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Quick-connect fittings provide secure, reliable connections with the ease of a simple push. Popularly used throughout plumbing, quick-connect fittings can be found in almost any application that requires transporting water. Everything from household under-sink water filtration systems to office water coolers and espresso machines employs quick-connects to make water treatment simple and efficient. 

While it’s rare for quick-connects fittings to be defective, leaks are common because of improper installation, damage, or forceful pressure. Here, we troubleshoot the most common quick-connect leak causes so you can enjoy your filtered water leak-free. 

What are the components of a quick-connect fitting? 

A quick-connect fitting is comprised of three elements: the connecting body, the collet, and the O-ring. The beauty of quick-connect fittings is in the simplicity of their design. The connecting body holds the fitting together and gives water a chamber to pass through. (Or air, as these fittings can also be used in pneumatic applications.) The collet provides the teeth for the fitting to bite down on the tubing and keep in securely in place. The O-ring provides the fittings with a watertight seal. Quick-connect fittings all work on this principle, except for SharkBite fittings, which use a unique push-to-connect design to establish connections. 

The design of the quick-connect fitting allows it to grab ahold of a piece of tubing with a simple push. Inside the body, the sides of the fitting taper together near the top of the fitting. When pressure is applied to the fitting (for example, when a piece of tubing is inserted) the collet is pressed up against this taper. As the collet pushes against the walls of the body, the teeth bite into the tube and secure it in place. The tubing then is pushed to the end of the fitting where it meets the O-ring. When the O-ring is compressed by the tubing, it compresses and creates a tight seal that prevents any water from escaping out the sides of the tubing as it passes through the fitting. 

Learn more about how quick-connect fittings work. | Explore how SharkBite fittings work

How do I install a quick-connect fitting? 

To install a quick-connect fitting, simply insert the tubing into the mouth of the fitting and push it through the collet until the tube reaches the O-ring. The design is simple, but these fittings are able to create reliable, durable connections with a simple push. Their ease of use and wide array of applications attribute to their popularity among the water treatment and filtration industry. However, when pushing the tubing into the quick-connect fitting, it’s vital to ensure the tubing has reached the O-ring. One of the most common causes of leaks is tubing that has not been inserted deep enough into the fitting. You can also use a locking clip to secure the collet remains in place and doesn’t slip off of the tube. 

How do I remove a quick-connect fitting? 

To remove a quick-connect fitting, push down on the collet as you pull the tubing in the opposite direction. When you apply pressure to the collet, it prevents it from rising up to the top of the body where the taper activates the collet’s teeth. If you simply try and yank the tube out of the fitting, the teeth will engage and you will be unable to extract the fitting. By pressing down on the collet, you are keeping the teeth from compressing around the piece of tubing. 

If you are struggling with a particularly stubborn quick-connect fitting, find an object you can use to leverage the pressure. For example, use the flat edge of a screwdriver to press the collect down as you pull the fitting toward you. If you are still unable to extract the tubing, use a collet release tool to press down the collet and remove the quick-connect fitting. 

Why is my quick-connect fitting leaking? 

The majority of leaking quick-connect fitting leaks are caused by a damaged O-ring, improper installation, eroded tubing, or too much torque placed on the tubing. Quick-connect fittings have a simple but powerful design. If the fitting is leaking, it is very unlikely the leak has sprung because of a manufacturer defect or faulty product design. The majority of leaks arise because a component of the fitting has been damaged or the fitting has been installed in a manner that is allowing water to bypass the O-ring. 

1. Improper installation 

When pushing the quick-connect fitting onto the tubing, ensure that you have pushed the tubing in far enough that it has depressed the O-ring and sealed the fitting. If the fitting is only pushed in past the collet and has not created a seal, water will be able to bypass the collet’s teeth and exit out of the fitting. When the tubing reaches the collet, it does create resistance. This push back can lead you to think that you have pushed the tubing all the way into the quick-connect fitting, but, it may not have reached the O-ring. 

One of the best ways to ensure your tubing reaches all the way into the quick-connect fitting is to measure the tubing. Take out a ruler and measure out 3/8ths of an inch away from the mouth of the tubing you’re going to insert into the fitting. Using a marker, draw a line at the 3/8ths point. When you push the tube into the fitting, the tubing should go in far enough that the mark disappears completely under the collet. This way, you will know the tubing has pushed all the way past the collet and has made contact with the O-ring and formed a tight seal. If the tubing does not get pushed to the O-ring, it will leak. Wetting the tubing is another method to make sure the tubing slides all the way into the quick-connect fitting. Moisture will help the tube slide through the fitting to the O-ring. 

