Effect of a Diffuser in a Pipe

http://en.wikipedia.org/wiki/Discharge_coefficient

Your pressure difference is function ONLY of the resistances between measuring points if the flow between points is always the same.

The pressure itself will depend on the presence or not presence of diffuser.

Friend, thank you for your time.

Could you explain bit more your point. Not able to come to the conclusion.

Theoretically if i calculate the losses, the case with diffuser at the end will have lesser exit loss as the flow velocity is reduced gradually. But the line between pressure tapping are same in both case and so my understanding is that the pressure loss (difference) in both cases are same for a particular flow rate measured by the pressure gauges.

Plot the whole length of duct with respect to pressure. B-side is lesser than A. The pressure effect increases the flow rate of the set up (with diffuser)> this is like vacuum effect from B-A

With the diffuser, the total resistance to flow is less.
Thus the flow rate increases.
Thus the pressure difference between the gauges increases.