Plastic pipes for heating

The organization of the heating system that in a private house, that the in a city apartment has always been classified as the most complex and large-scale. Everything is important here literally, and any seemingly small thing can play its value. And one of the basic requirements, if you do not use calculation of for generating thermal energy, are high-quality materials and components for mounting the entire system.

More years 20 ÷ 25 back from hosts housing a special alternative and there was - for the water circuits had to use exclusively metal pipes of different diameters. This imposed a lot of inconvenience and technological difficulties - from the large weight of pipes and problems with the organization of their transportation, to the need for special equipment for their installation and, accordingly, the ability to properly use them, the availability of skills in working with metal. It's a different matter now - plastic pipes for heating have replaced plastic products.

This opened very wide horizons for the independent work of domestic craftsmen. No, certainly, that the heating system has turned out qualitative, steady skills are necessary, but to learn, to mount any plastic pipes is much easier than to perform, for example, electric arc welding. Even threading on a steel pipe and reliable "packing" its is a much more laborious process than, for example, installing a compression fitting or soldering polypropylene. The equipment is not so expensive, it's easy to rent it for "ridiculous" money, and for many types of pipes - the in general, the has a set of spanners.

The article will consider several varieties of polymer pipes - from their technical characteristics, merits and demerits, to the main technological receptions for installation in a heating system.

What requirements must be met when selecting pipes for heating

Sortamen t t rubbings - extremely large. They differ among themselves with the base material of manufacture, diameters and thickness of the walls, the absence or presence of any reinforcement, physical characteristics - flexibility, the degree of linear expansion, the ability to attach and retain the desired shape, resistance and temperature and pressure loads, ultraviolet radiation and otherparameters - up to the color design.

However, one must understand that heating is a very specific system in which all elements experience extreme or close to them loads. And any pipe, just for reasons of economy or ease of installation, this is not suitable.

• Plastic pipes for heating must be able to withstand the high temperatures of the heat carrier circulating through them. Although in modern systems, the upper limit of heating does not usually exceed 70 - 80 degrees, yet the "reserve" laid by the technologists should not be less than 95 ° C .With such heating, the work should not be deformed, lose its strength properties( plastic should not "swim" from the elevated temperature).
• Where there are high temperatures there is always increased pressure. Hence, plastic pipes for heating should is guaranteed by possible in the system of baric loads, including sudden jumps, and water hammers. This is especially important for house wiring of central heating systems, where the hosts can not control the level of the supplied coolant pressure.
• Pipes should have a smooth inner surface, on of which the will not accumulate build-up of salts or scale, and which will not create an increased hydraulic resistance for coolant circulation.
• Plastic pipes for heating should have the minimum possible coefficient of linear thermal expansion. Otherwise they simply will either sag on heating, or on the contrary , they can have unnecessary internal stresses when the temperature decreases.

• One of the main advantages of quality polymers is inertness, not susceptibility to corrosion or chemical decomposition. This is especially important in the case when is used as a coolant, not ordinary water, but some chemical formulations.
• The polymer itself does not oxidize, but can pass oxygen into the coolant. And this is likely with time will lead to corrosive processes on the metal surfaces of boilers, regulating, shut-off, installation fixtures. Modern technologies allow successfully to combat this phenomenon - heating pipes can be equipped with special "oxygen barriers".
• Pipes should be durable - heating is always mounted for a very long time, and the operating resources of the pipe should not be any lower than the rest of the system elements.
• Not all tenants will enjoy the constant sound of running water under pressure. So, still one requirement for heating pipes - their " low noise ".The smooth inner surface of the channel must ensure a smooth, without turbulence, movement of the liquid, and the material of the walls - not resonating, effectively muffling possible sounds.

• Well, of course, since a significant part of the heating system is usually in sight, the pipes with their appearance should not "destructively influence" the interior of the premises. In other words, they should be if is not beautiful , then in any case - very accurate.

Modern technologies in the manufacture of plastics and composite materials allow the creation of products, practically , which fully meet the for all specified requirements, to a greater or lesser extent. At present, various plastic pipes are widely used in the arrangement of heating systems, but polypropylene and polyethylene are the most widely used, in various combinations and designs.

Polypropylene pipes

General concepts of the material

Polypropylene( PP) as a raw material for pipe products has been used for a long time. But to apply it in conditions of high temperatures and high pressure allowed only the creation of of modern modifications of of this material.

So, all polypropylene products are distinguished by a pronounced chemical inertness - they can be used to transfer even very aggressive compounds. But according to the strength criteria and the thermal stability , there are quite large "variations":

• homopolypropylene was the first widespread popularity of this material( there are different designations - for example, "type 1" or PP-N ).Pipes from PP-H are high-strength, chemically inert, but they can not withstand high temperatures. Their typical use is cold water supply, drainage systems, ventilation ducts, technological production complexes, not connected with the heating of liquids.
• Polypropylene "2 types", or block copolymer of polypropylene( PP-2 or PP-B ) - retaining all the advantages of its predecessor, has already more significant capacity to withstand the thermal load. However, , extreme temperatures, around 80 - 90 ° With it not will transfer even a short time. The scope of PP-B pipes is, in principle, the same as that of PP-H. is possible its application in hot water supply systems with a limited heating threshold, in systems " warm floors", where temperatures should not exceed 45 - 50 ° C .
• Significantly has expanded scope of polypropylene development of the technology for creating so-called " Random Copolymer " .During the synthesis of this material, fragments of the ethylene molecule are introduced into the molecular chain of propylene, which dramatically changes the performance of the products for the better.

Static polypropylene "third type", PP-3, PP-R or PPRS - is just that material that is excellent for pipes exposed to both compression and thermal stress. While does not deteriorate the chemical of inertness and environmental compatibility of the material, a similar upgrade dramatically increases the elasticity, toughness, resistance to elevated temperatures.

Polypropylene PP-R has become one of the main materials for the production of pipes for a wide variety of applications. It is used both in pure form, and creating multilayered structures.

Pipes can vary in color - be white, greyish with varying degrees of saturation, green or in shades of blue and like .By the way, this does not say anything about their features, but rather the desire of some leading manufacturers to somehow distinguish their products.

The black color pipes can be an exception - this color is usually given to products that are highly resistant to ultraviolet rays. And still - pipes for sewerage or for drainage systems it is customary to impart an orange color. One for heating installation is neither black nor orange pipes will not meet, so to consider their is not no no need.

The longitudinal color strip on the pipe will say more. Everything here is simple and obvious - the blue bar indicates the possibility of using exclusively in the cold water supply system, and the red one indicates the increased heat resistance of the pipe. By the way, the bands are not applied to all products - it is better to pay attention to the marking.

The fact is that PP-R pipes differ in several parameters. The first, of course, what attention is paid to is the outer diameter and wall thickness of the pipe. Standard sizes of diameters, which are used in the creation of home heating systems - 16, 20, 25, 32, 40, maximum - 50 mm. As a rule, larger pipes for use in the heating system of a private house are simply not needed - there are not so significant volumes of heat transfer. However, diameter in itself is a parameter that does not speak much, and it can not be considered in isolation from the pipe type indicator, in the name of which the value of the nominal working pressure of the hydraulic system is indicated. In total, four of these types are defined - from PN -10 to PN -25.Features and applications - in the attached table:

Type of polypropylene pipe	Nominal operating pressure	Sphere of use of pipes
MPa	technical atmospheres( kgf / cm²)
PN 10	1.0	10.197	Cold water supply, as an exception - warm floors with levelheating up to 45 ° C
PN 16	1.6	16.32	Cold and hot water supply with water temperature up to 60 ° C
PN 20	2.0	20.394	Cold and hot water supply, heating systems with a low level of coolant pressure
PN 25	2.5	25.49	Hot water supply and all types of heating systems, including central heating systems( with a coolant temperature of up to 95 ° C)

The scope of application is not indicated from scratch - this is the result of studies in which we studiednot only the ultimate capabilities of the pipes, but also the duration of their trouble-free operation precisely under such extreme conditions.

