Pneumatic Tubing Technical Information

Pneumatic tubing is an essential part of many applications as it carries compressed air in and, in some cases, compatible fluids between system components. While outside diameter is an important consideration, engineers and buyers must also evaluate operating and burst pressure, temperature, tubing material, chemical exposure, flexibility, bend radius, fitting compatibility, and environmental conditions. Polyconn has supplied pneumatic parts and tubing to industrial operations for more than 45 years, serving OEMs, MROs, and distributors with a broad selection of pneumatic tubing and hose, including plastic pneumatic tubing and other pneumatic components. This guide outlines general tubing selection principles; always verify specifications for the exact tubing product being considered to ensure your application runs smoothly.

How to Select Tubing for a Pneumatic System

Tubing selection should begin with the complete operating environment, not just the system’s normal PSI. Many conditions should go into tubing selection and the environment of use to ensure proper selection is made. To select tubing for a pneumatic system, identify the system’s operating conditions by documenting:

• Normal operating pressure
• Maximum possible pressure
• Pressure spikes or pulsation
• Ambient and conveyed-fluid temperature
• Fluid or chemical exposure
• Indoor or outdoor use
• UV, moisture, abrasion, weld spatter, oil, and cleaning-agent exposure
• Required flexibility and movement
• Required flow rate
• Tubing size and wall thickness
• Compatible fitting type

Tubing suitable for stationary compressed-air routing may not be the best choice for robotic motion, washdown service, vehicle systems, chemical transfer, or retractable tool connections.

Understanding Pneumatic Tubing Working Pressure

Working pressure is the maximum pressure at which tubing is intended to operate under specified conditions and is calculated as a ratio of burst pressure by dividing the burst pressure by an appropriate safety factor. The safety factors include 3:1 and 4:1 depending on the severity of the application. Tubing working pressure is not necessarily universal as the allowable pressure can change with:

• Temperature
• Tubing material
• Outside diameter
• Inside diameter
• Wall thickness
• Age and condition
• Exposure to chemicals
• Repeated flexing
• Installation method
• Fitting compatibility

Working Pressure Calculation Example

To calculate working pressure, retain the formula: Burst pressure ÷ Safety Factor = Working Pressure, as presented in the following examples:

• Example 1: 450 PSI @ 75°F / 3 to 1 safety factor = 150 PSI working pressure
• Example 2: 450 PSI @ 75°F / 4 to 1 safety factor = 112 PSI working pressure

What is Tubing Burst Pressure?

Tubing burst pressure is the pressure at which a tubing sample fails under specified test conditions. Burst pressure differs from working pressure as a failure-test value instead of an operating limit and hence should not be treated as an acceptable operating pressure. The difference between burst and working pressures provides a safety margin in applications. A laboratory burst rating does not account for every real-world variable. Several conditions can reduce burst or working pressure, including:

• Elevated temperature
• Material degradation
• Chemical incompatibility
• UV or ozone exposure
• Cuts, abrasion, kinking, or crushing
• Improper tube insertion
• Mismatched tubing and fittings
• Excessive bend stress
• Repetitive motion
• Pressure surges
• Incorrect wall thickness

How Temperature Affects Tubing Pressure Ratings

Thermoplastic tubing is highly affected by temperature, as the tubing generally becomes softer as temperature rises. The softer material in thermoplastic tubing reduces its pressure-bearing capability. Additionally, lower temperatures cause some materials to become stiffer and less tolerant of impact or repeated flexing. Careful consideration and possible temperature conversion must be used for proper tubing use, such as:

• Confirm both ambient temperature and the temperature of the air or fluid passing through the tube.
• Do not assume a pressure rating published at room temperature applies at the application’s maximum temperature.
• Account for localized heat from machinery, ovens, welding operations, sunlight, or compressed-air discharge.
• Consult the exact product data for temperature limits and pressure derating.

Pneumatic Tubing Materials and Common Applications

Several material options are available for proper tubing selection and should be utilized for different applications. Depending on the need, different materials will serve better than others. Review the following for tubing material options and common applications that use them.

Polyurethane Tubing

Polyurethane tubing and polyurethane coiled tubing are generally selected where flexibility, repeated movement, abrasion resistance, and compact routing are important. Potential applications include:

• Robotics
• Packaging machinery
• Pneumatic controls
• Moving machinery
• Pick-and-place equipment
• Air tools
• Retractable coils

Nylon Tubing

Nylon tubing is generally more rigid than polyurethane and is commonly considered where dimensional stability, higher pressure capability, or a wider operating-temperature range is needed, subject to the selected tubing specification. Potential applications include:

• Industrial machinery
• Instrumentation
• Lubrication lines
• Pneumatic control panels
• Vehicle or mobile-equipment systems
• Fixed compressed-air routing

Polyethylene Tubing

Polyethylene tubing is often considered for economical, lightweight, lower-pressure routing and applications requiring compatibility with certain fluids or chemicals. Potential applications include:

• General-purpose pneumatic controls
• Laboratory equipment
• Instrument lines
• Fluid-transfer systems
• Low-pressure air lines

PVC Tubing

Polyvinyl chloride (PVC) tubing is a more flexible option that may be appropriate for certain air, liquid, or low-pressure applications, depending on reinforcement, formulation, temperature, and chemical exposure. This tubing option is better suited for indoor applications with controlled environments.

