The manual balancing valve (MBV) must provide a unique combination of two functions to the hydronic system: the ability to selectively throttle the flow to a terminal device or branch circuit (several terminal units or sub-branches), and the ability to measure the resulting flow.
The MBV operates with a fixed, although manually adjustable, resistance. The flow through the MBV depends upon the degree to which it is throttled and the differential pressure placed across it.