Step-by-step installation of a bend with a union on copper and plastic pipe

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Step-by-step installation of a compression elbow on copper and plastic pipe

Installing a compression elbow is a daily task for every plumber, as well as for a skilled DIY enthusiast who wants to connect a radiator, extend the heating distribution, or change the direction of the pipe in the boiler room. Despite its apparent simplicity, this is where the most leaks, malfunctions, and unnecessary repeated installations occur – especially when transitioning between different materials or fittings. This article will guide you through the entire process step by step, for both the most common types of pipe: copper pipe and plastic (multilayer) pipe of the HEPWORTH system. You will find specific torque values, recommended tools, the most common mistakes from practice, and tips that will save time and money.

What is a compression elbow and where is it used

A compression elbow (in English: elbow with union nut or compression elbow) combines in one fitting a change in the direction of the pipe and a removable or threaded connection. On one side it has a compression or crimp connection to the pipe, and on the other side it has an external or internal thread depending on what follows – typically a radiator valve, a ball valve, a pump, or another device.

In practice, we most often encounter situations where the pipe comes from the wall or floor and needs to be connected to a valve that is oriented in a different direction. Or the other way around – a thread comes out of the device and a pipe needs to be connected to it, which continues in another direction. For these situations, for example, Compression elbow 1/2" x 15 exists, which connects a metric pipe diameter of 15 mm with a 1/2" inch thread.

The category of compression elbows and reduced elbows is much wider – in addition to combined pieces, there are also pure elbow fittings without a thread, such as K-piece 15 x 15 or K-piece 22 x 22, which connect two pipes of the same diameter without changing the profile. If you need to change the direction under a smaller angle, there are 45˚ elbow 15 x 15 and 45˚ elbow 22 x 22. The choice of a specific piece depends on the pipe material, diameter, angle of the branch, and the way of connecting to the device.

Tools and materials before starting the installation

Proper preparation before installation is half the success. From practice I know that most of the problems with leaks do not arise from the use of poor parts, but from the lack of tools or a skipped step. Before starting, prepare the following:

For copper pipe

Copper pipe cutter – not a disc saw, but a manual pipe cutter. It provides a clean, perpendicular cut without chips that could contaminate the system. A standard diameter of 15 mm can be handled by an inexpensive cutter for a few euros, while for 22 mm and 28 mm a more robust version is better.
Reamer – every copper pipe cutter usually has one built-in, or you can buy a separate one. It removes the internal burr after the cut, which would otherwise interfere with the flow and could damage the seal.
Cleaning cloth or sandpaper (grit 120–180) – for cleaning the surface of the pipe at the joint location.
Cleaning paste / soldering preparations – not necessary for compression joints, but essential for soldered elbows. For compression elbows with a union, it is sufficient to have a clean, oxide-free surface.
Two adjustable wrenches or pipe wrenches – one holds the body of the elbow, the other tightens the nut. Never tighten the nut without holding the body – you risk twisting the entire joint.
PTFE sealing tape (Teflon) – for the threaded part of the elbow, where it connects to an external/internal thread of the device.
Hemp fiber + sealing compound – an alternative to PTFE tape, some plumbers prefer it for larger threads (3/4" and more).

For plastic (multilayer) HEPWORTH pipe

Plastic pipe shears – the blades must be sharp, not blunt, otherwise they deform the cut into an oval. Note: for multilayer pipes (with an aluminum layer), use shears intended for PEX-AL-PEX or PE-RT/AL/PE-RT, not standard polypropylene shears.
Calibrator (sizing tool) – an absolute necessity for plastic pipe. After cutting, the inner diameter of the pipe is slightly deformed and must be returned to the correct circle. Without a calibrator, you will not be able to properly insert the internal adapter and the joint will leak.
Internal adapter (insert) – for each compression joint on a plastic pipe, a metal or plastic internal reinforcement is required, which prevents the pipe from deforming when tightening the nut.
Lubricant (silicone spray or soapy water) – facilitates the installation of sealing rings and prevents them from twisting during installation.
Two adjustable wrenches – the same principle as with copper.

