Gas pressure loss through piping is the reduction in gas pressure that occurs as a gas flows through a pipe and encounters resistance to flow. The pressure loss is primarily caused by friction between the moving gas and the pipe wall, and additional losses occur at fittings and components such as elbows, tees, valves, reducers, entrances, and exits. For a given piping system, pressure loss generally increases as gas flow rate and velocity increase, and it is affected by pipe diameter, pipe length, internal roughness, gas density, gas viscosity, and the geometry of fittings and other components.
Gas Pressure Loss through Piping Formula |
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\( p_l \;=\; \dfrac{ \mu \cdot l \cdot v_g^2 \cdot \rho }{ 2 \cdot d }\) (Gas Pressure Loss through Piping) \( \mu \;=\; \dfrac{ 2 \cdot d \cdot p_l }{ l \cdot v_g^2 \cdot \rho }\) \( l \;=\; \dfrac{ 2 \cdot d \cdot p_l }{ \mu \cdot v_g^2 \cdot \rho }\) \( v_g \;=\; \sqrt{ \dfrac{ 2 \cdot d \cdot p_l }{ \mu \cdot l \cdot \rho } } \) \( \rho \;=\; \dfrac{ 2 \;d \cdot p_l }{ \mu \cdot l \cdot v_g^2 }\) \( d \;=\; \dfrac{ \mu \cdot l \cdot v_g^2 \cdot \rho }{ 2 \cdot p_l }\) |
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| Symbol | English | Metric |
| \( p_l \) = Gas Pressure Loss | \(psi\) | - |
| \( \mu \) (Greek symbol mu) = Friction Coefficient | \(dimensionless\) | - |
| \( l \) = Pipe Length | \(ft\) | - |
| \( v_g \) = Gas Velocity | \(ft\;/\;sec\) | - |
| \( \rho \) (Greek symbol rho) = Gas Density | \(lbm\;/\;ft^3\) | - |
| \( d \) = Inside Diameter of Pipe | \(in\) | - |
For gas systems, the pressure loss calculation differs from that for an incompressible liquid because gas density changes as pressure changes. Consequently, gas piping calculations generally account for the compressibility of the gas and the relationship between pressure, temperature, and density. For relatively small pressure drops compared with the absolute upstream pressure, the gas may sometimes be treated as approximately incompressible over the section being analyzed. For larger pressure drops, a compressible-flow equation is required.
In engineering, gas pressure loss is commonly evaluated using a Darcy-Weisbach based relationship or specialized compressible-gas-flow equations. The Darcy-Weisbach approach relates friction loss to the friction factor, pipe length, pipe diameter, gas velocity, and gas density.
