The total volume of flow would remain the same. It would cause a slight increase in velocity of flow through the valve however it still remains under the code maximum of 8ft/sec in copper pipe, and given that the valve is made of brass instead of copper, pipe wall erosion from excessive velocity would not be a problem.

FHL (Friction Head Loss) is the actual loss in pressure incurred from the friction of the liquid rubbing the inner wall of the pipe as it flows. The problem here is that while the flow in GPM might be increased proportionally the FHL will increase exponentially. By example, an 1-1/4" line at 15gpm will have a FHL of 0.020psi/ft (2psi/100ft) but if we double the flow to 30gpm the FHL jumps over 3 times to 0.073psi/ft (7.3psi /100ft).

On the "Fitting Insertion Loss" charts a the actual loss introduced by a fitting is expressed as a equivalent length of straight pipe. By example, while a 90deg elbow may only add a physical length of 1/2" the fitting insertion loss is 3ft, which means the elbow introduces the same amount of friction loss as 3ft of pipe.

Now let us put it all together...

1-1/4" type L copper @15gpm has a FHL of 0.073psi/ft
1-1/2" type L copper @15gpm has a FHL of 0.020psi/ft

The difference is 0.053psi per foot, but the fitting insertion loss for a Ball Valve is .5ft so if he installs a ball valve the velocity of flow will remain the same and the pressure will drop 0.053psi / 2 = 0.0265psi.

The bottom line, the pressure drop would not be enough to give it a second thought.

Control valve is made of Noryl not brass.

Control valve has a twin valve bypass mounted on the rear of the valve.

"The bottom line, the pressure drop would not be enough to give it a second though"

That's what I thought... thanks

Justalurker and Lazypup,

Thanks so much for a very professional and thorough answer!