Revision history [back]

Looks as though you are using the outside diameter of the pipe instead of the inside (72.9mm for 90mm pipe See Appendix 16 of Engineering in emergencies). The pipe will give about 4.5 -5.0 l/s over that gradient., which will probably be ample for that population, especially if they continue to use river water for washing etc. Maybe you could consider a twin pipe if the next size up is not available (at least for part of the line if you need the full flow all the time). Max pressure on the pipe would be 15 bar if there is a stop valve at the lower end. If no valve you will need to allow for overflow to pass safely around the tank (and not wash out its foundations!) It will flow full over those lengths which lie below the grade line but air pockets will form at the high spots. I suggest tapping the pipe at the high spots and putting in bleed valves if air valves are not available. This would require occasional opening of all those valves to let the air out (tedious task). Is the pipe being buried below the frost line? Freezing could be a problem in those parts of the pipe which remain full at zero flow. Regards, Alan Reed