When using a jacket containing one of the latest water resistant zips (fig 1a), and having spoken to several friends who have used these zips, there was a general consensus that they leaked.
For my undergraduate student project I set about quantifying the leakage observed by users of the water resistant zip. In doing so I discovered a failure mechanism which occurred during movement or gaping of the zip.
The zips are nominally water resistant because two stiffened silicone membranes positioned just above either set of zip teeth meet when the zip closes and provide a water resistant seal or cover above the zip. How do the zips fail? When such a zip is compressed along its length i.e. there is motion in the upper body such as power walking or climbing that tends to compress or bend the zip, the two halves of the membrane separate enough (~ 0.3 mm) to allow water in. Clearly a zip that is only water resistant when not compressed i.e., when the user does not move, is not an effective product for mountaineers and outdoor enthusiasts.
Having found the problem and cause of the leakage I decided to see if there was an alternative, more water resistant, fastening device that could be used in a jacket. I initially looked around the outdoor market particularly at fishing and diving kit where near waterproof zips are already in use, but the weight of the zips and the force required to operate them means that they would be total impractical for use in mountaineering jackets. It was the stationary market where I found my ideal fastening device, a zip used on an A4 plastic file bag (fig1b); it uses a tongue and grove method of joining the two halves, overlapping each edge in a continuous fashion.
To test the stationary zip against the market zips I constructed an experimental rig (fig 1c) which simulates what happens during use, it uses a rotating finger to apply pressure from the inside of the jacket to simulate usage or motion and a spray of water to simulate rain.
I compared the plastic-file zip and a current market water resistant zip on the test rig and showed the water resistant zip leaks whilst the file zip remain water tight.
The file zip has a smooth sealing mechanism and is durable, the only real problem occurs when in the closed position part of the zip can come apart, this does require a huge amount of lateral force and a simple reopening and closing of the zip soon sorts it out.
So far the file zip has only been incorporated into a custom pocket so that it could be tested against the water resistant zip on the experimental rig. Organising a donor jacket so it can be put in to a real dynamic mountaineering test situation is the next step.
No video has been submitted with this project.
No notes have been submitted with this project.
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