Well, Leslie gave you a sneak peek a week ago but I insisted that I be the one to write this post and I haven’t been ready until now.
We’ve written several times about the new diffuser basin and how exciting it is for us. For me, the most exciting part of that project is being able to do a redesign on the filter mold to optimize the new diffuser basin.
I occasionally go on deliveries with our staff. Moving a 165 pound filter into place is HARD. It’s back breaking, in fact. The first thing I thought of when I learned about the new diffuser basins is that a filter optimized for a basin could be made lighter after the old diffuser plate ridge was eliminated. At the same time we began working on the diffuser basin project, we also went through the process of redoing the mold design so we could produce the new filters after using up our old inventory.
Well, a big order for molds came in just after we received our first shipment of diffuser basins. I made an order for steel for the new mold design back in August and at this point we have three of the new molds on line! The next section is going to be geared towards people who think like engineers so I will write it in bullet points. If you don’t think like an engineer then skip down to the conclusions.
Design advantages include:
- The “heart” of the mold, or inside section, is now composed of only 4 pieces of 1/8″ thick steel instead of the previous 8 pieces, 4 of which were 1/4″. This makes it MUCH easier to weld the center section straight. A straight center section pulls easier as well.
- The old diffuser plate ridge was 1/4″ thick. Eliminating the ridge means eliminating a substantial amount of concrete, which means a weight savings.
- Eliminating the diffuser ridge also means that the molds pour more easily, reducing the chances of voids showing up in the finished filters.
- The new mold revision corrects for an inconsistency which was incorporated in the previous (2008) mold revision. We had over-zealously reduced the sand column height by a few inches which caused it not to correspond with CAWST specifications. Filter height is now restored which makes us happy because we like to be in line with CAWST standards and hopefully make the World Health Organization happy as well.
- The new filter is 5 lbs less than the old filter: 160 lbs versus the previous 165 pounds.
- The new mold is also lighter and uses less steel, particularly the more expensive 1/4″ steel. The mold functions more smoothly because of the very straight “heart” center section, putting less strain and wear on the puller and 1″ puller nut.
- It may be possible to thin the walls by 4-6 mm on the outside dimension, and also by a smaller amount by decreasing the taper on the center section slightly.
The new filter is easier to build, deliver and install. Water quality will be slightly improved even over the very good previous design because of the diffuser basin and corrected sand column height. We will save a modest amount on materials because there is less concrete required per filter.
There may be room for even more improvement. So far, we haven’t had a single one of the new filters come out of a mold with cracks, leaks or voids. If the trend continues, then we may be able to further optimize the filter by slightly thinning the walls from current 25-27mm down to 20-22mm thick. The workers all seem to feel it would be easy, but I would like to do more testing. An important consideration is that we eventually sell all of the molds we build to other organizations that send technicians to come train with us and start new programs in Haiti. Most of them never have access to the concrete vibrators we use, so consolidating the wet concrete is more difficult. I suspect we will be able to do some wall thinning however.
I was disappointed the new filter only weighs 5 pounds less than the old filter, but thinning the walls could easily remove 10-20 more pounds. We have steel for 16 molds at the moment which which won’t take very long to move through inventory at which point we can try out a thinner walled design if we decide to. How do I know we will move through those 16 molds so quickly? Well, we built a total of 112 (112!) molds of the 2008 revision which have all been sold to other Biosand filter projects. I was originally hoping for a 30 pound reduction in weight, but by bringing the sand bed height back up we gained most of that weight back again.
Ultimately, how does this development translate into an advantage for the Haitian people?
Clean Water for Haiti has installed over 18,000 filters in the past decade, and in the next decade we hope to install many, many more. Every little improvement we make to the hardware will be a small improvement for each of the tens of thousands of filters we plan to make in the future which adds up to a huge advantage overall.
Part of the reason we have been able to complete the diffuser basin/ mold optimization project is because we have been short of funding so we’ve been directing our energy into projects that don’t need much money right now. Now that we have the optimized design, I’ll be excited when we can get production cranked up to full speed again. Would you help us to do that?