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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 present issues to your water filtration systems. That's why it is so important to know how quick-connect fittings work. To help you understand how a quick-connect fitting works and what to consider when using them, our Master Water Specialist, John Woodard, explains what it takes to keep your fittings running efficiently and leak-free.

What is a quick-connect fitting? 

The term “quick-connect” simply refers to the ability to connect tubing to a fitting very quickly. Introduced to the water treatment industry in the late seventies, and early eighties, 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 fitting work? 

The beauty of the quick-connect fitting is its simple design. It's comprised of three individual components: a collet, an O-ring, and the 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. So, 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 do you install and disconnect 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 be sure 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.

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. In order 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?

Fittings are used almost anywhere you move water. Quick-connect fittings are also used in under-counter point of use systems, like the Neo-Pure ultra-filtration system. In this unit, 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. Make sure the chemical is compatible with the plastic material you are using. 

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

The only thing that separates a male fitting from a female fitting is where the fitting thread is located. 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?

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 leaking is that the tubing did not get pushed in all the way, and the O-ring is not 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 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-release 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. This has to do with 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 have to 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 made to handle the transport of water, they will only provide specs and ratings for that kind of application.  

Quick-connects are rated for their chemical compatibility. It's very important for you to check what material fitting you use if you're running fluids with certain chemicals through them. If you run a fluid with chlorine in it through your system, you want to make sure that the plastic fitting you're using can withstand 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 half-inch, three-quarter inch, one 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. So, a 3/8 CTS fitting 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 them the super-seal fittings. 

There is a lot to know when it comes to quick-connect fittings. 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. 

Browse quick-connect fittings from our top brands.


2 comments

  • Great question, David! Can you use DMfit and John Guest fittings or Parker and LiquidFit interchangeably? The answer is a resounding yes. But make sure the sizing of the fittings is the same, CTS or OD.

    John Woodard, Master Water Specialist on

  • Are the various makes interchangeable?

    David Evans on

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