Abstract: A method and apparatus for coupling a primary loop with a secondary loop for circulating processing fluids therebetween comprising in combination a first connection for the feed line of the primary loop and a second connection for the return line of the primary loop; a third connection for the feed line of the secondary loop and a fourth connection for the return line of the secondary loop; a crossover line coupling the four connections; first valve means for controlling the flow through the primary loop; first sensor means responsive to the flow across the crossover line to control the first valve means; second valve means in the path of flow through the crossover line; second sensor means responsive to the temperature of the process fluid in the secondary loop to control the second valve means; a common controller for the first and second sensor means adapted to control the first and second valve means as a function of the sensed temperature and flow; and a common controller for the first and second sensor