Specialty Tubing

Specialty tubing is selected for unique and niche requirements where additional tubing won’t satisfy. This tubing handles applications in specific industrial, medical, or automotive systems. Different specialty options include:

• D.O.T. Nylon Tubing
• FEP Tubing
• Kynar Tubing
• Multi-bore Tubing
• Multi-Color Ribbon Tubing
• Static Dissipative Tubing
• Weld Spatter Tubing

Pneumatic Tubing Chemical Resistance

Chemical resistance is critical in the tubing selection process, as different tubing material options present different resistance options. Chemical exposure may occur internally through the conveyed medium or externally through washdown, spills, vapors, and environmental contamination. Chemical compatibility should be evaluated whenever tubing contacts:

• Oils
• Lubricants
• Fuels
• Coolants
• Cleaning Agents
• Acids
• Alkalis
• Solvents
• Food-Processing Chemicals
• Process Fluids

Factors that Affect Chemical Compatibility

Chemical compatibility involves several factors and can be identified using a chemical resistance chart. This chart serves as a screening tool and not a substitute for reviewing the actual operating conditions. Several additional factors that affect chemical compatibility include:

• Chemical identity
• Concentration
• Exposure time
• Temperature
• Pressure
• Tubing material
• Stress and flexing
• Combined chemical exposure
• Whether contact is continuous or intermittent

Tube Size, Wall Thickness, Bend Radius, and Airflow

Pneumatic tubing and pneumatic air hose dimensions influence both mechanical performance and system performance. Several dimension requirements should be used to select the ideal tubing for any application. Review below for more details about specific dimensional requirements.

Outside Diameter and Inside Diameter

Outside diameter determines fitting compatibility for many push-to-connect systems, while inside diameter affects available flow area. Small inside diameters can create pressure drops over long runs or in high-flow applications so tube and fitting sizes must be matched correctly.

Wall Thickness

Wall thickness influences several factors in tubing, including:

• Pressure capacity
• Kink resistance
• Flexibility
• Weight
• Minimum bend radius
• Coil performance

Minimum Bend Radius

Tubing should not be bent more tightly than recommended because an overly tight bend can:

• Restrict airflow
• Flatten the tube
• Increase stress
• Cause kinking
• Shorten service life
• Pull the tubing sideways within a fitting

Tube Coil Terminology and Selection

Several common terms are used for tube coil, including:

• Material Memory: Tubing’s tendency to return toward its formed shape. Polyurethane and nylon are commonly used for coils because of their material characteristics, while other materials may be selected for cost and chemical compatibility.
• Retractability: How effectively the coil returns after extension and is affected by material, wall thickness, coil diameter, temperature, extension frequency, and age. Heavier or overstretched coils may retract less effectively.
• Coil Diameter: The diameter of a coil, with a tighter coil improving retractability. Tubing must be flexible enough to form and operate without kinking or excessive stress. The appropriate diameter depends on tube size, material, wall thickness, and required extension.
• Working Length: Usable extension of the coil that is a percentage of the total tubing length. Polyurethane allows a working length of 80-90%, whereas nylon has a working length of 67-75% due to rigidity.
• Retracted Length: Length of the coil not including ‘pig’ tails that affects storage, equipment clearances, ergonomics, and whether the coil must fit around a support or inside an enclosure.
• Coil Tails: Straight, uncoiled sections of tubing at both ends of a pneumatic assembly. Straight tails make it easier to connect the coil to tools, fittings, machinery, or fixed piping without placing the coiled section directly against the connection point.

Common Coiled-Tubing Applications

Several applications better use coiled tubing instead of straight tubing, including:

• Pneumatic hand tools
• Assembly workstations
• Packaging machinery
• Robotics
• Service vehicles
• Retractable blow-off lines
• Maintenance stations
• Moving machine components
• Equipment requiring self-storing air lines

Tubing Installation and Inspection Best Practices
Several factors go into installing and inspecting tubing for best results. Best practices to use include:

• Cut tubing squarely with an appropriate tube cutter.
• Avoid crushed, angled, or burred ends.
• Insert tubing fully into the fitting.
• Do not exceed the recommended bend radius.
• Support long runs.
• Prevent contact with sharp edges and hot surfaces.
• Allow sufficient slack for moving equipment.
• Protect tubing from abrasion.
• Inspect periodically for discoloration, cracking, flattening, swelling, hardening, leakage, or damaged fitting connections.
• Replace damaged or chemically attacked tubing rather than attempting a temporary repair.

Polyconn is Here for Pneumatic Tubing Selection

Since 1981, Polyconn has been the go-to pneumatic parts and components supplier for OEMs, MROs, and distributors. Our parts are used across all industries to keep fluid power systems moving in several applications. Customer service is very important to us, as you can expect to talk to a real person when calling in. Our highly trained and experienced team will work with you to help select the right tubing for your pneumatic application that meets the right size, material, pressure, length, coil requirements, and whether it's air or fluid. View our catalogs to find additional pneumatic components to have Polyconn be the one-stop shop for all your requirements.

Contact our team today for questions or selection assistance for your pneumatic tubing, or request a quote for more detailed requirements.