Grantee Research Project Results
Final Report: AguaClara's Ram Pump for Zero Electricity Drinking Water Treatment
EPA Grant Number: SV840017Title: AguaClara's Ram Pump for Zero Electricity Drinking Water Treatment
Investigators: Cowen, Todd
Institution: Cornell University
EPA Project Officer: Aja, Hayley
Phase: II
Project Period: August 1, 2020 through July 31, 2022 (Extended to July 31, 2023)
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2019) Recipients Lists
Research Category: P3 Awards
Objective:
AguaClara Cornell is a multidisciplinary student project team program at Cornell University, housed in the College of Engineering, that researches and installs sustainable water treatment solutions committed to long-term environmental, social, and economic sustainability. Since 2005, the AguaClara program has been steadily improving water treatment technology performance with a specific focus on increasing the accessibility of safe drinking water to those who cannot afford the traditional water treatment plant. With the themes of economic accessibility and environmental sustainability in mind, AguaClara water treatment plants are designed operate without electricity and built with locally sourced materials, and have been implemented in Honduras. The plants use fluid mechanics principles to eliminate the need for mechanical controls. By reducing the number of moving parts, the AguaClara plants have far fewer failure modes than conventional mechanical plants. AguaClara produces cleaner water with lower capital and operating costs than conventional plants in Honduras, and thus, there is an effort underway to bring AguaClara technologies to the United States. A critical component of AguaClara plants is liftng treated water to the top of the plant for preparing coagulant and chlorine stock. The project objective was to design and fabricate a novel inline (vertical pipeline with zero waste) ram pump, which uses potential energy to lift a small amount of water to a higher elevation while routing the “wasted” water from the ram pump to the local community for drinking water; hence this is a zerowaste ram pump.
We have five original objectives: 1) Modify the ram pump design to increase the pumping efficienc. 2) Simplify tuning for different driving heads and to maximize the flow rate of high pressure water. 3) Test the ram pump in the field for reliability and ease of use. 4) Scale to different sizes of water treatment plants. 5) Evaluate alternative designs for simplified fabrication.
Summary/Accomplishments (Outputs/Outcomes):
We have made significant progress on objectives (1), (2), and (5) but for several reasons, we were unable to make progress on objectives (3) and (4). The pandemic started in March of 2020 and that slowed down our project and importantly prevented travel to Honduras. At the close of the project period we have arrived at an elegant solution that is an alternate design that does in fact simplify fabrication (objective 3) and is now ready to testing in the field (Objective 4) as well as at different scales for different size facilities (Objective 4). Further, we only just resumed AguaClara’s travel to Honduras in 2023, and as such, there has been no opportunity to field test a prototype but we have learned that Honduras plant operators in many cases built their own ram pumps but did not heavily rely on them as in general they failed. The majority of plants continue to carry the required water for the chemical stock tanks by hand.
During the performance period work focused on both theoretical and experimental efforts to improve the Cornell AguaClara Ram Pump system developed in previous years by the AguaClara program. Our goal was to produce a more accurate theoretical framework for evaluation of the system and use this framework for future improvements in development of our prototype ram pump. We initially focused on the Phase 1 approach of a multi-spring solution to operate the pump check valve. Our goal was to produce a robust spring configuration that led to repeatable spring tension/length settings that allowed flow rate to be optimized in the ram pump. Our Phase 1 configuration did not allow repeatable and optimizable forces to be applied to the check valve. We found that some configurations of the spring system led to lateral oscillations of the spring system and others to both large and small oscillations in the longitudinal forces in line with the opening and closing of the check valve, preventing the target operating pressure (head of 6 meters of water) to be achieved. We found that by implementing a stronger bottom spring connected to the check valve the entire spring system was stabilized and oscillations were inhibited, allowing a flow rate optimum to be robustly investigated and determined.
The ram pump team next used an experimental approach to better understand the role of springs and spring constants more generally with regard to the opening and closing of the ram pump check valve, with a focus on simplicity, robustness and translatability to field scale AguaClara plants. They revisited the value of the dual-spring configuration, finding that the weak spring contributed little toward performance but added complexity and made the decision to eliminate the weak spring. The ram pump team then turned its attention to fully characterizing the range of single strong spring constants that met the design criteria of delivering the requisite flow rate against the minimum driving hydrostatic head of 5 m. On a broader scale beyond the Cornell University laboratory and ram pump prototype, the determined optimal spring constant range will allow ram pump implementation in ram pumps across all AguaClara plants, each with its own driving pressure head. Simplicity in optimizing and calibrating the system eases the process for plant operators and again, prevents the stoppage or a inconsistent flow delivery of clean, accessible water. In parallel with moving toward a single-spring check valve control, the team theoretically estimated the time for check valve closure, which was estimated based on fundamental fluid mechanics and Newton’s second law to be 38 ms.
