Sealing of threaded connections of heating systems

New technologies for designing heating systems for low-rise private houses use several options for connecting all elements into one system. But no matter how advanced the technology, it is still impossible to bypass assembly using threaded connections in construction.

Crane groups, connections to heating registers and distribution units, all these points are connected using threaded connections. And if welding or soldering pipes allows you to create a reliable connection without the use of sealants, then if there is a thread, you cannot do without a sealant. And which seal to choose for installation is not as easy a question as it seems at first glance.

Why is additional sealing of threaded connections necessary?

So, before moving on to choosing the optimal option for sealing threaded connections, it is worth carefully studying all the options where this installation method can be used. In the heating system of an apartment or house with a gas double-circuit heating boiler, the threaded connection units will be used:

On cold water supply taps from the water supply system;
On the gas supply valves to the boiler there is a gas valve from the gas pipeline, a gas filter and the inlet itself into the boiler;
On the hot water supply pipe to consumers;
On the supply line of hot coolant to the heating system;
On the pipe for the return supply of cooled coolant to the boiler;
At connection points for heating devices - at the inlet and outlet of the radiator;
On the heated towel rail (if there is one);
There is a heated floor at the line distribution node in the system.

This number of points where a threaded connection is used is far from complete, since it describes only the minimum version of the heating system for an ordinary apartment. But even in it, each node has its own characteristics. So, for gas equipment, and a gas heating boiler refers specifically to this type of equipment, the connection of the gas pipeline must be done in strict compliance with the rules. Here it is necessary to make a reliable seal to prevent the leakage of natural gas.

At the connection point for the direct and reverse coolant supply, it is necessary to make a seal, taking into account the fact that when the coolant heats up and cools down, the metal parts will expand and contract. This means that the hermetic seal must withstand not only the maximum expansion of parts, but also ensure integrity during uneven expansion or contraction of the connection when the temperature drops.

The joints of heating radiators will also experience such mechanical stress, because when hot coolant is supplied, the metal, especially in cast iron batteries, expands more slowly than in shut-off valves made of brass or aluminum alloy.

And of course, in addition to the temperature factor, the seal must also take into account the chemical factor, because with repeated heating and cooling, the chemical composition of the water changes. Not to mention that in some systems, instead of the usual prepared water, antifreeze is poured or chemicals are added to prevent the water from freezing in the event of a breakdown.

Now that you can see how many problems can arise when operating a heating system with a minimum number of threaded connections, the importance of installing seals during installation becomes obvious.

How to quickly fix a leak

Here are some methods for emergency pipeline repair. Each of them can eliminate the leak even if it is not possible to close the water supply to the system. This will allow you to save your home from flooding before specialists arrive.

If the water leak is caused by depressurization of the threaded connection of the pipeline with the distribution or shut-off valves, you can try to tighten it. There is no need to apply excessive force to avoid stripping the threads. If there is no positive effect, as soon as possible, reassemble this unit and replace the seals (tow, gaskets, FUM tape).

A leak in a straight section of pipe can be quickly eliminated using special metal clamps with a rubber seal. If there is no factory bandage at hand, then a homemade one is made. To make it, you can take, for example, an old bicycle tube or a boot top. A rectangle of suitable dimensions is cut out of rubber, which is tightly wrapped around the pipe and tightened with clamps or wire. It is important that at least one tie is located directly at the site of damage.

In addition to soft rubber, you can use mounting tape to make a bandage.

Despite its simplicity, repairing a leaking pipe cannot be carried out using this method if the water supply is located close to the wall.

It is quite possible to make reliable clamps of the required size yourself from a strip of sheet metal of suitable width by drilling holes for installing tie bolts along its edges.

You can also significantly slow down the flooding of your home until the water supply in the riser is cut off using wooden wedges. If the hole in the pipeline is small, just drive a regular toothpick into it. Such a wedge swells with water and is able to withstand pressure for some time until repair services arrive.

If the heating system pipes are slightly damaged, to temporarily stop the leak, try wiping the crack with a handful of salt. In the event of a significant pipeline leak, it will be more difficult. To urgently eliminate it, you can try to apply several turns of a bandage to the defective area, periodically sprinkling it with salt. In this way, it will only be possible to temporarily stop the leakage of water as long as it remains hot.

Types and characteristics of threaded connections in the heating system

Today, when installing almost all heating systems, both new types of connecting elements and traditional options, where threads are cut on steel pipes, are used. Each type of carving has both positive aspects and disadvantages.

To choose the right seal, it is worth considering all the elements in more detail.

Cast iron radiators

For connection, both modern options are used in the form of fittings with American females, and traditional ones in the form of pipe bends on couplings with locknuts. The thread in the cast iron body of the radiator nut has chips and irregularities, and can also be cut at an angle, which complicates the selection of threads on the fitting. In this unit it is necessary to use a sealant that will ensure reliable filling of all voids along all thread turns.

Drives and couplings

Threaded connections of pipes and couplings also have their disadvantages. During work, the thread is cut with a margin of 3-4 turns, while the pipe profile itself may have significant deviations. Simply put, it may not be round, which is why the threads are of different depths and profiles - from triangular with an acute angle to trapezoidal. A nut and coupling made of cast iron may also have thread defects in the form of chips, broken threads, different heights and depths of threads. Such a connection requires that the seal not only fill all the cavities, but also be elastic - when screwing a cast iron coupling onto a rigid seal, it can simply burst.

Fittings with American women

Fittings with American females produced by well-known manufacturers of shut-off and connecting valves have standard threads made in accordance with high quality standards. At the same time, this threaded connection also requires sealing since the thread most often has great depth and clear edges.

Eliminating leaks at the junction of a cast iron pipe

If a sewer pipe made of cast iron is leaking at the junction, you can fix the problem using:

cement mortar;
lead cones.

In both cases, the work procedure is the same and consists of the following steps:

All unusable residues (residues of cement screed or lead) are removed from the joint;
the junction of cast iron pipes is cleaned of dirt and corrosive deposits, and then dried with rags;
if lead is used to seal the joint, then new cones are placed in the resulting hole and then covered with cement mortar prepared in a ratio of 1:10 (10 parts of cement are needed for one part of water);
procedure for sealing a joint without lead:
the bandage is dipped in the solution and placed in the hole between the pipes;
The final filling of the connection is made.

Sealing the joint of a cast iron pipe

It takes approximately one day for the cement to dry completely.

Materials for sealing threaded connections

Today there are no highly specialized materials for sealing one or another type of threaded connection. The materials on the market are applicable to almost all installation points and materials, however, provided that the work is carried out by an experienced specialist. Therefore, it is important to know and understand all the strengths and weaknesses of sealing materials.

End gaskets

Installing a sealing end gasket between parts in modern heating systems has very limited use. At the same time, this option can well be used for end-tightened connections. For installation, paronite, fluoroplastic or rubber gaskets are used. The positive side of this method is the ease of installation and reliability of the connection. The clamped gasket between the two planes ensures both tightness and reliability of the connection. The disadvantage of this method is that when clamped, the gasket is deformed, and quite often it simply narrows the internal lumen. Such a narrowing negatively affects the fluid flow rate, which ultimately leads to a loss of temperature in the coolant and slow heating of heating devices.

Another disadvantage is the need to carefully prepare the joint surfaces so that during installation there is no misalignment of the gasket. For those who do not have experience installing such gaskets, it is recommended to have 1-2 gaskets in stock, since if installed incorrectly after disassembly, the gasket is not reused, but replaced with a new one. Another tip is that it is recommended to apply sealant to the gasket before installation to ensure that all voids are filled as tightly as possible.

It is recommended to purchase gaskets for installation for heating systems, although almost all gaskets made of rubber, paronite and fluoroplastic can withstand temperatures of +100-120 degrees, not all react equally to contact with water and antifreeze.

FUM tape

PTFE tape is actively used for installation of water intake fittings for hot and cold water supply systems. It is also used for heating systems. Compared to other types of materials, it is easy to use, perfectly seals the connection and does not lose its properties during operation. The latter is very important when carrying out repair work - such connections can be easily dismantled even after many years of active use.

FUM tape is available in several sizes, which allows you to choose the right option for the job. A positive point is that it does not react with water and antifreeze. It also easily withstands high temperatures and repeated heating-cooling cycles.

However, when working with it you need to consider:

When sealing connections with very tight threads, it will tear and be squeezed out when screwing on the thread;
If the connection is not tight, leaks are possible, since the tape is not able to adhere to the metal and expand in volume upon contact with water;
When used, it is most effective on connections up to 25 mm, so when screwing a plug or nut into a cast iron battery, it is worth using another material for sealing.

Sealing thread

This is a relatively new material for filling cavities between joint parts. The thread is made of Teflon or fluoroplastic. Therefore, it has approximately the same properties as tape. But, given that it has a different cross-section and fills the cavity between the turns more tightly, its use for sealing becomes more attractive.

In addition, there are samples of plumbing thread that consist of several fibers; these types are recommended for use with liquid sealants.

Hemp or linen span

A material of plant origin traditionally used in sealing threaded connections. To seal threaded connections, it is used in conjunction with liquid or gel sealant.

Flax is used for installation in connections of large and small diameters. When used correctly, linen can last quite a long time. The truth has significant drawbacks:

Not everyone can wind a flax span correctly and not the first time; the work requires experience and dexterity;
As a material of plant origin, it has a limited service life;
Reacts to changes in temperature and humidity, reacts to chemically active substances;
During repairs, great effort is required to separate the joint, which was sealed with flax span.

