Compression fittings for pipes: types, advantages, connection and installation

In the construction of water supply systems and heating systems, steel is being widely replaced by polypropylene, low-density polyethylene and even composite metal-plastic. For each type of pipe blank, new connection methods had to be developed. Compression fittings for pipes are increasingly being used instead of welding. The connection diagram has become somewhat more complicated, but at the same time more convenient and practical for installation or repair.

What are the advantages of compression fittings for HDPE pipes?

Low-density polyethylene (HDPE) is considered a rather inconvenient material in terms of connection. But the polyethylene pipe itself has high performance characteristics:

• bending strength – 120-170 kgf/cm²;
• ductility, elongation before rupture can be up to 500%;
• upper limit of operating temperature 130-140℃;
• withstands freezing.

However, polyethylene does not weld well. To make the seam on a HDPE pipe monolithic, you have to use turnbuckles and accurately control the temperature.If for industrial pipelines the use of special equipment and trained personnel is considered acceptable, then for domestic water pipelines welding HDPE pipes is difficult and expensive.

Therefore, welding was replaced with a compression fitting for polyethylene pipes. Practice has shown that abandoning soldering in favor of a compression fitting simplifies the process of laying HDPE pipelines by an order of magnitude.

Advantages of using a compression fitting:

• the installation process on pipes and connections takes 3-5 minutes;
• low price - the compression fitting is made not from HDPE, but from more durable and rigid polypropylene PPB or block copolymer;
• simple design - consists of 5 parts, including a rubber gasket;
• Possibility of disassembly, inspection, repair, repeated use.

Anyone can install and remove a compression fitting on a HDPE pipe, even those who first encountered the problem of connecting polyethylene water pipes. Minimum tools required. Experienced craftsmen make do with a cutter and calibrator. For a beginner, you may need a mounting spring and wrenches.

The cost of a compression fitting is low. For example, a coupling for a 20 mm HDPE pipe costs $1.5-2.

How HDPE pipes are connected with compression fittings

The connection scheme for polyethylene pipes with compression fittings cannot be considered ideal; there are also disadvantages. For example, to ensure the tightness of the joint, rubber gaskets are used, which dry out and lose elasticity over time. Therefore, during operation, the joint may begin to leak; the union nuts must be tightened to seal the joint.

Crimp couplings, adapters, elbows, tees on polyethylene lines must not be subjected to mechanical load - the joint must be unloaded by installing compensation supports.

Pipe preparation

The holes in the compression coupling must match the outer diameter of the pipe. But this is only in theory. In fact, both fittings and HDPE pipe blanks are produced by a huge number of small and medium-sized enterprises, so there may be deviations in size.

Before purchasing, you need to cut off a small piece of the HDPE pipe on which you plan to install the coupling, and in the process of selecting a compression fitting, check how tightly the end of the pipe blank fits inside the body. The rubber sealing ring should fit onto the prepared edge of the pipe with little effort.

Most amateurs who undertake to install a compression fitting on a PE pipe neglect preparation. It is mistakenly believed that it is enough to cut the edge evenly and you can insert the workpiece inside the coupling.

An unprepared pipe fits tightly inside a high-quality coupling-connector - if you apply a lot of force, you can even break the rubber seal. You can't do this.

Sequence for preparing the coupling edge:

1. Using a cutter, we cut the pipe so that the cutting line is strictly perpendicular to the axis of the pipe blank.
2. Using a calibrator, chamfer 20^O. If the seal ring does not fit on the pipe due to the increased diameter of the workpiece, then you will need to remove part of the polyethylene at a distance of 4-5 mm from the end.
3. If sagging is noticeable on the polyethylene pipe, or the shape is clearly different from round, calibrate that part of the surface that will go inside the compression fitting.

After processing, the chamfer surface and the first 4-5 mm of the workpiece should be as smooth as possible. No lubricants, adhesives, sealants or sealants are used when installing the crimp coupling on the pipe.

The pipes are connected thanks to the wedging action of the rubber ring. When screwed along the thread, the nut moves forward and presses through the bushings onto the end surface of the rubber. The force is quite large, so the pressure on the elastic material is transferred to the leading edge of the pipe and clamps it inside the housing.