Installation of a compression elbow on a copper pipe – step-by-step procedure

Step 1 – Measuring and cutting the pipe

Measure the exact length of the pipe you need. When measuring, take into account the depth of insertion of the pipe into the elbow – for a 15 mm compression elbow it is typically 12–14 mm, for 22 mm it is approximately 15–16 mm. If you are unsure, check the documentation for the specific fitting or simply insert a piece of pipe into the elbow dry and measure the insertion depth with a pencil.

Cut the pipe using a copper pipe cutter with even pressure – rotate the cutter around the pipe and gradually press the cutting wheel. Never cut in one single motion – this causes deformation of the cross-section. After cutting, there will be a sharp bend on the inner edge – immediately remove it with a reamer (reamer) for at least 5 turns.

Step 2 – Cleaning the pipe surface

Thoroughly clean the surface of the copper pipe at the location of the future joint (approximately 2–3 cm from the end) with a cleaning cloth or sandpaper. Copper oxidizes quickly and oxides significantly reduce the tightness of the compression joint. The surface must shine like a mirror – a dull, oxidized surface is the most common cause of leaks in copper pipes.

Step 3 – Installing the nut and olive

Before inserting the pipe into the elbow, slide the nut and then the sealing olive (compression ring) onto the pipe. This mistake – forgetting the olive or installing the nut backwards – is trivial, but it happens very often in practice when working quickly. The nut must be threaded onto the pipe with the thread facing towards the body of the elbow, and the olive must face before the thread, i.e., closer to the body of the elbow.

Step 4 – Inserting the pipe and pre-tightening the nut

Insert the pipe into the body of the elbow until it reaches the stop. Then manually thread the nut onto the body of the elbow so that the thread engages correctly – do not force the nut, otherwise you will cut the thread. Manual tightening should go smoothly for at least 3–4 turns without resistance. If you feel resistance from the beginning, the nut is not centered – unscrew it and start again.

Step 5 – Tightening with a wrench

Hold the body of the elbow firmly with one wrench and tighten the nut with another. Tighten slowly and evenly. For standard 15 mm compression elbows, a tightening of "1.5 turns" after manual pre-tightening is sufficient – you do not need to worry about the exact torque. In practice, this means: tighten by hand, then with a wrench for an additional 1.5 to 1.75 turns. Do not try to tighten it "as much as possible" – with excessive torque, the olive will plastically deform, break the sealing function or the fitting body itself may crack.

Approximate tightening values for copper pipe:

Diameter 10 mm: approx. 10–12 Nm
Diameter 15 mm: approx. 15–18 Nm
Diameter 22 mm: approx. 25–30 Nm
Diameter 28 mm: approx. 35–40 Nm

Step 6 – Sealing tape on the threaded part

If the compression elbow has a thread on the other side, e.g. 1/2" external thread, wind PTFE tape around it. Wind the tape in the direction of the thread (clockwise when viewed from the end of the thread) – 3 to 5 even layers from the first to the last thread. If you wind the tape in the opposite direction, it will unwind during tightening and create a false sense of tightness without real sealing function.

Alternative: hemp fiber with sealing paste. Evenly wind the fiber around the thread and apply a layer of paste – this method is more reliable for thicker threads (3/4" and larger). More on this topic can be found in the article Sealing of the joint – most common problems during installation of reduced elbows.

Step 7 – Screwing into the device and checking

Screw the threaded part of the elbow into the mating part (valve, tap, pump). The same rule applies here: at least 3–4 threads manually, then with a wrench. Usually, a tightening of 1–2 turns with a wrench after manual pre-tightening is sufficient – it depends on the material of the body and the type of sealing. Brass threads into brass: 25–35 Nm; brass into steel ball: 30–40 Nm.

