Friday, March 24, 2017

Construction day: Part 3

Today was a long day. I've been on my feet for most of it, building lids to go on the larval traps I'll deploy this summer. Not many people realize how much construction science can involve, so I'll walk you through the process.

Not exactly candy: my PVC lids super glued to neoprene
For the lids, I needed a sturdy plastic that wasn't too bulky, so I pulled out some PVC sheet I had left over from an earlier project. I ordered a special hole saw (it drills giant holes) and set to work. I was actually using the hole saw for the opposite of its intended purpose, because I wasn't concerned with the holes themselves; I wanted the discs the hole saw would punch out. I headed to the shop to use the drill press, and two hours later, I had close to 90 little discs, the exact diameter of my larval traps.

Step two. The PVC alone won't be enough to seal the traps, so I needed something a bit more waterproof. I super glued neoprene to the PVC discs - actually, more accurately, I super glued the PVC discs to a sheet of neoprene, remarked to myself that they looked like candy buttons on paper, and cut them out. I drilled holes through the center of the discs, then threaded rubber bands through the holes. The rubber bands will hold the lids in place so my traps are sealed while they're being deployed, then pull the lids off after about a day. I want the lids to open once the samplers have settled into their places so they can start catching larvae.

Larval trap lid and galvanic release setup
To make sure the lids open at the right time, I'm using what's called a galvanic release. They're most commonly used by fishermen to keep floats underwater until the fisherman is ready to come back. The release is made of metal that corrodes at a known rate in seawater. The size of the release determines how long it holds together, and in my case, the releases last about a day. That's just the right amount of time for my samplers to be deployed and get settled in place before opening.

The design I'm using is modified from one my Ph.D. advisor came up with. Essentially, the trap lids are held on by tightly-stretched rubber bands, and when the galvanic release corrodes through, the rubber bands are no longer connected and the lid flies off. I actually tested the lid setup off of the dock near my lab to make sure the lids would open but stay connected to the trap housings, and it worked.

Friends, I am tired, but it's nice to see my construction projects coming together. Slowly but surely, everything will get built!

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