Enthelpy and Isentropic compression/expansion

[RoRoRo]

In a certain thermodynamics textbook, specific work done by an isentropic compressor/pump in an ideal rankine cycles, is given by the following;

Wpump = h2 - h1
Wpump = v(P2 - P1), where v = v1

When I carry out these two calculations between any two states, I get vastly different answers.

For example, compressor in a rankine cycle operating between the following conditions for saturated water;

P1 = 20 kPa
v1 = 0.001017 m3/kg
h1 = 251.42 kJ/kg

P2 = 500 kPa
h2 = 640.09 kJ/kg

Wpump = h2 - h1 = 640090 - 251420 = 388 670 J/kg

Wpump in = v(P2 - P1) = 0.001017 ( 500000 - 20000 ) = 488.16 J/kg

I assume that I'm missing something. Is there any explanation for why I'm seeing such a huge discrepancy in results for two supposedly equivalent expressions?

 

[Chestermiller]

Is the liquid water saturated in both states?

 

[RoRoRo]

I was assuming that the water was a saturated liquid at both states but because the process is isentropic, its actually a compressed liquid at state 2. I think...

 

[Chestermiller]

I was assuming that the water was a saturated liquid at both states but because the process is isentropic, its actually a compressed liquid at state 2. I think...

Correct.