Our final efforts revolve around optimization engineering of the pump. Specifically, optimization was carried out based on a requirement for minimal operator interaction, long material lifetimes, accessibility of parts for maintenance within the system, and overall pump efficiency. In this final effort we specifically looked beyond coiled springs as we focused on objective (5) and investigate flat springs. The first attempt to optimize the spring revolved around a theoretical model of the pump states as they relate to the spring states. The pump was said to exist in one of two states while running: closed or open. In the open state, water is not being pumped but the weight (force) from a water column above the valve is applied to the valve plate and drives the plate toward the closed state. Once the downward force of the water overcomes the upward force supplied by the spring holding the valve plate open, the valve closes, and water is pumped. When the valve closes, a water hammer pressure wave is generated and as the pressure dissipates, the spring force reopens the closed valve, thus restarting the cycle. In an attempt to model the cycle, the Navier-Stokes equations, which govern fluid flow, were solved under the conditions in the closed state and then again under the conditions in the open state. Once solved, the behavior of the water was related to the behavior of the spring by a differential equation. It was believed that spring properties such as spring constant and damping coefficient were experimental variables that could be optimized for a ram pump with given parameters. To verify this hypothesis, a pre-experimental phase was conducted to examine the effects of using weaker and stronger springs in the setup.
During the pre-experimental phase, data for a wide range of spring constants was collected and verified through multiple trials. Ultimately, qualitative and quantitative factors indicated that there were very few springs that met the design standards. Notably, the coil spring would often experience micro-oscillations, that due to its geometry, would throw the spring into a non–vertical oscillation in addition to the intended vertical oscillation. In this scenario, the spring would run unreliably, and would often fail due to these misalignments. Additionally, for the pump to operate, the position of the spring had to be set within a very precise range, a magnitude of only a few millimeters, that would not be easily adjustable for operators without precise measurement tools. Although each of these factors alone are not enough to conclude the coiled springs were not the optimal springs for the purposes of the AguaClara ram pump, the resulting decision matrix indicated that an alternative spring type may be more suitable.
We conducted a literature review into alternative springs and found that flat spring characteristics better align with the requirements of the AguaClara ram pump. Unlike coiled springs, flat springs do not experience non-vertical oscillations. There is less uncertainty in the motion of the spring because it can be more easily stabilized and adjusted on a flat, fixed surface. Additionally, the ranges at which the flat spring will oscillate inelastically are more clearly defined and the flat spring behavior follows its theoretical prediction well. Once it was decided to test the flat spring, a design in CAD that fit within the constraints of the current lab setup was generated.
The flat spring setup was designed to incorporate key testable variables such as spring length, width, and thickness that could be adjusted with relative ease. Additionally, the setup aimed to limit the required equipment without compromising structural integrity, so that the frequent and aggressive vibrations that occur while pumping would not interfere with pump operation or the data analysis. After completing four separate iterations of the CAD design a complete prototype model was constructed in the lab.
Before carrying out experimental testing of the flat spring prototype, a thorough literature review into the mechanics of the flat spring was conducted in order to develop hypotheses about the expected experimental behavior in the open and closed states. Then a more comprehensive experiment was initiated in which different springs of a given thickness were run to their failure points in order to better understand how the springs behave, and at what range they will work. Ultimately, it was concluded that the optimal flat springs to use are both long and wide in size so that the angle of deformation will be minimized (less than 2.5 degrees) and the desired deformation length can still be reached. With a smaller angle, the flat spring oscillates within the elastic deformation region and preserves integrity for long-term usage.
The members of the AguaClara RAM pump subteam change either every semester or every few semesters. This is standard for all AguaClara subteams, in accordance with graduating seniors and joining new members. This rotation of team members does not significantly impact the continuity of the research as each semester builds on the work of the previous semester’s efforts. Data collection was done through ProCoDA (an inhouse developed National Instruments Labview process control and data acquisition tool) software and a pressure sensor with 1% absolute accuracy. A 600 RPM Golander peristaltic pump was used that had a reported bias error within 0.5%. The subteam used an online training module by Cornell University’s Environment, Health, and Safety to train in laboratory safety. There were no environmental concerns due to the use of tap water in the experiments. Members participated in weekly technical discussions with the entire team. In addition, members received feedback from graduate students and PIs regarding exploring different avenues, experimental procedures, and general academic support. Data collection involved real-time monitoring of pressure and flow rates. The data were verified by comparison with theoretical calculations. The data files and documentation were uploaded to the team Github repository.
Conclusions:
The team’s main findings were that despite our original hypothesis that a multi-spring coilspring based check valve control system would be optimal, in fact a single flat spring control valve is simpler, more robust, and has better behavior characterizes. These findings came through our detailed work toward objectives (1), (2) and (5). Primarily due to Covid, we were unable to field test a prototype or try different sizes in the field but our new check valve control approach is ready for these next steps.
The approach of using a single flat spring meets the technical requirements of controlling the open and closed states of the ram pump check valve robustly and is cost competitive with the originally proposed multi-coil-spring solution. The laboratory operated prototype with the flat spring modification shows great promise as a robust low-cost solution for AquaClara plant operators, who are actively seeking solutions to avoid having to hand-carry required water for the chemical stock tanks. The developed approach achieves the desired goal of increasing automation for the AguaClara plants without the need for electricity and will help to ensure robust potable water supplies for the communities already served by AguaClara plants. Further, the more automated and robust these plants become, while maintaining operability without electricity, the more communities that will potentially become interested in adopting the technology to serve their habitants.
Progress and Final Reports:
Original AbstractP3 Phase I:
AguaClara's Ram Pump for Zero Electricity Drinking Water Treatment | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.