A Guide to Air Line Fittings, Aluminium Piping and Compressed Air Fittings

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Also called air line fittings and air pipe fittings, compressed air fittings are usually used to connect air compressors with air tools. While there are many different types of compressed air fittings, they all help to ensure steady air flow and pressure in pneumatic systems. Quick-release type pneumatic couplings are commonly used in situations where lines are connected and disconnected on a regular basis. As such, they are often used to help power mobile equipment. Faulty air pipe fittings can result in air leaks and power loss. 

Aluminium piping 

Aluminium piping or tubing comes in a range of thicknesses and diameters. This type of piping is used in a wide range of applications due to its outstanding strength-to-weight ratio as well as extreme durability and corrosion resistance. The most popular aluminium alloys include 2024, 3003, 5052, 6061 and 7075. Aluminium alloy 6061 is particularly popular for applications that require medium to high strength due to its weldability, corrosion resistance and affordability. Aluminium piping is utilised in a wide range of applications in the construction, automobile and aerospace industries. It is also a popular element of household furniture. 

Compressed air water traps 

Moisture build-up in air compressors is a common problem. An excessive level of moisture in compressed air can lower its quality and even damage the air compressor. Luckily, there are a number of ways to remove moisture from air compressors. One of these is by using compressed air water traps.  

Compressed air water traps work by collecting moisture at the bottom of a bowl and then draining it. While compressed air water traps present a relatively simple way of getting rid of moisture from compressed air, they are not usually used in isolation but rather as a part of a system. Compressed air water traps are usually utilised in applications that require very dry air including sandblasting and painting.  

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Also called compressed air sockets, quick connect couplings are used to connect one end of a pipe, tube or hose to a power tool or other equipment. Compressed air sockets are commonly used in dental surgeries where tools need to be frequently connected and disconnected. Compressed air sockets come in a range of materials, sizes, threads and grades.   


Appropriate air line fittings can help to ensure the smooth operation of a pneumatic system. Here are just some of the more popular pneumatic fittings and their functions.  

  • Couplings are used to connect two pipes with a similar diameter by soldering, threading or welding. 
  • Adaptors are used to connect two pipes with different diameters by soldering, threading or welding. 

  • Union fittings are usually threaded for easy connection and disconnection. 

  • Caps and plugs are used to close off air flow. 

  • Elbow fittings change the direction of air flow by 45 or 90 degrees. 

  • Tee fittings are T-shaped intersections that either merge or split flow. 
  • Cross fittings are 4-way intersections that have either one inlet and three outlets or three inlets and one outlet. 


Air line fittings are crucial to ensuring that different components of an air compressor are connected. In fact, without them an air compressor would simply not function. Whether it’s banded fittings, tee fittings or beaded fittings, pneumatic fittings direct air into lines, ensuring the desired pressure for different applications such as painting a car or operating a nail gun. 

Compressed air fittings can be classified into three different shut-off types.  

  • Couplings without a shut-off valve deliver the best flow rates since they feature no obstruction. However, the flow must be stopped before the couplings are disconnected.   

  • Couplings with a single shut-off valve close immediately when disconnected trapping the media at one end. They offer greater control than couplings without a shut-off valve and are frequently used with compressed air tools. 

  • Couplings with a double shut-off valve close the flow at both ends (the socket and the plug) when the connection is broken, trapping the media at both ends. They are commonly used in environments where even a slight leak could have disastrous consequences.  

Here are some of the considerations to take into account before choosing air line fittings. 

  • Seal: Is the seal type compatible with the media (this is particularly important if you are planning to transfer chemicals)? 

  • Material: What are the air line fittings made from? Some of the common pneumatic fitting materials include stainless steel, nickel-plated steel and nickel-plated brass. 
  • Connection: Is the connection type male or female? 

  • Size: Air line fittings usually range between 4 and 13 millimetres. 

  • Operating pressure range: What pressure range are the pneumatic fittings designed to operate in? 
  • Operating temperature range? What temperature range are the pneumatic fittings designed to operate in? 

Pipes used in compressed air pipe systems are usually made from plastic or metal. Here are just some of the pros and cons of different types of pneumatic tubing.  

  • Plastic piping: Usually made from polyethylene, high-density polyethylene or acrylonitrile butadiene styrene, plastic pipes are lightweight and corrosion-resistant. They also feature a smooth surface that is ideal for laminar flow. 

  • Aluminium piping: Lightweight and easy to put together, aluminium piping has anti-corrosive properties.  

  • Stainless steel piping: Heavy and pricier than most other pipe types, stainless steel tubing is rarely used in compressed air systems. Stainless steel piping is highly durable.  
  • Galvanised steel piping: Reasonably resistant to corrosion, galvanised steel piping features coating. This can be a risk when it comes to pneumatic systems since it can flake off.  

  • Copper piping: Simple to cut and weld, copper pipes are lightweight and smooth enough to facilitate laminar flow. Plus, they are corrosion-resistant.  

Excessive moisture build-up in compressed air can not just lower the quality of compressed air but also damage the air compressor. Here are some of the best ways to dry compressed air. 

  • Use a compressed air water trap to collect and drain moisture. 

  • Regularly release water and oil from the air compression tank. 

  • Use a refrigerated air dryer or a desiccant air dryer. 

  • Use absorptive materials such as sulfuric acid to absorb moisture. 

Some pneumatic fitting applications require extra functionality. Here are some additional features offered by specialised air line fittings. 

  • Some pneumatic fittings can be connected under pressure. 

  • Expansion couplings and joints are often used in systems that are mobile due to loads, thermal cycles or service shock. 

  • Pneumatic fittings can have surface plating or coating to increase their corrosion, chemical and temperature resistance. 
  • Pneumatic fittings can have swivelling or rotating ends. 

  • Pneumatic fittings can be insulated against extreme temperatures.  

  • Some pneumatic fittings come with integral lining. This type of air line fittings is often used in the food processing industry or other applications that require sanitary conditions.  

Compressed air fittings are commonly used to connect hoses, pipes and tubes. It is important to know exactly what vessel type is being used within a pneumatic system to determine what air line fittings are best for the job at hand. 

  • Hoses are more flexible but less durable than pipes and tubes. They commonly come with multiple layers. 

  • Tubes are rigid and more durable than hoses. They are typically sized by their outer diameter. 

  • Just like tubes, pipes are more rigid than hoses. They also tend to have a larger diameter than tubes. Tubes are normally sized by their internal diameter.