Calculator inputs
Example data table
| Case | Flow | Fluid SG | Valve style | Service band | Suggested size |
|---|---|---|---|---|---|
| Booster pump discharge | 250 m³/h | 1.00 | Silent spring | Pump discharge | 3 in (DN80) |
| Process water return | 90 m³/h | 1.02 | Swing check | General process | 2 in (DN50) |
| Light slurry transfer | 55 L/s | 1.15 | Ball check | Light slurry | 4 in (DN100) |
| Viscous blend recirculation | 350 gpm | 0.98 | Lift check | Viscous liquid | 4 in (DN100) |
Formula used
1) Liquid sizing by Cv: Cv = Q × √(SG / ΔP), where Q is flow in US gpm, SG is specific gravity, and ΔP is valve pressure drop in psi.
2) Pressure drop from a known Cv: ΔP = (Q / Cv)² × SG. This estimates the loss through each listed standard size.
3) Line velocity: v = Q / A, where A = πD² / 4. The calculator compares the result against a service velocity band to reduce chatter or excessive slam risk.
4) Effective valve Cv: Cveffective = Cvbase × style factor × viscosity factor. The viscosity factor is an advisory derating for thicker liquids.
5) Pressure margin: Margin = (Pupstream − Pbackpressure) − cracking pressure − valve loss. Positive margin means the opening duty looks more comfortable.
These are practical preliminary formulas. Final specification should always follow manufacturer data, project standards, and surge analysis requirements.
How to use this calculator
- Enter the design flow and select the matching flow unit.
- Set liquid specific gravity and estimated viscosity.
- Add upstream pressure, downstream backpressure, and the maximum acceptable valve loss.
- Choose the valve style, service band, and line orientation.
- Use automatic mode for a recommended size, or switch to manual mode to test one nominal size.
- Press the calculate button to show the result above the form.
- Review the summary, graph, and comparison table before exporting CSV or PDF files.
- Confirm the final choice with vendor Cv data, closure characteristics, and project code checks.
Frequently asked questions
1) Why does check valve sizing depend on velocity?
Check valves need enough forward velocity to open stably. If the valve is oversized, the disc may flutter, wear faster, and create noise. A smaller, correctly sized valve often improves closure behavior and reduces pressure loss uncertainty.
2) Is this calculator suitable for final procurement?
This page uses liquid Cv relationships, estimated bore diameters, and service velocity bands. It is suitable for quick sizing studies, budgeting, and preliminary layouts. Final selections should still be checked against the manufacturer’s published Cv data, face-to-face dimensions, and project code requirements.
3) Why is specific gravity required?
Specific gravity shifts the required Cv and the predicted pressure drop. Heavier liquids need more pressure to pass the same flow through the same valve. That is why the calculator asks for fluid density relative to water.
4) Can I include cracking pressure in the check?
Yes. Enter your real upstream pressure, downstream backpressure, and the expected cracking pressure. The result section compares available pressure margin against cracking pressure plus valve loss to show whether opening looks comfortable or marginal.
5) What happens with viscous liquids?
High viscosity can reduce effective flow capacity and slow disc movement. This calculator applies a simple advisory derating factor, so results become more conservative as viscosity rises. For thick liquids, always confirm the final choice with vendor performance curves.
6) Which valve style is best?
Swing checks usually have high capacity and low cracking pressure. Silent and spring-loaded styles close faster and help limit slam. Dual-plate valves are compact. Ball and lift styles may suit dirty or vertical services, depending on the line arrangement.
7) Can I force a pipe size that already exists?
The calculator can evaluate a manual size, but it still compares that size with other standards. If your chosen valve shows excessive velocity, high loss, or low pressure margin, the recommendation panel will flag the issue.
8) What should I do after getting a recommended size?
Use the selected size, predicted loss, velocity, and margin as a starting point. Then review surge risk, closure time, installation orientation, material compatibility, temperature, code class, and the manufacturer’s exact hydraulic data before issuing the design.