Installation of compression fittings for HDPE pipes

The advantage of using a crimp coupling is that it can be used to make a simple and reliable connection of two branches of a water pipeline or to make a transition from HDPE to another type of pipe.

Installing a one-way ferrule

The most common type of compression fitting is a body in the form of a cylindrical glass with a thread and a union nut. For a one-way coupling, the PE pipe is connected only from the nut side. The opposite part of the body has a fitting for installing a PVC hose.

To assemble, we put a nut, usually blue or green, on the pipe. Next you need to put on the parts in the following sequence:

1. The crimp ring is white with oblique ribs located around the perimeter.
2. Insert the leveling mushroom sleeve.
3. Lastly, we place the rubber sealing ring on the pipe.

All that remains is to insert the end of the pipe blank with the ring inside the body, level it and set it to depth. After this, we put the nut on the thread and tighten it with a little force.

If the preparation and assembly were carried out correctly, the fitting will be firmly held on the PE pipe - it will be difficult to pull it out of the body.If the end comes out of the coupling with a relatively small force, it means that the assembly was performed incorrectly - the ring did not fit onto the PE pipe.

Connecting two polyethylene pipes with a double-sided coupling

A common scheme for using compression fittings is the usual joining of two pipes of the same diameter. Craftsmen often advise making the connection using additional pipe cutting, but of a larger size. In this case, its internal diameter must be equal to the external size of the workpieces being connected.

The connection is made using glue or sealant. In theory, everything is simple, but in practice, despite the simple circuit, minimal cost and availability, this method does not guarantee a reliable connection. Therefore, to connect two pipes, it is better to use a double-sided coupling.

The fitting is assembled according to the same scheme as for the one-sided model. The only difference is that some manufacturers use additional conical rubber rings that seal the gap between the nut and the outer surface of the pipe. In this case, they are placed on the pipe blank immediately after the nut.

Compression fittings for metal-plastic and PE pipes

The backbone of metal-plastic pipe blanks is an aluminum sublayer, sealed between the outer and inner layers of soft PE polyethylene. As a result, the metal-plastic pipe acquires relatively greater rigidity and strength, and therefore is able to withstand high internal water pressure.

At the same time, the presence of polyethylene does not allow applying a large compressive force - it will simply tear the polyethylene surface, and the aluminum will collapse due to contact with water.

Therefore, to fix metal-plastic, two types of compression fittings are used:

• with a split nut and a crimping outer nut;
• with compression of the outer surface with a steel sleeve.

In both cases, fixation inside the fitting is performed due to the deformation of the metal-plastic wall. Due to radial compression, the aluminum layer takes on a wavy shape and engages with the parts of the compression adapter.

In the first case, compression is performed by tightening the union nut, pressing on the split sleeve. The method is simple, but not very reliable, since there is a risk of damage to the polyethylene coating by the sleeve.

Conveniently, if necessary, compression fittings for metal-plastic pipes can be disassembled, removed and reused. Crimping adapters of the same design are used to join sections of water pipes made of PE polyethylene.

In the second case, fixation is performed by pressing and crimping a steel sleeve. Unlike the split sleeve design, the force is distributed more evenly, so the risk of damage to the polyethylene when installing a pipe blank inside the fitting is practically minimized.

When assembling the most critical sections of water supply or heating systems, it is recommended to use fittings with a sleeve, tools and metal-plastic pipes from the same manufacturer.

Sleeve adapters are not universal - they are used only for metal-plastic and for a certain pipe diameter.

Compression fittings with built-in fitting

This type of connector is used for relatively soft polyethylene blanks.The problem with using classic PEX pipe fittings is that the XLPE walls, even with mesh reinforcement, are not rigid enough to withstand mechanical bending loads. Simply put, if you install a soft PEX pipe in a sleeve, then when you try to turn the pipeline, a crease and squeezing of the flow area may occur.

Therefore, for PEX pipes, compression fittings with an increased length of the seating surface are used. After assembly, the edge of the part appears to protrude beyond the end surface of the nut by 4-5 mm.

For assembly, a nut and a split retaining ring are placed on the pipe blank. Next, the end of the soft pipe is put on a fitting with a rubber seal, the split sleeve is pulled on by hand and the union nut is screwed on. Thanks to the protrusions on the inner surface of the locking ring, the material of the PE pipe walls is securely held inside the fitting, without crushing or through cutting.

