Compressed air | Compressed air system and components

Pneumatic control systems rely on a steady supply of compressed air, which must be readily available in the right quantity and pressure to match the system’s capacity.

Air, the essential working medium in pneumatics, is a cost-free resource found abundantly in the atmosphere. Atmospheric air comprises a mix of gases, including oxygen, nitrogen, water vapor, traces of other gases, and impurities like dust and soot.

The composition of air can undergo continuous changes, depending on factors such as moisture content, environmental conditions, and the presence of solid pollutants in the air.

Maintenance

Maintaining the quality of compressed air is of paramount importance. This involves the removal of excess moisture and the filtration of undesirable particles to ensure the smooth operation of pneumatic systems and equipment.

Environmental factors, such as climate and air quality, can influence the composition and quality of atmospheric air, which can, in turn, affect the performance of pneumatic systems.

Due to the ever-changing composition of atmospheric air, it is crucial to continuously monitor and control factors like moisture and impurities to uphold the desired air quality.

Compressed air is dry and clean is the primary prerequisite for the efficient functioning of pneumatic systems. While atmospheric air is readily available and cost-effective, its quality must be managed to meet the demands of pneumatic equipment and processes. This involves the regulation of moisture levels and the removal of impurities to guarantee dependable system performance.

Characteristics of Compressed air

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The characteristics of compressed air are truly remarkable, contributing to its rapid and widespread adoption in various applications. Several key attributes make it an ideal choice:

1. Availability: Compressed air has gained popularity due to its ready availability. It can be easily generated from air, which is abundant and found virtually everywhere.
2. Transportation: Compressed air can be efficiently transported over extended distances through pipelines without the need for return to storage.
3. Temperature Insensitivity: Compressed air is not affected by temperature fluctuations, ensuring reliable operation even in extreme temperature conditions.
4. Storage Flexibility: It can be stored in reservoirs and accessed as needed, allowing for intermittent operation of compressors and transportation from storage.
5. Safety: Compressed air poses no risk of explosion or fire, eliminating the need for costly explosion protection measures.
6. Cleanliness: It is a clean medium, preventing contamination, which is crucial in industries like food, wood, textiles, and leather.
7. Simplicity: Operating components are straightforward in design, resulting in cost-effectiveness.
8. Speed: Compressed air is exceptionally fast, enabling high working speeds, with pneumatic cylinders reaching 1-2 meters per second.
9. Adjustability: Compressed air components allow for infinite adjustment of speeds and forces.
10. Overload Safety: Pneumatic tools and components can be loaded to the point of stopping, making them overload-safe.
11. Preparation: Compressed air requires proper preparation to remove dirt and humidity.
12. Compressibility: Achieving uniform and constant piston speed can be challenging with compressed air.
13. Economic Efficiency: Compressed air is economical up to a certain force requirement, typically between 20,000 and 30,000 N.
14. Exhaust Noise: Historically, exhaust air could be noisy, but this issue has been resolved.
15. Cost Considerations: While compressed air can be relatively expensive as an energy source, its high-energy costs are often offset by its performance benefits. The overall economic efficiency of pneumatic equipment must consider factors beyond just power costs, such as wages, installation, and maintenance.

Compressed air’s unique combination of characteristics makes it a versatile and valuable medium for various applications, offering advantages that often outweigh its energy costs when examined in the broader context of operational efficiency.

What is Absolute Humidity

Absolute humidity pertains to the water content found in the Earth’s common atmosphere, and this amount can range from minimal levels to a maximum corresponding to the saturation point. In the atmosphere, water exists in the form of superheated steam.

When the atmosphere reaches the saturation point, it implies that the steam within the air is in a saturated state. Absolute humidity, in this context, refers to the precise amount of water, often referred to as steam or vapor, present within one cubic meter (Nano Metar) of air.

Relative Humidity

Relative humidity represents the quantity of water vapor present in a volume of air, typically expressed as a percentage. It indicates the relationship between the actual amount of water in one cubic meter (Nano Metar) of air and the saturation level, which is the maximum quantity of water that air can hold in one cubic meter at a given temperature.

Mathematically, relative humidity is calculated as:

Relative humidity (%) = (Absolute humidity / Saturation quantity) * 100%

In most industrial applications, air with a relative humidity below 100% is considered satisfactory and referred to as dry air. However, it’s essential to maintain a safety margin to prevent condensation in tools susceptible to corrosion.

Humidity in the air varies with changes in pressure and temperature. It’s important to note that a given volume of compressed air can only absorb as much moisture as the equivalent volume of air at atmospheric pressure. During compression, as an example, a compressor intakes seven volumes of air and discharges it as one volume but at a pressure seven times higher. If the intake and discharge air temperatures remain the same, there will be an excess of six volumes of water condensed from the compressed air. The saturation level of air for water vapor is temperature-dependent, with higher temperatures allowing the air to hold more water.

