Air Flow Compressed Air Pipe Line

Overview

Engineering reference data for Air Flow Compressed Air Pipe Line in gases and compressed air.

Key Formulas

Ideal Gas Law

$PV = nRT$

Pressure × Volume = moles × gas constant × temperature.

Boyle's Law

$P_1 V_1 = P_2 V_2$

At constant temperature.

Charles's Law

$\frac{V_1}{T_1} = \frac{V_2}{T_2}$

At constant pressure.

Variables

Pressure Drop Guidelines

The pressure drop in compressed air pipelines depends on pipe size and is typically specified as a percentage of the applied pressure over a given length.

• For Schedule 40 pipes ranging from 1/8" to 1/2": Pressure drop is 10% of the applied pressure per 100 feet of pipe.
• For Schedule 40 pipes ranging from 3/4" to 3": Pressure drop is 5% of the applied pressure per 100 feet of pipe.

This can be expressed as:

$\Delta P_{100} = k \times P_{\text{applied}}$

Where:

• $\Delta P_{100}$ is the pressure drop over 100 feet of pipe (in the same units as $P_{\text{applied}}$).
• $P_{\text{applied}}$ is the gauge pressure at the pipeline entry.
• $k$ is the pressure drop coefficient:
  • $k = 0.10$ for pipe sizes 1/8" to 1/2".
  • $k = 0.05$ for pipe sizes 3/4" to 3".

Example Calculation

Given: A 1-inch (DN25) Schedule 40 compressed air pipeline operating at an applied pressure of 7 bar.

1. Determine the pressure drop coefficient ($k$): For a 1" pipe, $k = 0.05$.
2. Calculate pressure drop per 100 ft ($\Delta P_{100}$): $\Delta P_{100} = 0.05 \times 7 \, \text{bar} = 0.35 \, \text{bar per 100 ft}$
3. Flow Capacity Estimate: From the capacity diagram for 7 bar applied pressure, a 1" pipeline can deliver approximately 60-70 normal liters per second (NL/s).

References

• Original Source

Flow Capacity Estimation

The diagrams referenced in the original content can be used to estimate compressed air flow capacity under two common measurement systems:

• Imperial System (psi): For applied pressures ranging from 5 to 250 psi
• Metric System (bar): For applied pressures ranging from 0.5 to 17 bar (for normal standard air)

These diagrams provide a visual method for estimating flow capacity in schedule 40 pipes without requiring complex calculations.

Example - Metric System Reference

The capacity of a 1" schedule 40 pipe at an applied pressure of 7 bar is approximately 60-70 liter/s of normal standard air.

Pipe Line Specifications

The flow capacity estimation is based on *Schedule 40 standard steel pipes. This is a common commercial pipe specification used in compressed air distribution systems.

Pipe Size Categories

The pipe sizing falls into two distinct categories with different pressure drop allowances:

The larger diameter pipes (3/4" to 3") have a more conservative pressure drop limit of 5%, which reflects the higher flow capacities and the need for more stable pressure in main distribution lines.

Pressure Range Reference

The flow capacity charts cover the following operating pressure ranges:

• Imperial (PSI): 5 to 250 psi
• Metric (Bar): 0.5 to 17 bar

These ranges cover typical industrial compressed air applications from low-pressure pneumatic tools to high-pressure air systems.

Diagram Usage Notes

The original Engineering ToolBox diagrams use normal standard air conditions for metric calculations. When using the diagrams:

1. Locate the applied pressure on the horizontal axis
2. Find the pipe size on the appropriate curve
3. Read the flow capacity on the vertical axis

Note: These capacity values are estimates for standard conditions (sea level, 68°F/20°C, 36% relative humidity). Actual capacity may vary with altitude, temperature, and humidity.

Pressure Drop Table