The First Stage
Mares has based the MR52X on its original MR52 first stage. It’s a balanced diaphragm design first seen coupled with the Abyss and Carbon second stages.
The MR52X has a newly designed valve and seat, giving what the maker claims to be a 600% increase in reliability. Like other Mares first stages, it features its patented DFC (Dynamic Flow Control), which increases the performance of the second stage by using a venturi system to minimise the intermediate pressure-drop during inhalation.
European standards insist on high-performing alternative second stages for use in emergency air-sharing, so the MR52X has two low-pressure ports fitted with the DFC.
The first stage has been constructed from marine-grade brass with a satin chrome finish. For weight-saving this has been machined to a low profile with polycarbonate inserts around the top and sides.
It features four lp ports (two with DFC) and two high-pressure ports set evenly either side of the valve body. There’s a choice of either 300bar DIN or 232bar international yoke connections.

The Second Stage
Mares has done something that’s very unlike it with the Fusion second stage. It has fitted a manually operated VAD/VAD+ control (Vortex Assisted Design), a first for any Mares regulator.
This is a two-position swivel turret set over the braided intermediate hose connection, designed to give extra airflow when you need to really gush the gas down.
The Fusion features Mares’ signature venturi bypass, but this one has a double curve to optimise the performance.
The whole of the second-stage body is crafted from marine-grade brass, with the same satin chrome finish as the MR52X first stage.
The purge button is very unlike the norm too. It occupies the centre of the regulator and is hinged at the base, requiring a tipping action to work. The exhalation ports are set at an acute angle and are narrow in profile, creating a streamlined footprint.

In Use
The MR52X is a compact unit and offered neat standard hose-routeing from its port placement.
I set it up with an electronic high-pressure transmitter as well as an analogue gauge and two second stages plus the BC inflator; everything fitted and was tucked away behind my head under water.
The Fusion second stage felt quite hefty, especially when conducting a pre-breathe on the boat, when it tipped forward, putting some strain on my teeth as I bit down to keep it in place.
Once in the water, however, it seemed to disappear and became almost neutrally buoyant. The rake of the exhalation port left it sitting just below my chin, and sent bubbles away from my face.
The resistance required to crack open the valve at the start of each inhalation was non-existent, making it feel very natural to breathe from. The exhalation-valve release pressure was low too, making breathing out as easy as breathing in.
The VAD/VAD+ control was very easy to access and turn. At first I couldn’t feel any difference in performance between the two settings, but then came the moment when I had to fin like a man possessed against strong currents on one of the Maldives channel dives.
I’m less fit than I used to be and had a huge camera to push through what at the time felt like treacle, and I was really sucking down the air. A quick turn to the + setting saw the Fusion delivering the much-needed goods.
The purge was one of the best I’ve seen on a modern second stage. It’s big, and the hinge at the bottom causes it to tip inwards, which makes it extremely easy to control the progressive flow rate.
I put the Fusion through my standard array of tests. Inverted it was dry, sharing air via an alternative supply didn’t affect the output, and it refused to freeflow when I spat it out of my mouth with the VAD on the + setting.
In a stationary position there were no bubbles passing in front of my face from the exhaust ports.
I also failed to detect any difference in the Fusion’s performance whether at 30m-plus deep or just below the surface.

I’ve been privileged to have dived with the Atomic T3, Apeks XTX200 and the Sherwood SR2 over the past 18 months and found these regulators to be at the very top of the performance tree. I can now add a fourth to this distinguished list – the Mares Fusion 52X.
It can’t truly be classed as a travel regulator, because I feel it’s a little on the heavy side, but on the upside its all-metal construction makes it seem bulletproof and, as owners of the famous Mares Abyss will testify, it should last a lifetime.
I’m told that the venturi bypass adds to the regulator’s coldwater attributes. Unfortunately
I can’t comment on this aspect, but what I can say is that I found this to be a very nice piece of underwater breathing apparatus.

PRICE £455
FIRST STAGE Balanced diaphragm
PORTS 4lp (2 x DFC), 2hp
WEIGHT Both stages combined (300bar DIN) 995g.
CONNECTION OPTIONS 232bar A-clamp, 300bar DIN.
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