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First, I have assessed potential solutions which utilize multiple 2-inch gate valves to avoid using the larger, more expensive valves. Cost analysis has shown that this is only feasible for a 3-inch flow control pipe, with 2 2-inch valves/pipes feeding in. Larger diameters require too many valves and fittings to increase the cost, and are less friendly for the operator.
Since, I have assessed another alternative design for the entrance tank that features the use of one or more Fernco flexible fittings as an "adjustable weir" configuration on the drain stopper pipes. This design is clearly more cost effective than any of the previous considerations. Upon completing this study, it is going to be subject to future laboratory research before implementation in Agua Clara plants.
Spring 2014 Contributions
I have worked with Runpeng Yu on updating the weir control system on the Stacked Rapid Sand Filters (SRSF). Our goal was to devise a means to adjust the backwash flow rate from the filter inlet channel. This is advantageous to plant operators in cases where the plant is not operating at the entire design flow rate. This is needed because in such cases, the backwash flow rate is too low and the desired bed expansion is not achieved during backwash.
We have developed a solution to this problem that features a removable gate on a weir in the filter inlet channel. This gate would be removed from the weir during backwash, causing the weir to act as a submerged orifice. Then, water would flow through a 10-cm deep flow control weir (restriction) that delivers the target Q to the filters. This target Q can be altered by placing "stop logs" at the bottom of this restriction. The Mathcad design code was completed in April 2014. The current focus is on updating the drawing code so that this design may be reflected in drawings on the Agua Clara design server.