Chemical sealants

The basis for the production of this group of materials is silicone. Among the advantages of silicone is its stability at high temperatures and neutral reaction with most chemically active substances.

During installation, silicone sealants provide lubrication of rubbing surfaces, making it easier to twist threads. After installation, the substance fills all cavities and ensures reliable connection.

There are drying and non-drying sealants. When sealants dry, after a certain time they become viscous or turn into a solid state. This group distinguishes between sealants that dry when exposed to air - the anaerobic type and substances that change their state upon contact with water.

The disadvantage of this group of sealants is that when they dry, they shrink, which means that over time, the coolant may start dripping in this place.

Non-hardening sealants remain liquid or gel-like for a long time, so such materials are easy to apply and, even after prolonged use, the joints are easy to dismantle. On the other hand, during installation and operation, there is a high probability that such sealant may be squeezed out of the thread.

Causes of fistulas

The reasons for the formation of fistulas on a water pipe most often come down to one denominator. This is the effect of corrosion.

The most suitable temperature indicator for corrosive formations is +15 degrees. Most often, pipe rolling materials are in this mode in the spring, summer and autumn periods.

Water located in the system also accelerates corrosive destruction. Over time, rust builds up inside metal pipelines.

The metal in such products becomes thinner every year. And then the moment comes when corrosion breaks through the wall completely. The result is a leak.

This problem must be eliminated immediately, without waiting until it turns into a big nuisance. If the leak is small, then it can be sealed under pressure without turning off the water supply.

The most common problems that result in a leaking heating pipe include:

long operating time and severe corrosion;
poor quality installation work, poor joints;
loads of different types on the components of the heating system.

Since water is constantly under pressure in the pipe, and air temperature changes act on it from the outside, condensation can form, which leads to oxidation of the metal and accelerates corrosion processes.

Leaks can form not only in a metal pipeline, but also in a plastic one. Naturally, the problem most often arises as a result of mechanical damage or improper installation, since this material does not corrode.

Rules for the use of materials when installing threaded connections

Linen is one of the most affordable and time-tested materials for sealing. It is best used to seal metal and cast iron joints. It is excellent for working on cast iron radiators, steel pipes and cast iron couplings. But to seal connections made of plastic and thin-walled elements, you should not use flax; with a slight increase in the effort when tightening, the thin metal or plastic will simply tear.

To work with tow, in addition to the flax itself, you also need to have a sealing material - packaging paste, synthetic sealant, oil paint or vegetable oil. It is not worth using synthetic alkyd or nitro enamel instead of oil paint; this will not help make the work easier and increase the bond, but during inspection it will make the work much more difficult.

A fresh bunch of flax tow is selected for work. The material must be well dried and have a natural color and smell. Brittle fibers or the smell of rotten hay indicate that the material is unsuitable for work - in just a few weeks this compound will have to be repacked.

The algorithm for working with flax tow is as follows:

Before work, the parts to be connected are twisted “dry” without a seal to determine the number of turns in the twist;
Notches are made on the external thread, this applies primarily to steel parts. This is not recommended for nuts made of cast iron - it is too fragile for such work;
A strand is selected from the bundle of such a size that when twisted into a thread, it fills 2/3 of the height of the thread;
The strand is combed out and smoothed; there should be no thickened areas or split ends;
The twist is divided into 2 parts - the smaller one should be 3-4 times the length of the thread circumference;
Stepping back from the edge of the thread 1.5-2 turns, flax is applied to the thread at the point of division into segments. The smaller segment is placed perpendicular to the thread and pressed with the thumb;
The larger segment is screwed onto the thread with tension, so that after making a full turn, it completely presses the smaller segment onto the thread;
After the second turn, both segments are wound with one bundle to the end of the thread;
At the end of the thread, without changing the direction of winding, a thickening is made - a bead and then winding is made to the beginning of the thread;
After the entire bunch of flax has been wound onto the thread in the direction of movement, the winding is smoothed;
At the final stage, plumbing paste or silicone sealant is applied to the surface.

When winding flax, an indent of one and a half to two turns of thread must be made to facilitate screwing the thread. In modern fittings, the threads initially have notches, so it makes no sense to make additional notches.

As for sealing paste or silicone, for a tight connection it is enough to impregnate the top layer of hemp, although if you impregnate the entire winding or pre-treat the external thread there will be no mistake.

How to work with FUM tape

Working with FUM tape is much easier and simpler than with other materials. True, unlike other materials, this must be done carefully and competently.

First of all, you need to pay attention to which connections are to be sealed. The larger the thread diameter, the thicker the tape needs to be selected. The second point is that the width of the tape should be no less than half the length of the thread. It is inconvenient to work with a tape that is too narrow, and you will have to wind it much more.