2. Uneven tubing

In order for the tubing to seal tightly with the O-ring, the tubing must have a clean, straight cut. If the mouth of the tubing is jagged or uneven, it will not create a watertight seal and leaks will spring as water flows through the fitting. If the tubing is cut at too much of an angle, it can cut into the O-ring and make a tight seal impossible. To achieve a cut that will lay flush with the O-ring, use a tube cutter. These handheld devices use an angled, razor-sharp blade to neatly slice through the tube. The tool is ideal for making perpendicular square cuts that allow for a proper, leak-free seal against the O-ring in the fitting. Though there are many types of plastic tubing available, the most common tubing used with quick-connect fittings is LLDPE. LLDPE tubing (an abbreviation for linear low-density polyethylene tubing) is compatible with all standard fitting sizes and commonly used with point-of-use drinking water systems like reverse osmosis or other under-sink units. LLDPE tubing is the most widely used tubing in the water filtration industry. 

Tubing can also become damaged if it is used and reused too many times, the tubing can start to become worn down. For example, if you are frequently connecting and disconnecting the fitting, grooves will start to form on the tube. Each time that fitting is removed, the tube gets a little more scratched. The deeper the scratches on the tube are, the less likely the tube will be able to create a strong enough seal with the O-ring to stay watertight. If there are any imperfections or notches on the tube, water can slip through and create a leak. 

Though it may seem obvious, it’s also important to make sure the outer diameter (OD) of the tubing matches the size of the fitting. Tubing with a 5/16 OD will slide into a fitting with a 3/8 push-in size easily, and may look like it’s created a tight fit. When the difference is so slight it may not be immediately apparent that an incorrect size has been used. However, the moment water is run through that tube, the fitting will leak everywhere. If a brand new fitting with clean-cut tube is leaking, it’s worth to check that they match in their size. 

Read more about the types of plastic water tubing

3. Torque or pressure 

Leaks can spring in fittings if the fitting is strained or too much pressure is placed on the fitting at a strange angle. If you are creating a bend or corner in the tubing, the tubing will start to displace the components of the fitting. This torque in the tubing will move the collet to the side and start to stretch out the O-ring. In this position, the O-ring can no longer create a seal and it will start to leak. It’s important to keep the tubing entering and exiting the fitting as straight as possible. 

If you need to wrap tubing around a bend, there are quick-connect fittings specifically designed to aid in this. An elbow fitting is an angled fitting designed to change the direction of the flow. These can be at 90° angles or short-radius 45° angles. Swivel elbows allow you to fully rotate one end of the fitting so the tubing can face whichever direction you desire. These fittings make it easier to create corners and bends in your plumbing without creating a pressure load and torquing the fitting. 

4. Damaged O-ring

If the rubber O-ring is scratched, chipped, or broken, it is unable to create a watertight seal. As previously mentioned, O-rings can become damaged by jagged tubing or improper installation. If a fitting is yanked too hard to one side, it can compress the O-ring and cause it to warp. Certain chemicals in water can also cause the O-ring to deteriorate. If your water has high levels of chloramines, over time these will break down the EDPM rubber material. Though uncommon, O-rings can also deteriorate one their own after prolonged usage and develop small leaks. 

If you have a damaged O-ring, it’s very simple to replace. There’s no reason to discard the whole fitting. Quick-connect O-ring replacements usually cost a $0.20-$0.50 per O-ring. 

How do I replace a damaged quick-connect O-ring? 

    1. Remove the collet. Using your fingers, extract the collet from the mouth of the quick-connect fitting. 
    2. Pull the O-ring out of its well. To remove the O-ring from the well, locate a thin, flat tool. Tweezers, a toothpick, or a nail file will all be able to reach down and loosen the O-ring. 
    3. Tamp a new O-ring into the fitting. Using a piece of tubing, push the new O-ring into the fitting. Push on the tubing until the O-ring flattens and stays in place. 
    4. Slide the collet back into the fitting. Replace the collet into the fitting, and your quick-connect fitting is back in action. 

Explore our comparison of SharkBite and John Guest quick-connect fittings


3 comments

  • I changed the washers in my filtration system near the valve .my push on fittings now leak a lot. could the water pressure in the system be causing that or have i damaged the push on

    zenon helinski on

  • We are so glad we could help you out, Jay!

    John Woodard, Master Water Specialist on

  • Thanks for this great tutorial. I had a leaking line in an RO/DI and couldnt figure out why. Turns out the O ring was mis aligned. Your video helped discover that issue and fix it! THANKS!

    Jay Santos on

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