Temperature( ° C)	Lifetime( years)	tube type
PN 10	PN 16	PN 20	PN 25
permissible excess pressure, kgf / cm2
20	10	13.5	21.7	21.7	33.9
25	13.2	21.1	26.4	33
50	12.9	20.7	25.9	32.3
30	10	11.7	18.8	23.5	9.3
25	11.3	18.1	22.7	28.3
50	11.1	17.7	22.1	27.7
40	10	10.1	16.2	20.3	25.3
25	9.7	15.6	19.5	24.3
50	9.2	14.7	18.4	23
50	8.67	13.9	17.3	23.5	21.7
25	8	12.8	16	20
50	7.3	11.7	14.7	18.3
60	10	7.2	11.5	14.4	18
25	6.1	9.8	12.3	15.3
50	5.5	8.7	10.9	13.7
70	10	5.3	8.5	10.7	13.3
25	4.5	7.3	9.1	11.9
30	4.4	7	8.8	11
50	4.3	6.8	8.5	10.7
80	5	4.3	6.9	8.7	10.8
10	3.9	6.3	7.9	9.8
25	3.7	5.9	7.5	9.2
95	1	3.9	6.7	7.6	8.5
5	2.8	4.4	5.4	6.1

As can be seen, from of the given data, to the use in the systemOnly pipes of the type PN -20( with reservations) are suitable for heating only - PN -25.

Advantages and disadvantages of polypropylene pipes

The use of polypropylene pipes has a number of advantages:

• The ease of the of the material itself predetermines the absence of great difficulties in transporting, delivering pipes to the work site - not the nor the specialized machinery nor the lifting mechanisms.
• Polypropylene is carried by to thermoplastic polymers, and is easy to welding. Installation PP-R pipes , although and requires special equipment, but still very simple. Anyone can learn the necessary skills literally "on the go."And equipment can usually be rented at a reasonable price at the right time. The process itself with cooking is very fast, and the installation of the entire system should not take to take much time.
• The material is completely harmless - it does not change the chemical composition of the of the circulating in the coolant circuit.
• The stabilizers available in the PP-R allow the plastic to perfectly tolerate temperature and compression jumps. Moreover, even freezing of water in the pipe will not end with the rupture of its wall - the necessary elasticity of polypropylene will help.
• Exactly what is needed for the - heating system is the low thermal conductivity of the pipes, especially when compared to metal pipes. This means that the absolutely absolutely unnecessary losses when transferring heat energy from the boiler to heat exchange devices( radiators or convectors) is minimized. So, depending on the of the contours, the savings can be serious - from 10 to 20%.
• Polypropylene perfectly extinguishes all noise or vibration generated from the coolant current through the pipes.
• The material can be safely attributed to the category of the most economical - at the cost of the pipes themselves and all the necessary components, from the fittings to the stop valves. And the assortment of various elements for mounting the most complex structures is very wide.
• With the purchase of quality material and competent assembly work, it will be possible to calculate the service life of the system in tens of years.
• The pipe itself does not require any additional measures for the its decoration - a smooth pleasant color allows you to inscribe the open sections of the piping heating system in almost any interior.

Do these pipes have serious drawbacks? Unfortunately yes :

• The first of them is , and probably even the most important one, which is often completely ignored - polypropylene not becomes barrier from practically free penetration of oxygen molecules from the air into the flowing coolant.

This seems to be an absolutely insignificant minus in the water supply or sewerage systems, but for some types of radiators or boilers this property becomes very serious disadvantage - it causes active corrosion of metal assemblies( steel, cast iron, aluminum).In addition, some systems are very fastidious to the chemical composition of the coolant, and "excess" oxygen plus oxidation products can disrupt it. In addition, oxygen penetration is the impetus for the development of colonies of aerobic bacteria, which are capable of significantly digging the T rub by products of its vital activity, thus violating the parameters of the normal circulation of the coolant.

