Diaphragm vs Piston Scuba Regulators:

One of the most common questions about choosing a  scuba regulator is, “Do I want a piston first stage or a diaphragm first stage?”  What is the real difference between the two, and as a buyer, what factors should I look for in making a decision?

Let’s start with a brief explanation of regulators in general.  The first stage regulator connects directly to the scuba tank, and converts the high pressure of the scuba tank to an “intermediate pressure” that your second stage can handle.  For most regulators, the IP (intermediate pressure) is set somewhere between 135 psi and 150 psi (roughly 9 – 10 bar).  The first stage regulator feeds your primary second stage regulator, octopus, SPG, LP inflator, and any other accessory that is gas fed.

Piston First Stage Scuba Regulators:

A piston first stage uses a piston that moves up and down against a large heavy tensioned spring.  When the regulator is pressurized by opening in the tank, the piston moves and allows air to past the high pressure seat.  When the pressure inside the regulator reaches IP, then it closes, and air stops flowing.  When you take a breath, it moves and lets air through.  While this is a simplified explanation of what happens, this is basically it.

Then we have balanced and unbalanced regulators.  A balanced piston first stage will provide the same IP all the way down until the tank reaches the IP.  An unbalanced regulator will have some IP drop as the pressure in the tank decreases.  In most cases, the balanced first stage would cost more than the same regulator in an unbalanced design.

While the piston regulator is simple in design, can provide for high gas flow, and are less expensive to maintain, there is the possibility of freezing up in extreme cold water.  This failure often causes the regulator to fail “open” and free-flow uncontrollably.

One great example of a piston regulator is the Atomic Aquatics T-3 regulator. The T-3 is environmentally sealed to keep out sand and salt from the piston, and helps prevent freezing.

Diaphragm First Stage Scuba Regulators:

A diaphragm first stage uses a thick piece of rubber (the diaphragm) pressed up against a precision machined metal pin seated on a spring and then the hard plastic high pressure seat.  There is also a spring pushing on the diaphragm from the opposite direction holding it closed.  When high pressure gas is introduced into the regulator, the spring against the plastic high pressure seat opens, and gas flows into the second chamber of the regulator until the IP is reached.  Then the regulator “closes” and this process repeats as you breathe.  The diaphragm design is easily balanced, and today, you’d be hard pressed to find an unbalanced diaphragm first stage.

The diaphragm by design has more moving parts than a piston regulator, and service kits might cost slightly more than a piston design.  Diaphragm regulators are a little better for those who are not as meticulous with cleaning their first stage after diving.  They’re also good in all water temperature, as the inner workings are not exposed directly to the water.

Some people might tell you that diaphragms don’t have as much air flow as a piston regulator.  While this may be true, there wouldn’t be a noticeable difference in most sport diving (including technical) applications.

Apeks diaphragm regulators are among the highest of quality.  These first stages utilize a unique what they call “overbalanced” design.  This means the intermediate pressure supplied to the second stage increases more than traditional balanced models as the diver descends to greater depths.

Whichever regulator you decide to get, DRIS has a wide selection of both piston and diaphragm regulators to suit your needs and desires as a scuba diver.  If you have more questions about which regulator is right for you, contact us.

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