Strategy Selection
Context: Water utilities in India operate for an average of 4.5 hours per day and at average of less than 10psi. Many customers cope with the irregular supply with roof tanks and by running long “spaghetti pipes” to locations of higher pressure water mains. Both these strategies make the effective system pressure even lower. Because of low pressure, many customers are forced to use their own pumps.
Standards permit the use of a private pump to increase pressure, but only after an underground isolation tank called a sump. However, in older and densely populated neighborhoods, there is no room for a sump. Many cities like India’s capital Delhi are therefore flooded with directly-connected booster pumps.
Problem: At the start of this project, officials from Delhi’s water utility were quick to blame most of their system problems on the presence of booster pumps connected “illegally” to their network – even claiming 90% of the contamination cases were caused by these pumps. Independent of the truthfulness of this claim, it means that contamination will not be solved without a solution to the booster pump problem; until pumps are dealt with, the water utility can continue to pass on blame to customers for contaminating the water and therefore they avoid having to address any of the more fundamental system causes of contamination.
2) Analysis: The (re)contamination of piped water can only occur when all three conditions are met (Lindley & Buchberger):
- A physical pathway exists for contaminates to get into the pipe
- Contaminantes are in the vicinity of the pipeline
- A pressure gradient allows the flow into the pipe
Water pipes in every city have some leakage and therefore pathways will always exist for contamination. Requirements for the separation of water and sewerage systems have not been followed in practice in India and many household water connections run though open sewers. Finally, since most systems in India are not usually pressurized, a pressure gradient cannot be relied upon to prevent contamination. Therefore, all three of these factors contribute to the frequent contamination of piped water in Indian cities.
To understand the effects of online-booster pumps, I considered their hydraulic grade line and how they could change pressure and flow locally.
Strategy: The legal alternate to directly-connected booster pumps are sumps, which discharge water to atmospheric pressure. Therefore, if a device were to mimic the hydraulics of a sump independent of the presence of a pump, the entire booster-pump-induced problem would be eliminated.
If such a device were located where the sump would have been placed, it would simply be a pressure sustaining valve whose set-point is set to atmospheric pressure.
Novelty: Implementing this strategy implies installing pressure sustaining valves immediately upstream of every customer’s pump, which in many cases will induce pump cavitation. However, because of the small size of the pumps this caviation does not significantly affect their lifespan. The counter-intuitive nature of throttling upstream of pumps led to many of the claims in this project’s patent.
Other Design Stages: The overview of this design is here, and more detailed entries about other design stages are linked to below:
- Problem Analysis & Initial Strategy Selection – choosing a pressure sustaining valve
- Concept Generation and Selection – choosing a Starting resistor
- Concept Refinement – inventing a stabilized Starling resistor
- Tamper Proofing – separating the user from the sensitive parts
- Increasing Durability – moving away from plastic parts
- Decreasing Costs – reducing the part count and complexity
- Field Testing – verifying performance in Delhi