With this drawback, manufacturers are struggling with by installing special chemical-organic or metal anti-oxygen barriers. As an example of - , a diagram of one type of pipe is reproduced in the figure. This, by the way, will help us in passing to understand the conventional designation m m layered pipes( shown in red ellipse and arrow ).

In the this , the role of the oxygen barrier is performed by an aluminum foil layer, usually welded overlapping the , so that no uncovered areas remain.

On of the outer surface of the pipe - designation: PP-RCT / AL / PPR.This is the layered structure:

1 - inner layer modified random-copolymer polypropylene with increased thermostatic qualities - PP-RCT.

2 - Aluminum interlayer - AL.

3 - the outer layer of their polypropylene PPR.

• The second serious lack of polypropylene pipes - a fairly large linear thermal expansion. It is clear that for heating systems, where they operate with very large temperature amplitudes, this becomes extremely important.

This problem is solved in exactly the same way - by laying an additional layer.

This can be a fiberglass layer( on the diagrams and in legend it has the abbreviation FG or FR).However, this solution is one-sided , as it helps to cope with the thermal expansion, but does not allow to fight with oxygen diffusion. For systems of hot water supply - quite an acceptable option, but for heating - obviously not enough.

And nothing to think up specially and it is not necessary - a high-quality aluminum layer gives the opportunity to solve both problems at once.

To add clarity to this question, cite table, which summarizes data on thermal expansion and oxygen diffusion for different types of single-layer and multilayer pipes.

( Note that the parameters of polyethylene pipes are listed in the table, the features of which will be discussed in the corresponding section of the publication.)

Types of polymer pipes	Accepted designation	Thermal expansion coefficient, 10 ¯⁴ / ° C	Oxygen diffusion indices, mg / m² ² per day
Single-layer pipes
Pipe made of cross-linked polyethylene	PEX	2	650
Pipes made of polypropylene	PPR	1.8	900
Multilayer composite pipes
Pipe made of cross-linked polyethylenewith barrier layer	PEX-EVON-PE	2	0.32
Polypropylene glass fiber reinforced pipes	PPR-FG-PPR	0.35	900
Aluminum-reinforced polypropylene pipes	PPR-Al-PPR	0.26	0
Pipes made of metal and plastic, high temperature resistant polyethylene	PERT-Al-PERT	0.25	0

If someone seems to understand the language of the tabular digits, it can look at the diagram, where the same parameters are more clearly indicated.

The summary on qualities of polypropylene pipes:

• From the point of view of simplicity of installation, durability of use in extreme conditions, in terms of solidity of structure, I have t with fiberglass reinforcement. For example, cases of , so that such a tube is stratified, in history simply not noted. Virtually all pipes of the PN-20 class are manufactured using this technology. It is quite possible to use them in the heating system if the system's efficiency does not imply the of a serious depending on the level of oxygen diffusion.
• Only the PN-25 pipe, which is manufactured exclusively with aluminum reinforcement, will completely eliminate all the disadvantages of polypropylene. This layer is also a reliable oxygen barrier, and repeatedly reduces the linear expansion of the pipe. The aluminum layer reaches their thickness from 0.4 to 0.7 mm, which allows the still and to reliably , if necessary, to keep the given pipe curvilinear configuration.

Video : what polypropylene pipes for which the is designed by

Installation of polypropylene pipes

The mounting technology will be reviewed only so that the reader has a stable opinion that this is a completely operable technological operation, and is afraid of its nothing.

We do not address calculations of installation planning and implementation of either - these problems are considered in the relevant publications of our portal, devoted to heating systems. Here - only the "basics" of welding.

For the installation, it will be necessary to purchase or rent special equipment for a while. Very often it is all assembled in a single case, for maximum convenience. In the photo you can see the complete set of such a kit:

The "suitcase" is equipped with a welding machine( soldering iron), with a power cord, on / off keys, temperature control. One can clearly see the "xiphoid" molded body of the heating element, with three holes in the in this case, which allow to place simultaneously three working heating pairs of different diameters - a coupling and a mandrel. These pairs are clearly visible below, right next to the case. They are fastened with a screw connection - both the screws and hex wrench must be included.

