T-Cell Construction, II
Entry posted by Swede
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After setting up overnight, there were just a few improvements I made to the cell before testing it with water. The first was the installation of "feet" to stabilize it and to give me room to get my fingers underneath it for lifting when full, if needed. This was simply sections of 3/4" PVC sheet, cut and beveled. By now I was getting pretty good at the cementing process. One of the things I learned is that the prime is especially critical. Heavy prime, with a quality primer, is best, and more cement, rather than less. This makes it messy, but the joints made in this fashion are superior. At least two heavy coats of prime are needed. The material begins to dissolve slightly underneath the primer, and this greatly improves the bond.
The garden hose was fired up, and the cell filled, after instaling two plugs in the pump ports. The test was uneventful.
Construction began on the lid, a 1 square foot panel of 1/2" PVC sheet. One of the critical features of this sort of cell is a good seal. Due to gas evolution, there tends to be a bit of positive pressure on these, and any splashed or creeping electrolyte can get forced past ill-fitting o-rings and the like. I worried a bit about the cell's upper surface that the lid was going to mate with. It consists of four panels, doublers, and other pieces. I did the best I could in making them all the same height, but the planar surface they formed was not perfect, and I knew I would have to rework this upper rim area in some way to achieve a good seal, even with a gasket or o-ring.
I thought about sanding it smooth, but then thought of a much better way to do it. I simply cut 4 strips from a 1/8" thick PVC sheet, each of them 3/4" wide, and glued them very carefully to the top rim. The natural sheet smoothness formed a perfect surface, requiring only a bit of smoothing where they meet at the corners.
Two of what will ultimately be four or five ports were drilled and tapped on the lid. One of them is again, the standard 3/8" NPT plumbing thread. The other is a 9/16" X 18 thread for one of the PVC tubing bulkhead fittings I got from U.S. Plastics. These were being closed out and were a real bargain at maybe a couple bucks each.
More ports will be drilled in a few days. Then, the critical packing groove for the seal itself will be cut into the lid, on the bottom side, with a vertical mill. I've not quite decided whether to try Viton O-ring stock, or PTFE packing cord, but the groove will be able to handle both if need be. I plan on using heavy stock, probably 3/16" round, for the seal.
After all the ports are threaded, the very last thing I need to engineer is the lid clamping system. Unless I can come up with a better way, I plan on gluing 4 blocks of PVC on the tank sidewalls, and into these, install 4 stainless steel studs, probably 1/4". The lid will be placed on the tank, and then two heavy PVC bars will be dropped over the four studs, and tightened with wing nuts. The bars will in turn press down hard on the lid, mashing the seal somewhat, and it should create a reasonably airtight system.
Instrumentation/ports in the CC lid will probably be:
- Temperature
- pH
- HCl dosing port
- Gas Vent
- Stirrer/bubbler
- Sample/topoff port
The body itself, for now, simply has an inlet and outlet port. Internally, I can always add fixed PVC tubing, deflection plates, stuff like that if needed, with the goal being crystal formation and harvest from this cell.
I'm off on yet another 3-day trip... what a waste of time, and sooo boring. In 17 years now as a commercial pilot, I've probably spent over 5 years in hotels. Too bad I cannot bring my hobbies along with me. I suspect the TSA would not like canisters of perchlorate in my bags.
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