REGULATOR SCUBAPRO A700 / MK25

The first thing you will notice is that the new regulator is constructed entirely from metal.
The A700 second stage has a spherical shape designed for strength, but is actually more compact than the S600 second stage.
Its internal aerodynamics are such that when I saw it performing on an ANSTI machine in the Scubapro R&D department in Sestre Levante in Italy, it was returning an external work of breathing of less than half a joule per litre - and that's with a 50bar supply pressure at a depth equivalent of 50m.
Once you go deeper than 50m, a big gap appears between the performance of this regulator and its closest competitors. The criterion for passing EN250 is 3 joules/litre and it was not so long ago that we were amazed to see a regulator pass the 1 joule/litre barrier.
High performance and huge airflows usually go hand in hand with freeze-ups and freeflows in cold, fresh water. Gilbert tells me that the thermal dissipation of heat through the metal (brass) is more than 380 times more efficient (by kg/calories) than with the Nylon used in the S600 second stage. This means that Scubapro has bitten the bullet at last, and produced a regulator that will not scare the daylights out of those who train in freezing lakes in winter.
To demonstrate how well this regulator functions in the coldest conditions, Gilbert gave us a demonstration with water in the ANSTI machine at only 3.4°C, and a supply volume of air at 154bar.
Cameras built into the test chamber revealed ice forming around both stages, but the test was run for considerably longer than required for EN250 coldwater testing without any ill effects. I brought a pressure/volume diagram home as evidence.
Despite some revolutionary design initiatives, most of the serviceable parts such as the main spring, valve seat and O-rings are interchangeable with those already in the Scubapro service technician's repair kit.

First Stage
When gas is depressurised on leaving the tank, it gets extremely cold. The entry-holes in the MK25 piston-type first stage, which allow water to flow over the pressure-sensing spring, have been tapered to allow for a better flow rate.
At the same time, heat-exchanging fins do their best to increase the surface area of the metal, and use whatever little warmth there is in the water to raise the temperature of the medium-pressure air before it passes down the large-bore supply hose, via one of the ports in the rotating turret.
The MK25 first stage is Scubapro's star performer, but should you place more faith in a dry-sealed diaphragm design, the excellent MK17 alternative is available.
This keeps all the water well away from the balanced technology mechanism, while heat-exchanging fins keep ice from forming or creeping if it does.
Both are supplied in mirror-polished chrome, to match the all-shiny A700 second stage.
Each first stage has two high-pressure ports plus four (MK17) or five (MK25) mp ports.
I was tempted to ask for five A700s to see how good they would be at supplying air to five divers at 50m-plus, but in fact getting hold of one A700 proved difficult enough. The unit that I used was not yet CE-tested.

Second Stage
The A700 second stage is distinguished by the very shiny appearance of the chromed brass. It has large entry holes to allow water to flow easily onto the pressure-sensing diaphragm, but these are positioned such that they are unlikely to be affected by a head-on current.
An improved lever mechanism offers variable lever ratios, with lots more airflow at extreme depths. The A700 has a forged front ring that is completely rigid, and a very dry exhaust valve.
The work of inhalation is so low that it has been a challenge to Scubapro engineers to reduce the effort needed to open the exhaust port to allow exhalation to be equally easy.
A small exhaust-T keeps work of exhalation low, at the expense of putting a few exhaled bubbles up into the field of vision of the user.
There is no traditional venturi plus/minus control to disrupt the airflow within the body of the second stage. Instead, a rotating co-axial orifice within the valve mechanism alters the angle of injection and takes care of an over-clean venturi (VIVA) effect that could lead to an exponential freeflow.
The poppet on the valve is balanced and smaller than usual, with a more rounded design to give less friction and pull open more easily, thereby reducing cracking effort.
Exhalation is optimised with a 5° angle of tilt designed into the unit. A laminar flow means that there is little turbulence otherwise.
Why A700? It is rumoured that the G250 was so-called because it was designed by Dean Garraffa, later a founder of Atomic Aquatics (see T2X test below). Italian designer Roberto Semeia designed the R series, whereas this one is the brainchild of Alberto Belloni, who cut his designing teeth in the R&D department of Mares down the road from the Scubapro factory. So the prefix A might reflect his name. It's a nice story, anyway.

Purge Control
This is oversized so that it can be operated easily while wearing thick gloves. It worked delightfully without any tendency to surprise with an unexpected gush of air, thanks to a low-friction disc incorporated into the design.
Also, because the body of the second stage is so bijou, it doesn't take much to extract all the water from it when you need to. The super-flow hose between the two stages seems able to transport as much air as anyone could need.

Comfort
Because it is so compact, very shiny with its highly polished chrome, and retro-looking with the revealed star-screw heads holding the front plate on, the A700 looks heavy.
This is far from the case, because once immersed it has hardly any weight. It's probably the smallest Scubapro regulator ever made.
If you think the cracking pressure required to initiate an inhalation is too low, it's simple to tighten it a bit by turning the BRA knob at the side. A gloved finger readily tweaks the coaxial VIVA control switch, and it proved easy to move it to the dive position once submerged, if I remembered to do so.
The orthodontic mouthpiece is reminiscent of that employed by Atomic - you may recall me raving about how comfortable this was!
I used the A700 during some dramatic dives in which up to 60 sharks were at times banging off my mask. This makes the heart race and boosts demand for oxygen, but I never found this regulator wanting.
It's all very subjective, of course, but the graph from the ANSTI machine told the whole story. It's interesting to note that the work on inhalation is now so low with this regulator that most of the effort of breathing is taken up with pushing open the exhaust port to exhale.
Such is the stupendous advance in regulator design we have witnessed over recent years. n

OTHER REGULATORS TO CONSIDER:
Atomic T2X, £999
Sherwood SR1, £379
Apeks XTX200 Tungsten (Swivel), £491

SPECS
PRICE £515 (MK17), £599 (MK25)
FIRST STAGE MK25 piston or MK17 diaphragm
PORTS 5mp, 2hp (MK25) or 4mp, 2hp (MK17)
SECOND STAGE ADJUSTMENTS VIVA control and BRA knob
WEIGHT 1kg
CONTACT www.scubapro.com
DIVER GUIDE