Breathing is believing. But first, some context.
Years ago, I got into an argument with an equipment retailer. One of my students was lining up to buy his first regulator. I advised Garth to choose a high-performance model.
The dealer was adamant that he shouldn’t, rudely telling his potential customer: “You’re not good enough for a premium valve yet”.
He insisted that Garth should buy a cheap model, one I suspect he wanted to clear from his stocks. Back then, the main independent guide to regulator performance came from DIVER’s ANSTI breathing-machine consumer tests and occasional US Navy Experimental Diving Unit lab reports, or from what other divers used or would let you try.
The most basic received wisdom was cost – the higher the price, the better the reg breathed.
A regulator can last for as long as you can get the spares needed for servicing – at least 10 years, so the demands you make on it could well change over time, perhaps as you move into tech, for instance.
Choosing a first reg that can progress with your future needs can be far cheaper than regularly upgrading or, most costly of all, compromising your safety by pushing a valve beyond its specifications.
Garth was not diving deep but was just a few dives away from doing so, and encountering some pretty wild currents at the same time.
None of us already making those dives trusted to cheap regs. So Garth bought one of the easiest-breathing and expensive regulators then made, leaving the “beginner” valve for the next sucker.
Surprisingly, consumers have only comparatively recently been offered any official guidance to a regulator’s performance. EN250 lays down limits for how hard a regulator can make you work to inhale and exhale, if its maker wants to sell that regulator in the EU – including, as I write, the UK.
The original standard set limits for a single diver breathing from the regulator. However, since the 1980s octopus use has been mandated for all students trained through PADI, and is ubiquitous among today’s recreational divers of all persuasions.
In 2014, the EU standards made a stab at catching up. EN250A was a higher benchmark, requiring the regulator to prove during breathing-machine tests that it can supply two divers breathing moderately hard at 30m as easily as it could supply one diver breathing at 50m, as per the earlier EN250 requirement.
So for anyone who plans to carry an octopus, an EN250A-certified regulator is the way forward.
I’ve been on a steep learning curve since I started reviewing equipment for DIVER. Regulator performance among budget models has particularly astounded me, but I had put this down to snazzy balanced first-stage designs.
What happens when you take a seemingly super-basic first stage and place it at the heart of a really low-cost regulator?
Oceanic is the first company to volunteer to let me try such a model, the EN250A-certified Alpha 10 SPX. It’s been an eye-opener.
The First Stage
SPX refers to the first stage, a neat, compact design. The ribbing helps draw heat into the first stage from the surrounding water to inhibit icing on coldwater dives. In fact it’s coldwater-rated, so its EN250A certification includes approval for diving in water as cold as 4°C.
The EN test is carried out at 50m in fresh water for five minutes, and the valve must not freeflow when breathed fairly hard. In reality, that’s not how most leisure divers diving inland through a UK winter operate but, while the water might be colder than 4°C and the dive far longer, it’s also usually shallower and more relaxed, so regulator cooling is lessened.
In practice the EN coldwater rating seems a good guide to real world reg anti-icing reliability, though coldwater diving procedures should also be followed.
Angled ports help with the hose layout. Ribbing increases the surface area to act as a heat-exchanger in cold water.
There are three medium-pressure take-offs on one side and two on the other, with an hp port on the right and left. The ports are fixed in position, with the mp ones slightly angled, making for easy hose layouts.
The Alpha 10 SPX has a flexi-hose, so coils up tightly for packing. I used a DIN connection, which I prefer, but a yoke model is available.
What makes the SPX interesting is that it’s an unbalanced piston design. This is mechanically the simplest, and so the least expensive, type of first stage to make. Its only moving part is a hollow piston through which air must pass to get from tank to second stage and into your lungs.
The high-pressure air entering the first stage from your cylinder pushes the piston upwards, so the air can flow through it from the SPX’s hp chamber into another air chamber at the piston’s other end. There it is reduced to a much lower pressure of around 9 bar, termed medium pressure, needed to supply your second stage, octopus and direct feeds.
Helping the hp air to force the piston into the open position is a spring. This exerts an opening force equivalent to the mp – about 9 bar. Water pressure adds to this opening force, accounting automatically for changes in pressure as you descend and ascend through the water column.
So, three forces – incoming hp air from your tank, the fixed-strength spring and the variable force of the surrounding water – all work together to keep the piston open.
But if it was always open, your regulator would simply freeflow and dump all your air.
Inside the mp chamber, once you stop inhaling air quickly backs up. This causes the pressure to rise and pushes the piston back into the closed position, shutting the air off.
Even though the mp is only around 9 bar, it’s spread over a much larger area of the piston, which is a disc the size of a small coin at its mp end compared to the hp end, which is only about the diameter of a straw.
So mp can easily overcome the higher combined tank pressure, water pressure and spring tension and shut off the air-flow.
When you inhale again, air-pressure drops in the mp chamber, the piston lifts and, once again, you get air for the duration of your breath.
In the costlier balanced-piston first-stage design, hp air from your tank surrounds the hp end of the piston but does not directly push on it. So falling tank pressure has almost no effect on ease of inhalation.
In the unbalanced model the pressure inside the mp chamber stays much the same through the dive. However, as your tank pressure falls as you breathe down your air-supply, the opening force also reduces. This should make it a little harder to open the valve and get the air flowing.
This is why, traditionally, unbalanced-piston regulators are thought of as becoming harder to breathe from below reserve tank pressures, say around 50 bar. Some divers used to see this as a plus, because it provided a physical warning that they were getting low on air.
The unbalanced piston was also considered poor at supplying high flow-rates of gas – exactly what might be needed if you share air through your octopus.