Pneumatic Hoses And Tubing

Pneumatic tubes and hoses transport compressed air from a compressor or a pneumatic system's main reservoir to its point of use. They enable the operation of machinery, actuation of controls, and transportation of materials or samples with efficiency and precision. This article explores the fundamentals of pneumatic hoses and tubing, like the basics in their design, purpose, and selection criteria.

Understanding pneumatic hoses and tubing

The distinction between hoses and tubing primarily lies in their construction and application:

• Pneumatic hoses:
  • Hoses are designed to withstand higher pressures and are often used in dynamic applications where the connection points may move or require frequent disconnection and reconnection.
  • They are typically more robust and flexible. Hoses are specified by their inner diameter (ID); this dimension controls the volume of air or fluid that can pass through the hose, affecting the flow rate and pressure.
  • Hoses typically come with fittings pre-attached at both ends. Control circuits leading to cylinders and actuators often utilize smaller ODs, ranging from 3.2 mm to 9.5 mm (1/8 inch to 3/8 inch).
  • They are preferred for tougher applications, frequently handled and transported across factory and workshop environments.
• Pneumatic tubing:
  • Tubing is generally more rigid than hoses, used in applications where the path of the air supply is relatively fixed, with less movement of the connected components.
  • Tubing is typically specified by its outer diameter (OD), which is crucial for fitting into connectors and ensuring a tight seal. Standard tubing outside diameters (ODs) for main air supply circuits typically vary from 6.3 mm to 12.7 mm (1/4 inch to 1/2 inch).

Main air supply and distribution in pneumatic systems

The core functionality and efficiency of pneumatic systems rely on the effective distribution of compressed air from the main supply point to the various components that require it, such as actuators, valves, and tools.

Rigid pipework for air distribution

In larger industrial environments, a network of rigid pneumatic pipework is commonly employed to distribute compressed air. This is due to the pipework's durability and its capacity to resist accidental impacts, which are frequent occurrences in busy workshops. Materials such as aluminum, copper, stainless steel, or rigid PVC are chosen for their robustness and longevity. However, the installation of rigid pipework comes with its set of challenges:

• Labor intensive and costly
• Potential for leaks
• Environmental sensitivity

Flexible hoses

For smaller setups or temporary installations, flexible hoses present a versatile and adaptable alternative to rigid pipework. Constructed from materials such as lightweight HDPE or heavy-duty rubber, flexible hoses offer the durability needed for industrial applications while being significantly easier to install and modify. Their flexibility is particularly beneficial in environments where the air supply lines need to be repositioned or adjusted frequently, allowing for a reduction in the number of fittings required and minimizing the impact of temperature fluctuations on system integrity.

Connections to pneumatic components

The final stage in the air supply chain is the connection of pneumatic components like valves, cylinders, and pressure regulators to the main air supply. For these connections, flexible air tubing or hoses are typically utilized, providing the necessary durability and flexibility to accommodate the movement and vibration of components.

Pneumatic hoses and tubes connect to appliances via fittings, which are specifically designed to ensure a secure and leak-proof connection. These fittings come in various types, including push-to-connect, compression, and threaded fittings. Push-to-connect fittings offer quick installation and removal, ideal for systems requiring frequent modifications. Compression fittings provide a robust seal for high-pressure applications, while threaded fittings ensure a tight connection in static systems.

Flexible vs rigid options

The decision to use flexible hoses or rigid pipework is largely dependent on the application's specific needs, including the size of the system and environmental considerations. Flexible options are generally preferred for their adaptability and ease of installation, particularly in complex or evolving layouts. However, it's important to select the appropriate material and diameter for the hoses or tubing to avoid inefficiencies and premature equipment failure.

Materials

It's crucial to consider the choice of materials for tubing and hoses especially considering the environmental conditions they will be exposed to. Hoses, for instance, can be constructed from multiple layers, including a nylon braid sandwiched between the inner and outer layers. This design not only enhances durability but also ensures the hose can withstand various operational challenges. The inner material must be resistant to oils and condensate, while the outer material should protect against atmospheric conditions.

Table 1: Materials for pneumatic tubes and hoses

Material	Description
Polyurethane	Exhibits durability and high resistance to wear and tear, blends the properties of plastic and rubber, and is notable for its strength, flexibility, resistance to kinks and chemicals, capable of handling pressures of 10.3 bar (150 psi) or more.
PVC	Economical, flexible, and offers broad resistance to chemicals and corrosion, suitable for applications requiring wear resistance and repeated sterilization.
Polyethylene	Favored for direct piping applications, suitable for low-pressure use, prone to kinking, rated for 9.3 bar (135 psi), cost-effective, lightweight, chemically neutral, with a constrained temperature range.
Nylon	More expensive compared to polyethylene, capable of withstanding temperatures up to 93 °C (200 °F) and pressures up to 55 bar (800 psi), resistant to chemicals, robust, and maintains integrity upon frequent bending.
Polypropylene	The most lightweight option available, known for its stability and electrical properties, resistant to chemicals, and provides UV protection in outdoor applications.

