Maurizio Baldinucci


What most stimulates the interest of a researcher who deals with the history of scuba diving gear is the extreme lack of information and data relating to a particular equipment or to a specific topic in general.
This is precisely the case of the Air King double hose regulator produced by Mares in Rapallo from 1959 to 1963 (see Figure 1 and Figure 2).

fig. 1 fig. 2

This is a model well known to collectors of diving equipment because of the extreme rarity of the units that still exist (there are fewer than ten known worldwide) and for the absolute lack of photos, diagrams and technical data in general. This despite the fact that it was a model produced in Italy and in particular by a company, Mares, which would have become one of the world leaders in the production of underwater equipment for recreational diving.
If the Air King is extremely rare for Italian collectors, you can imagine what it would be for foreign ones, most of whom have never heard of it. Of course one of the reasons for this extreme rarity, as it happens for other equally rare equipment, is the phenomenon of the so-called "hidden" collectors widespread in Italy, that is, of the numerous enthusiasts and private collectors who jealously guard their pieces without letting know their existence if not to the most trusted friends. Unfortunately, this type of collection, while legitimate, is absolutely arid from the point of view of the diffusion of knowledge on the history of diving equipment. It is therefore probable that other Air King units exist in some attics, basements or private collections around the country and, in this case, these are inevitably destined to be forgotten following the same fate as their owners.
The title of this article (the elusive Mares Air King) was taken from the comment of an USA collector concerning some photos of a very rare model "61" unit. These photos appeared a few years ago on social networks and were related to the unit (see Figure 3 and Figure 4) belonging to the collection of Nick Icorn, one of the greatest figures of the USA scuba diving history who passed away in 2013. This collection of recreational and professional diving equipment is one of the richest and most complete in the world and is currently hosted at the Flashback Scuba Tacoma Museum in Washington state.

fig. 3 fig. 4

The decision to write this article was taken when, quite casually, I noticed some photos of one of the rarest and most known versions of this model, the "B. 60 ", in one of the many groups of diving history fans on social networks. In years of research on the net and in the old books dedicated to diving history I had never seen one of these units and then I said to myself that it was better to take this opportunity and to start outlining the history of this regulator. I profit of this opportunity to thank the lucky owner of this unit, the Ligurian collector Piero Quarone, who kindly provided me with photos of this regulator, photos used in this article.
As often happened in those years for other equipment that would become very rare among the nowadays collectors, the main reason for their rarity was the low, sometimes very low, number of pieces produced, almost always motivated by the poor sales success of the model in question. And this situation also occurred for the double hose Mares Air King which was never capable to take off in a market at that time dominated by the Mistral by La Spirotechnique. This regulator had entered Italy in 1956, through the license agreement with Salvas before and with the Spiro-Sub subsequently (starting from 1959) and would have later been distributed, in both Mistral and Royal Mistral versions, by Technisub after 1962.
Unfortunately, the Air King was defeated by the comparison with the Mistral both in terms of performance, as we will see in the article, and from the sale price point of view, depending drastically on the construction complexity of the regulator but also on the numbers of produced units.
The same fate was also shared by other Italian models, that were put into production in that period by other manufacturers to contend the Mistral’s market shares. One of these was undoubtedly the Salvas Aquasprint (see Figure 5 and Figure 6).
Contrarily to what happened for the Aquasprint, which in any case was capable to achieve a decent market share, even if certainly not comparable to that of the Mistral, for Air King this result was not possible especially because of the extreme volatility of its design. This underwent numerous and drastic changes during the few years during which this regulator remained in production. These continuous changes, together with the predictable performance and reliability issues that made these changes necessary, ended up discouraging potential customers of this regulator

fig. 5 fig. 6

The first official appearance of the Air King is found in a Mares advertising flyer dated 1959 (see Figure 7). However, the first official denomination is that of "Air King 60" which indicates the starting year of the actual sales phase and it is precisely in the year 1960 that Mares launched an advertising campaign to launch these new equipment. The occasion was offered by two important diving-related events that took place in that year: the World Spearfishing Championship of Lipari and Ustica (see Figure 8) and the Genoa International Expo (see Figure 9 and Figure 10).

