Air pressure loss through piping is the reduction in air pressure that occurs as compressed or pressurized air flows through a piping system. It is a common in many fluid transport applications, including compressed air systems, ventilation systems, pneumatic systems, and HVAC systems.
Air Pressure Loss through Piping Formula |
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\( p_l \;=\; \dfrac{ \mu \cdot L\cdot v_a{^2} \cdot \rho }{ 24 \cdot d \cdot g } \) (Air Pressure Loss through Piping) \( \mu \;=\; \dfrac{ 24 \cdot d \cdot g \cdot p_l }{ L \cdot v_a{^2} \cdot \rho } \) \( L \;=\; \dfrac{ 24 \cdot d \cdot g \cdot p_l }{ \mu \cdot v_a{^2} \cdot \rho } \) \( v_a \;=\; \sqrt{ \dfrac{ 24 \cdot d \cdot g \cdot p_l }{ \mu \cdot L \cdot \rho } } \) \( \rho \;=\; \dfrac{ 24 \cdot d \; g \cdot p_l }{ \mu \cdot L \cdot v_a{^2} } \) \( d \;=\; \dfrac{ \mu \cdot L \cdot v_a{^2} \cdot \rho }{ 24 \cdot g \cdot p_l } \) \( g \;=\; \dfrac{ \mu \cdot L \cdot v_a{^2} \cdot \rho }{ 24 \cdot d \cdot p_l } \) |
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| Symbol | English | Metric |
| \( p_l \) = air pressure loss | \(psi\) | - |
| \( \mu \) (Greek symbol mu) = Air Friction Coefficient | \(dimensionless\) | - |
| \( L \) = Pipe Length | \(ft\) | - |
| \( v_a \) = Air Velocity | \(ft \;/\; sec\) | - |
| \( \rho \) (Greek symbol rho) = Air Density | \(lbm \;/\; ft^3\) | - |
| \( d \) = Pipe Inside Diameter | \(in\) | - |
| \( g \) = Gravitational Acceleration | \(ft \;/\; sec^2\) | - |
The pressure loss is caused primarily by friction between the moving air and the internal pipe wall, but it is also affected by fittings and components such as elbows, tees, valves, reducers, expansions, filters, regulators, and other restrictions. In a piping system, pressure loss increases as the air flow rate and velocity increase, and it generally increases with pipe length, pipe roughness, and the number of flow restrictions. Conversely, using a larger pipe diameter generally reduces pressure loss because the air velocity is lower for the same volumetric flow rate.
For straight pipe, air pressure loss is commonly evaluated using the Darcy–Weisbach relationship, with the calculation adjusted as necessary for the compressibility of air. Unlike liquids, air is a compressible fluid, so its density changes as pressure changes. Consequently, for significant pressure drops, the inlet pressure, outlet pressure, temperature, pipe diameter, pipe length, air flow rate, and pipe roughness must be considered rather than treating air density as constant. In practical compressed-air systems, excessive pressure loss can reduce the pressure available at downstream equipment, causing inadequate actuator performance, reduced tool capacity, or other operating problems.
