Cv of Valves in Series and Parallel
Combine the flow coefficients of valves and fittings installed in series (one after another) or in parallel (side by side) into one equivalent Cv, and find the flow through the set at a given pressure drop.
- Series: 1/Ceq² = Σ(1/Ci²)
- Ceq = 89.44
- Q = Ceq × √(ΔP ÷ SG) with ΔP in psi = 340.6 gpm
Share of each item
| Item | Cv | Flow | Pressure drop |
|---|---|---|---|
| Item 1 | 100 | 340.6 gpm | 0.8 bar |
| Item 2 | 200 | 340.6 gpm | 0.2 bar |
Combining Flow Coefficients
Parallel: Ceq = C₁ + C₂ + …
Q = Ceq × √(ΔP ÷ SG) (gpm, psi)
C are flow coefficients in Cv (Kv = Cv ÷ 1.156), ΔP the total pressure drop in psi and SG the liquid specific gravity. The rules assume turbulent, non choked liquid flow and items close enough to share the same flow (series) or the same pressure drop (parallel).
Worked example
A Cv 100 valve in series with a Cv 200 strainer acts like a single Cv 89.4. At 1 bar (14.5 psi) of water it passes about 341 gpm (77 m³/h).
Frequently Asked Questions
How do Cv values combine in series?
Pressure drops add, and ΔP ∝ (Q/C)², so the inverse squares of the Cv values add.
How do Cv values combine in parallel?
Flows add at the same pressure drop, so Cv values add directly.
Can I use Kv instead of Cv?
Yes, the same rules apply as long as all values use the same unit.
Learn more on the blog
Control valve flow coefficient (Cv) explained
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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