The official inauguration of the new HYT headquarters on the shores of Lake Neuchâtel also provided a glimpse into the altogether more discreet premises of Preciflex, at Rue Prébarreau in the city centre of Neuchâtel. It is in this building, covering 750m2 of floor space, that 23 employees work on the research, development and production of the company’s unique fluid modules. Here we split this highly complex element down into its individual elements.

 

HYT fluid modules

The fluid modules used in HYT watches are currently available in three different colours. The brand is bringing production of the fluids in-house to reduce the development time for new colours. © Preciflex

 

Research and development
But first, a word about R&D. This is a crucial element in the HYT project, since Preciflex has essentially invented a new technology that did not exist before, either in watchmaking or any other field. As a result, a number of different aspects had to be considered, from modelling the speed of the retrograde flow for the fluid displaying the hours to complying with numerous international standards and simulating ageing of the fluids (which is done by heating the fluids to 70°C for three months, which equates to three years of use at ambient temperature).

 

HYT capillary

The capillary used in the HYT fluid module has walls that are the thickness of 1/4 of a human hair. © HYT

 

The meniscus
Those who remember their school chemistry lessons will recall that the meniscus is the curve at the top of a liquid caused by surface tension holding it to the walls of its container, particularly visible in narrow containers such as a test tube. In the case of the HYT timepieces, the meniscus occurs at the interface between two immiscible fluids – one coloured, the other colourless – and it indicates the hour as it is slowly pushed around a capillary tube by a pair of bellows. The slightest difference in temperature or pressure within the capillary, or the presence of just one particle of air or a foreign body, could affect the movement of the fluids and thus the precision of the display (think of the “legs” left when you swirl wine around in a glass). With ten different materials in contact with the fluid, avoiding such problems is no easy task, which is why the liquid is inserted into the capillaries inside a vacuum bell.

 

HYT bellows

A diagram of the bellows used in the HYT 1 timepiece indicating how they operate. © HYT

 

The bellows
The bellows, whose side walls are the thickness of one quarter of a human hair, have to be filled entirely with liquid to a level of airtightness that is 10,000 times greater than that of a good wristwatch. The presence of just one micro-bubble of air could play havoc with the time display. Such bubbles in early production models of the H1 led to discrepancies in the display of up to 30 minutes – a problem that was solved by the development of a thermocompensator connected to the fluid module.

 

The interface
The rotation of the watch movement has to be translated into a lateral movement to drive the bellows. This is done by means of a snail-shaped cam. But given that the capillary that houses the liquid is only 0.8mm in diameter (its precise diameter is difficult to measure), the modules and cams are classified into six different groups and matched accordingly.

 

The priming tool used by Preciflex

The priming tool used by Preciflex, which injects the fluid into the capillary in a vacuum. © HYT

 

Priming
The term for this process that is unique to Preciflex had to be invented. It comprises a staggering 60 different steps from start to finish to fill the capillary with the two fluids. In summary, the air is expelled from the module up to five times in a vacuum bell before the liquids are injected. An additional complication arises with the H2, whose V-shaped bellows have to be filled in a vertical position, which requires a different (rotating) machine.

 

Priming the fluid in the capillary

Priming the fluid in the capillary © HYT

 

Cycling
Once the module has been filled with the fluids, they are tested at different speeds. Although the two fluids are immiscible, they nevertheless remain in contact and have to be “married” together. This is done by altering temperatures in a range of 10°C to 40°C to adjust the viscosity of the fluids. Note that there is a risk of the fluids losing viscosity at extremely low temperatures, but as long as you have the watch on your wrist they should maintain a constant temperature that is close to body temperature.

 

Calibration
Once the fluids have been injected and married, the module has to be calibrated to ensure that the meniscus arrives at the 12 o’clock position to coincide with 12 o’clock precisely according to the beating of the mechanical movement. Since the snail cam pushes the bellows by mere tenths of a millimetre, this process of calibration is extremely delicate. Any slight imprecisions at this stage are corrected by removing “micro-drops” of fluid from the module.

 

HYT H2

The H2 model by HYT. The V-shaped arrangement of its bellows makes the priming process for the fluids even more difficult. © HYT

 

Not just for watchmaking
Given the huge amount of research (and investment) ploughed into this new technology, it is hardly surprising that Preciflex wants to see it applied beyond the realms of watchmaking. The company’s micro and meso-fluidic expertise, its growing patent library and its in-house skills in fields as varied as fluid mechanics, micro-mechanics, electronics, chemistry (the company is now starting to produce its own fluids) and optics make it predestined to adapt the technology for applications such as the diffusion of liquids in cosmetics, micro-injections for the medical industry and types of indication (how about a car dashboard with fluid displays?).

 

The next step for HYT?
The most logical next step seems to be an expansion in the liquid displays within the watch. After all, now that the hours have been mastered, the minutes and seconds need to follow. This will undoubtedly pose a challenge to the movement designers, under the leadership of Dominique Renaud, who will need to provide the necessary power for such indications. Although HYT and Preciflex have also hinted that it is the fluids themselves that may soon be providing the power in the movement.