Keg Line Length & Carbonation Calculator | Draft Balancer

Carbonation and regulator. Henry’s law relates dissolved CO₂ to its absolute partial pressure. For ordinary beer we implement the empirical pressure–temperature–carbonation fit published by Bill Pierce in Brew Your Own, rather than substitute pure-water solubility data. With temperature $T$ in °F and carbonation $C$ in volumes, its sea-level gauge pressure in psi is

The local setting is $p_g=p_s+p_0-p_{atm}$ after consistent pressure conversion. The same fit is inverted for the eventual carbonation at a measured setting. An inverse result outside 1.2–4 volumes is flagged as unvalidated extrapolation. Standard-atmosphere pressure follows hydrostatic equilibrium and an ideal gas with a linear temperature lapse.

Line sizing. Conservation of mechanical energy between the beer surface and the free outlet gives

Here $v=4Q/(\pi D^2)$ and $Re=\rho vD/\mu$. Churchill’s all-regime correlation supplies the Darcy friction factor. The term 1 is the outlet velocity head, not an extra empirical faucet loss. Upstream fitting loss is lumped at the inlet; faucet and shank loss occurs at the far end. This extends Soltys’s published Bernoulli–Darcy model to include specified fitting losses.

Pressure and warming. At fractional position $s=x/L$, use $z=sh$ and $T=T_{beer}+s\Delta T$. Flowing static liquid pressure is $p_g-(1+K_{entry})\rho v^2/2-s(\Delta p_{friction}+\rho gh)$. With the faucet closed it is $p_g-s\rho gh$. Compare both with the local equilibrium pressure for the selected CO₂ content. The first crossing is interpolated across 101 samples; −1 internally means no crossing.

Bottles and ABV. The Brewer’s Friend residual estimate is $C_r=3.0378-0.050062T_F+0.00026555T_F^2$, multiplied by $p_{atm}/p_0$ using Henry’s law for an airlock with a CO₂-rich headspace. A measured value overrides it. Required gas mass is $\max(C-C_r,0)\rho_{CO₂}V_b$. Stoichiometry gives four CO₂ molecules per sucrose molecule, or two per glucose molecule; divide gas mass by the corresponding mass yield. Hydrated glucose includes its bound water. The manual reports CO₂ density 1.9768 g/L at STP (s6, PDF p. 69). ABV before priming is $131.25(OG-FG)$ percent.

One circular tube of uniform bore; pure CO₂; a fully open faucet; steady, incompressible single-phase liquid flow; constant density and viscosity; straight-line elevation and temperature profiles. Keg liquid-surface velocity is negligible. Density is final specific gravity times 1000 kg/m³. The default 1.57 mPa·s viscosity and 4.8768 µm vinyl roughness follow Soltys’s assumptions, not a universal beer or hose specification. Entrance coefficient 0.5 and faucet/shank coefficient 2 are editable engineering estimates, referenced to tube velocity. Coils, fittings, deposits and actual faucet geometry may need measured coefficients.

The carbonation correlation approximates typical beer; alcohol and extract effects are not separately corrected. The calculated ABV does not alter this fit. Beer is assumed initially at the target carbonation when pressure profiles are evaluated, including when a different measured pressure is selected.

Bottle sugar is pure and completely fermented; all newly produced CO₂ is assigned to the liquid. Headspace gas, yeast growth and sugar moisture are neglected. The temperature-based residual estimate assumes unpressurized fermentation under a CO₂-rich airlock. The pressure-profile and sugar stoichiometry equations are derived here from energy and mass balances; they are not copied line-length or dosing tables.

Use for preliminary sizing and troubleshooting of conventional short, single-tube beer systems: keg temperature 0–12 °C, target carbonation 1.2–4 volumes, tube bore 2–12.7 mm and altitude −400 to 4000 m. The local temperature must remain at or below 26.7 °C (80 °F). Residual-carbonation estimation is restricted to 0–30 °C. These are the tool’s operating limits, not a guarantee of uniform correlation accuracy. Published pressure checks cover 33–42 °F and 2.1–2.9 volumes; expect practical equilibrium uncertainty of a few tenths of a psi or more for unusual beer.

The tube length must be positive and long enough to span the height. Friction in the 2300–4000 Reynolds transition range is uncertain despite a smooth correlation. Very long, coiled or complex systems require a detailed design.

A negative CO₂ equilibrium margin identifies supersaturation, not the onset or amount of visible foam. Pure-CO₂ equilibrium beer commonly becomes supersaturated immediately during flow because static pressure falls; metastability and the short residence time can still permit a satisfactory pour. Downstream values are a single-phase extrapolation once bubbles form. The plot stops before the faucet’s final pressure drop; use cooling and measured pour behaviour to refine the design. The closed-faucet curve assumes the same entered temperature profile; actual idle warming can be larger.

No gas blends, nitrogenated beer, pumps, two-phase pressure losses, nucleation kinetics or bottle-pressure rating checks. Use measured residual CO₂ after spunding or previous carbonation. The bottle estimate neglects headspace and is a practical mass-balance approximation. Bottle only fully fermented beer, weigh and distribute sugar evenly, and respect container and fitting pressure ratings. ABV is a temperature-corrected hydrometer estimate before priming, not a legal alcohol determination. Installation and pressure-system modifications belong to a qualified person.

Measured-pressure mode can still size a feasible line when the target equilibrium gauge pressure is zero or negative. The recommended positive regulator setting is then shown as a dash; a positive pure-CO₂ regulator cannot maintain that target. Eventual carbonation outside 1.2–4 volumes is explicitly marked by a warning as an unvalidated extrapolation, and eventual carbonation above 3 volumes triggers the container-rating warning as well as a high target. Keg applicability failures show warnings and withhold only the affected line or pressure-profile results, with a dash or an unavailable message. Independently valid bottle-priming and ABV results remain available.