Break Pressure Tank vs Pressure Reducing Valve
I am working on an extension to a water network in a refugee camp. The extension is to a lower area outside of the previous boundary, with the taps being between 65 and 80 metres below the reservoir. The peak flow rate to this zone will be around 24 l/s currently, but could be expanded to 30 - 35 l/s in future.
We can either install a break pressure tank or a pressure reducing valve. Which would be preferable, or what would be the factors affecting this decision?
Using a pressure reducing valve can lead to extra maintenance challenges.
I, instead,the a break-pressure tank used has sufficient volume, it can also act as a local service reservoir, and with greater volume emergency storage. Providing such storage near to the end of the extension pipe will mean that the supply pipe diameter to it can be smaller. This will be because it will not need to take the peak flow rate; if sufficient storage were provided it could be designed even for the average 24-hr flow rate!
Agree fully with Brian. In Rwanda we also used the smaller pipe diameters to distribute the flow to storage tanks in each area in proportion more or less to the population served. This meant that over consumption / leaks in one area only affected that area. We were also very careful with the main line laying, trying to ensure that they fell and then rose again at a constant rate of say 3-5% with high points always below the level of the downstream receiving tank if at all possible, and low points at the limit of the pipe pressure rating.
Hi Angus et alia, Great question and great responses. The major criteria are the cost and the sustainability. In Guatemala, pressure relief valves need to be imported. Even a pressure relief box needs a float valve, similar to the ones we use in toilets in the US. These valves are typically available even in rural areas. We have preferred boxes to pressure reduction valve for a number of reasons. We even have plans for them. Cost also depends on the availability of local materials to build the box. We build the boxes out of stone masonry, cement, limestone, and rock; very labor-intensive. I have yet to see a plastic pressure relief box. I plan to talk to a local entrepreneur to see the possibilities. Keep up the great work... Bruce
Check the pressure ratings of your pipe as well. 6.5-8 bars (minus pipe-friction losses especially if using small diameter pipes) are not too bad for good quality HDPE pipe (PN10 or PN16) at typical temperatures. See also: https://www.engineeringtoolbox.com/do... (includes a safety margin of course)
That way you preserve pressure in the pipes for further extensions or peak demand periods.
Here in the mountains of Nepal often a combination of small BPT and small flow reducers directly at the taps is used. Normally the BPT are only found in the (often very steep) delivery pipe from the spring source to the main RVT. After that the flow reducers at the tapstands are sufficient and allow a very fine-grained demand management at each tapstand.
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