• Ross QLD Scuba

Different Regs for Different Divers? Part 1 - First Stages

Updated: Aug 5, 2019

Over the years of working in the diving industry. I've seen pretty much all the styles, combinations, and budgets of regulators being used by a variety of divers. With such a large availability of different styles of reg from different manufacturers. Choosing the right regulator for you can be challenging, as there are so many choices and variables. To help guide your decisions in a more educated way, I am going to breakdown the main types of regulators on the market, as well as the pro's and con's for each type. Although initially written for those looking to purchase their first set of regulators, I believe that there is something here for all levels of divers to take away. There is always more to learn, and having a firm understanding of how your life support system operates will make you a safer, more confident diver. Due to the nature of the topic, this post has turned out much longer than originally intended. However, stay with it until the end, I'm certain it will answer some of the questions you may have regarding regulators. Starting at the cylinder: the first stage regulator is what attaches to the cylinder. It is the First stage of pressure reduction, hence the name. Now when it comes down to it, there are 3 main styles of first stage:

1) Unbalanced Piston

2) Balanced Piston

3) Balanced Diaphragm

These all do the same job: reduce the high pressures of the cylinder to an intermediate pressure. However, their method of reduction is slightly varied. The intermediate pressure is controlled in all types by a spring which also has the added pressure of the ambient surroundings which combined get the IP (Intermediate Pressure). This allows the IP to change as a diver descends and ascends. Therefore, IP is always relevant to the external pressure.

The Unbalanced Piston

This is the most basic regulator on the market. As the name suggests, it utilizes a piston that when the air flow is turned on, will allow flow through the shaft of the piston to the bottom side of the piston head. This air pressurizes and pushes the piston back towards the start of airflow pushing the seat of the piston into a sealing surface effectively sealing off the flow.

This is the most basic variety of first stage on the market however, they are still a great performer for certain applications. For new divers these are a solid regulator on the cheaper end of the budget that will last a lifetime. They're cheap to maintain and service however the ability to tune them involves disassembly to put thin "shims" against the spring to increase the tension thus increasing the pressure required to overcome the spring itself and push the piston seal into the sealing surface (knife edge) above the top of the piston shaft.

I see these regulators quite a lot in school applications as they're cheap to purchase, cheap to maintain, yet will last a lifetime. This also makes them a good option for someone looking to purchase their own regulators but may not need to have a performance regulator.

A few downfalls of these regulators however, is their flow rate and ability to adapt to pressure changes both external and from the cylinder.

Being that the intermediate pressure (the pressure that is given to the second stage) is solely based on the air pressure pushing against the spring tension, as the cylinder pressure gets lower, the intermediate pressure gets lower as there is not as much "push" behind it. So as the cylinder pressure gets lower or the diver goes deeper, the pressure required to overcome the Spring and ambient pressure becomes a larger difference.

The Balanced Piston

This Regulator while similar to the Unbalanced Piston; in that it uses a piston to flow air and still uses a spring to set the IP. However, instead of the air flowing through the side of the piston shaft, the top of the piston is open and it uses the whole diameter of the piston shaft to allow flow through. This gives it a much larger flow rate as the air is able to flow through a hole around 5-6mm in diameter, instead of approx 0.5 on the unbalanced piston. The Term Balanced also changes the way it works in that instead of the air pressure pushing against the spring tension, there is air pressure on both sides of the sealing surface. By having air pressure on both sides, the spring tension is still used to set the IP but isn't also required to hold back the air pressure as it would on a unbalanced setup. This results in both higher flow rates and also constant IP regardless of depth and/or cylinder pressure.

For a visual on the different "holes" for the air to flow through on Balanced vs Unbalanced please see the below photo.

Balanced Piston on the Left, Unbalanced Piston on the Right

Balanced piston regulators are used quite a lot by divers who are heavier breathers, dive deeper sites, or like the ease of breath in any situation. Regulators like the Scubapro MK25 are considered one of the top performing regulator on the current market. if you look at this link to youtube, in 2013 Scubapro Korea had 135 Divers breathing off a single Mk25 first stage. Admittedly, that was only at 1m or so. However, an average breathing rate per person is anywhere from about 12-20L/min so 1780-2970L/min was flowing through the regulator. These style of regulator have more parts in them then an unbalanced piston but they are just as bulletproof provided they are maintained according to manufacturers specifications and cleaned with clean fresh water after each dive.

The Cost to purchase these is a little bit more than the unbalanced piston regulator. However, for divers looking for something that can easily last them a lifetime with basic maintenance and uncompromising performance these are a great option. The main downside to balanced piston regulators is their cold water performance. For use in water under 10 degrees Celsius you can run the risk of freezing them when you inhale or purge as the expanding airflow can drop the temperatures of the brass quickly and suddenly.

The Balanced Diaphragm

The Balanced Diaphragm regulator is probably one of the most common styles of regulator out today, with every manufacturer making diaphragm regulators. Instead of using a piston, they use a rubber diaphragm which is still affected by the ambient pressure to adjust the IP of the regulator.

As can be seen, a lot more parts are required in a diaphragm regulator than is found in the piston style. This however does NOT affect reliability, provided the regulator is of good quality to start with and serviced and maintained regularly. The balanced Diaphragm is likely the most common style of regulator on today's market, if it had reliability issues that would be a hard claim to make. The pro's of the diaphragm regulator are very similar to the Balanced piston. In that it isn't plagued by the IP drop of the unbalanced piston as the cylinder pressure gets lower, and the air flow is quite a lot larger then the Unbalanced piston reg too. They are also a lot less susceptible to freezing in colder water then the either the Balanced Piston or Unbalanced Regulator styles.

Compared to the Balanced piston, the airflow rates in the Diaphragm regulator are not as high as the Balanced Piston. Considering the regulators I personally use (Cressi T10SC/Master) are rated at 4500L/Minute flow from the first stage; there is no scenario where a recreational diver, or even a technical diver at 100m would require that amount of airflow, so there is plenty of buffer. The Main benefit to the diaphragm regulator is the cold water performance. Unlike on either of the piston styles, there is no water touching metal on the surfaces that have airflow.

In both piston styles, the air flows through the piston shaft and as mentioned, expanding gas cools down the surfaces it touches. the knife edge on a Balanced Piston regulator on a single inhale can get to ~ -50C. In the Diaphragm reg's, the water sits in the Spring chamber and adds to the spring tension just like the piston reg's. But, all the airflow happens on the underside of the diaphragm meaning they are much less likely to freeze than a piston reg. Some Diaphragm reg's come with an environmental seal standard or as an add on you can purchase. This adds another diaphragm above the spring which uses a 'push rod' to transfer the ambient pressure of the water to the base diaphragm keeping water out of the regulator all together. These are the recommended regulator for cold water diving (ie, below 10c) or for contaminated/dirty water.

So hopefully that wasn't too much to take in regarding the First stages available. However, if you are fully informed on what regulators are available it can greater improve the quality of your diving. there will be a second post coming shortly explaining the differences between second stages. For now, I hope you enjoyed the article and found it informative. Of course if you have any questions don't hesitate to send us a message, email or even call to have a chat. Many thanks,


+614 2414 0464

2/28 Devlan St, Mansfield, QLD, 4122, Australia

©2019 by QLD Scuba Services.