4 - University of Idaho



4. Concept Selection

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4.1 Decision Matrix

Implementing the use of a decision matrix (Table 1), team CIA compared the three concept designs. The criteria for comparison used the needs analysis document for generating categories. Risk solutions (ability to eliminate risk), portability, safety, cost, and feasibility were the governing categories in which each concept design was evaluated. Team CIA used a scale from one to five; five relating to the best possible performance. As shown above, the lever arm design had the greatest score (15.5) followed closely by the slow sand filter design (15).

4.1.1 Definition of Criteria

Risk solutions describes the teams ability to resolve foreseen risks associated with the design. Portability defines the degree to which the filter can be manually carried. Safety describes the filter’s ability to produce safe drinking water (less than 5 NTU and particle size less than 0.2 microns). Cost evaluates the design’s anticipated cost for construction. Lastly, feasibility considers the materials needed to build the filter. The more abundant the materials are the better the rating.

|  |Slow Sand |Lever Arm |Press Pump |

|Risk Solutions |4 |2.5 |2 |

|Portability |1 |4 |3 |

|Safety* |4 |3* |3 |

|Cost |3 |3 |1 |

|Feasibility |3 |3 |1 |

|Total |15 |15.5 |10 |

Table 1: Decision matrix with rating criteria of risk solutions, portability, safety, cost and feasibility.

Being that the top two designs rated closely, team CIA incorporated our client Eric Morris to make the final decision. Discussing with Mr. Morris, the lever arm filter became the final design chosen. While the slow sand filter may have a low risk, the slow sand filter is a stationary design. The team and Mr. Morris need to make a portable filter. The lever arm filter involves risks associated with a new design, but team CIA has assessed these risks and has planned solution approaches. Eric Morris and team CIA concluded that the lever arm design meets the needs and goals of the project.

4.2 Chosen Design: Lever Pump Filter

4.2.1 Lever Pump Filter

Overview

The lever pump filter comprises of an upper and lower reservoir (five gallon buckets), a side tube (PVC piping) which contains the multiple stage filter media, and a lever arm. (Figure 3) Dirty water pours into the upper reservoir. An upstroke on the lever arm pulls the side tube up and opens the inlet check valve. Dirty water enters the side tube pressure chamber. A down stroke on the lever arm then closes the inlet check valve and pushes the dirty water through the filtration materials. Options for filtration materials include woven fabric, charcoal, ANU coffee/clay, moringa seed, and ceramic. The water passes through the first material (fabric or ANU coffee/clay) stage which focuses on eliminating turbidity. The next stage concentrates on biological matter removal (moringa seed or ceramic). The multistage process elongates the filter life because it prevents turbid water from clogging the biological filter material. After the water flows through the side tube in is clean and enters the lower reservoir. Another valve on the top of the side tube squirts water if the filter has been exhausted and needs maintenance. When the pressure in the side tube increases to an unreasonable amount due to filter material clogging, water will naturally squirt through the top valve.

Figure 3: Illustrates the Lever arm filter.

Risks and Threats

Foreseen risks and threats of the Lever Pump filter are mainly associated with the mechanical apparatus. The filter has moving parts (lever arm and side tube) which will predictably see large amounts of stress that could lead to fracture. The lever arm forces the water through the different filter materials. Depending on the pressure needed and the area of the filter materials, the constructing materials for the lever arm need to be durable and possibly more expensive. Another anticipated risk involves education about filter construction and use. The design is relatively complex and if it is assembled incorrectly, the filter will not produce clean water or may not work at all. Testing of parts and theories of this design have been performed, yet the design as a whole has not been tested. Team CIA will first collect data on the individual filter materials and then test them as an assembled unit. This method will help the team troubleshoot the design.

Benefits

Advantages to the lever pump filter attribute to its maintenance and accessibility. The side tube assembly allows the users to take apart exhausted pieces of the filter. Replacement of these tired materials enhances the life of the filter, allowing the frame (skeleton) to have many uses. Portability is another benefit to the lever pump design. The filter breaks into three major components: upper and lower reservoir and the side tube. Disconnecting these parts and putting the buckets together and side tube in the buckets, facilitates manual transportation. Both stationary and transient people can use the filter because of its mobility which expands the demographics of its use. The filter is not gravity fed; therefore, the user controls the speed of the water filtered.

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