Calculation sequence
Step-by-step method
- Convert SI entries to gpm and psi when required.
- Multiply flow by the square root of specific gravity divided by valve pressure drop.
- Convert Cv to Kv for reference.
MechanicalIntermediateHydronic Controls
Control-Valve Cv Calculator
Calculate required liquid valve flow coefficient Cv from flow, pressure drop, and specific gravity.
Why it matters: Cv links valve flow and pressure drop but does not by itself confirm authority, rangeability, or actuator performance.
Calculated result
Engineering evaluation
Required liquid valve coefficient (Cv)50 Cv
- Metric flow coefficient (Kv)
- 43.25 m³/h at 1 bar
- Entered liquid flow (Q)
- 100 gpm
- Entered valve pressure drop (ΔP)
- 4 psi
Engineering interpretation
The entered flow and pressure drop require approximately Cv 50 (Kv 43.25). Select and size the actual valve using manufacturer data and the full control requirement.
Important limitations
- Check valve authority, rangeability, inherent/installed characteristic, minimum controllable flow, cavitation, noise, actuator close-off, and glycol corrections separately.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
Cv = Q√(SG/ΔP), with Q in gpm and ΔP in psi
Kv = 0.865Cv
Current substitution
Cv = 100√(1/4) = 50; Kv = 0.865×50 = 43.25.
Equation legend
Inputs and calculated quantities
- Q
- Liquid flow — gpm or L/s
- ΔP
- Valve pressure drop — psi or kPa
- SG
- Fluid specific gravity — ratio
- Cv
- Required liquid valve coefficient — Cv
- Kv
- Metric flow coefficient — m³/h at 1 bar
- Q
- Entered liquid flow — gpm
- ΔP
- Entered valve pressure drop — psi
Applications
How this calculation is used
Building design
Screen a required valve flow coefficient.
Construction
Compare submitted valve Cv with design flow and pressure drop.
Commissioning
Relate measured flow and valve differential pressure to an effective Cv.
Quality controls
Assumptions and limitations
Assumptions
- Entered values describe one stable operating condition and use consistent measurement boundaries.
- Fluid or air properties and geometric dimensions are representative of the evaluated system.
Limitations
- This is a preliminary evaluation and field-verification tool, not a final sizing or code-compliance determination.
- Manufacturer data, adopted codes, project criteria, and professional engineering review remain controlling.
Field use
Verification procedure
- Confirm the approved reference, measurement plane, and instrument calibration.
- Stabilize the system and record dimensions and operating data.
- Compare the calculated result with project documents and manufacturer data before disposition.
Common engineering mistakes
- Using outside dimensions rather than clear inside dimensions.
- Combining values from different loads, device positions, or measurement conditions.
Technical basis
References and source standards
- ASHRAE Handbook—FundamentalsCurrent handbook chapters covering duct design, fluid flow, heat transfer, insulation, and measurement; verify the licensed edition during professional review.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement