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The most leak-resistant joints for pneumatic lines are those that have been soldered or brazed. However, two big drawbacks to these ultra-reliable joints are installation cost and extreme difficulty if a joint has to be replaced at a later time (also see “Considering Other Issues” below).
For these reasons, many different type of fittings have found favor in pneumatic systems because they are much less labor-intensive at installation, and lines can be removed and replaced many times with little effort.
But what about leakage? As long as the appropriate fitting is chosen for the application, there’s no reason why a connection using threaded fittings should be just as leak-tight as a brazed or soldered joint. Just as people untrained in brazing or soldering should not be making these types of connections, people untrained in working with pneumatics should not be installing fittings. In fact, the International Fluid Power Society offers certification for working with connectors and conductors.*
Material—An Import Consideration
The type of material making up the fitting is a primary characteristic determining success of the application. Using a material that will be attacked by a hostile environment. cannot contain the pneumatic pressure, or doesn’t stand up to physical stresses transmitted to the fitting will likely lead to a catastrophic failure. On the other hand, specifying a material that far exceeds the parameters of the application wastes money.
Carbon steel is strong, with a high resistance to heat. An alloy primarily of iron and carbon, steel is typically alloyed with other metals to improve its corrosion resistance. In addition, steels used for pneumatic fittings often have coatings or platings that offer greater greater corrosion resistance than the steel itself.
Strong, durable, and corrosion-resistant, with high temperature ductility and good conductivity, brass is an alloy of copper and zinc. It is the most common metal for smaller compression and threaded fitting typical of pneumatic systems because of its machinability and good mechanical properties.
Aluminum is lightweight and corrosion-resistant, but because of its low strength in its pure state, aluminum is usually alloyed with zinc, copper, silicon, manganese, and/or other metals to improve its strength and hardness.
Exhibiting high strength and high corrosion resistance, stainless steels contain less carbon than an alloy of plain steels and are alloyed of steel that contains more than 10% chromium. They have the strength and durability of steel while also providing excellent corrosion resistance, albeit typically at a higher cost.
Moving to plastics, polypropylene is a thermoplastic widely used for pneumatic fittings because of its price, broad compatibility, and relatively high strength. It exhibits good bi-axial strength and yield-elongation properties and can be used in exposed applications because of its resistance to UV, weathering, and ozone.
Composites consist of different materials merged together so that the fitting exhibits the favorable properties of both materials. They also exhibit low electrical and thermal conductivity.
But whatever the material, configuration, or application, dozens of suppliers exist that offer a wide variety of fittings to choose from. We have tabulated data from dozens of suppliers and provided them in the accompanying table. However, the table is not just a list of who’s who. It contains hard specifications indicating sizes, designs, materials, and ratings offered by each.
*Learn more about IFPS Certification for connectors and conductors at http://bit.ly/HP0216-IFPS.
Considering Other Issues
Poor plumbing practices can cripple a pneumatic circuit even if it was designed with the best engineering practices and assembled with the most up-to-date components. Undersized lines, elbows instead of bends, incorrect component placement, and long piping runs are just a few of the limitations that can restrict compressed air flow.
Other problems, such as using tapered pipe threads or lines with thin walls, can make a circuit a maintenance nightmare that requires daily attention. Fortunately, numerous publications (including our own eBooks on our website) can assist in specifying correct line size and conductor thickness to give low pressure drop and safe working-pressure limits.
An important characteristic that often is overlooked is the length and size of lines between the valves and actuators. Piping between the valve and actuator should be as short as possible and of the minimum diameter to carry the required flow. The reason for this is that all the air in the pipes between the actuator and valve is wasted every cycle. These runs must be filled to make the device move but the air it takes to fill them does no work. During each cycle, air in the actuator lines exhausts to atmosphere without helping cycle time or force. For this reason, always mount the valve close to the actuator ports.
