Factoring in Fittings
Considering connection criteria for a successful application
Understanding the proper applications for various types of connectors is critical when designing a system or installing equipment. Installations can become routine, but it is important to evaluate each situation for new or unusual criteria.
An easy way to remember how to cover your bases is the acronym STAMP, which stands for size, temperature, application, media and pressure. Considering these factors with each new application is important due to the increasing number of applications using aggressive fluids or cleaners and the potential risks associated with a failed connection.
Size refers to tube outside diameter (OD), hose inside diameter (ID), port connection and thread size. Connectors fall into three general categories: pipe, which has thread connections; tube, which seals on the OD of the tubing; and hose, which seals in the ID of the tubing. Thread considerations include, but are not limited to, specific thread pitches and threads per inch.
Standards vary by industry and country. An important first step in selecting the right connector is determining a suitable connection—whether the connection’s seal will be on the inside or outside of the tube, or if it will be threaded.
If the connection will be threaded, gather information on thread size and pitch.
Temperature refers to the minimum and maximum temperatures of the media being conveyed. It is one of the most important factors when working with a new application, because the temperature affects a connector’s ability to withstand chemical attack and system pressure.
Plastic connectors with pressure and chemical compatibility properties typically are weakened by extreme temperatures. While you often see information such as “working pressure: 150 psi,” it is critical to remember that a stated rating is just a snapshot that typically covers normal or ambient conditions of 77°F. That same fitting in an application closer to 100°F may handle much lower pressures and be subject to chemical attack.
Application refers to conditions of use including, but not limited to, vibration, environment and external temperature. Vibration can quickly fatigue a connection or tube that would last for decades in “normal” conditions. The environment surrounding any tubing or connector routing also should be considered. Areas that have frequent cleanings by aggressive chemicals need to be carefully factored into any application decisions.
Routing of lines is probably the most difficult, yet most significant, consideration for a system or installation. Proper routing involves getting a connecting line from one point to another through the most logical path. Always try to leave fittings and joints as accessible as possible. The most logical path should avoid excessive strain on connections.
The composition of the media being conveyed and its compatibility with fittings or valves is the top consideration for a new application. If you are using tubing or connectors for the first time with new media, evaluate the chemical compatibility of the tubing and fittings. Fittings that seal on the OD of the tubing also may include a seal, such as an O-ring. Every push-to-connect fitting also will have an O-ring or seal. This material is as important to evaluate as the body material.
The system pressure at the location, including pressure spikes, is key to a successful long-term solution for routing tubing and connectors. It is important to understand the pressure on a connector.
Manufacturers often rate a connector’s pressure at a fraction of the actual failure mode. For example, a fitting rated at a working pressure of 100 psi actually may start to leak near 200 psi and would burst at 400 psi. This safety factor exists to cover unknown or unusual circumstances in applications or manufacturing. Using a connector above the recommended manufacturer’s working pressure is strongly discouraged.
Remember STAMP the next time you have a new or unusual system or installation. Understanding the size, temperature, application, media and pressure before you plumb a new system can save trouble in the long run. If you have any questions about a specific application, contact the manufacturer for guidance.