The purpose of proportional flow control devices, with protection from cross-contamination via hydronic water, for use in drinking water installations is to control the flow of potable water based on the pressure of hydronic water from a hydronic system. The device performs this hydraulically and has integral cross contamination protection between the potable and hydronic water. This device is typically installed in conjunction with a heat exchanger and a part of a hydronic system loop.

This device consists of a single potable cold water supply inlet and outlet, and a single hydronic supply inlet and outlet, a means of dynamic flow control, an atmospheric vent, and two sets of three dynamic seals between the potable and hydronic flow paths.