clock & barometer repairs
01277 658800   Billericay


Atmos bellows refill & repair

Atmos clocks by Jaeger LeCoultre (Image 1) represent the highest standard of horological engineering and service intervals can be as long as 25 years. You can read more about these clocks on the ATMOS page.

One vital part that can fail after many years, however, is the bellows, which is housed inside the large drum (the "motor") (Image 2) on the back of clocks after the ATMOS I (which was virtually a prototype). Made from thin folded stainless steel and brass, the bellows contains chloroethane (ethyl chloride), which has a low boiling point (12.3C) so the bellows expand and contract with changes in temperature. A heavy compression spring inside the bellows helps control the thermal range of expansion so variations from 16C to 24C continually wind the mainspring (Image 3). The mainspring is designed to run the clock for up to 12 months so failure of the bellows will not result in the instant failure of the clock; in fact, it might start losing time but it will be many months before the clock stops.

Looking in the left side of the clock just in front of the motor you will see a small pulley with a gold chain running along the top half and a spring underneath. They join at the same point on the pulley and generally that joint will be near the top if the bellows is contracted (flat). A better check is to remove the case, take off the nuts securing the motor and measure the depth from the top to the bottom of the centre hole. At room temperature (21°C) a good bellows will measure less than 28mm; anything more suggests a deficient bellows and above 33mm, it will not perform. At 40mm it is completely flat.

A bellows can be recharged if it is not leaking but it's vital to do it cold, to evacuate all the air first and to use the right amount of chloroethane; too much and the bellows will be overstressed when expanded and/or remain expanded at cooler room temperatures; too little and it might not expand at all against the force or the compression spring. Both mean that there will be too little lateral movement so the clock will not wind itself. I've seen a variety of techniques utilising carpenters' G-clamps, ice packs and buckets of water so the final results of a recharge must be quite varied! I built something a little more sophisticated with a vacuum pump to produce more consistent results.

But recharging alone is not always enough; bellows sometimes fail because the gas escapes, and repairing a leakage poses additional challenges. Just tracing the leak can be difficult since air pressure and underwater testing simply will not always reveal slow or tiny leaks. I tend to use a hand pump designed to take blood pressure readings as it's easily controllable but I've heard of some repairers simply blowing into the bellows - heaven only knows what damage the moisture does internally once mixed with chlorine.

Repairing a leak has added problems. A failure of the joint between the brass and stainless steel parts (like the fill pipe) is usually repairable by re-soldering. Chloroethane contains a corrosive halogen but the self healing qualities of stainless steel when exposed to air may mean that there is no discernible reason for a collapsed bellows when air-pressure tested. Stress fractures, corrosion pitting and failure of the welded seam in the side of the bellows will often be much more difficult and perhaps beyond a solder repair; many a bellows has been declared unrepairable for that reason. I have experimented on solderless solutions like TIG and laser micro-welding, internal latex lining and external sealing but none yet seems to be better than lead solder.

In case you're thinking, why bother with repair when you can fit a new replacement bellows; well a new bellows would probably cost over £500 IF you could buy one. You'd be hard-pressed to get one at any price, however, as Jaeger won't sell them to you or even, I believe, to any of their Agents. The only way to obtain new bellows for your clock is to take it to the local Agent who will ship it to Swizerland where JlC will service the movement and install new bellows. Servicing is pretty costly and seems to take months from what I've heard. Used bellows from scrapped clocks come up from time to time but if you're thinking of buying one, you MUST first check that it is the correct one for your clock's calibre and that it has not already part-collapsed (Image 4) or been filled with air instead. Expect to pay a hefty price, too. I started recharging my own after a reoaairer in the US offered me a repaired one for USD450 trade, "to help me out". Factoring inpostage, Import Duty, VAT and fees, that was almost £500! and it had no guarantee whatsoever. Image 5 shows a solder-repair to the steel part of another bellows; it's not pretty (and it's NOT one of mine) - it failed after a refill as it could not take the pressure. So a money back guarantee when you're spending that much is essential.

Now, there are only a handful of independent repairers worlwide and none operate with Jaeger's explicit approval. A TV aerial amplifier builder in the US offers a refill service but because of the distance and interference from Customs at both ends, it can be slow. And it's difficult to post anything 'Signed For' because he uses a PO Box address.

I don't know of anyone else in the UK currently offering a similar service (please let me know if you hear of one). It usually takes three to four weeks (most being the test period) but do please bear in mind that I do not have the resources of Jaeger LeCoultre - this is, after all, just an extended hobby. But you can be reassured that I will do my best to provide a reliable and cost-effective service. Find all the costs in my Prices page.

As always, please do NOT post or bring anything to me without contacting me first.


  • A fairly common Jaeger LeCoultre Atmos 'Living On Air' clock 528 calibre with square dial powered by gas-filled bellows on the back
  • The Atmos 'Motor' from a 528 calibre, comprising container, cover heavy spring and bellows to keep the mainspring wound
  • The mainspring barrel from an Atmos 528 calibre, dismantled to show the mainspring
  • Two Atmos bellows at room temperature, the one on the left having completely collapsed.
  • Another repairer's solder repair found on an Atmos bellows, ugly but nonetheless effective, having lasted for years