Choosing the Right Fitting

STÄUBLI pneumatic fitting

To choose the most suitable fitting for your application, you need to consider the type of connection, the environment, the nature of the fluid and its characteristics, and the materials compatible with your application.

• Connection type: Quick-connect, permanent, or removable. You need to check accessibility, both for assembly and maintenance purposes and determine the shape of the fitting, e.g. straight, T-shaped, or angled.
• Environment: You must take into account the ambient temperature, especially extreme temperature changes, risk of frost or UV exposure, rain or humidity, possible splashing water or mud, the level of protection required if the fitting is used in a hazardous area, possible impacts, vibrations, etc.
• Fluid type: You need to choose the right fitting for the fluid (compressed air, air, water, oil, etc.), its temperature, pressure, and required flow rate (which depends on the nominal diameter [DN] of the pipe).
• You may need to check that the connection complies with any standards to which your installation may be subject.
• Material: The material of the fitting (stainless steel, brass, plastic, etc.) and of the sealing system (nitrile [NBR], fluorine rubber [FKM], ethylene rubber [EPDM], etc.) must be compatible with the material of the pipe that it is being connected to.

ELAFLEX fuel fitting

Different types of fittings are available for different applications. Here are some examples:

• Quick couplings or push-in fittings: There are different quick-connect fittings systems.
  • Washer-type fittings: used with polymer tubes, they are engaged by a simple push and disconnected by the push of a button. The tube can be mounted on a splined inlet and can be screwed or even welded. These fittings are generally very compact.
  • Clamp fittings: These are extremely robust fittings used in aggressive environments and for high-pressure circuits. They are mainly used for grooved metal tubes.
  • Reverse clamp fittings: offer a double seal and secure disconnection. They are used for very high pressures.
• Screw-in fittings: These are designed to be dismantled, usually with a wrench. It’s a good idea to check that there’s enough space around the fitting to dismantle it if necessary.
• Guillemin symmetrical couplings (also known as fireman’s fittings): These are widely used in the chemical, petrochemical, food, transport, and agricultural industries. They are made up of two half-couplings that lock together when turned. These fittings can be mounted on the pipes in a variety of ways, e.g. through a ring socket, male thread, female thread, or weld fitting. This type of fitting is considered a screw fitting and requires a special tool for assembly and disassembly. These fittings are available in aluminum, stainless steel, brass, bronze, or polypropylene.
• Weld-on fittings and crimp fittings: These are permanent fittings, particularly used for hydraulic circuits.

RTC Couplings quick coupling

Quick couplings today are highly reliable products. This type of fitting is recommended if you plan on disassembling it regularly. Quick couplings do not require tools once each part is attached to its tube. When choosing your quick coupling, it’s important to check how the two parts of the coupling will connect to the pipes or ducts: by screwing, crimping, or interlocking.

This type of fitting is rather expensive. If you don’t plan on regular dismantling, it may make more sense to choose a screw-in fitting.

AIGNEP brand screw-in fitting

Screw-in fittings are good for when you’re planning one-off operations that may require them to be dismantled.

As a general rule, screw-in fittings are designed to be handled with a wrench, but some models are designed to be screwed in by hand. Most screwed fittings have built-in seals.

EFFEBI crimp fitting

You can choose a weld-on or crimp fitting when the fitting will be used in a permanent installation such as a water supply circuit. These fittings are designed for use with brass or copper pipes.

Weld-on and crimp fittings are the most economical, as they do not require sealing systems or mechanical systems. However, their installation requires a certain amount of know-how to ensure that they hold up well over time.

The material of the fitting must be compatible with that of the pipe on which it is to be mounted and with the fluid present in the circuit.

When using a threaded fitting, it is essential to ensure that it is compatible with the one already installed in the circuit.

First of all, it is necessary to check the thread direction: Standard threads have a right-hand thread and are screwed in a clockwise direction, but there are also threads with a left-hand thread, for example for gas cylinders or when there may be a need to unscrew a standard thread.

Finally, it is important to know the standard used, for example:

• ISO metric thread: This is the most common type of thread. These are sealed with a ring seal at the bottom of the thread. Cylindrical threading and tapping are identified by the letter M followed by the nominal diameter in millimeters and the pitch indicated in millimeters (e.g. M8x1). For gas connections, a cylindrical thread is indicated by the letter G, and the tapered thread by the letter J.
• American UN thread: This is a cylindrical thread whose dimensions are given in inches and the number of threads per inch. It is identified by the letters UNC for unified coarse pitch and UNF for unified fine pitch threads.
• NPT American thread: This is a tapered thread that seals with a jointing compound such as Teflon. NPTF threads are similar but do not require a jointing compound to be added.
• BSP thread: This is a specific thread for gas. It can be cylindrical (BSPP), in which case it is sealed with an annular seal at the bottom of the thread, or conical (BSPT), in which case it is sealed with a jointing compound in the thread area (e.g. Teflon).

It is important to choose a fitting shape that is adapted to the circuit where it will be installed. For example, there are:

• Straight fittings for seamless connections.
• T-fittings for connections that branch.
• Elbow fittings are used to connect pipes that join at an angle.
• Reduction fittings are used to connect two pipes of different diameters. This type of fitting allows you to reduce the fluid flow rate.
• Orientable fitting or swivel fittings are used for connections made at specific angles.