Pipe Size Selection

It depends on a few factors, but one basic guideline is this:

Keep the olein velocity around 6 ft/s. (velocity = volumetric flow / inside area of pipe [keep units consistent!!])

Realize that it is a compromise:

1) Larger pipe = slower velocity = less pressure drop = less problems with hammer/etc.. = more capital cost = lower operating cost (smaller, less powerful pump required)

2) Smaller pipe = exact opposite of above.

Pay particular attention to pump suctions; keep the lines as big as practical to allow for lower velocity/less pressure drop to help minimize risk of cavitation.

If you are in fact enquiring about how to calculate the NPSHA & the system curve to allow for pump selection, well, that is a little more involved.

I would then suggest you download the legally free book @:

http://www.pumpfundamentals.com/pump_book.htm