fig. 7 fig. 8

During this initial period we can assume that a first modification of the Air King 60 model regulator (see Figure 11) was necessary with the consequent need to distinguish the new version identified with the name Mares Air King B. 60. This version is clearly recognized by a decal showing the letter "B" and applied in the center of the regulator’s front shell (see Figure 12 and Figure 13).

fig. 9 fig. 10


fig. 11

The fact that in the 1960 advertising documentation almost exclusively the B.60 model appears and that no existing units of the previous model 60 are known, suggests that this first version was built in a semi-prototype configuration only and in a very low number of units.

fiog. 12 fig. 13

The only known physical specimen relating to the very first version of this regulator that we have been able to find is the one represented in Figures 14, 15 and 16. The sample belongs to an old diver, Massimo Bavarello, 88 years old, a friend of Ludovico Mares who often helped during the sea trials of the prototypes manufactured by the Rapallo company.

fig. 14 fig. 15 fig. 16

The existence of this sample, although in fairly degraded conditions, nevertheless allows us to argue what the initial technical solutions were, solutions then abandoned or modified in the further version of the regulator, the B.60. First of all, it is surprising that the front half-shell of the regulator body was not provided at all of openings to connect the external environment with the balancing diaphragm. The only existing openings are located in the rear part of the body and, also missing the mushroom type exhaust valve in the central position (valve which will later become standard on all subsequent versions), we can guess that these openings were used both to equalize the pressure with the external environment and as an outlet for exhaled air. The connection between the corrugated hoses and the body of the regulator is also very different from that of subsequent versions. In this case, both hoses are connected to a single outlet duct welded to the regulator body, suggesting that the type of breathing circuit was of the "pendular" type with both hoses used in both the inhalation and exhalation phases. Probably the mouthpiece in this first version (unfortunately missing in the example shown in the previous pictures) was not provided with "Acquastop" type one-way valves, thus being able to inhale and exhale air through both hoses connected to it. It was certainly a single-stage regulator (the cylindrical element connected to the regulator body shown in the previous pictures is actually a simple junction block used to connect the rigid pipes coming from the cylinders) even if the photos do not allow to see the internal part of the regulator and therefore the details of the pressure reducing valve.
The fact that the B.60 regulators appear almost exclusively in the commercial documentation of 1960 and that no other surviving examples of this first model are known, suggests that the latter was built in a semi-prototype version and in a very low number of specimens. No documentary traces of this very first model have been found (manuals, diagrams or drawings). Therefore, the technical changes introduced on this regulator, which motivated the transition from the first version 60 to the next version B. 60, are those deduced by observing the few photos available of this only remaining sample.
For models B. 60 and later, it was possible to found functional diagrams showing very clearly the different functional principles but also the potential performance weaknesses.
The Mares Air King B. 60 is a double hose and two stages regulator whose functional scheme, as regards the second stage, is shown in Figure 14.
The "downstream" type second stage pneumatic valve delivers an upstream intermediate pressure of 6 bar. This pressure value is regulated by an unbalanced first stage diaphragm type valve installed on the rear of the main body of the regulator (see Figure 15) and consisting of the various components shown in the photo in Figure 16.
One of the original aspects of this project was that of the second stage lever spring, a spring that worked in traction rather than in compression as in most of the second stage valve mechanisms of competing regulators. This system allowed a simple adjustment of the spring preload by means of a small knurled knob (see also Figure 17 and Figure 18).
Even the air exhaust system was inspired by an alternative solution used by some manufacturers compared to that used on the Cousteau-Gagnan patented self-contained breathing apparatus, including the Mistral.
Instead of using the classic "duckbill" valve installed between the upper surface of the balancing diaphragm and the regulator body’s external shell, this model included a "mushroom" type air exhaust valve mounted in the internal chamber of the regulator’s body, underneath the diaphragm and along the regulator’s body longitudinal axis (see Figure 14, Figure 19 and Figure 20).

