Same flow law, very different gas: density above air, inverted altitude correction and steeper drops at equal volume.
Piped LPG networks — typical of areas without natural-gas coverage, fed from a tank through a pressure-reduction group — are calculated with the same flow law as natural gas: the general flow equation with Colebrook-White friction. What changes are the gas properties, which enter the formula's terms:
The correct setup is therefore to declare the composition (propane/butane in the real supply fractions) and let density, viscosity and compressibility follow from it — not to apply «LPG table» coefficients devised for a different mixture.
In the pressure-drop law the relative density multiplies the loss: at equal volumetric flow an LPG loses about 2.5–3 times more than natural gas. The comparison rebalances at equal energy, though: LPG's volumetric heating value is in turn about 2.5–3 times that of natural gas, so the same power at the customers needs proportionally less volume.
LPG is denser than air: the altitude correction changes sign. Climbing, the gauge pressure decreases by about 0.06–0.08 mbar per metre (depending on the mixture) instead of increasing as with natural gas: on a hilly network the uphill customers are the penalised ones, and the minimum-pressure checks must be watched exactly there.
Piped LPG networks typically run at low pressure downstream of the reduction: the limits of the low-pressure class apply — velocity within 5 m/s and a guaranteed delivery pressure (see the Italian pipeline classes) — with the twist that even modest elevation differences erode the margin from the «wrong» side.
In Gasnetics LPG is a mixture like any other: pick the preset (propane G31, commercial mixture) or declare the composition, and the engine derives density, viscosity and compressibility, applies the altitude correction with the right sign and checks velocities and pressures per class. The automatic sizing picks the diameters on the same criteria as natural gas — on LPG's numbers.
No: the flow law is the same as for natural gas — what changes are the gas properties. Relative density, viscosity and compressibility are computed from the propane/butane composition, and they enter the same terms of the general flow equation.
Because LPG is denser than air (relative density about 1.5 for propane, more with butane): the gas column weighs more than the outside air column, so climbing the gauge pressure decreases — the opposite of natural gas — by about 0.06–0.08 mbar per metre depending on the mixture.
At equal volumetric flow yes: the drop grows with relative density, and LPG's is about 2.5–3 times that of natural gas. But at equal delivered energy the comparison rebalances, because LPG's volumetric heating value is in turn about 2.5–3 times higher: less volume is needed for the same power.