Very well, if the is equipped with special scissors for cutting the right pipe sections.

Roulette is useful for marking, level - for the correct placement of pipes horizontally or vertically during installation, they are neither a "regular" place.

Finally, gloves, which, by the way, many do not use in vain, as getting a skin burn of hands when working with a soldering iron is easy.

If PN-20 or PN-25 pipes with an aluminum reinforcement layer are used, - shader , which before soldering, is required to remove the foil layer to the required depth of penetration. The tool can be manual or in the form of a nozzle for the ( screwdriver ).

The assembly process is carried out by the in the following order( for the example of a single seam):

On the , the heating plate of the welding machine( soldering iron) on the opposite sides is tightly screwed on the heating couplings and mandrels of those diameters, which will be involved in the installation work. For example, having three possible positions, you can prepare pairs for 32, 25 and 20 mm.

The soldering iron stops on the stand and is connected to the electrical network for heating. The desired heating temperature is set on the thermostat. When working with polypropylene pipes, the optimum temperature is about 260 ° With .Sometimes on the temperature regulators are marked with the marks corresponding to the diameters of the welded pipes.

While the welding machine is warming up( 10 - takes 15 minutes for this ), you need to prepare the parts for the connection. A pair of mating elements is always a section of the pipe( even the shortest) and some profile part - from the simplest couplings to cranes, valves, adapters, tees, bends and , .The mating parts of the parts should not have places of strong contamination, sizing - otherwise cleaning and degreasing, for example, with alcoholic wipes should be carried out.

The pipe must be cut strictly perpendicular to the axis - this is easy to do with special scissors. No burrs should remain.

Since we are considering pipes in the context of a heating system, this will most likely be a reinforced version. Hence, two options for preparatory work are possible.

If the pipe type PP-R / AL / PP-R ( in any particular variation), the pipe end to be welded is to be treated with the by the shader. The pipe is inserted into the cutting part of the device. Turning the shader , manually or with the help of a drill, will allow the installed knives to remove the upper layer PP-R and layer of aluminum foil, otherwise the provocation with mutual diffusion and copolymerization of polypropylene will not work.

A properly tuned shader will remove the desired layer to the required depth and length of the - pipe section, there is no special control required.

If you use the pipe with fiberglass reinforcement , the shader is not required. Just from the end of the pipe is made a marker transverse mark of the depth of the penetration. The specific value depends on the diameter of the pipe.

( has another one option - when the pipe has an aluminum reinforcement, but this layer is placed deeply, and does not interfere with welding. A typical example is the DIZAYN OXY-PLUS pipe, when working with which the stripping process becomes unnecessary.this point needs to be clarified immediately).

Below is a table that shows the main parameters for welding with polypropylene pipes.

Pipe Ø( mm)	Warm-up time for welding( mm)	Heating time( s)	Time from joining parts to complete polymerization of the weld( min)
20	14 ÷ 16	6	2
25	15 ÷ 17	7	2
32	16 ÷ 20	8	4
40	18 ÷22	12	4
50	20 ÷ 25	18	4
63	24 ÷ 30	24	6
75	26 ÷ 32	30	6
90	29 ÷ 35	40	8

The soldering iron has already warmed up - this should be signaled by an indicator light, which, like you iron, turns off when the desired temperature is reached. On two sides on a heating pair is put on the mating parts - the pipe section is shoved up to the mark or until the end of the treated shader of the site in the coupling, and the figured part - puts its hole on the mandrel to the stop. It is necessary to try to carry out this operation, if possible , practically at the same time, so that the necessary heating is ensured.

Then, the warm-up time is counted - it is indicated in the table. Immediately after its expiration, both parts are simultaneously removed from the heating elements.

