Balancing Valve
(Cv) Auditor
Audit valve flow coefficients against measured pressure drops to verify loop flow distribution accuracy.
Hydronic Balancing, Pressure Drop, and the Cv Coefficient
The Cv (Flow Coefficient) is the universal metric for defining how much water a valve can pass under a specific pressure drop. It is mathematically defined as the number of gallons per minute (GPM) of water at 60°F that will pass through a valve with a 1 PSI pressure drop across it. In large hydronic systems, valves at the end of long pipe runs have lower available pressure than those near the pump. Balancing valves allow us to artificially increase the pressure drop at "near" terminals to match the "far" terminals, forcing the water to distribute evenly throughout the building. If a valve's calculated Cv is inconsistent with its manufacturer design, it indicates that the valve is either fouled (clogged), partially stuck, or undersized for the current riser flow requirement.
Frequently Asked Questions
A: A standard globe valve has an unpredictable Cv that changes depending on how many turns open the stem is. A Venturi-style valve has a precision-machined internal throat that creates a predictable, stable pressure drop at any given flow rate. By plugging differential pressure gauges into the Venturi ports, an engineer can read a constant, accurate GPM flow without guessing stem position.
A: In an unbalanced loop, the "path of least resistance" hogs all the chilled water. Near-loop terminals become freezing cold, while far-loop terminals suffer from starvation, leading to constant tenant comfort complaints. Unbalanced systems also force the pump to run at higher speeds to reach the "starved" areas, needlessly elevating the entire plant's utility load.