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Diaphragm and Piston First Stages

Diaphragm and Piston First Stages is the first place your air goes to once it leaves your scuba tank.

The first stage of your regulator has a large task to perform. It needs to break down 3000 psi (pounds per square inch) to about 150 psi to make it easier for your second stage to deliver the air to you at an ambient pressure.

Breaking down that much pressure is very demanding and it requires a precise mechanism to accomplish it safely.

Regulator manufacturers have their own ideas of how to best accomplish this task, but they generally settle on some version of a balance/unbalanced piston or balanced diaphragm based system (a diaphragm regulator can�t be unbalanced).

Balanced & Unbalanced Scuba Regulators

Let�s talk about balanced and unbalanced scuba regulators for a minute to understand what I mean by that.

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.

Sound complicated? Don�t worry about it.

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.

Moving on to 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

The more parts something has, the more opportunity there is for something to go wrong.

On the reverse side 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 route is very important for a piston regulator.

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

So which is better, Diaphragm or Piston?

When it comes to choosing between the two; I�d take into account the brand of regulator, whether or not my local dive shop is able to service it, and whether or not I�m willing to follow an after-dive maintenance program religiously.

Most importantly, make sure that the regulator you choose is one that�s comfortable when you dive.

Have a look here for more information on regulators.

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