Further, without any pause, the details are combined - the heated section of the pipe is inserted with the necessary force into the hole of the figured element. Depth - to the previously made mark or, in principle, the same - to the full depth of the heated section. When combining, you need to ensure that it passes coaxially, without distortion. Rotating parts around the axis when they are combined is not allowed - to accurately fit better beforehand, before starting warm-up, designate the appropriate risks for the necessary position of their relative location.

The joint parts are held with a small force in this position for about 20 seconds. Then the node should completely cure - the necessary for this time is also indicated in the table.

If for some reason the weld is unsuccessful, the only way to fix it is to cut out the defective or even questionable area in order to weld a new one, with given the error. At the stage of editing, performing such an operation is not at all difficult , but when the system is launched, serious may appear in the repair.

So, welding a polypropylene pipe is not so complicated that it can not be learned in the shortest possible time. It is yet one big plus of this kind of pipe.

Video: lesson for welding( brazing) of polypropylene pipes

Polyethylene pipes

The second extensive group of polymer pipes for heating( quite often constructively intersecting with the first, polypropylene) is a product based on what would seem to be the usual polyethylene.

Immediately make a reservation - it's certainly will not go to those varieties of polyethylene that serve for the manufacture of a wide variety of household products - for all the advantages of this plastic, it is still not sufficiently stable, especially under high-temperature conditions. Nor will conventional polyethylene pipes be considered as "technical", since in heating they also have places .Speech will go about the modified types polyethylene.

Crosslinked polyethylene

If we consider the molecular model of conventional polyethylene, one can not help but notice the pronounced linear structure of the "chains", which are practically not connected by interatomic bonds between themselves. But if you try to create such connections artificially, or, as says, "sew" linear molecules with jumpers, create not flat , but their spatial structure.

This task scientists chemists was solved. Polyethylene, however, did not lose in its positive qualities, and at the same time acquired a whole "bouquet" of remarkable performance characteristics. So, the material turned out to be plastic, elastic, its tensile strength increased. In addition, polyethylene " has acquired memory" - is a unique property of to aspire to return to the once defined shape after deformation from various kinds of loads. Agree that it is for pipe products that this quality - in general is irreplaceable.

The has a higher degree of cross-linking( than has more intermolecular bonds) - the better the material is. The crosslinked polyethylene has the common PEH labeling, but is obtained by various technological techniques.

• One of the highest degrees of cross-linking gives processing of the raw polyethylene feed with peroxide( the number of cross-links reaches 85%).Such material has the marking of REX-a, is probably the most qualitative in its line, but also the most expensive because of the complexities of the technological production process.

Pipes made on the basis of REX, of course, of the appropriate class, are quite suitable for use in heating systems.

• Simpler and cheap Variant NT Impact - the impact of during obtaining the desired polymer by water vapor. The result is polyethylene PEX-b. Unfortunately, this technology did not lead to a qualitative improvement in the product obtained - the less low, no more than 65%, but not even the main .The very synthesis of is not amenable to to fine-tuning, and it is almost impossible to guarantee uniform declared characteristics of the material. Moreover, even in the PEX-b pipes installed in the system it is impossible to completely stop the process of further cross-linking - the it continues constantly, although, of course, very slowly. However, , the pipe changes its physical properties over time, becomes more rigid , gives certain shrinkage. As the result - the connections on the fittings sometimes give a leak and require braces, and multilayer pipes using PEX-b - do not differ in structural stability( they can be laminated).It is characteristic that the European standards do not allow the use of pipes based on PEX-b in systems with high temperatures and liquid pressures, including those in heating systems.

. It is possible to use PEX-b in heating only in a single-layer version, in the system of warm floors, where the heating does not exceed 45 degrees, andthe contour is unbroken, without any joints, that is, it starts and ends directly on the collector - here it will be possible to audit the of the fittings and conduct them regularly as necessary .

• Crosslinked polyethylene PEX-with is produced by by processing the processed feedstock by a directed electron flow. The method is quite inexpensive, productive, allowing to obtain a material of acceptable quality, although inferior to more perfect analogues. Pipes PEX-with may well be used in plumbing systems, but for heating their resource, apparently, will be not enough.

There are some other specific technologies of cross-linking, but they have not received a special distribution.

