What is a Quick-Connect Fitting and How Does It Work?

Posted by
John Woodard on November 22, 2023

Quick-connect fittings, also known as quick-connect couplings, have made water treatment faster and more efficient than ever before. However, if they aren't installed correctly, they can cause issues with your water filtration systems. As a result, it is important to know how quick-connect couplings work so that you can avoid problems. In this article, you can learn the function of quick-connect fittings, their types, and answers to common questions about QC couplings.

What is a quick-connect coupling? 

Quick-connect fittings provide a long-lasting seal in tubing that can be connected extremely quickly. The term “quick-connect” simply refers to the ability to connect tubing to a fitting with little effort and time. Introduced to the water treatment industry in the late 1970s and early 1980s, quick-connect fittings revolutionized the way we put water equipment together. The quick-connect fitting is the fastest way to provide a water-tight connection between tubing and your water treatment applications. 


How does a quick-connect coupling work? 

The beauty of the quick-connect fitting is its simple design. It is comprised of three individual components: a collet, an O-ring, and a body. The body of the fitting conceals the O-ring and collet on either end. Your tubing is meant to be inserted through the collet, through the O-ring, and into the body of the fitting. These three components create the water-tight seal.

As pressure increases inside of the tubing, the water or air forces the collet into a groove on the inside of the fitting. The grooves compress the collet so that the little teeth on the inside of the collet dig into the tubing, making it virtually impossible for the tubing to disconnect. Consequently, the harder you pull on the tubing, the tighter the collet holds onto it. As the collet continues to hold the tubing in place, the O-ring seals the space between your tubing and the fitting that it is connected to, making it water tight. The most common reason for experiencing a leak with a quick-connect fitting is that the tubing did not get pushed into the fitting all the way.

How to install a quick-connect fitting

To install tubing into a quick-connect fitting, you must simply insert the tubing through the collet and O-ring, and into the body of the fitting. The only trick is to make sure you have inserted the tubing all the way into the fitting. If you have not pushed your tubing past the O-ring on the inside of the fitting, you will experience a leak because the O-ring is not sealing properly. One way to ensure that your tubing has been inserted all the way is to mark the end of it at about the three-quarter inch line. When you press the two pieces together, the three-quarter inch line should disappear into the fitting.

How to remove a quick-connect fitting

When a tube is installed in a fitting, the collet grabs onto it with its teeth. This feature holds the tube in place so that it does not slip out. When you pull on the tubing, the collet works against you and clamps harder onto the tube. To release it, you must pull the collet down towards the fitting (to release its teeth from the tubing) and pull the tubing away from the fitting. This easy process allows you to connect and release this fitting easily and quickly so you can work quickly and stay productive. 

What are quick-connect fittings used for?

Quick-connect couplings are used in many hydraulic and pneumatic applications. Quick-connect fittings are also used in under-counter point of use systems, such reverse osmosis and ultrafiltration systems. In many of these systems, the quick-connect fittings are built right into the system to make installation as easy as possible for residential users. A variety of OEM manufacturers use quick-connect fittings on products that move or filter water. These fittings are also rated for pneumatic use for compressed air or gas.

Quick-connect vs quick-disconnect fittings

Unlike quick-disconnect fittings, quick-connect couplings form a permanent seal and are more difficult to remove than quick disconnects. If you are using your fittings for an application where the fitting may need to be removed regularly, such as during a filter change, quick-disconnect fittings are preferrable to quick-disconnect couplings. Likewise, if you want a long-term fitting that will not need to be removed regularly, quick connects are a great option.

Types of quick-connect couplings

The most common types of quick-connect fittings are the following:

  • Ball and sleeve fittings have a ball shape at the male end of the fitting that fits into a sleeve in the female end.
  • Push-to-connect fittings work exactly as their name implies. To install a push-to-connect fitting, simply push one end of the fitting into the other.
  • Bayonet quick connects connect and disconnect with a 1/8 or 1/4 turn. Instead of using threads to connect, bayonet couplings use
  • Cam-lock quick connects are tabbed fittings that are used in hoses. The tabs on the female end of the fitting lock the male end in place.
  • Luer-lock fittings connect by rotating them into place. They are commonly used for single-use applications in the medical field.

Popular quick-connect fitting brands

We carry quick-connect fittings from multiple top brands, including John Guest, SharBite, LinkTech, and NeoFit. Every manufacturer chooses to build, size, and shape their fittings differently. Once you have a basic understanding of what a quick-connect fitting is and whether or not you need them, then browse the different brands that Fresh Water Systems offers so you can decide which kind of quick-connect fitting is right for you.

John Guest is the leading manufacturer of push-fit fittings. These are commonly used for residential and commercial plumbing and drinking water systems.

SharkBite fittings feature a push-to-connect design, allowing for efficiency and ease of use in plumbing systems.