Advantages of Compressed air

1. Abundant Availability: Compressed air benefits from the vast availability of atmospheric air, making it readily accessible.
2. Compressibility: The compressible nature of air allows it to be stored efficiently in compressed form.
3. Storability: Compressed air is easily storable, enabling its use when needed without requiring immediate generation.
4. Transportability: Air can be transported over long distances through pipelines, eliminating the need for return lines.
5. Temperature Insensitivity: Compressed air is remarkably insensitive to temperature variations, ensuring consistent performance in various temperature conditions.
6. Safety: Compressed air is considered relatively safe, as it poses no risk of explosions or fires.
7. Clean and Non-Polluting: It maintains a relatively clean and non-polluting quality, making it suitable for various industries.
8. High Speed of Operation: Compressed air’s fast expandability allows for high-speed operations, facilitating rapid work processes.
9. Variability: Pneumatic systems offer the flexibility to vary speeds and forces, making them adaptable to a wide range of applications.
10. Overload Safety: Pneumatic elements are designed to be overload safe, providing an extra layer of protection.
11. Ease of Learning: Pneumatics is a technology that is relatively easy to learn and understand, making it accessible to a wide range of users.

The advantages of using compressed air encompass its availability, compressibility, transportability, temperature insensitivity, safety, cleanliness, high-speed operation, variability, overload safety, and ease of learning. These characteristics make compressed air a versatile and valuable choice for numerous applications.

Disadvantages

1. Preparation Requirements: Compressed air necessitates thorough preparation to remove dirt and humidity, which can affect its quality.
2. Variable Piston Speed: Achieving a uniform and constant piston speed can be challenging when using compressed air as a power source.
3. Economic Limitations: Compressed air is cost-effective only up to a specific force requirement. Beyond a certain point (typically between 20,000 and 30,000 N), other power sources may become more economical.
4. Noisy Exhaust: The exhaust air produced by compressed air systems can be quite loud, resulting in noisy operations.
5. Relatively High Cost: Compressed air is considered a relatively expensive means of conveying power due to factors such as energy costs, equipment, and maintenance expenses.

While compressed air offers several advantages, it also comes with disadvantages related to preparation requirements, variable piston speed, cost limitations, noisy exhaust, and overall expense. These factors should be considered when evaluating its suitability for specific applications.

Components of Compressed Air Systems:

Power Source:

• Compressors
• Air blowers

Preparation

• After cooler
• Main lines filter
• Air dryer
• Oil filter
• Filters
• Regulators
• Gauges

Storage:

• Air receiver
• Distribution pipes
• Line network
• Storage tank

Transmission:

• Pipe lines
• Tubing
• Fittings

Control:

• Logic elements
• Relays
• Interlocks
• Timers
• Programmers
• Direction control valves
• Flow control valves
• Pressure control valves
• Time control valves

Actuators:

• Cylinders
• Motors
• Strip feed units, etc.

Feedback:

• Sensors
• Limiting devices

Disposal:

• Silencers
• Exhaust cleaners
• Condensate traps
• Mufflers

This breakdown categorizes the components of compressed air systems into distinct groups for a clearer understanding of their roles and functions within the system.

Power Sources:

• The most common power source for pneumatic systems is the compressor, chosen based on pressure and air consumption requirements.
• Compressed air from the compressor is typically hot and contains solid particles like dust and dirt, as well as oil in liquid and vapor form, and varying amounts of water depending on atmospheric humidity.

Preparation:

• An after cooler is essential to lower the temperature of compressed air, causing most suspended water to condense and be drained.
• Further cooling results in additional liquid formation, which is removed by the main line filter, along with solid contaminants.
• Efficient main line filters are essential for economical operation and system longevity.
• The use of suitable air dryers helps remove additional moisture.

Storage:

• Compressed air is easily storable in receiver tanks and an extensive network of pipelines, providing energy storage.
• Sufficient storage volume is crucial to offset power failures and emergencies. Preventing wastage due to leaks is essential.

Transmission:

• Air can be efficiently transported through pipelines over long distances, eliminating the need for return lines.
• Proper pipeline sizing, minimizing leaks, and managing pressure drops are critical for system efficiency and economy.

Service:

• Preventive maintenance is required for the moving parts of pneumatic equipment to ensure longevity and efficient service.
• Maintaining clean, moisture-free, and properly lubricated compressed air quality is essential for equipment reliability.
• Air filters remove pipe scales, dirt particles, and water carried through pipelines into the system.
• Pressure regulators maintain constant system pressure despite line fluctuations, while lubricators ensure optimal lubrication for trouble-free operation.

Control:

• This valves direct the output from the system program to power devices, with directional control valves, usually pneumatic or solenoid-operated, being the norm.
• Control valves determine speed, force, and distance of travel for the resulting actions.

Power:

• Pneumatic systems utilize various power devices, including air cylinders, air motors, torque units, feed units, indexing devices, vibrators, and other pneumatic tools.
• Selection of compressed air as the power source depends on factors like maximum load, distance, speed, hoist capacity, and rotary power.

Feedback:

• This mechanisms acknowledge task completion and trigger the next stage of the operation cycle.
• Feedback methods include visual, time-based, position-based, and pressure-based indicators.

Disposal:

• Compressed air can be easily discharged to the atmosphere without return lines, but two forms of pollution should be considered:
  • Noise: Air discharge generates noise, which must be controlled with silencers and mufflers to ensure worker efficiency.
  • Contaminants: Discharged air can release oil, solid particles, and fine mist from lubricating oil, requiring proper handling and filtration.

This breakdown clarifies the various components and aspects of pneumatic systems and their functions within the system.

Air can be compressed:

Gases, such as air, inherently lack a fixed shape; their form is dynamic and adapts to their environment. Even the slightest resistance causes them to change shape, conforming to their surroundings. Air, a gas, possesses the remarkable property of compressibility, meaning it can be squeezed into a smaller volume. Simultaneously, air naturally seeks to expand when given the opportunity. This characteristic showcases the dynamic nature of gases like air.