Installation of a compression elbow on a HEPWORTH plastic pipe – step-by-step procedure

Plastic pipes, specifically the HEPWORTH system (PE-RT, PEX or multi-layer PEX-AL-PEX), have several essential differences in installation compared to copper. Neglecting them is the source of most complaints and repeated service visits.

Step 1 – Cutting the plastic pipe

Cut the plastic pipe only with sharp scissors or a cutter suitable for the material. The cut must be perpendicular to the axis of the pipe – a deviation greater than 2° will cause the internal insert to sit at an angle and the sealing will not be evenly loaded. After cutting, visually check the shape of the cross-section – if the pipe is slightly oval (which is common in multi-layer pipes), you must calibrate it.

Step 2 – Calibration of the inner diameter

This is a step that many people skip and then wonder why the joint is leaking. Insert the calibration tool into the pipe and turn it a few times to restore the circular cross-section. At the same time, most calibrators for multi-layer pipes also remove the internal burr after cutting. After calibration, check the diameter with a caliper: the tolerance should be within ±0.1 mm.

Step 3 – Inserting the internal insert

Insert the internal metal or plastic insert into the pipe cross-section. For a stiffer pipe or larger diameter (22 mm and above), help yourself with a light blow from a rubber mallet – the insert must be inserted until it reaches the stop, when its edge is in contact with the front surface of the pipe. If the insert is not inserted until the stop, the pipe will deform during tightening of the nut, the insert will shift and the joint will leak during pressure testing.

Step 4 – Installing the nut and sealing rings

The nut and O-rings (seals) must be on the pipe before inserting it into the body of the elbow – the same principle as with copper. Some types of HEPWORTH compression elbows have pre-mounted seals in the fitting body, in which case you only need to install the nut. Lightly grease the seal or O-ring with silicone lubricant – this ensures that it does not twist during installation and does not have folds through which water could leak.

Step 5 – Inserting into the body of the elbow and tightening

Insert the pipe with the insert into the body of the elbow until it reaches the stop and manually pre-tighten the nut. For plastic systems, the tightening torque is stricter than for copper – the manufacturer usually specifies exact values in Nm. Approximate tightening values for HEPWORTH compression joints:

16 mm pipe: approx. 18–22 Nm
20 mm pipe: approx. 22–28 Nm
25 mm pipe: approx. 30–36 Nm
32 mm pipe: approx. 40–48 Nm

Caution: for plastic fittings (body made of polymer), the torques are lower than for brass fittings, because cracking of the body is a risk. If you are working with a brass body fitting (typical for the HEPWORTH CLICK or PRESS system), you can tighten slightly more strongly.

Step 6 – Threaded part and sealing tape

The procedure is the same as with copper pipe – PTFE tape in the direction of the thread, 3–5 layers. I recommend using PTFE tape of width 12 mm for 1/2" thread and 19 mm for 3/4" thread – it is much easier to work with than a thin 8 mm tape.

Step 7 – Pressure test before closing the structure

Before covering the distribution lines (e.g. in underfloor heating, in embedded lines in a groove), always perform a pressure test with cold water at at least 1.5 times the operating pressure (for standard heating: operating pressure 2–3 bar → pressure test 6 bar for 2 hours). Any pressure drop during the test indicates a leak – fixing it before covering is much cheaper than after pouring the screed. More information can be found in the article Why the elbow is leaking and how to fix it without replacing the entire joint.

Reduced elbows – specifics when changing diameter

Reduced elbows connect two pipes of different diameters and simultaneously change the direction. Their installation has several differences compared to elbows of the same diameter:

The first rule is never to mix different materials without the correct transition piece – for example, a copper pipe directly on a plastic one without a brass transition is not good practice from the point of view of corrosion or tightness. More about choosing the right fitting for your system can be found in the articles How to choose the right elbow for HEPWORTH plastic pipe and Dimensioning elbows when transitioning between different pipe diameters.