Polyethylene of increased heat resistance RE- RT

Production of cross-linked polyethylene PEH studies for its modification are not limited. Literally revolutionary innovation was technology that allows to control the spatial construction of polymer molecules, and enabling to immediately put into the created material the necessary operational qualities.

One of the products of this technology is polyethylene PE-RT ( abbreviation for the long English name for polyethylene with increased heat resistance).

The particular structure of the molecular with very frequent branched bonds gives the a number of additional useful qualities to the .Pipes based on PE-RT are excellent for heating systems - as if they were designed for them:

• Durability of pipes - about 40 - 50 years.
• The material, in contrast to the PEH, has pronounced thermoplastic properties, that is, it can be welded. And this dramatically improves the performance and safety of heating systems.
• The material is not afraid of even prolonged frosts, and after the thawing of pipes it retains its qualities to the full.
• Repairability of systems with PE-RT pipes - is much higher than with any other .

Most likely, over time, PE-RT pipes will crowd out, and even completely replace the REX.If you take a comparison of almost identical in the structural structure of multilayer pipes, the gain is clearly in favor of RE-RT :

Pipe operating indicator	PEX-AL-PEX	PERT-AL-PERT
Rated operating temperature, ° C	95,0	95,0
Maximum permissible peak temperature, ° C	110,0	124.7
Elasticity of the pipe walls, MPa	1100	660
Connection method	Exceptionally mechanical - threaded or compression fittings	Mechanical fittings and thermoplastic welded fittingsConnections

Types pipes based on polyethylene pipes

without metallic reinforcing

Briefly of them have already been mentioned. This is the case with both the REX and PE-RT - a good variation of the nt for the and laying the contours of the warm floor. The elasticity of such pipes is high, so it is possible to position the loop of the contour fairly close. Pipes are easy to lay, and their large length in the bays allows you to lay out the contour of any permissible of the length of the without any joints.

And again, you can note the obvious gain on the performance of polyethylene PE-RT .The table below shows the main parameters of such pipes using the example of the two most common diameters, 16 and 20 mm.

Technical and performance indicators	PERT 16 × 2 mm	PERT 20 × 2 mm
Pipe volume( liters / meter)	0.113	0.201
Weight( kg / meter)	0,07	0.127
Minimum bending radius-	60	100
Temperature( ° C)	20	20
Operating pressure( bar)	20	20
Service life( years)	over 50	over 50
Temperature( ° C)	75	75
Operating pressure( bar)	10	10
Service life( years)	over 50 years	over 50
Temperature( ° C)	95	95
Operating pressure( bar)	6	6
Service life( years)	over 50	over 50
Limit(bar)	6	4.5
at temperature( ° C)	110	110
Limiting pressure( bar)	11	10
at temperature( ° C)	90	90
Elongation coefficient max at t = 95 ° C( 1 / ° C), PE-RT pipe	1.8	8.2 E-5
Thermal conductivity coefficient( W / K m)	0.41
Internal surface roughness( μm)	0,125( Class 10)
Estimated material strength( MPa)	6.3

The pipe can be completely uniform throughoutits thickness. However, as we remember, this is not very good for heating systems in terms of free oxygen diffusion. To eliminate this drawback, a special technology is applied - the placement of a special oxygen barrier EVON .This name is also the abbreviation , which refers to the chemical composition of the interlayer: Ethylene-vinyl alcohol is a special copolymer based on ethylene-vinyl alcohol.

The EVON layer is successfully used both in pipes made of cross-linked polyethylene PEH and in the case of PE-RT .

Metal-plastic pipes based on polyethylene

What is commonly called "metal-plastics" in most cases is a multilayer pipe, in which some types of cross-linked or heat-resistant polyethylene with an aluminum layer between them are used. The variants here may be different: REX -AL- REX , RE-RT - AL- RE-RT , RE-RT -AL- REX , or even with using outdoorpolypropylene layer - RE-RT - AL - PPR.

