The second stage is pneumatically balanced, a feature until recently normally associated with premium-priced regulators, not entry-level models.
The advantage is reduced cracking effort, the effort demanded of your lungs to “open” the second-stage valve to start the air flowing.
As when trying to open a fire-door against its spring, most second stages, including the Brut Pro, have a door-like valve held closed by a spring. Without it your regulator would freeflow, and most of the air would be wasted.
In a non-balanced second stage, the spring must be comparatively strong to hold back the incoming air from the first stage.
Because air-pressure from the first stage increases in line with increasing depth, the spring must be strong enough to prevent a freeflow even on deep dives, but it’s stronger than it needs to be at shallow depths.
A pneumatically balanced second stage is more refined. The spring is contained in a tube that fills with pressurised air, which helps it to close the valve by also pressing on the valve to keep it shut.
The second stage is light and has a comfortable mouthpiece.
While the steel spring in a second stage has a fixed strength, and so exerts a constant closing force, in the Brut Pro the air pressure varies with depth changes. In effect, it works with the spring, supplementing its closing force as you go deeper and slackening off as you return to the shallows – hence the term “balanced” second stage.
This means that a lighter spring that needs less effort to crack can be used, making inhalation easier. The effort needed to crack the valve is much the same at any depth.
Once the valve has been cracked on each inhalation, you don’t want to exert a lot of energy keeping the air flowing.
On an hour’s dive you might take 1200 breaths, so sucking air out of your tank could start to feel like extracting a McDonald’s shake through a thin straw.
To keep the air flowing with the least effort on your part, a venturi takes over – the flowing air is routed through the second stage to create a vacuum that keeps the diaphragm depressed and the second-stage valve open for you.
When a train flies by and you feel the air behind it tug at you, that’s the venturi effect.
It’s usual for even a basic second stage to have an on/off control for the venturi, to prevent freeflows when it isn’t in your mouth, such as when surface-swimming or chatting at the surface. It’s also used to prevent octopuses purging unintentionally.
Octopus second stage.
The Brut Pro lacks this switch, and I think that’s commendable. Here’s why. When you turn off the venturi, you make breathing harder. So when divers forget to turn the switch to the dive position, or don’t even know that they should, carbon dioxide headaches can result.
When an octopus is set this way, there’s anecdotal evidence to suggest that the breathing resistance can send an already stressed out-of-air diver into a panic and cause the reg to be abandoned altogether.
Sherwood has eliminated the chance of any such confusion as well as reducing production costs.
On Sherwood’s website, some pictures of the Brut Pro do show the second stage as being fitted with a venturi switch, however. Go figure.
I used the Brut Pro on a recent trip to the Maldives. I’m used to swift currents there, but on this trip we hit them only once. With a 30m limit, I and the Brut Pro got a fair work-out, though I’d have liked to have tried it deeper.
All regulators have their own breathing characteristics, and evaluating and reporting on them is highly subjective.
I never felt air-starved using the Brut Pro, but I did feel that I was making more effort to inhale than I might have expected, given the balanced first and second stages.
That said, breathing resistance seemed uniform and smooth regardless of workload.
When I tested the octopus at 30m with Christoph of Aquaholics breathing as hard as he could in time to my own inhalations, I could not detect any decline in performance whatsoever.
Even sharing, Christoph thought the Brut Pro compared very favourably to his own top-of-the-line reg, which surprised me a little, until he let on that he had detuned it to save air!
At the end of the day the Brut Pro meets the EN250A standard and it is, after all, marketed as Sherwood’s bottom-of-the-range regulator. A more expensive model including, I presume, one from Sherwood’s own line-up, will exceed the EN250A standard by a greater margin and should provide an easier breathe.
The second stage is lightweight and the mouthpiece comfortable on long dives. The exhaust T does a good job of diverting bubbles away from the user’s field of view. It’s low-enough profile that I had no problems getting my mask up to my camera viewfinder. The purge is easily pressed with gloved hands.
I like to test how easy it is to clear a flooded second stage that’s inverted, because in a sharing situation it’s easy to insert regs, other than side-exhaust models, upside-down by accident.
The Brut Pro was a little harder to clear consistently than my own regulator. I retested this several times, because sometimes it cleared perfectly but at other times I’d have to breathe past a few dregs of water.
Once cleared, it doesn’t leak – some second stages I’ve tried continue to flood until turned the right way up.