The second rule is the direction of reduction. Water should encounter as little resistance as possible at the point of reduction – this means that a reduction from a larger to a smaller diameter when flowing to the right is more hydraulically advantageous than a reduction from a smaller to a larger one. In practice for heating, this means: place the reduction as close as possible to the outlet on the supply line, not in the middle of the distribution pipe.

When installing a reduced elbow with compression, the side with the larger diameter is connected first, as it has a larger wrench grip. If you tighten the smaller nut first and then try to stabilize the larger side, you risk deforming the already assembled joint. More technical details on this topic are provided in the article Reduced elbow or reduction separately – what is more cost-effective.

Most common mistakes in practice and how to avoid them

Over the years of working with plumbing systems, I have seen dozens of customers with the same and completely unnecessary problems. Here are the most common ones:

Forgotten nut or olive before inserting the pipe – if you realize this only after tightening, you have to disassemble the entire joint. With compression elbows, this is possible, but the olive is single-use – after disassembly, it is usually deformed and needs to be replaced.
Nut installed upside down (reversed) – it fits, but does not compress the olive properly. The joint looks correct at first glance, but it will leak during pressure testing.
Excessive force when tightening – with fittings made of rigid polymer, the body can crack; with brass fittings, the thread can shear. Both repairs are expensive.
Missing PTFE tape on the thread – the thread itself does not seal, and a thread seal is always an essential part of the joint.
PTFE tape wound in the wrong direction – when screwing in, it unwinds and is unevenly displaced between the threads.
Missing insert in the plastic pipe – the joint may seal for a while, but with temperature fluctuations (expansion of plastic), the pipe deforms and the joint starts to leak after months, typically during the first heating season.
Copper pipe not de-burred after cutting – the burr from the cut edge damages the sealing surface of the olive at first insertion and will never seal properly.
Ignoring calibration of the plastic pipe – an oval cross-section causes asymmetric loading of the seal and over time, a micro-leakage can occur.

Procedure after installation – testing and commissioning

After completing the installation of all joints and before filling the system with water, visually inspect each joint. Look for signs of paste, incorrectly wound tape, a bent nut or pipe that is not fully inserted (when viewed from the side, the nut is unevenly spaced from the body of the fitting).

Fill the system with water slowly and during the first filling, allow air to escape through the air vent – trapped air in the system increases pressure locally and can create a false leak or, on the contrary, damage a weaker joint. After filling, let the system remain under static pressure for 30 minutes without the pump running and check all joints with a dry paper towel – any moisture indicates a leak.

For systems with operating pressure up to 3 bar (typical apartment heating), a pressure test at 6 bar is standard. Apply pressure using a hand pump with a pressure gauge, not directly from the supply – uncontrolled pressure from the supply may exceed the test pressure.

Service disassemblability of compression joints

One of the major practical advantages of compression elbows with nuts compared to crimped or soldered joints is disassemblability. If you need to replace a device (e.g., a radiator valve), it is enough to unscrew the nut, replace the device, and reassemble the joint. The olive on copper is usually replaced (it is cheap, costing only a few cents), and O-rings on plastic pipes can usually be reused if they are not visibly deformed.

Warning: on old installations (15 years or older), the olives on copper pipes may "stick" to the surface of the pipe due to oxidation and thermal stress. In such cases, it is better to cut the pipe 5 cm behind the original joint and use a new piece of pipe, rather than try to forcibly remove the olive and risk damaging the pipe.

Frequently asked questions (FAQ)

Do I have to change the olive every time I install a compression elbow, or can I reuse it?

With copper, the rule is: an olive after the first tightening is single-use. When unscrewing, it is plastically deformed and a new tightening will not achieve the required seal. An exception is when you only manually pre-tightened the joint (without a wrench) and immediately unscrewed it – in this case, the olive has not yet been permanently deformed. With plastic pipes, it depends on the type of fitting: O-rings are usually reusable if they are not visibly damaged. If in doubt, better replace them – O-rings are cheap and a service call for a leak is expensive.