Contact Manufacturers of Pneumatic Fittings
Summarized below is basic contact information for the dozens of suppliers of pneumatic fittings listed in the table. We list the phone number and web address for all companies and full contact information for those companies that are featured advertisers in the February print issue of Hydraulics & Pneumatics.
Adaptall Inc., (800) 463-8134, www.adaptall.com
Adsens Technology Inc., (626) 854-2773, www.adsens.net
Air Logic, (800) 558-5950, www.air-logic.com
Airtrol Components Inc., (262) 786-1711, www.airtrolinc.com
Alkon Corp., (419) 333-7000, www.alkoncorp.com
American Couplings, Div. Dixon Valve & Coupling Co., (410) 778-2000, www.dixonvalve.com
Anderson Fittings, (708) 535-9030, www.andersonfittings.com
Anderson Metals Corp., (816) 471-2600, www.andersonmetals.com
Anver Corp., (978) 568-0221, www.anver.com
Ark-Plas Products Inc., (501) 453-2343, www.ark-plas.com
Bimba Mfg. Co., 25150 S. Governors Hwy, University Park, IL 60484; (800) 442-4622, (708) 534-8544, Fax: (708) 235-2014; www.bimba.com
Beswick Engineering Co. Inc., (603) 433-1188, www.beswick.com
Chicago Fittings Corp., (815) 334-8000, www.chicagofittings.com
Coilhose Pneumatics, (732) 390-8480, www.coilhose.com
Colder Products Co., (800) 444-2474, www.cpcworldwide.com
Coronet Parts Mfg. Co. Inc., (800) 428-0015
Eldon James Corp., (970) 667-2728, www.eldonjames.com
EPCO Products Inc., (260) 747-8888, www.zeroleak.com
Fairview Fittings, (716) 614-0320, www.fairviewfittings.com
Festo Corp., (800) 993-3786, www.festo.com/us
Fittings Unlimited Inc., (800) 348-8467, www.fittingsunlimited.com
Flaretite Inc., (810) 750-4140, www.flaretite.com
Fluid Line Products Inc., (440) 946-9470, www.fluidline.com
Industrial Specialties Mfg. Inc., (303) 781-8486, www.industrialspec.com
LDI Industries, (920) 682-6977, ldi-industries.com
Lenz Inc., (937) 277-9364, www.lenzinc.com
Malone Specialty Inc., (800) 874-3077, malonespecialtyinc.com
Manastrip-M. M. Corp. (518) 664-2089, www.manastrip.com
Mead Fluid Dynamics, (877) 632-3872, mead-usa.com
Mid-America Fittings (800) 633-6771, www.midamericafittings.com
Numatics Inc., Cylinder Div., (615) 771-1200, www.numatics.com
Nycoil Co., (336) 495-0004, www.nycoil.com
Parker Hannifin Corp., Pneumatic Div., (269) 629-5000, www.parker.com/pneumatics
Parker Hannifin Corp., Tube Fittings Div., (614) 279-7070, www.parker.com/tfd
Pisco USA Inc., (630) 993-3500, www.pisco.com
Pneucon, (800) 545-1355, www.pneucon.com
Pneumadyne Inc., (888) 559-0177, www.pneumadyne.com
Powertrack Int’l Inc., (412) 787-8520, www.powertrackhose.com
Preferred Products Design Inc., (203) 877-4399, www.preferredproductsdesign.com
Pressure Connections Corp., (614) 863-6930, pressureconnections.com
Puregas LLC, (800) 521-5351, www.puregas.com
SMC Pneumatics Inc., (800) 762-7621, www.smcusa.com
Swagelok Co., (440) 248-4600, www.swagelok.com
Tompkins Industries Inc., 1912 E 123rd St., Olathe, KS 66061, (800) 255-1008, Fax: (800) 959-3333, salesAtompkinsind.com, www.tompkinsind.com
World Wide Fittings, (847) 588-2200, www.worldwidefittings.com
World Wide Metric, (732) 247-2300, www.worldwidemetric.com