How do diving regulators work?

We all use them, but how many divers understand how they work? Diving regulators are not only impressive bits of technical kit, but are also likely to be one of the first things new divers buy when they start diving. They have undergone many changes since the first demand regulator in 1864, being made safer, more robust and reducing the weight. In this post we are looking at how the modern types of regulator work.

Scubapro regulator
Scubapro regulator - Often the first regulator divers have!

Basic Principles

In a nut shell - your regulator reduces the pressure in your diving cylinder down from 232 or 300 bar to a pressure that you can breathe. It accomplishes this in two stages (hence why your regulator has stages!). The 1st stage which attaches to your cylinder and reduces the pressure from your tank to around 10 bar.

The second stage lowers this 10 bar of pressure down to an ambient pressure (<0.05 bar differential) which is comfortable to breathe in any depth of water.

In Greater Depth

To understand how your diving regulator works, its easiest to start from when you breathe in underwater. That means (counter intuitively) we should start from the 2nd stage and work back to the diving cylinder.

diving regulator, 2nd stage, second stage
2nd stage - how it works

As you take a breath through your 2nd stage, your lungs suck the air from second stage chamber, and reduces the pressure in the 2nd stage. The water pressure outside pushes on the diaphragm (shown in orange on the image) just inside the front cover. It does this to try and balance the pressures between the two areas. This pushes on the Venturi lever (shown in red, named after the Venturi effect) and opens the valve allowing air from the first stage to enter.

When enough air (and therefore pressure) has entered the second stage, the diaphragm is pushed down towards the front cover and closes the valve. This is what is known as a demand regulator. As you demand air, your regulator will give it to you. Conversely there are positive pressure regulators which work slightly differently.

This design is brilliant, as it uses the ambient pressure of water to keep pressure difference below 0.05 bar whatever depth you are diving at. Although there are variations on this design, such as adding dial-a-breaths, this basic design is employed throughout all diving second stages.

1st stage, diving regulator, first stage
1st stage - how it works (diaphragm)

So how does the first stage work? In contrast to the second stage there are a few different ways the first stage can be constructed. You may have heard terms such as balanced vs. unbalanced or piston vs. diaphragm. However the main principle remains the same regardless of the construction and operates in a very similar way to the second stage.

As the valve opens on the second stage, air flows down your intermediate pressure hose. This causes the diaphragm (orange) to be pushed up by the water pressure opening the valve (red) to allow air from the tank. When enough air has entered from the cylinder, the diaphragm is pushed down and the valve closed.

Balanced vs. Unbalanced

The terms balanced and unbalanced crop up when talking about diving regulators, but what do they actually mean? If we look at the picture of our first stage again:

diving regulator, balanced, unbalanced, 1st stage, first stage
Difference between balanced and unbalanced diving regulators

The difference between the the balanced and unbalanced first stage comes down to the area behind the valve. If it can balance (get it?) the pressure on both sides of the valve there will be uniform pressure acting on the spring (green) regardless of the depth or cylinder pressure. If it can't balance the pressure i.e. unbalanced, then at greater depths or lower cylinder pressures the regulator will struggle to regulate the pressure. This means more resistance on breathing at the 2nd stage.

So why are there unbalanced 1st stages? They seem to have huge disadvantages compared with the balanced regulators. As with everything it comes down to cost. It is far cheaper to manufacture unbalanced regulators and so they cost less. If you are an entry level diver you may not be going to the depths that you notice the breathing resistance increase. Also an increase in breathing resistance gives another indication that your cylinder is running out, some divers prefer to have this warning alongside their SPG.

In truth we are seeing fewer and fewer unbalanced regulators in for servicing. The cost has been brought down considerably on the balanced regulators meaning that they are more accessible for newbie divers as an entry level diving regulator. As divers are upgrading their equipment they tend to opt for a balanced regulator, and trade in their unbalanced one with the manufacturer, which then get removed from circulation.


This post was aimed at providing an overview of how diving regulators work. As you can see they are incredible machines, and quite intricate. This is why manufacturers recommend getting them serviced regularly, as any small debris entering the regulator or soft seal perishing can have disastrous consequences. If you have any further questions or anything to add, please get in touch either directly with us or by posting in the comments below.

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