5.3: Piping Systems for Compressed Air Distribution
- Page ID
- 116631
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Once compressed air has been cooled, dried by the aftercooler, and stored in the receiver tank, it is ready to be distributed through the piping system. There are three main types of piping systems commonly used:
- Grid or Dead-End Systems
- Unit or Decentralized Systems
- Loop Systems
Grid Systems (Dead-End)
The grid or dead-end system is the simplest type of piping system. It consists of a central main line with smaller feeder lines and headers branching off. The main pipes decrease in size as they extend further from the compressor, while the feeder lines are generally of uniform size. Outlets are strategically placed along the feeder lines, and adjacent legs of the system can be cross-connected to serve areas between feeders.
While the grid system is the least expensive and simplest to install, it has a significant drawback: there is only one flow path. This single flow path can cause air starvation for workstations located at the far end of the system when upstream demand is heavy.
Unit or Decentralized Systems
In a unit or decentralized system, there may be two or more grids, each with its own dedicated compressor. These individual systems can be interconnected if needed. Since the compressors are located closer to the points of air use, supply lines are shorter, which reduces pressure drops. This results in more uniform air supply and system pressure.
Decentralized systems offer greater versatility than single grid systems and can be easily adapted to changing requirements within the facility.
Loop Systems
The loop system is the preferred or recommended setup for air distribution. This type of system allows for optimal conductor sizing and ensures equal distribution of compressed air throughout the plant. It provides parallel paths for air to reach all workstations, which helps prevent air starvation during periods of high demand. In cases of heavy, momentary air demand, a receiver can store compressed air energy and meet peak demands without causing serious pressure loss.
Installation Considerations
When laying out a piping system, especially a loop distribution system, certain considerations can improve efficiency and reduce problems:
- Minimize Fittings: Reducing the number of fittings in the system will help prevent leaks and lower pressure drops.
- Use Tubing Over Pipes: Tubing offers smoother internal surfaces than pipes, allowing better airflow and reducing pressure drops. Additionally, tubing systems require fewer fittings, reducing potential leak points.
- Avoid Tight Bends: Keeping bend radii large will minimize pressure drops. Pipe fittings, particularly 90° bends, cause five times the pressure drop of a properly designed large-radius bend.
- Proper Slope for Mains: Main distribution pipes, feeders, and headers should have a slight slope, around ¼ inch per foot, to ensure condensed water is swept to drains by the airflow. Water legs with automatic drains should be installed at low points in the system to prevent water buildup.
- Drop Leg Design: Drop legs, used to supply air to tools or workstations, should be taken from the top of the main header. The drop leg bend should be of the same size as the main line or bent with a large enough radius to ensure minimal pressure drops. This design helps prevent dirt and water from entering the drop line. Drains should be installed at the bottom of each drop leg to remove any water that accumulates.
The Cost of Air Leaks
Unlike hydraulic leaks, pneumatic air leaks do not typically cause visible housekeeping issues. However, addressing them is crucial for maintaining system efficiency and reducing unnecessary operational costs. Air leaks lead to wasted compressed air, reduced tool performance, and increased energy consumption.
For instance, a single leak equivalent to a ½ inch (13 mm) hole can waste approximately 12 million cubic feet (340,000 m³) of air per month. Given an average cost of $0.10 per 1,000 cubic feet (472 dm³/s) of compressed air, this results in an estimated monthly loss of $1,200. The greater financial burden, however, arises from the additional electricity required to keep the compressor running to compensate for the air loss. Furthermore, frequent operation of the compressor to counteract leaks increases maintenance requirements and shortens the system’s overall lifespan.
The efficiency of pneumatic tools is also significantly affected by air leaks. A pressure drop of just 10 psi (0.7 bar) can reduce tool efficiency by 15%, with performance continuing to decline as pressure decreases further. To maintain optimal performance, it is essential to implement routine leak detection and corrective measures.
Methods for Detecting Air Leaks
Regular inspection and repair of leaks are fundamental to ensuring system reliability and efficiency. Several methods can be used to identify and locate air leaks:
- Audible Detection: Leaks can often be identified simply by listening for the hissing sound of escaping air. This method is most effective during times when the plant is quieter, such as during shift changes, weekends, or scheduled downtime.
- Soap Solution or Leak-Detecting Fluid: A simple and cost-effective method involves applying a soapy water solution or commercial leak-detecting fluid to suspect areas and connections. The presence of bubbles indicates an air leak, making it easy to pinpoint the exact location of the issue.
- Two-Clock System: A more quantitative approach to leak detection involves the use of a two-clock system integrated into the compressor controls:
- One clock records the total elapsed time.
- The second clock is linked to the compressor motor control and runs only when the compressor is actively operating under load.
- By activating both clocks during non-operational periods (such as weekends) and comparing the readings after a set duration, the amount of air lost due to leaks can be accurately measured. Some modern automated systems can even provide permanent records of these readings, facilitating ongoing monitoring and trend analysis.
- Pressure Decay Test: This method involves shutting down the system and timing how long it takes for system pressure to drop to a minimum level. Conducting this test during non-operational hours, such as at night when the facility is idle, allows leaks to be identified without interference from normal operations. Once leaks are detected, repairs can be prioritized accordingly.
Maintaining System Efficiency
Routine leak detection and timely repairs play a critical role in reducing operational costs and maximizing efficiency in pneumatic systems. By implementing a comprehensive maintenance plan that includes regular inspections and employing effective detection methods, facilities can significantly reduce energy waste, improve tool performance, and extend the lifespan of their compressed air systems.
Proactive air leak management not only leads to cost savings but also ensures a more sustainable and reliable pneumatic system operation.