The DA 516 is a differential pressure controller that is adjustable. Its function is to keep a constant differential pressure over the load (a branch of several fan coils, for example), regardless of pressure variations in other parts of the distribution system. The DA 516 will control the pressure between the controller itself and another point in the system, the pressure of which is transmitted to the controller through a capillary tube. The controlled pressure set point is adjustable within a specified range. Because it provides a selfadjusting restriction, the DA is well-suited to variable speed pumping applications.