Calculator Inputs
Enter absolute pressures in bar(a). This model gives quick preliminary sizing estimates for regulator selection and seat sizing.
Example Data Table
| Case | P1 bar(a) | P2 bar(a) | Flow Nm³/h | SG | Temp °C | Z | Pipe mm | Cd | γ | Safety |
|---|---|---|---|---|---|---|---|---|---|---|
| Small industrial branch | 5.0 | 2.0 | 90 | 0.60 | 20 | 0.99 | 40 | 0.80 | 1.30 | 1.15 |
| Process skid supply | 7.0 | 2.5 | 180 | 0.62 | 20 | 0.98 | 50 | 0.80 | 1.30 | 1.20 |
| Higher demand station | 10.0 | 4.0 | 350 | 0.65 | 30 | 0.97 | 80 | 0.82 | 1.28 | 1.25 |
Formula Used
This calculator uses practical preliminary sizing relations. It is suitable for quick engineering checks, not final certified regulator selection.
- Gas density: ρ = ρair,std × SG × (P / Pstd) × (Tstd / T) ÷ Z
- Actual inlet flow: Qactual = Qstd × (Pstd / P1) × (T / Tstd) × Z
- Mass flow: ṁ = ρ1 × Qactual
- Pipe velocity: v = Qactual ÷ Apipe
- Required flow area: A = ṁ ÷ [Cd × √(2ρΔP)]
- Equivalent orifice diameter: d = √(4A / π)
- Speed of sound: a = √(γRT)
- Mach number: M = v ÷ a
- Seat load: F = Pout × Adesign
Assumptions include steady flow, simplified gas behavior, and idealized discharge through the control opening.
How to Use This Calculator
- Enter the upstream absolute pressure in bar(a).
- Enter the desired downstream absolute pressure in bar(a).
- Provide required standard gas flow in Nm³/h.
- Set gas specific gravity relative to air.
- Enter process gas temperature and compressibility factor.
- Supply pipe inner diameter and expected discharge coefficient.
- Enter heat capacity ratio and a safety factor.
- Press calculate to display results above the form.
- Review pressure drop, densities, velocity, Mach number, and required orifice size.
- Use the CSV or PDF buttons to export the results.
Frequently Asked Questions
1. What pressure units should I enter?
Enter absolute pressure in bar(a). If your plant data uses gauge pressure, convert it to absolute pressure before using the calculator.
2. Why does the tool ask for specific gravity?
Specific gravity lets the calculator estimate gas density relative to air. Density strongly affects mass flow, velocity, and regulator opening requirements.
3. What is the compressibility factor used for?
The compressibility factor adjusts ideal-gas behavior. It improves density and flow conversion estimates, especially at elevated pressure or for non-ideal gases.
4. Is the design orifice diameter the final selected seat size?
No. It is a preliminary engineering estimate based on entered assumptions and safety factor. Final sizing should follow the regulator manufacturer’s certified data.
5. Why is Mach number shown?
Mach number helps indicate whether the gas velocity is becoming high relative to local sound speed. High values can signal noise, instability, or additional losses.
6. Can I use this for natural gas only?
No. You can use it for other gases too, provided you know the gas specific gravity, compressibility factor, and approximate heat capacity ratio.
7. What does seat load tell me?
Seat load estimates the force acting on the regulator seat area at outlet pressure. It is useful when checking actuator, spring, or trim requirements.
8. Is this calculator enough for compliance approval?
No. Use it for screening and comparison only. Final approval should include standards review, manufacturer sizing tables, and project-specific safety verification.