Selecting a hose or tube for a pneumatic system

• Application requirements:
  • Operating pressure: Know the maximum operating pressure of the system. Hoses and tubes are rated for different pressures, and selecting one that cannot handle the system's pressure can lead to failures.
  • Temperature range: Consider the temperature range within which the system will operate. Some materials can become brittle and crack in cold temperatures, while others may soften and deform under high heat.
  • Media: Identify the type of media (air, water, oil, etc.) that will flow through the hose or tube. Some materials are better suited for certain types of media due to chemical compatibility.
  • Environment: Consider external factors such as exposure to chemicals, UV light, abrasion, and extreme temperatures, which can affect the lifespan and performance of the hose or tube.
• Choose between hose and tube
  • Flexibility: Hoses are generally more flexible than tubes, making them ideal for moving parts or applications where the hose needs to be routed around obstacles.
  • Cost: Tubes are often less expensive than hoses and are a cost-effective solution for applications where flexibility is not a critical factor.
  • Installation: Consider the ease of installation. Tubes can be easier to install in tight spaces due to their rigidity.
• Material compatibility:
  • Compatibility with fittings: Ensure the hose or tube material is compatible with the fittings used in the system to prevent leaks and ensure a secure connection.
  • Chemical compatibility: The material should be resistant to the media being transported and any chemicals it may come into contact with externally.
• Size and length:
  • Inner diameter (ID): The ID should be large enough to handle the flow rate without causing excessive pressure drop but not so large as to be unnecessarily bulky or expensive.
  • Length: Consider the length needed for the application, including allowances for bending and routing. Avoid unnecessary length that can lead to pressure drops and potential entanglement or damage.
• Special requirements:
  • Anti-static properties: In environments where static electricity is a concern, consider hoses or tubes with anti-static properties.
  • Customization: For highly specialized applications, manufacturers can produce custom hoses and tubing that meet specific dimensions, pressure ratings, and material requirements. This includes hoses with multiple layers, reinforced walls for extra strength, or embedded conductive wires for static dissipation in environments where static electricity could pose a hazard.
  • Standards and certifications: Pneumatic hoses and tubing must often meet specific industry standards and certifications to ensure they are safe and effective for their intended use. These can include standards related to food safety, medical use, or flame resistance, among others.
  • Safety factors: Pneumatic hoses and tubing are designed with a safety factor, typically ranging from 3:1 to 4:1. This means that the burst pressure of the hose or tube is three to four times higher than the maximum operating pressure. This safety factor is crucial for preventing accidents and ensuring the system's integrity under unexpected conditions.

Hose storage

To maintain a safe work environment and to ensure no damage is done to the hose, they are often stored on reels or they are coiled.

Air hose reels

An air hose reel is a cylindrical device designed for hose storage. Typically mounted on walls, ceilings, or floors, it ensures the hose remains organized and free from kinks. Many air hose reels feature a self-retracting mechanism powered by a spring, although manual hand-cranked models are also available. These reels are commonly paired with pneumatic tools or used in situations that require a temporary supply of compressed air.

The operation of a self-retracting hose reel involves extending the hose to the required length. During this process, the reel emits a rattling noise, indicating that the hose can be locked in place by simply releasing it. To activate the spring-loaded retraction feature, a slight outward pull on the hose is necessary. It's important to maintain a firm grip on the hose during retraction to ensure it rewinds smoothly and safely. Releasing the hose prematurely can lead to the dangerous whipping of the hose end, posing a risk of injury or damage.

The primary benefit of using a hose reel is its ability to automatically store the hose, contributing to a clean and secure work environment. Additionally, it protects the hose from premature wear and tear caused by being stepped on, dragged, or accidentally struck by objects in the vicinity, such as tools or vehicles.

Coiled air hose

Coiled air hoses are commonly utilized in garages and workshops to deliver air to pneumatic tools, such as impact wrenches or blow guns. Their lightweight and self-retracting design ensures they occupy minimal space. Typically, the hose is not coiled entirely up to the fittings; instead, a short uncoiled section, known as a tail, is left on both ends. The variation between the hose's extended and retracted lengths is influenced by the coil's diameter. For instance, a standard coiled air hose might extend up to ten times its retracted length. The production of coiled air hoses requires materials with excellent elastic memory to enable the hose to revert to its original coiled shape after being extended. Consequently, materials like rubber, which lack this property, are not used. Instead, Nylon, PU (Polyurethane), or PVC (Polyvinyl Chloride) are typically chosen for these hoses due to their suitable characteristics.

FAQs

What is pneumatic tubing?

Pneumatic tubing transports compressed air to operate pneumatic tools and systems, made from materials like polyurethane or nylon.

How do you maintain compressed air tubing?

Regularly inspect for leaks, ensure proper installation, and replace damaged or worn sections.