How many layers of PTFE tape is the correct number?

For a standard 1/2" (G1/2) thread in a water heating system, 3–5 layers of PTFE tape are sufficient. More layers are not necessarily better – with an excessive amount of tape, you may have problems with tightening (the thread offers too much resistance) or the tape protrudes into the flow cross-section. More important than the number of layers is the even winding and the correct direction (following the thread direction).

Can I connect a HEPWORTH compression elbow directly to a copper pipe?

Theoretically yes – if the tube diameter matches the fitting diameter and you have a compression elbow with a brass body. However, for long-term reliability, it is recommended to use transition pieces designed by the manufacturer for the specific system when transitioning from copper to plastic. The reason is the different thermal expansion of materials and potential galvanic corrosion in the presence of water with high mineral content. If you are unsure about the correct choice, read the article How to determine the correct diameter and elbow angle for your piping system.

Can I use a 90° elbow where a 45° elbow would be appropriate?

From a hydraulic perspective, a 45° elbow is always more advantageous – it causes a lower pressure drop (approximately 40–60% less local resistance compared to a 90° elbow). A 90° elbow is sometimes geometrically necessary (limited space, wall, ceiling installation), but if you have a choice, prefer a 45° elbow. A more detailed analysis can be found in the article 45° Elbow or 90° Elbow – When to Use Each Type. For smaller diameters (15 mm and 22 mm), 45° elbows are also available, such as 45° Elbow 15 x 15 and 45° Elbow 22 x 22.

How can I tell that a compression elbow is sufficiently tightened without a torque wrench?

The basic rule for compression elbows: manual pre-tightening + 1 to 1.75 turns with a wrench for diameters 10–22 mm, approximately 1.5–2 turns for 22–28 mm. Visual indicator: the olive should be slightly visible "sunk" into the surface of the pipe (for copper), but the pipe should not be deformed or visibly compressed from the outside. If in doubt, invest in a cheap torque wrench – for 20–30 euros, you can save a lot on potential returns and repairs. I always recommend using a torque wrench for critical points (hidden installation, underfloor heating).

What should I do if the thread "spins freely" during tightening?

The most common cause is damaged threads – either you started tightening the nut at an angle (cross-threading), or you used an incompatible thread (e.g. NPT instead of BSP). At the first sign of abnormal resistance, stop immediately and check whether the threads can be tightened manually. A damaged thread in the brass body of the fitting cannot be repaired – the fitting must be replaced. On threaded parts of devices (valves, taps), thread repair may be possible with a thread repair kit, but only for steel bodies, not for brass, where the repaired thread would be too weak for pressure loads.

Conclusion – Summary of Key Rules

Installing a compression elbow is not rocket science, but it requires a systematic approach, the right tools, and respect for the differences between materials. For copper pipe, the key is a clean cut, deburring, a clean shiny surface, and the correct orientation of the olive. For HEPWORTH plastic pipe, an internal insert and diameter calibration are essential – without these two steps, you cannot reliably seal a compression joint.

Always seal threaded parts of elbows with PTFE tape or hemp with paste; never rely on the metal thread alone. And remember: too little tightening does not seal, too much tightening damages the fitting. Both extremes are unnecessary and can be easily avoided with the correct working procedure.

To choose the specific part for your installation, browse the full range of reduced elbows, including Compression Elbow 1/2" x 15 for connecting a threaded connection to a 15 mm pipe, or T-piece 22 x 22 for the same diameter without a threaded connection. If you are deciding between types or diameters, I also recommend reading other articles from the Knowledge Center – External Thread vs. Internal Thread on Elbows – What Difference Does It Make? and Common Questions About HEPWORTH Reduced Elbows.

Do you have a question about this topic?

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