Fittings are used extensively to facilitate the connection of tubing and hose to the various components that make up all pneumatic systems. A wide variety of fittings are available to meet application criteria and personal preference:
Barb fittings are a simple way to connect flexible tubing or hose. The tubing is simply pushed over a barb that is slightly larger than the inside diameter (ID) of the tubing. A hose clamp is often added to secure the tubing more tightly. While easy to use, barb fittings have a higher risk of leaking or of the tubing popping off.
Compression fittings use a small barrel-shaped piece called a ferrule that slips over the outside diameter (OD) of the tube and is then compressed between a nut and the other half of the fitting. While creating a very secure connection, removing the tubing later can be difficult and often the tubing is deformed to the point that a new tube must be used to reconnect the fitting.
With push-to-connect fittings, flexible tubing is easily connected by inserting the tubing end into the fitting. To release the tubing, the circular release ring is pressed and the tubing is pulled out. Due to their ease of use, and solid reliability, push-to-connect fittings have become one of the most popular fittings for machinery and automation assemblies.
Plastic/brass push-to-connect fittings typically use strong thermoplastic with stainless steel tube-gripping claws, and threaded components made of nickel-plated brass. These fittings provide an excellent solution for most applications. In harsher environments (high temperature and wash-down applications), more expensive all-metal push-to-connect stainless steel fittings are sometimes required.
While they don't typically connect directly to tubing or hose, brass connectors, bushings, elbows, tees, and plugs are often required to adapt or convert between thread sizes, or for other miscellaneous connections to many pneumatic devices.
Quick-disconnect air couplings are great for situations where the air line needs to be connected and disconnected frequently. Swivel style QD fittings are particularly handy on hand tools, and allow maximum freedom of movement with the tool, and help prevent kinking of the attached hose.
Getting tubing connected between valves and cylinders often requires more than just a simple male connector or elbow. Several special purpose push-to-connect fittings are available to improve integration and operation of pneumatic systems. For example, flow control valves are often used on cylinders to control their speed, and they frequently require these special fittings.
Other useful and convenient fittings include mini shutoff valves, mini gauges, check valves and quick exhaust valves. These devices should be considered to control machine pneumatic functionality and to monitor air usage.
Specifying and installing fittings and tubing sometimes feels like a puzzle, and you will likely find during the assembly process that you missed some fittings. It’s common to require multiple orders to get everything connected as desired. Due to their relatively low cost (and the fact that most fittings are sold in 'multi-packs'), it may be advantageous to purchase extra fittings with each order, and develop an inventory of fittings for use on future projects.