Pipes carrying litre/min from A to B - HELP

[Ruffian]

I was unable to attend a class in which we learned this, so any explanation would be appreciated (working and answer would be appreciated).

If a pipe is of 150mm dia. is carrying 40 litres/min from a site and it is replaced by 2 100mm dia. pipes carrying the same volume, what difference does it make to the head required to pump it?


Thankyou.

 

[pixel01]

The cross section of the 150mm pipe is approximately double the 100mm pipe. So the two cases are equivalent. But the smaller the pipe the more resistance to the liquid motion so the second case, the pump must be stronger for the pressure drop is somewhat higher.