!!Safety Warning!!
Compressed air can put out an eye, cause severe injury, or death. Proceed at your own risk. The unit I built operates at 3 bar pressure. Champagne bottles typically contain 6 bar. Would you attempt to handle your Cristal without eye protection, hard hat, face shield, and cut-resistant gloves? There are nearly two dozen champagne-accident fatalities each year.* Be safe! *Source article
After any service inside a watch, I always check for leaks. A common way to do this is using the Bergeon 5555/98 tester shown here:
Here’s how it works: The watch is suspended in a see-through chamber, right above the water line. The chamber lid is sealed and a manual air pump is used to increase pressure to 3 bar (44 psi). Wait for three minutes. If there is any leak path at this pressure, air will have had some time to enter the case and equilibrate toward 3 bar.
Next, submerge the watch under the water by pushing down on the hanging rod. Immediately release all the air pressure in the chamber by opening the bleed valve on the lid. If there were a leak in the watch, the higher pressure air that had infiltrated the watch will now escape and you will see a steady stream of air bubbles. If you see a leak, note the location and remove the watch for repair.
The test is safe for the watch as water cannot leak into the case. A big advantage of this test versus other methods is that you can pinpoint the exact location of the leak (e.g. crown area, case back, chrono pusher, or crystal seal).
I go inside enough watches that this would be a handy tool. But it costs 555 £ at CousinsUK. Plus more for shipping. So I built a tool to do the same test for $70.36, shown here:
The test chamber is simply a housing for a water filter. It is rated to a max operating pressure of 8.6 bar (125 psi). The burst pressure is not quoted by the manufacturer, but it is typically >2x the rated operating pressure. For liability reasons, the manufacturer says it should only be used for its intended application of filtering water -- not compressed air systems. The clear plastic is styrene acrylonitrile, and the blue lid is polypropylene. Both plastics are often marketed as “shatterproof,” i.e. they don’t fragment into shards when they fail. Though I test at only 3 bar (44 psi), my system is also protected from overpressure by a safety valve that will open at 4.8 bar (70 psi).
Here is the complete bill of materials:
From filtersfast.com:
$16.69 / 158599 / Pentek clear filter housing
From mcmaster.com
$4.43 / 8063K38 / Schrader air fill valve
$5.86 / 9151K52 / Pipe tee
$7.57 / 89895K227 / Stainless tubing
$5.76 / 4912K72 / Ball valve
$5.26 / 48435K769 / ASME rated safety relief valve 70 psi
$11.05 / 9545K63 / Size 13.5 rubber stopper, pack of 3
$6.25 / 9545K27 / Size 2 rubber stopper, pack of 25
$7.49 / 8576K82 / Rubber sheet 6”x6”x1/16”
Here is a photo of the tester with parts labeled.
And here is how the test works.
First attach the watch to the stainless dip tube using the rubber strap. Wrap it around the spring bars like a zulu strap. The strap has four punched holes that fit tightly over the dip tube. You can shake this assembly around and the watch won’t budge. It’s quick to load and unload, yet there’s no risk of scratching or dropping the watch. Note that you get a clear view of the front, back, and sides of the watch.
Partially fill the clear chamber with water.
Screw on the blue lid. Hand-tight is adequate. The watch remains dry, suspended above the water line.
Attach a bike pump to the Schrader valve. This is the same standard valve found on bike and car tires.
Raise the pressure to 3 bar (44 psi) then wait for three minutes.
Remove the bike pump. Flip over the test chamber. The watch will now be submerged under water.
Immediately open the ball valve to relieve the chamber pressure. Air from the top of the chamber will rush through the stainless dip tube and exit out the ball valve. In <2 seconds, the vessel will have returned to ambient pressure.
Look for leaks. A leak will appear as a steady stream of air bubbles. There will always be a few residual bubbles around the case, especially near a rotating bezel. The difference between residual bubbles and an actual leak is quite obvious. Even for a minuscule leak.
No leaks on this test, just some residual bubbles. When the test is complete, flip over the chamber, unscrew the lid, and remove the watch.
Here are some details on how I built the tester:
I pushed two small rubber stoppers (Size 2) in the center hole inside the blue lid. Their job is to hold the dip tube in place. These stoppers come bored-through with a hole diameter of 0.20”. So they grip firmly on the 0.25” stainless tubing and hold it in place securely. Once the tubing is pushed through the holes into the lid, you will have a nearly impossible time to get it back out (which is a good thing, it will never fall apart unexpectedly). I cut the rubber stoppers with a utility razor so that they both fit inside the blue lid when stacked. To be clear, I cut a little bit off their length, not their diameter.
The two big stoppers (Size 13.5) are also slipped over the dip tube prior to mounting it on the lid. These serve to reduce the free volume of the chamber. Therefore you need less air volume when pressurizing to 3 bar. Also they allow the watch case to sit more toward the center of the chamber, which makes it easier to view when checking for leaks.
I cut the stainless steel dip tube to size with a tubing cutter, and bent it with a tubing bender.
If you don’t have access to these tools, you can cut tubing with a hacksaw and just use a straight tube piece. I added a bend to the tubing so that the watch could sit centered in the chamber. This bend is optional. It’s nice to have, but there’s plenty of excess room in the chamber even if the watch is mounted off the centerline.
The rubber strap that I used to secure the watch is 1/16” thick. I cut it to size with a rotary cutter in order to get a very straight cut. A pair of scissors would work just fine too. I used a standard paper punch to make the holes. I selected ECH rubber because it is unlikely to tear, and has minimal odor.
All the metal thread connections are NPT (National Pipe Thread tapered thread). They require the use of a thread sealant. I used Teflon tape. Wrap 3 layers of tape in direction of threads, don’t cover the first thread. Do not overtighten the fittings. If you don’t have Teflon tape around the house, you can get a roll at the hardware store for ~$2.
I assume most everyone has access to a bike pump with a built-in gauge, so I didn’t include it in the cost of materials. They can be bought for <$20.
