Is it bad to.......

[rljlll]

downsize the output pipe? for example

http://www.marinedepot.com/md_viewItem.asp?idproduct=IK1133

uses a 1in output and mine is 3/4". now if a downsize it at the pump with what the RC headloss caculator said it would work but will doing that ruin the pump since it is made for a 1" pipe not 3/4" pipe?

 

[azrednex]

It'll be fine, more water presure will result and the pump will work a little harder, no biggy.

 

[AZDesertRat]

The pump will actually draw less power since it is doing less work, ie pumping less water. You will cut the flow or delivery rate but increase the velocity since its going through a smaller pipe. I would definitely make sure the suction side is at least 1" and prefferably 1.25 or 1.5" for best service. Any less and you run the risk of cavitation, microbubbles and shortened pump impeller life.

 

[rljlll]

OK so enlarge intake from 1" to about 1.25-1.5" and reduce output to 3/4" and everything with be hunky dory?

 

[AZDesertRat]

If you are looking for maximum flow then use 1" for the discharge side. If flow is not the issue 3/4" will work but possibly reduce the flow up to 25% or more if its used for the entire length.
I got on an elevator at work today and someone asked me how things were going, when I replied Hunky Dory everyone laughed at me!