Support request to determine pipe size for water in Kenya community
I would like to determine the right pipe size to deliver water for a community. The water will be delivered to 10 taps assuming the taps are open at the same time. The terrain is as shown in the attachment. Any ideas would be well appreciated.
Douglas White of MM, Cambridge (and a RedR UK affiliate) has responded to your question as follows:
Regarding the RedR question "pipe size for Water in Kenya community":
· Assume supply delivered by gravity and not pumped. From the cross-section there appears to be a gravity head of 30m over a pipeline length of 2.7km;
· I would consider the first consideration to be the hydraulic gradient associated with the alignment, as there are two high points along the route which could become an issue should the frictional losses be high enough such that the hydraulic gradient is lower than the pipeline itself. The following calculation for the frictional losses has been calculated using Colebrook-White equation (though other methods would be equally appropriate), and a suitable pipe material and diameter selected;
· Flow-rate and pipe material. I’ve initially assumed a flow of 5l/s (i.e. 0.5l/s for each tap) in my calculations. For a uPVC pipe (which I would anticipate to be the most commonly available material), taking a roughness value of 0.2mm and nominal losses for fixtures and fittings, the headloss would be around 0.71m/km pipeline for a DN150mm pipe, and 1.77m/km for a DN125mm pipe. These values seem acceptable given the pipeline profile; anything below DN125 produces a head-loss which is probably too high to effectively convey the flows;
· Using this data, the maximum flow capacity for the 2.7km pipeline would be 20.5l/s for a DN150 pipe and 12.0/s for a DN125 pipe. These figures would need to be reviewed against the required flow at the tapstand, as well as the available supply at the Ilturisho borehole;
· Other considerations should be:
o Will the pipe be buried or laid above-ground?
o How will it be protected from damage, particularly from vehicle loading?
o What are the connection details, i.e. will the joints be flexible to account for any settlement or pipe movement?
o What are the ground conditions, is excavation safe and practical?
o Are there likely to be any buried cables or pipework that the contractor will need to be aware of before digging?
o Will the pipe material degrade or corrode, what are the potential health hazards for the end-users?
Trust that helps. Look forward to learning what you implement.
Kind regards, Leigh
LC Jones RedR KP Moderator
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