If you ask a buyer what makes a torch waterproof, most say the body, or the lens. The real answer is a few cents of rubber — the o-rings sitting in the threads at the head and the tail. Get those wrong and the nicest machined body in the world fills up with water.
We buy our o-rings from a small vendor in Wenzhou, a couple of hours south. Wenzhou is full of rubber and small-parts shops, and you can get o-rings there for almost nothing if you do not care what you get. We learned the hard way that you should care.
Years back, before this vendor, we had a run that failed our water test more than it should. The rings looked fine. Turned out they were a cheaper compound that took a slight set — they squashed flat and stayed flat instead of springing back, so after a few open-and-close cycles the seal got lazy. A torch that passed water test new would leak after a customer changed the battery a dozen times.
So now we pay a bit more for nitrile rings with a known hardness, around 70 shore A, from this one shop in Wenzhou who has not changed his compound on us. We also lightly grease them on assembly, silicone grease, which most factories skip to save the few seconds. A dry o-ring drags and can roll out of its groove when you thread the tail cap; a greased one seats and seals every time.
I visit the Wenzhou guy maybe twice a year. It is not a glamorous trip — his place is a narrow unit with bins of black rings everywhere and a dog that hates me. But that relationship is why I sleep fine about our waterproof claim. The whole supply chain for the thing that actually keeps water out is one stubborn man and his bins.
The thing I want buyers to take from this: when you are comparing two torches that look identical, the difference you cannot see is usually the seals and whether anyone bothered to grease them. We did. It costs us pennies and a little time, and it is the cheapest insurance against a return there is.
One more — we keep spare o-rings in every box. They wear, they get lost, and a thirty-cent ring should never be the reason a good torch ends up in a drawer.