fig. 17
fig. 18 fig. 19

Questa soluzione, che è la stessa utilizzata anche nel modello “Aquasprint” della Salvas citato in precedenza, fu mantenuta anche nelle varianti successive anche se con vari miglioramenti, come vedremo nel seguito dell’articolo.
Regarding the inhalation and exhalation circuit, this consisted of the classic two corrugated hoses, one for the inhaled air and the other for the exhaled air, connected to a metal "T" type mouthpiece. This mouthpiece was equipped with "aqua -stop” mushrooms type check-valves (unfortunately no longer available in the collected unit) as shown in Figure 21 and Figure 22.

fig. 20 fig. 21
fig. 22 fig. 23

Another unique feature of this regulator was the position of the outlets connecting the corrugated hoses to the regulator’s body which were placed parallel to each other and located in the upper area of ​​the body itself (see Figure 12 and Figure 13).

fig. 24 fig. 25

The same position was also maintained in the next model "61" and then modified in the last model which was released on the market and identified as "S" model. Even the aesthetic shape of the regulator remained always the same with the preservation of the front half-shell of the regulator’s body, for which molding the same tooling was always used. Also the connection system between the two half-shells remained the same, with three tie rods spaced of 120 ° each other and the related threaded and knurled knobs. These elements would remain practically unchanged until the end of production (see Figure 23 and Figure 24).

fig. 26 fig. 27

Mares tried to improve this new SCUBA unit by adding other features that were not available in competitor models. One of these accessories, of which unfortunately we do not have any photographic documentation, was the system described in a rare technical documentation relating to this product: "... One of the variants of this device compared to the others of the same class is a steel articulated rod that runs in the back of the unit and along the tanks. This device serves for multiple uses; on the ground to keep the whole unit in an almost vertical position; in the water to carry special shaped weights which advantageously replace the weight-belt. The system is very practical because in the event of an emergency, with a simple action, the rod is released and the weights slide away ... "
Due to the increasing success of the Mistral and considering the probable weakness of this Mares model when compared to the first (we can suppose the higher inspiration effort, due to the lack of a Venturi breathing assisting device, and the higher production cost related to the regulator’s double stage configuration), in the following year, 1961, there was the launch of a completely revised model, even if aesthetically the same as the previous one: the Air King 61 model.
This version was a single stage model that the Rapallo company presented with these words: "... it is a conventional single-stage self-contained breathing apparatus very similar in its construction parts and in its functioning to the famous Mistral ...".
And in fact the functional scheme shown in Figure 25 confirms this description.

fig. 28

The air delivery valve becomes an "upstream" type valve as in the Mistral and its actuation lever is doubled in order to maximize the actuation force of the lever without increasing too much the inspiration effort on the balancing diaphragm. As can be seen from the scheme, the principle of the exhaled air exhaust system remains unchanged; in addition, there is no injector to trigger the Venturi effect as used in the Mistral.
The several elements of this regulator can be observed in Figures 26, 27, 28 and 29 which refer to one of the very few known units still existing in the world.

fig. 29 fig. 30
fig. 31 fig. 32

For sure, the new model should have been much cheaper than the previous one, thanks to the limited number of components compared to versions 60 and B. 60, but we believe that its performance has never been comparable to that of the Mistral. In particular, the main doubt remains that of the effective efficiency of the Venturi effect device which, according to Mares, should have been produced in this way: "... In this regulator instead of the tube (the injector of the Mistral nda) there are two small calibrated orifices, as in multi-stage regulators ... "
Furthermore, there remains the strong doubt of the probable accumulation of carbon dioxide during breathing, an accumulation favored by a not proper separation of the inspiration circuit from the exhalation one. In fact, even if the mouthpiece was equipped with one-way check valves, so circulating the air in the two corrugated hoses in a correct way, the two hoses received and discharged air within the same area. This would allow the carbon dioxide, existing in high concentration in the exhaled air, to be partially reintroduced into the air inhaling flow.
Another year passes and, in 1962, there was another change in the design of this regulator with the replacement of model 61 with the new model called "S" (see Figure 30 and Figure 31).
Even if the aesthetics remain almost the same as in the previous models, the regulator functional scheme is completely revised, as shown in the diagram of Figure 32. This functional principle and the main internal construction components of this model can be analyzed in detail in the schematic drawings of Figure 33, Figure 34 and Figure 35. The most important updates and the main solutions adopted by Mares' designers on this new model are listed below:

  • Replacement of the "upstream" valve, similar to that used on the Mistral, with another type of "upstream" valve: the tilt valve. For this reason the new model was called "S" from the s of "spillo" (the Italian name used to indicate the tilt valve). There are two possible reasons for this drastic change: avoid infringing the Mistral's Cousteau-Gagnan patent, thus preventing a possible legal action by La Spirotechnique, and / or standardize the air feeding valve on the type chosen also for the single hose regulator model that Mares had put on the market the year before (the Air King Minor model). This model was equipped with the same tilt valve. The change of this valve forced Mares to completely relocate the body of the air feeding valve laterally to the main body of the regulator and with its longitudinal axis partially inclined with respect to the axis of symmetry of the regulator’s main bod
  • fig. 33

    fig. 34

  • Addition of an air exhaust rubber duct, mounted between the exhalation hose connection outlet and the central exhaust valve (see Figure 36). This solution would have definitively solved the problem of the accumulation of carbon dioxide in the respiratory circuit.
  • Modification of the central exhaust valve with the significant increase of the air flowing section and therefore the consequent reduction of the expiratory effort (see Figure 37).
  • Addition of knob actuated adjustment device between the balancing diaphragm and the top of the tilt valve (see Figure 31 and Figure 32). This system made possible the adjustment of the gap between the balancing diaphragm and the top end of the tilt valve. In this way this gap could be minimized so having a faster air delivery flow immediately after the initial breathing inhaling effort. A decal with the letter "S" in white color on a blue background was applied in the center of this knob, so indicating the model "S".
  • Introduction of a new yellow mouthpiece made entirely in plastic material. This mouthpiece was also equipped with one-way check valves (see Figure 38).
  • fig. 35 fig. 36 
    fig. 37 fog. 38
  • On the price list of the regulator two special hoses having smooth surfaces, both internally and externally, and an internal resisting jacket were included (see Figure 39). The use of these new hoses would have significantly reduced the diver's breathing effort.
  • The change and the relocation of the air feeding valve also led to the repositioning of the regulator’s body hoses outlets which, from the previous position with outlets side by side at the top, rotated 90 ° and in opposite directions to each other (see Figure 39).

    This solution could have been the final one but the operational use of this regulator showed one of the fundamental limits of the tilt valve. In fact, the rubber sealing material of this valve had a reasonable life when subjected to the low pressures typical of the single hose regulators second stages (10 bar maximum) but absolutely insufficient when loaded with much higher forces corresponding to the typical pressure values existing in the first stages (150-200 bar).
  • fig. 39 fig. 40
    fig. 41 fig. 42

    It was therefore necessary to submit the regulator to another further modification which went into production just before this regulator definitively went out of production, we believe in the period between the end of 1962 and the whole of 1963.
    The first stage (practically the same used in the Air King Minor) came back again and was mounted on the back of the regulator body (with a new increase in production costs). Moreover, the diaphragm and tilt valve gap knob-actuated adjusting device was eliminated. This device was considered excessively fragile and not so useful. The final version of this model, still called "S", is shown in Figure 40 and Figure 41.
    This model can still be seen in the Mares price list of 1963 (see Figure 42) but disappears definitively from the 1964 price list (see Figure 43).
    In summary: a real mess, lived dangerously by Mares for about four years with many technical and economic efforts but with very few results from a sales and industrial point of view. The Ligurian company, which would become a few years later, also thanks to the purchase by the US company AMF, one of the major industrial brands in this market, paid the price of having thrown itself headlong into this adventure without having a solid technical experience and know-how in the specific area, a real ability and even the time to subject its prototypes to rigid experimental validation protocols, before they are marketed.

fig. 43 fig. 44
fig. 45 fig. 46

It also payed the poor organization and the lack of financial resources of the main competition that was dominating the market in those years (especially La Spirotechnique).
It did not go much better with the subsequent single hose models, precisely the Air King Minor first (see Figure 44) in 1961 and with the Corallo later from 1966 (see Figure 45).
Even these models were never really competitive with respect to similar products offered in the same period (one above all the Aquilon put on the market by La Spirotechnique in 1963).
The definitive success of the Mares regulators would come a long time later, and precisely during the 70s, with the MR-12 model.

fig. 47 fig. 48