As we recall, the aluminum layer, as in the case with polypropylene, dramatically improves the mechanical characteristics of the pipe, reduces its linear expansion when heated, becoming an insurmountable obstacle to oxygen diffusion.

With plastic pipes, when you purchase them, you need special care. Even with the best quality material, it is impossible to fully guarantee the absence of stratification between the polymer and aluminum - all even in a significant difference in the indicative heat conductivity and temperature expansion. In inexpensive pipes of low quality( and such, alas, in spontaneous markets are extremely many), the bundle, on the contrary, is guaranteed with a probability close to 100%.And the is the direct path of the to the of a serious accident with very unpleasant consequences, so the over is in the heating system, and the worst thing is if the pipe breaks and circuit warm floor under the concrete screed.

Therefore, , no "pennies" - for the heating system should be purchased exclusively high-quality pipes from well-known manufacturers whose originality the seller must confirm with the appropriate certificate.

Installation of pipes on the basis of polyethylene

Installation of pipes on a polyethylene basis can be carried out in several ways, depending on the acquisition of a particular product by one or another connecting fittings. So, the main methods are the connection with compression fittings , pressing fittings or special welded fittings .

Some well-known companies produce kits for mounting junctions, which only fit to the pipes of its own production. They may have specific installation features that are slightly different from others. Nevertheless , basic principles of still remain unified.

1. At home, without the use of a special tool, it is most convenient to mount metal-plastic pipes for compression threaded fittings.

Assembly process is simple:

• The pipe is cut using special scissors, strictly perpendicular to the axis. Should be a smooth, accurate edge.
• The fitting is disassembled. On the cut pipe section, the crimp nut( threaded to the joint side) is put on, and then the brass ring is cut.
• The inner surface of the pipe at the junction with the fitting is preferably a bit to floss the outwards, for example, with the calibrator .

• Then the finished end of the pipe is completely, until it stops, worn on the fitting of the fitting. Note that the rubber gasket must remain in its groove.

• The cutting ring advances to its place - close to the fitting and then the crimp nut is screwed on. Only spanners are required. Do not overtighten the nut too much. Then, after the in the system is applied to the crimping , the test pressure is applied, it is possible, if necessary, to carry out a tightening.

Installation of all other connections is done in the same way.

Video: installation of metal-plastic pipes for threaded compression fittings

2. Installation of pressing fittings is somewhat more complicated, and besides it already requires a specialized tool.

This technology can be used with both plastic and plastic pipes. Here, the most remarkable property of cross-linked polyethylene is used, in accordance with which the seeks to return to the form previously assigned to it( the molecular "memory" of the material).

Fittings can be used in various types - brass, steel or even polymeric - made of high-strength plastic.

materials. The operating procedure is approximately as follows:

• compression fitting. The fitting sleeve is pre-dressed on the connecting pipe.
• A treated cut pipe end is inserted special expander. With its help, the body of the pipe expands so that it can be freely dressed on the fitting branch pipe. Almost immediately, the "memory" of polyethylene is switched on, and it begins to return to its original position. This process ss all is then activated when the temperature rises.
• After the pipe is put on the on the fitting, a sleeve is pressed into the fitting. This requires a large and directed effort, so you can not do without a special tool - pressurizer .Manual or with any drive.
• Once the sleeve has been put in place, the process with the bork node is complete.

This process is very well illustrated in the video.

Video: installation of polyethylene pipes with pressing fitting

Variants, by the way, can be slightly different - for example, a fixed crimp sleeve has already been installed on the fitting. After installing the pipe, both are crimped from the outside with a special tool.

Video: Several mounting options for metal-plastic pipes

AND, finally , it is possible to mention a welded joint using a special welding machine for PE-RT pipes. The technology for obtaining welded joints differs little from that used for PP-R -, other heating and polymerization parameters are simply used. True, such a method of connection is not amenable to all kinds of PE-RT pipes - it is necessary to clarify at once - when buying them.

And at the end of the publication it will be appropriate to place a visual summary diagram that will help to answer the question - which pipes should we give preference in this or that case: