Initially, a rigid cylinder is divided into two equal volumes by a piston held in place by a pin. Side A contains M1 lbm of water at 300 °F, 300 psia, and side B contains M2 lbm of water at 500 °F, 680 psia. The pin is then pulled, and the piston moves until the pressures on both sides of the pin are equal. Heat transfer keeps the temperature at 500 F on both sides of the piston.