By Josh Cosford, Contributing Editor
Push-to-connect fittings are a staple in pneumatic systems worldwide. Earlier pneumatic compression fittings using nuts and sleeves were more complicated and fussy, with no standard between manufacturers to allow interchangeability. If you needed to replace a sleeve, for example, you were often limited to a few manufacturers offering the same shape, and in some cases, the compression of the tube would restrict airflow slightly.
When push-to-connect fittings were introduced, users experienced trepidation, as it seemed the new design offered no clear method of sealing, while their capacity to hold tightly was also in doubt. Users quickly recognized the reliability concerns originally placed upon push-to-connect fittings were misplaced, and this style of fitting now enjoys widespread use.
There’s no surprise with their popularity. Other than ensuring the tube is cut squarely to ensure effective sealing and connection, these fittings are easy to install and easy to plumb. They’re literally as simple as tightening them into the port and then just inserting the tube. There are no sleeves or nuts to fiddle with, which are small and easy to lose.
Although simple in appearance, they’re filled with tiny and intricate parts that seal and lock the tube in place. The seal sits within the fitting where it interfaces and seals from the outside diameter of the tube, and it’s important to push the tube fully inside the fitting until it rests on the shoulder. Fore of the seal (typically just an O-ring) is the tightness ring, which pushes on the gripping collet to prevent the tube from pulling out unless the release ring is first pushed downward to release the collet.
Push-to-connect fittings are available from many manufacturers in a dizzying array of materials, thread forms, tube sizes and construction materials. You can also expect every combination of shapes, such as elbows, unions, tees and branches, as well as straight (inline) connections.
Most commonly, you will find plastic-bodied fittings with brass or metal thread, itself usually pre-applied with sealant. These are inexpensive to manufacture, reliable and available in all configurations.
For applications with specific ambient conditions not suitable for plastic, manufacturers offer a few more suitable choices. For high temperature or ultimate reliability, full brass construction is a traditional option many designers prefer to use. However, not all manufacturers still offer full-brass options, so pay attention to their current catalog. Where brass is still almost exclusively available is in the transportation industry. DOT-approved fittings are either fully brass or brass and composite and reliable enough to withstand vibration and UV for approved use on air brakes, tire inflation systems and other heavy-duty trucking applications.
For use in high-temperature and food and beverage applications, stainless steel offers the most reliable solution. Stainless steel (particularly 316SS) makes a perfect choice when plumbing in and around food and beverage manufacturing for many reasons. Its corrosion resistance prevents rust or other oxides from breaking off and contaminating food. It is also easy to clean and non-reactive so even aggressive sterilization and cleaning chemicals do not harm the fitting or connection.
Push-to-connect fittings have risen to stardom and have been adopted across all industries using pneumatics. They’re exceptionally easy to use, inexpensive and offer myriad materials and constructions. Rarely do you see new(ish) technologies so thoroughly displace the old guard so well as have push-to-connect fittings.
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