In article ,
(Chris) wrote:

Can i send a 3/4" ouput from a pump into 1/2" will the effect just be of
adding head to the system or is it really something not to do?

You will increase back pressure, which is a bit like adding head to the
system. The result we be a big reduction in flow - but it won't harm the
pump. The question is why would you want to - either get a smaller pump
or a bigger pipe.

Roger Sleet
Roger's Aquatic Pages http://www.sleet.plus.com