Piping Question

We have a system that has 1 inch pipe though the whole circuit ( cooling water ) and the control valve body is 1 ½. This is the only circuit like this and all the rest are 1 inch pipe and 1 inch control valve.
The odd circuit cools a roll that is about 7 feet higher than the rest but I am thinking that this ½ larger control valve makes no difference since the piping is the same size but others say it does.
I thought GPM through a pipe was limited by the pipe diameter? If this is true would the smallest pipe in the system be the limiting factor?

It depends on the type of control valve you have. In some cases the control valve presents a fairly big restriction to the flow and is the limiting factor. Going to a larger valve will usually help the flow in those cases.

The valve size makes a difference. How much of a difference depends on the amount of head loss through the valve compared to the total head loss through the system. If the valves are installed in a piping system with long runs of pipe and a lot of fittings then the valve won't matter much. If the valve is in a very short piping system and represents most of the head loss then it makes a big difference.

As Mendonsy indicates the type of valve makes a big difference too. A full port ball valve offers little restriction. A globe valve can be a big restriction.

it's a motorized valve that looks like this https://www.google.com/search?q=mot...%2Fplate01%2Fproduct.asp%3Fid%3D18794;472;461

That's probably a ball or plug valve, but it still doesn't provide enough info to answer your question. Piping must be analyzed as a complete system - a single component may or may not be critical.

Or, the original 1" valve failed, and the only replacement part on hand was the 1-1/2" valve.

-rpoet

No all restriction need to be added up, and the height too, with a certain flowspeed the pipe will need a certain watercolumn to get this speed, a bent is for example 1/2 meter pipe, an elbow is 1 meter a 1" valve is 3 meter a 1.5"is 2 meter etc.