When it comes down to buying a regulator, whether you're a brand new diver or a seasoned bubble blower, you must decide whether to get a "piston" or a "diaphragm" first stage. Everybody asks, "What's the difference?" We help our divers choose the right regulator by first asking questions about what type of diving they typically do.

Sometimes it makes no difference which kind you choose and simply comes down to brand recognition, style, price, or other non-performance related attributes. Sometimes it does make a difference - cold water performance, ease of breathing, hose routing options, balanced vs. unbalanced. Here we will help you understand why you might want one type over the other for your diving.
What does a 1st stage do anyway?
A regulator first stage has two functions. It has the big job of reducing the gas pressure in the tank down to just 145 psi, and then distributing that gas to the second stages, pressure gauge, and inflator hoses. It's a big job because it has to be able to move enough breathing gas to supply as many as two divers (in case of air sharing) at depth and at any tank pressure.
Record set in 2013 - 135 divers breathing off of ONE Scubapro MK25 (a piston 1st stage)

Piston First Stages
In a piston first stage, gas flows from the tank and passes through a hollow metal piston into a secondary chamber (where the low pressure ports for your 2nd stages and inflator hoses are located). As air pressure in the secondary chamber increases, it pushes against the piston head on the opposite side of the shaft. When pressure in the chamber reaches an intermediate pressure of about 145psi, the piston is forced against the seat, and high pressure air from the tank stops flowing. This process repeats with every breath we take.
Diaphragm First Stages
Diaphragm first stages have a diaphragm, pin, and heavy spring that operate the valve between the two chambers in the first stage. When pressurized, air flows through the regulator and pushes the diaphragm outward until an intermediate pressure of about 145psi is reached and the seals a high pressure seat against an orifice causing air to stop flowing. When you take another breath, air flows again and the process repeats.

Diaphragm first stages come in "environmentally sealed versions" too, meaning they are completely sealed off from the water. This feature makes them particularly good for cold water diving as they are more resistant to freezing.
So which one is best?
Well it depends on your needs. Let's look at some of the things that divers should consider.

Cold Water performance - Historically, diaphragm regulators are preferred for diving in cold water due to their resistance to freezing. However, major improvements in cold water performance have been made to piston regulators over the years, and most modern piston regulators have great performance in the temperatures that most divers are diving. If you're going under ice, well, you may want to stick with the environmentally sealed diaphragm first stages... This year, Scubapro came out with the MK25 EVO and the MK2 EVO which are 30% more resistant to freezing than their non-EVO predecessors.

Hose routing - for recreational divers, either style really does the job, since most recreational divers only need  ports for their two second stages, a low pressure inflator hose, and a pressure gauge. Both piston and diaphragm regulators have sufficient low and high pressure ports for this job. Sidemount divers and technical divers lean towards piston first stages because of the additional hose routing options available on piston regulators with a swiveling turret and a 5th low pressure port on the bottom (e.g. the Scubapro MK25 regulator). The swivel turret is great for deco regulators, and the 5th port makes for the perfect set up for backmount doubles.

Balanced vs. unbalanced - In a nut shell, if a regulator is balanced, it means that it makes no difference what the pressure is in your cylinder - the regulator will "breathe" the same (well, until the tank runs out of gas, but that shouldn't be happening anyway...)
If it's unbalanced then as tank pressure drops, intermediate pressure drops, and breathing performance drops with it, especially at depth. Balanced first stages are little bit of a higher price tag, but with that comes performance, too. We'll go into a bit more detail about balanced vs unbalanced regulators in a future blog post.

Price - There's a whole range of prices out there in the world of regulators. When considering a regulator, look at features and how those features meet your needs. Also consider the post-sale support for the equipment you're buying.
Is there a dealer nearby who can provide the periodic servicing that every regulator needs? Will parts be available for years to come? Sometimes a "great buy" isn't so great if you need to send it away to some remote location every time it needs service.

Buying a regulator is a bit of an investment, but it's a piece of equipment that can last you a really long time if you take the time to choose the right regulator from the beginning. At Submerged, we want you to spend your hard earned money enjoying diving and training, not replacing a regulator because you out-grew it or it didn't meet your expectations. Our pledge to everybody who walks through our door is to spend the time guiding them towards the perfect selection based on their interests, goals, and budget. It's not beginner gear or technical gear or professional gear - it's dive gear - and we want to make sure that our divers feel good about their gear choices when they walk out the door.


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