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Pressure drop calculator — low-pressure liquefied gas (LPG: propane / propane-butane)
LPG pipe sizing — steel
Or
Local losses (optional)
Pressure drop calculator for low-pressure liquefied gas (LPG) installations
Professional calculator for sizing pipework and computing pressure drop in liquefied gas (LPG) installations operating downstream of the regulator at low pressure (≤100 mbar, typically 37 mbar gauge ≈ 1.05 bar absolute). The tool supports two fuels: technical propane (C₃H₈, typical for tank-based residential heating) and propane-butane 60/40 mix by volume (typical for bottles and portable appliances).
Calculations are based on the Darcy-Weisbach equation with the friction factor λ from Colebrook-White (Re ≥ 2300, turbulent) or as 64/Re (Re < 2300, laminar). Three pipe families are supported: steel (PN-EN 10255), copper (PN-EN 1057) and polyethylene (PE 80/100, SDR17 and SDR11). For each, diameters are selected to satisfy v ≤ 6 m/s (PN-EN 1775) and unit and total pressure drop are reported including local losses via the equivalent-length method. Designed for gas installation designers, certified gas fitters and supervising inspectors.
How to use the calculator in 4 steps
Pick the fuel: technical propane (typical tank installations — pure propane C₃H₈, LHV ≈ 26.7 kWh/m³) or propane-butane 60/40 mix (typical bottles and portable appliances, LHV ≈ 27.8 kWh/m³). The fuel choice affects both power/flow conversion and pressure-drop calculations (~3-4% difference).
Pick the pipe material (Steel / Copper / PE tabs) and enter LPG flow in m³/h or appliance power in kW — values auto-convert per the selected fuel LHV. Note: m³/h refers to operating conditions (~20 °C, 37 mbar gauge), NOT to Nm³ (normal conditions).
Optionally expand the "Local losses" panel — for steel and copper enter the real pipe length plus the count of each fitting (elbows, tees, cocks, reducers). The calculator adds equivalent length from tables for the chosen diameter and reports the total drop. For PE the fittings panel is disabled in MVP — manually add 10-20% to the pipe length as a margin.
Read the results: for each of the 5 proposed diameters (2 smaller, the proper, 2 larger) the calculator shows gas velocity and unit pressure drop [Pa/m]. With length and fittings — also the total drop [Pa]. Check that it stays within the allowed range (≤300-500 Pa for 37 mbar regulator).
What the liquefied gas calculator computes
From the supplied gas flow the tool produces a full set of data for designing a pipework section:
- Recommended diameters — chosen from the pipe size table for the selected material (steel DN, copper, PE SDR) so that gas velocity does not exceed 6 m/s (PN-EN 1775). 5 diameters around the proper one are shown for comparison of velocity/drop trade-off.
- Unit pressure drop R [Pa/m] — loss per metre, computed via Darcy-Weisbach with density and viscosity of the selected fuel. Friction factor λ accounts for pipe roughness (steel 0.15 mm, copper 0.0015 mm, PE 0.007 mm).
- Equivalent length of fittings L_eq [m] — local losses (elbows, tees, cocks, reducers) converted to the equivalent length of straight pipe, from tables for the internal diameter (Polish engineering practice, Cieżak / Mańkowski).
- Total pressure drop ΔP [Pa] — product of unit drop and computed length (real + equivalent). Key value for checking whether the installation maintains the minimum pressure required by appliances (typically 18-25 mbar for most LPG devices behind a 37 mbar regulator).
Input fields — what to provide
Gas flow or appliance power
Enter LPG flow in m³/h or the thermal power of the appliance in kW — the calculator auto-converts using the LHV of the selected fuel. Conversion: 1 m³/h ≈ 26.7 kW for pure propane, 27.8 kW for the 60/40 mix. NOTE: m³/h values refer to operating conditions (~20 °C, 37 mbar gauge downstream of the regulator), NOT to normal conditions (Nm³).
Fuel selection (propane / mix)
Technical propane C₃H₈ — typical for Polish residential tank installations (butane freezes in winter, so year-round outdoor installations require pure propane). Propane-butane 60/40 mix by volume — typical for 11 kg bottles and portable appliances. The fuel choice affects density, viscosity and LHV — yielding ~3-4% difference in pressure drop and ~4% in power/flow conversion.
Pipe section length (optional)
Enter the real pipe length from the supply point (downstream of the regulator) to the most distant appliance. This is added to the fitting equivalent length when computing the total drop. Without a length the calculator shows only the unit drop R [Pa/m] for each diameter.
Number of fittings and valves (optional)
In the expanded "Local losses" panel, enter the count of each component (elbows, straight-flow tees, branch tees, cocks, reducers). The calculator derives their combined equivalent length from tables for the chosen diameter. For PE pipes the fittings panel is disabled in MVP (no validated Polish equivalent-length table for PE in gas service); for typical tank-to-regulator service add 10-20% to the pipe length manually.
Design tips and limitations
Fuel choice MATTERS: propane and the 60/40 mix differ in density (1.90 vs 2.15 kg/m³ at 37 mbar) and heating value (26.7 vs 27.8 kWh/m³). The wrong fuel can under- or over-size the result by a few percent — significant on long runs. PE pipes are permitted only outdoors and buried, and only on low-pressure sections downstream of the regulator (≤100 mbar); use steel or copper indoors. Medium-pressure sections (tank to first-stage regulator, above 100 mbar) require a separate calculation model. The calculator performs hydraulic calculations only — it does not replace a proper gas installation design (PN-EN 1775 and local regulations, appliance pressure requirements, ventilation, safety valves, regulator sizing, material approvals).
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