One of our running goals these past three weeks has been to design a custom, non-return valve for our pump so that out-flowing chlorinated water does not leak back into our water source and compromise our testing by resulting in higher chlorine concentrations than desired. The challenge has been to design a non-return valve that prevents as much back-flow as possible without hindering out-flow. So far, we have tried a ball-valve design, which presents problems for both of those goals. We think a flap-valve design would work better, but so far our flap made of the plastic from a yogurt container has been leaky. Modifications to try next include using a rubber or leather flap as well as incorporating an actual hinge into our design.
Other observations from this week’s round of testing: The pipes in our testing set-up are getting quite rusty! We’ll need to work around this and ensure that our chlorination system does not corrode whatever pipe material we’ll be working with in Dhaka. (Chlorine tends to oxidize iron into iron oxide, which usually sediments out and can be filtered, but this also means we’d have less free chlorine available to actually disinfect the water supply!)