step-by-step assembly of crimp fittings
PEX pipe crimping is now the standard in professional heating, but the quality of the entire system depends exclusively on the precision of each individual connection. Any inaccurate cut, inappropriate insertion length, or incorrect crimping pressure can lead to permanent leaks and costly repairs behind the walls.
Preparation of materials and tools before starting work
The first and most critical step is the correct preparation of the pipe end, which must be perfectly flat and free of burrs and scratches that could interfere with the O-ring's seal. When working with 17 mm pipe, as is common in standard underfloor heating distribution, you must use a high-quality metal saw or special cutters to ensure a perpendicular cut to the pipe axis without deformation.
Next, check the condition of the crimping dies on your hydraulic or electric crimper to ensure they are clean and undamaged, as even the smallest dirt will transfer to the connection point. To ensure proper system function, always verify that you are using crimping dies that exactly match the fitting size, for example, for a PRESS 90° elbow - for PEX pipe - 17x17 you must use dies designed for this combination.
Technique for correct cutting and removing the burr
After measuring and cutting the pipe, there follows a phase operation that is often underestimated by beginning plumbers – the removal of the internal burr created during cutting. The burr that remains inside the pipe prevents the full insertion of the pipe into the fitting and creates turbulent flow, which reduces system efficiency.
For this purpose, use a special burr remover that gently cleans the interior without damaging the pipe wall. This step ensures that when fitting a T-piece PRESS - for PEX pipe - 17x1/2"Fx17, full contact between the end of the pipe and the bottom of the fitting is achieved, which is a prerequisite for the sealing ring to function.
Accurate insertion depth measurement and marking
A key factor for sealing is the exact insertion depth of the pipe into the fitting, which is defined by the manufacturer's diagram for the given size. For 17 mm pipe, this depth is usually set at 16.5 mm, and a deviation of just a few millimeters can cause either a leak or deformation of the sealing ring during crimping.
- Mark the insertion depth on the clean pipe using a marker or a special scale on the ruler.
- Always check that the pipe is inserted up to this mark, not just "halfway".
- When using a PRESS insert - for PEX pipe - 17x17, be careful not to confuse the sides with internal and external threads if it is a coupling with a valve.
- Insertion depth is also critical when connecting two pipe pieces through a coupling, where both sides must be inserted symmetrically.
Crimping process and verification of correctness
When the pipe is correctly inserted and marked, position the crimping dies so that they are oriented according to the marks on the die body, which indicate the correct position for the given diameter. Crimping should proceed smoothly and without interruption, and the automatic stop of the machine signals that the required crimping pressure and deformation of the brass body have been achieved.
After the process is completed, let the joint cool and then visually check whether the crimping mark (deformation) is even and closed around the entire circumference. If you see gaps or irregularities on the strip, the joint is considered non-functional and must be immediately replaced, as the risk of leakage is 100 % in this case. In practice, we have seen cases where the plumber forgot to rotate the dies by 90 degrees, leading to an unstable connection.
Common errors leading to leaks and their prevention
The most common cause of leaks in crimped systems is the failure to maintain the cleanliness of the pipe surface, as even microscopic sand or grease between the O-ring and the body will cause a leak during pressure testing. Another common error is the incorrect choice of crimping dies, for example, using dies for a 15 mm pipe on a 17 mm pipe, which leads to insufficient compression or brass cracking.
- Never use a pipe that has already been crimped or mechanically damaged.
- Check the condition of the sealing rings in the fitting; if they are dry or cracked, replace them immediately.
- When installing in tight spaces, ensure that the crimping dies have sufficient space to close without hitting surrounding objects.
- Do not forget to regularly calibrate and maintain the crimping tool to ensure accurate pressure.
Visual inspection of the crimping mark and diameter measurement
The inspection of a completed joint must not be limited to visually detecting deformation, but must also include precise measurement of the outer diameter of the crimped section using a caliper.
Frequently asked questions
How long do I have to wait before carrying out a pressure test?
The crimped joint is immediately watertight, and you can start the pressure test right after the process is completed, without waiting for it to cool down, unless the ambient temperature is extremely low.
Can I dismantle a crimped joint and reuse it?
No, a crimped joint is one-time use only; after crimping, the brass is permanently deformed and the sealing ring loses its elasticity, so a new fitting must be used.
How can I distinguish original fittings from cheap imitations?
Original products have clearly engraved brand markings, diameters, and certifications, whereas cheap imitations often have blurred characters and inconsistent material weight.
Proper installation of crimp fittings ensures a safe and long-lasting heating system without the need for future wall or ceiling interventions. By following these simple rules and procedures, you can avoid costly repairs and be confident that your system will operate smoothly for many years without issues.
Do you have a question about this topic?
Not sure or dealing with a specific situation in your home? Write to us – we are happy to help.