How to Install 1/4 Inch Tube Fittings for Leak Free Instrumentation Systems

Installing a 1/4 inch tube fitting to make it leak free may seem like a simple task, but out in the field it can create a system that runs all day long or a system that runs perfectly. These fittings are typically used in laboratories, water treatment facilities and industrial control lines where even a little leak can be catastrophic. Many times the problems are not from defective parts but from small mistakes made while installing the Threaded tube fittings . If the tube is not cut straight or if the nut is overtightened, or even if there is dirt on the fitting surface it could cause problems. With proper measures and a little precaution you can ensure a nice clean seal that won't leak when pressure is applied.

Tools needed for 1/4 inch tube fitting assembly

Ensuring you have the proper tools available before you start will not only help installation go smoothly, but will help eliminate future leaks. While most 1/4 inch tube fitting assemblies will not need heavy machinery, having some basic tools can make a world of difference in how clean and secure your connection will be. The first thing you will want to have is a quality tube cutter. This ensures you will have a straight cut on your tubing. A leading reason for a poor seal on High pressure fitting is from a ragged or angled cut. Some people will use a saw, but this will most likely cause burrs that can damage the fitting or cause micro cracks. Having a deburring tool or small reamer can be beneficial. Once you cut your tube, the inside edge can be sharp and jagged. Deburring it out allows the tube to insert correctly as well as prevent scoring the fitting surface. Also have an adjustable wrench or sized appropriately spanner on hand. This is used to tighten down the fitting nut. You should never go by feel. A good wrench allows you to have more control so you do not overtighten and warp the ferrule. Marker or tape can be used to mark your depth of insertion on the tube. This may seem like a simple step that can be ignored; however it allows you to push the tube in as far as possible then tighten. This ensures you get a good seal every time. Have a clean rag or wipe close by. The smallest amount of dust, oil, or metal shavings can cause leaks if they find there way into the connection area. In one particular workshop installation, we had a technician that was consistently getting small leaks on a water line during change out of fittings. After talking with him we found out he was not deburring the tubing after cutting. Once he added a simple wiping down step the leaks stopped occurring.

Step by step tube cutting and deburring

Begin by getting the length of tubing required. Keep the tube in the same position and make a distinct mark with a marker or tape where the cut is. This will prevent the need to guess later and ensure the cut is correct. Insert tube into an appropriate tube cutter and screw it into the surface loosely. Squeeze not too hard at the beginning. Turn the cutter round the tube in even turns. Tighten cutter after each of several rotations. Continue doing this until you have cut the tube. Slowness is better in this case to prevent crushing the tube or leaving a jagged edge. After separating the tube, test either end. The incision is not supposed to be bent or flattened. When it appears to be not straight, it is better to re-cut than attempting to correct it at a later stage when fitting. Next go to deburring. Use a deburring tool or a small reamer to clean the inside of the tube on the edge. Turn it around to take away the sharp bits. Press, but not too hard, and you will smooth out the inside. Sharp edges within the tube may ruin the ferrule or prevent a tight seal. Next, clean the outside edge as well. Run the deburring tool or a fine file towards the outer rim. This process aids the tube to get into the Stainless tube fittings without scratching the surface of the seal. After deburring, wipe the tube with a clean cloth. In a single field case, a technician in a small water system set up continued to experience pressure drops. The problem was identified by the minute plastic shavings remaining in the tube after cutting. After doing the cutting and deburring steps more cautiously, the system remained under pressure without any leakage. Clean cut and smooth edges can be considered small details, but they will produce the greatest difference on the reliability of the entire connection.

Proper nut tightening technique

After cutting, deburring, and fitting the tube, the next step is to tighten the nut and everything is in place. This section requires a hand, not power. The majority of leaks occur here, not due to the badness of the fitting, but due to the fact that the nut was either loose or over-tightened. The first step is to slide the nut over the tube and to assure that the ferrule fits correctly inside the fitting body. Insert the tube as deep as it can go. You ought to feel it take its rest. Keep the tube in place as tightening occurs. Have an appropriate wrench that fits the nut. Start tightening by hand until it becomes tight. This helps keep the threads aligned and avoids cross-threading. When hand-tight, replace with the wrench. Spin the nut. As the tube is attacked by the ferrule you will feel it attempting to hold on. This is normal. It is important to squeeze by just the right amount to squeeze the ferrule and form a tight seal, but not to squeeze the tube to death. The most popular error is to take more turns to be safe and it usually results in deformation and leakages in the future. When setting up a field, one of the rules is to screw tight until you experience some resistance then tighten it a quarter turn. After that, stop. In case you are not sure, it is always good to run the system at low pressure to begin with and then you can make some adjustments. A technician in one of the maintenance jobs in a small instrumentation panel continued to work with slow leaks despite replacement of fittings. The issue was found to be caused by over-tightened nuts that had slightly oval-shaped the tubing. After he adopted a lighter tightening policy, and a method of quarter-turn control, the leaks ceased altogether, and the system maintained itself under pressure weeks.