Nov.07.2024
The Cv/Kv value is an important parameter and technical indicator for control valves.
I. Cv Value
The Cv (Circulation Volume) value is an abbreviation for the valve flow coefficient, representing the valve's flow capacity. It signifies the volume flow of the medium through the valve per unit of time while maintaining a constant pressure in the pipeline.
The Cv value is defined as the flow rate of water in gallons per minute passing through the valve under the condition of full valve opening, with a pressure difference of 1 pound at both ends of the valve, and at a temperature of 60°F (15.5°C).
II. Kv Value
The Kv value also represents the flow coefficient, similarly denoting the volume flow (or mass flow) of the medium through the valve per unit of time while maintaining a constant pressure in the pipeline.
The Kv value is defined as the flow rate of water in cubic meters per hour passing through the valve under the condition of full valve opening, with a pressure difference of 1 bar at both ends of the valve, and at a temperature of 20°C.
III. Relationship between Cv and Kv Values
Due to different pressure units and volume units, there is the following relationship: Cv = 1.167Kv (flow units: m³/h, pressure units: bar).
The flow coefficient of the valve depends on the flow path structure, including the size of dimensions, changes in dimensions, and changes in flow direction, etc. Cv value is not a design parameter but a value obtained through actual experimental measurements. From the flow calculation formula, it can be seen that pressure drop has a direct effect on flow.
For a given liquid, the flow through a given valve depends on the pressure drop. For a given gas, with P1 given, when P2 is greater than half of P1, increasing the pressure drop can increase the flow; when P2 equals half of P1, the fluid exits the valve at sonic speed, and at this point, the flow increases to its peak, further increasing the pressure drop will no longer increase the flow; when P2 is less than half of P1, the flow through the given valve depends on the inlet pressure. When the pressure drop is zero, the flow is zero, and the fluid is in a static state.
