Piping questiong

[gizmoguy]

I have a water source that comes from a drain pipe under the street that is spring fed.  It always supplies enough water to keep a 4" pipe full.  I am going to put a box under the pipe with a outlet pipe that will run around 90' for a 15' drop.  My question is this:  Will I get more power by running a 6" pipe the distance and put a 6" to 4" converter on at the end, or just stick with 4" all the way.  My idea on the 6" to 4" is that there is more water in the pipe so there would be more pressure at the converter because of the extra weight.  Can you help me figure this out?

Thanks!

Gizmoguy

[dnix71]

The power available is flows times drop. If a 4" pipe is always full, then you could get more flow with a 6" even if it isn't full.

The pounds/square inch pressure at the bottom of the pipe is the same regardless of pipe diameter, but the total pressure will be greater with a larger diameter pipe (feet of head is feet of head).

Go with 6" all the way until you get to your turbine, then install whatever adapter is needed. If you restrict the flow at the turbine to match the flow from the spring, the water will back up to the top of the pipe drop and you will get the max head at the max flow.

A 6" pipe will pass 2.25 times as much water as a 4" pipe (all other things being equal.

[Ungrounded Lightning Rod]

If you have such a choice you want to use the larger pipe to reduce pressure drop due to friction with the pipe.

Pressure of still water doesn't depend on pipe diameter, just height of the water column.  But flowing water loses some pressure due to friction so you want to avoid that.  The difference in pressure drop between 4 and 6 inch pipe is significant.

[terry5732]

Your adaptor can change the gpm to psi ratio but it will not change the power available

The only time you would need a bigger feed pipe is if you would otherwise have a back-up

You said it filled the 4" but not the rate

[gizmoguy]

Thanks for the replies!  The flow is about 420 gpm.

-Gizmoguy