Threaded Crimping Adapters

They are used primarily for connecting pipes to threaded outlet fittings located on manifolds or heating radiators. Structurally, the adapter consists of a brass adapter with a reverse cone and two rubber sealing rings, a collet-type split ferrule and a threaded union nut.

The thread sizes on the manifold fitting and on the inner surface of the nut must match both in diameter and pitch. When tightening parts, an axial and radial force occurs, which is transmitted to the collet body.

Fastening polyethylene pipe on the adapter is ensured by compressing the walls with a collet sleeve.Unlike other models of fittings, the sleeve has not one through cut, but several small cuts evenly spaced around the perimeter. As a result of the radial pressure from the nut, the edges of the sleeve are compressed and securely fix the pipe on the seating surface of the adapter.

Compression fittings for steel pipes

The idea behind collet couplings was to develop a quick connection between two metal pipes. In its design, the compression fitting resembles double-sided couplings-connectors used for quick merging of sections made of low-density polyethylene (HDPE). But since all the parts, with the exception of the seal rings, are made of metal, the design, unlike HDPE, turned out to be compact and durable.

A compression fitting for joining two parts of a steel water pipe consists of the following parts:

• a cylindrical body in the shape of a glass with two inlet holes and threads on the outer surface;
• two union steel nuts with internal thread;
• two steel split bushings;
• two clamping rings;
• two pairs of rubber seals.

If we are talking about a transition coupling, then the nut, split bushing and rubber ring will be one copy each.

How a compression fitting works - there is an annular conical groove inside the nut. The split bushing has an asymmetrical shape, one of the sides has a rounded surface.

For assembly, a nut, a split sleeve, a clamping ring, and a rubber seal are sequentially put on the pipe. All this is inserted into the body and screwed along the thread until it stops.

You will need to tighten it with force, but the last half-turn should be soft.The gaps between the parts are selected, and the main load falls on the deformation of the rubber. If the resistance is stiff, then most likely the clamping ring is misaligned and the connection needs to be disassembled. Steel fittings are initially twisted by hand until they stop, then pressed with a pipe wrench.

You should not try to simplify the design of compression fittings for steel pipes. For example, if a rubber or pressure ring was lost. Any attempt to replace the rubber with sealant, and instead of the pressure ring to use the first thing that comes to hand or cut from a tin can ends in an accident.

The body of the compression fitting is made of brass or stainless steel. Ordinary steel is rarely used, since the metal quickly rusts when in contact with black rubber. There are steel models with an anodized coating, but they are significantly inferior to stainless steel adapters.

Can compression fittings be used for copper pipes?

Steel crimp adapters must not be used on copper piping. Direct contact of two dissimilar metals in an aqueous environment becomes the cause for the development of electrochemical corrosion. Steel will collapse quickly, literally in a few weeks.

Copper is widely used in heating systems, so bronze and brass compression fittings for copper pipes are used for joining. Moreover, several types of adapters can be used.

The simplest option is press fitting or sleeve adapter. The design of the connector is similar to a sleeve for soldering copper joints, with the only difference being that an O-ring is placed inside the pipe, rather than solder, and the thin-walled body is crimped with press jaws.

The second type of compression fittings is used for joining copper pipes with a high phosphorus content. This is the so-called solid copper. In this case, crimp couplings are used with joints sealed with elastic EPDM rings. The design of such a fitting is similar to devices used for steel pipelines.

Compression adapters with a tapered sleeve are used to connect thin-walled soft copper pipelines. The nut is placed on the pipe blank, after which the end of the latter is flared until a landing cone is formed.

All that remains is to insert the conical sleeve into the body, then place the pipe, put on the nut and tighten it with a wrench until the copper settles. The connection is reliable and can withstand heating to any temperature. The only drawback is that this type of compression connection is only applicable for small diameter pipelines.

The idea of ​​using compression fittings to connect pipes in practice turned out to be quite successful, easy to implement and reliable in operation. Joining pipes with an adapter is easier and more convenient than using soldering or a welding machine.

Method of connecting a fitting and a HDPE (PE) pipe: video.

Tell us about your experience of joining with compression couplings - how durable was the connection, and what problems arose when using adapters? Save the article to your bookmarks so as not to lose useful information.