LinkTech offers a wide variety of quick-connect fittings that are suited to specific applications.

NeoFit quick-connects can be used for various residential and commercial water flow applications. They are NSF-certified for fluid transportation and pneumatic applications.

What is the difference between a male and a female fitting? 

The primary difference between a male fitting and a female fitting is the location of the fitting thread. On a male fitting, the thread is located on the outside, and on a female fitting, it is located on the inside.  

The water treatment industry uses several other terms to describe fittings, like connectors and adapters. The terms connector and adapter really mean the same thing. If you want to be specific though, an adapter is typically a fitting that changes venue. On one end, there is a thread connection, and on the other, there is a stem adapter. However, they both are still connectors. The threaded side connects to other threads, and the stem side connects to tubing. 

What makes a quick-connect fitting watertight?

The O-ring inside a quick-connect fitting forms a watertight seal that prevents leaks. As long as your quick-connects are not subject to environments with excessive vibration or movement, they should always stay in place. The O-ring inside of a quick-connect usually remains in good condition for a long time, however, after many years of service the O-ring could dry out and cause a slow-drip leak. If the fitting is manufactured correctly and without defects, this should never happen. 

If our fittings operate in an application like a motor home or a boat or equipment with a pump, the motor vibration could cause the tubing to gradually slip out of place. To prevent this from happening, you can equip the fitting with a locking clip. The locking clip holds the collet up so that the teeth remain pressed into the tubing at all times, allowing the tubing no room to slip out.

What makes a quick-connect fitting leak?

The most common reason for a leaking quick-connect coupling is that the tubing did not get pushed in all the way, preventing the O-ring from sealing properly. One trick is to measure 3/4 an inch and draw a line on the tubing going into the fitting. That line should disappear into the fitting. 

Another reason that you may be experiencing a leak is that the tubing was not cut properly. If the tubing is cut in a diagonal shape rather than a square cut, the O-ring may not have been able to seal all the way around the circumference of the tubing.

Another potential issue is a lacerated O-ring. If the tubing doesn’t get cut properly, and it has a sharp point, the sharp point could damage the O-ring, making it impossible to seal.

Too much side torque or side load could also result in a leaking fitting. If you try to bend the tubing to make a connection to your water treatment system, the tubing itself could elongate the O-ring into an oval shape that will create a lapse in the seal and cause the fitting to leak.

Frequently taking the tubing apart and putting it back together can cause gradual damage to your tubing. The metal teeth on the inside of the locking collet bite hard into your tubing. Every time that you remove the tubing from the fitting, you could be scraping away small bits of the tubing. Over time, this frequent removal could cause your tubing to be scratched so deeply that it bypasses the O-ring, allowing water to pass. If you are in need of a fitting that you can connect and disconnect over and over again, you might want to consider using a quick-disconnect fitting.

Learn more: What is a quick-disconnect fitting?

What temperatures and pressures can a quick-connect fitting withstand? 

Quick-connect fittings are rated to withstand pressure based on temperature and the fitting size. The warmer the water, the lower pressure the fitting will withstand due to the expansion and contraction of the plastics. The larger the tubing and more rigid the tubing, the more pressure the fitting can withstand. Pressure and temperature must be looked at together to determine the pressure limit.

Can you use quick-connect fittings with gas and air? 

Most quick-connect fittings are rated to handle liquid compressed air and gas. Some manufacturers are specific about how they rate their fittings. If they are manufactured to handle water transportation, they will only provide specs and ratings for that kind of application.  

Quick-connects are rated for their chemical compatibility. If you are running fluids through a fitting, ensure the material of that fitting can withstand the chemicals it is exposed to. If you run a fluid with chlorine in it, for example, you want to make sure that the plastic fitting you are using is compatible that chemical compound.

How do you know what size tubing is compatible with a quick-connect fitting? 

Knowing how tubing and fittings are sized is very important. There are two main sizing types when dealing with plastic tubing, and they are very different. Smaller diameter fittings, that are measured by outer diameter (OD), are specifically designed for use with LLDPE type tubing, or low linear density polyethylene. The larger fittings, in 1/2 inch, 3/4 inch, 1 inch, and above are considered CTS, or copper tube size, fittings. CTS fittings are made to be compatible with PEX tubing, which is a polyethylene-type tubing. These fittings are made in very specific measurement classes. A 3/8 CTS fitting, for example, is not going to work in an application that requires a 3/8 OD fitting.

Most fittings are rated to work on copper tubing as well, but it is not the best kind of tubing to use with OD and CTS fittings. If you want to use copper or stainless steel tubing, it is best to look for fittings made specifically for those types of applications. John Guest is one of these manufacturers that makes compatible fittings with stainless-steel. They call these “super-seal” fittings.


If you have any additional questions, please do not hesitate to contact us.

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