All about regulator second stages….

We’ve covered some basics about regulator first stages and now it’s time to talk about second stages.

Even though there are numerous manufacturers building scuba regulators, many of them fall into some general categories: configuration, downstream or pilot valve, balanced or unbalanced, and adjustable or non-adjustable.

Let’s take these one by one. First, the most common configuration for a second stage has the diaphragm and purge button on the front cover. Many manufacturers today realize that their regulators are used with divers who wear gloves or heavy mitts, so they have designed the second stage covers to activate the purge system no matter where the diver presses on the second stage cover. An example of this is on the Aqualung Titan second stage, shown at right.

The other version has the purge button located in the center of the second stage cover, and requires the diver to press only that button to purge the second stage. The second configuration has the purge button and diaphragm located on the side of the second stage. You may hear these referred to as “side breathers” as they exhaust the diver’s bubbles to the side, rather than from under the chin.

Downstream or pilot valve designs…..downstream are the most common. When the diver inhales, a lever inside allows the air from the tank to flow, while a pilot valve is a more complicated piece of engineering…when you inhale a small valve releases air pressure that in turn opens a larger valve and allows the air to flow to the diver. The advantage here is that it provides a greater airflow with less effort. An example of a pilot valve design is the old Oceanic Omega second stage or on some Poseidon regulators.

Balanced or unbalanced….sometimes referred to as a “mechanical” or “pneumatically balanced” second stage. An unbalanced second stage uses a heavier spring to keep the internal valve closed. This means the force required to open the valve and allow air to flow is slightly more than with a balanced valve. When a balanced or pneumatically balanced design is used, the spring inside the second stage is much lighter, requiring less force to open the valve and allow air to flow.

Adjustable vs. non-adjustable….All second stages use internal adjustments that the technician uses to allow the regulator to perform at it’s best. When an adjustable second stage is used, generally on higher end models, the diver can control the spring tension inside, which can be beneficial when swimming into a current for example. The diver can “de-tune” the regulator to avoid free-flows. The adjustable feature is not designed for the diver to “save air” by de-tuning, because in doing so, the diver is actually depriving themselves of oxygen, causing them to require more air.

Regulator First Stages, continued

A few days ago, I talked about the differences between piston and diaphragm first stages. There is another aspect of first stages that needs to be addressed: balanced versus unbalanced. The differences can be a factor when purchasing a regulator. Let me explain….
In an unbalanced first stage the cylinder pressure presses on the internal valve and assists in opening it. As the cylinder pressure drops, this design will have a drop in performance. The balanced design routes high pressure air around both sides of the internal valve opening. This cancels out or “balances” the cylinder pressure so that the breathing performance stays constant throughout the dive, without regard to how low the tank pressure goes.

Most regulators today feature balanced first stages, but there are some entry level/opening price regulators that still use the unbalanced design. These tend to be adequate for shallow water diving and can be an inexpensive option. Above all, diver safety is primary, so be sure to consider all aspects of where you think you will be diving to help make the right choice in a regulator.

Regulators..Piston or Diaphragm?

We get a lot of questions from new and relatively experienced divers about which regulator to buy…a piston first stage or a diaphragm first stage. Well, let’s take a quick look at the differences and talk about some advantages and disadvantages to each. In another post, we will address second stages.

Piston First Stages Advantages:

• Fewer moving parts-easier to service (in most cases)
• Easily accommodate designs with swivels for easier hose routing
• Generally less expensive

Piston First Stages Disadvantages

• They are open to surrounding water, so if you dive in silty water or salt water, they may need service more often
• If you dive in cold water, they may have a tendency to free-flow easier than diaphragm first stages

Diaphragm First Stages Advantages

• Internal parts are sealed from surrounding water-better for cold or silty water
• Qualified individuals can make adjustments in the field without disassembling the entire first stage
• Easier to purchase with an environmental seal-much better for cold water

Diaphragm First Stages Disadvantages

• Few swivel designs
• More internal parts
• Sometimes more costly to service (parts cost)

So, there are advantages and disadvantages to each style of regulator first stage. When you are ready to invest in your own Scuba regulator, be sure to ask yourself some questions, such as where am I going to do most of my diving…cold fresh water, warm salt water? What are the service intervals for the brand/model I’m considering? What is the warranty in terms of parts replacement? Where do I see myself diving 5 or even 10 years from now? Be sure to think about your budget, and it is always recommended that you purchase the regulator you think you will use for the next 5-10 years, as many of the regulator brands we carry and service will last that long or longer, with proper maintenance.