There is unsaturated steam in the cylinder under the piston at a temperature T.

There is unsaturated steam in the cylinder under the piston at a temperature T. How will the saturated gas pressure change when it doubles?

When compressed, the pressure rises slightly – there is a rapid condensation of “excess” steam. On the contrary, with an increase in volume, the pressure will first drop, and with a rapid increase, the pressure will drop as many times as the volume increases. Then, after the water has evaporated, the steam will become saturated again, and the previous pressure is restored.