Rankine Cycle pressure I don't understand why in (Ideal) Rankine Cycle we assume that pressure remains constant at the boiler and the condenser. Shouldn't water pressure change, when water goes from liquid to vapor (boiler) and vice versa (condenser)?
 
 A: 
Shouldn't water pressure change, when water goes from liquid to vapor (boiler) and vice versa (condenser)?

No, it shouldn't. Because water is on a constant pressure line during the processes (from point $1$ to $2$ in the boiler and from point $3$ to $4$ in the condenser) for both cases.

In addition, phase of a matter doesn't depend on the pressure only. For example, we can have water in gas, liquid and solid phases at the same pressure.
A: Yes, pressure changes at evaporation or condensing. But it is nevertheless constant throughout the pipe. 
If you force water through a long pipe, and then heat it up very much at the middle so the water evaporates at that point, then it will get harder for you to push the water through, since the expansion will work against your force. 
So you must apply more force. That is, the pressure has to be bigger. It has to be bigger at any points in the pipe - not only at the point of evaporation. 
It is true that the pressure will raise when you start evaporating water at a point of the pipe, but this new increased pressure (at the new flow-steady-state) will be the same throughout. 
