The EPSA (super) compressor rediscovered and re-invented

A water-resistant watch with two crowns is a (super) compressor watch, right? Not quite. In a way, this could be true for vintage watches, but in fact, not always. And for today, this is even more doubtful, as nearly all double crown & internal bezel watches just use traditional sealing technology and only look like the watches from the past.

Our Ultradive and OPS watches are equipped with two crowns. And then some, because the true (super) compressor or bayonet compressor technology goes deeper than the naked eye can see. So, let’s dive in!

The technology behind the super compressor was introduced in the 1950s. At that time, it was not easy to design and build a water-resistant watch, especially for mass production. The sealing materials were not yet as reliable as today, and some materials we use nowadays were not even invented or developed to sufficient quality standards. So, watch brands had to be very inventive to achieve water-resistance. A company that was ahead of its time, was Ervin Piquerez SA, also known as the abbreviation EPSA to watch connoisseurs. The designers and engineers of the company, which was at some point in time the largest manufacturer of watch cases in the world and worked for all the big watch brands, had several groundbreaking ideas during the 1950s and addressed the problem of achieving water tightness in many clever ways.

The (super) compressor technology

Up till the early 1950s, sealing materials were usually not of the quality and characteristics that were needed to withstand rising water pressure. In many cases, the materials would deform and make the sealing pressure fade over time, resulting in leakages. The technicians from EPSA had a brilliant idea how to solve this problem:
Ervin Qipquerez (EPSA) compressor bayonet system patent drawing
Ervin Piquerez SA technologies for water resistance - different compressor versions and inventions

they invented a case back technology, called ‘compressor’, which would put the sealing under slight pressure in everyday use, resulting in water resistance under normal circumstances and during snorkeling / shallow diving. When diving lower, the rising water pressure further compressed the case back into the case, resulting in a tighter fit.

This avoided high pressure on the sealing over longer periods of time and meant that the sealing materials would last much longer.

To come up with an idea like that – to use the force that you want to keep out of the watch to increase the sealing pressure and to make the watch more watertight – is the kind of engineering genuineness that still fascinates today. It has a certain Aikido philosophy to it: use the opponent’s force or attack against himself.

Different compressor system versions

Based on this basic engineering principle, EPSA developed several versions of this design:

  • brevet 313813 – ‘compressor’ – announced to the patent office 30. October 1953
  • brevet 314962 – ‘bayonet compressor’, also called ‘EPSA-STOP’ (used exclusively for Enicar SA Lengnau) announced 2. November 1953
  • brevet 317537 – ‘super compressor’ announced 22. November 1954
  • brevet 420999 – ‘compressor 2’ for rectangular cases, announced 15. November 1963

The ‘compressor’ system was a snap-fit case back which could compress and thus increase water tightness. The ‘EPSA-STOP’ or ‘bayonet compressor’ system was a further development of this, and the case back did not snap-fit but was secured by a sophisticated bayonet system, which would also allow the case back to compress under water pressure:

patent drawing of the Ervin Piquerez (EPSA) bayonet compressor back
Ervin Piquerez SA technologies for water resistance, the super compressor SC2

And finally, the most famous and probably most complicated of these systems, the ‘super compressor’, which combined a screw-in case back design with the compressor feature – also allowing compression of the case back to happen.

EPSA also invented a special crown system, called ‘MONOFLEX’, which was also using compressor technology. And finally, EPSA was responsible for developing the internal turning bezel:

The complete concept EPSA had created in the middle of the 1950s was ‘GRAND FONDS’, and it included all technologies mentioned here: compressor case back, compressor crowns, internal turning bezel and specially designed plexiglass crystals, usually with metal ring reinforcements. However, this name was never recognized by the consumer market. GRAND FONDS was usually named ‘super compressor’, at least during the last few years. Yes, it’s confusing.

Famous examples for the super compressor design and technology were (amongst others) the Jaeger-LeCoultre Polaris, the Longines Diver ref. 7150-1, the IWC Aquatimer, the Universal Polerouter Sub, the Vulcain Nautical Cricket, LIP Nautic Ski, Fortis MarineMaster and Hamilton 600,

You can find an overview of super compressors and their history  here and here.

Today’s compressor technology at Sherpa Watches

As we are bringing back the most legendary models of the old Sherpa series of watches from the 1960s, we decided to update the ‘EPSA-STOP’ or ‘bayonet compressor’ system. It is improved by using modern sealing materials and higher precision manufacturing, as well as a new design. This allows to only introduce the case back in one orientation and guarantees a perfectly aligned EPSA logo (the iconic diver helmet!) on the case back.

This new design tightens the case back to the sealing in a way that everyday actions can be performed easily and safely, while tightening the sealing further when exposing the watch to higher pressure from outside. In other words: the Ultradive and OPS will go as far (or deep) as you dare to go, without succumbing under pressure.

In upcoming articles, I will outline the technology of the MONOFLEX crowns and our use of the internal bezel.

Ervin Piquerez SA invention, the second crown for manipulating the inner bezel