be applied to the seal because the full force of the air in the tank is constantly trying to push into the regulator.

By contrast a balanced regulator equalizes the force of the air coming from the tank so that no extra force is necessary to maintain a seal.

All you really need to know is how a balanced regulator performs verses an unbalanced regulator.

Back in the early days of modern regulators, the difference between balanced and unbalanced regulators was huge.

Balanced regulators were easy breathing to the last breath and unbalanced regulators became more difficult to breathe with as the tank pressure went down.

At the time, a lot of people preferred unbalanced regulators because they could tell when they were running out of air (high pressure gauges weren’t standard then).

These days, however, modern technology has made the difference between balanced and unbalanced a lot tighter.

Unbalanced regulators are still more difficult to use at lower pressures, but nowhere near as difficult as they used to be.

Diaphragm and Piston Regulators

As far as the difference in performance, it’s negligible.

The average diver won’t be able to tell the difference. In fact, the difference barely registers on sophisticated diagnostic equipment.

There is a difference in regulator maintenance and repair however.

A diaphragm regulator is sealed from the environment. The water pushes in on the diaphragm which transfers pressure and allows the regulator to operate as it would on the surface. Being sealed from the elements has its advantages.

A diaphragm regulator will corrode less than a piston regulator. However this advantage is offset by the number of moving parts it takes for a diaphragm regulator to work.

On the other hand a piston regulator usually lets water into the first stage. There’s no need to transfer pressure since the water is ever present and transfers the ambient pressure directly.

Of course, having all that saltwater inside your regulator means it’s more likely to corrode. Your after-dive maintenance routine is very important for a piston regulator.

On the plus side, these regulators have only one major moving part and are notoriously durable.