Beijing Bicycles: tire valves
Today I tried to replace my bicycle’s inner tube, but because the tire is so tight over the rim, and because I don’t have nice smooth tire tools, I ended up puncturing my brand new inner tube while putting it back on. What a disappointment!
It turns out that the old inner tube’s problem was the valve; the rest of it is still OK. In China, we have two types of valve: the newer style Schrader valve, like we use in the US, and an older one that I’ve never seen before. I was surprised, when I disassembled it, to find how it worked.
The valve itself, on the lower left, is simply a metal tube; one end is closed and has a small hole drilled through the side, and the other end is threaded. A rubber tube is slid over the closed end and up over the flared part of the valve. Normally, the rubber covers the holes, preventing air from escaping the tire. When inflated with a pump, the incoming air exceeds the tire’s air pressure, and goes through the holes, pushing out from under the rubber tube, and into the tire. The area where the rubber tube covers the flare doubles as a seal where the valve seats against the stem. So simple!
Another nice feature of these tubes is that all of the valve stems I’ve seen are threaded on the outside and come with a nut that tightens down on the inside of the rim to secure the valve. This eliminates the problem where an inner tube misalignment causes the stem to protrude at an angle, making it hard to attach the pump.
To assemble, the valve is inserted closed end first into the valve stem. A metal cap is then screwed down to press the valve into its seat and make a tight seal. The assembled valve is shown on the lower right, and an adapter to use a pump designed for a schrader valve is pictured at the top and top left. The adapter simply clamps onto the valve head, pressing a rubber seal against the top of the valve.
It seems this valve is called a ‘Woods valve’. Pictures on other websites show a valve with a similar head, but the valve itself looks quite dissimilar. However, Woods valves for sale on one site say they are for vintage bicycles and ‘cheap Chinese wheelbarrows’, so these may well be interchangeable parts.
You can tell from the picture how cheaply these parts are made. The valve body is crudely cast from a cheap alloy. Note also how after assembly, the valve body and the valve cap aren’t even nearly concentric. This is typical of many products here that are manufactured for the local market: the standard of quality is very minimal, but this is the subject another blog.
Just for fun, below is a picture of two inner tube boxes. It’s curious that the glue that holds them together has split on every box I’ve seen; Beijing has a quite dry climate.