After selecting the tape, the operating algorithm is as follows:

Both parts are twisted without a seal, and the number of thread turns is determined;
Afterwards, the thread is inspected - if for a hemp seal it is important to make notches on the external thread, then for FUM tape this is not necessary, the tape fits perfectly on the metal without additional notches.
The next step is to inspect the internal thread - its edge should have a chamfer, so that when screwed on, it does not tear the tape but bends under itself;
Stepping back 1-2 turns of thread from the edge, apply the tape and press it with your thumb;
The seal is wound in the direction of the thread - for right-handed in the direction of movement clockwise, for left-handed counterclockwise;
The tape is wound with little effort and tension, so that when the first turn of the tape passes, all the contours of the thread are visible, but the tape does not break through;
After winding 3-4 turns, the winding is done further in the direction of the thread;
2-3 turns before the end of the thread, a thickening is made - a bead made of an additional 3-4 turns of tape.

After winding is completed, the edge is simply smoothed in the direction of movement. The tightening is done manually until significant resistance begins, then it is pressed using keys.

Sealing thread for sealing threaded connections

This type of sealing material became known relatively recently. It is based on polyamide or fluoroplastic fibers. It can be a monolithic thread or a thread consisting of several fibers. The cross section of the thread is most often round or oval. The advantage of thread is that, unlike tape, it is stronger and cannot be torn by hand. It is more elastic and better suited for filling external threads than tape, here you can see how much the thread has filled it. In addition, elasticity makes it possible to more reliably seal cavities in the thread, since after compression it tends to return to its original shape.

To work with small-diameter connections, it is recommended to use a thread of a smaller diameter; for large diameters, it is recommended to use a thread of a larger diameter.

When working, it is recommended to adhere to the following algorithm:

Check how the internal and external threads fit together;
Check how the chamfer is removed on the internal thread, if necessary, make it;
Having retreated 1-2 turns from the beginning of the thread, press the thread to the thread, leaving the tip 2-3 cm free;
Start winding the thread along the thread with a slight tension so that it is evenly distributed over the depressions;
Through the turn, press the remaining tip to the thread;
Continue winding to the edge of the thread;
Having reached the edge, make a bead and, without changing the direction, continue winding to the beginning of the thread.

Considering that plumbing thread like FUM tape is made from synthetic materials, it does not need to be coated with silicone sealant or plumbing paste.

Plumbing glue sealant

Today, plumbing adhesive sealant is one of the newest and most promising means of sealing threaded connections. This is a rather specific type of seal and must be used carefully, given its price.

There are several types of plumbing adhesives on the market today - one-component, ready-to-use products. Two-component formulations that must be prepared before use by mixing in a certain proportion. And third, adhesives that are applied to metal heated to 100-120 degrees.

This type of sealant has wider application prospects than flax with FUM tape. Using glue, you can seal and fix not only metal joints, but also metal and plastic, which is very important when installing a heating system.

However, like any other promising technology, the use of glue also has certain disadvantages. First of all, most compounds glue degreased metal joints. This is a significant disadvantage of the technology, since most radiators, metal steel pipes and couplings have greasy stains on their surface. The fact is that to protect the metal surface from corrosion, lubricants and compositions that contain machine oil or grease are used. During turning, when a thread is cut into a piece of pipe, a greasy lubricant is applied, and after machining, the couplings and locknuts are simply dipped into machine oil for cooling.

The second downside is using heat to get a reliable connection. And although not all compounds require this operation, it significantly limits the use of glue for sealing threads.

Well, the last drawback of plumbing glue is that after applying it to the surface and joining the parts, it takes time for the glue to simply dry. And this significantly increases the installation time of the system.

But, despite the disadvantages, adhesive technology is increasingly making its way into the market, improving every year. Today, the general scheme for working with glue is as follows:

After checking the threaded connection “dry”, the parts are unscrewed;
Both halves of the thread are treated with a degreasing spray or denatured alcohol;
The tube with glue is opened, and the glue is carefully applied evenly along the entire length of the external thread;
When applying glue, do this as carefully as possible to prevent drips;
Next, the parts are connected and finally clamped with a key;
To allow the glue to harden, the parts are set aside for the time specified in the instructions for the glue.

Anaerobic sealant

This type of sealing material, like glue, belongs to a new generation of synthetic materials. Like adhesives, they are offered ready-made in small packaging. This must be taken into account when planning purchases, since one tube is usually enough for 2-3 compounds.

There are two ways to use anaerobic sealant - the first involves its independent use without additional funds. The second option involves the use of anaerobic sealant as an additional means for impregnation or strengthening of the connection. In the first case, the sealant fills the voids in the thread with the outer and inner parts tightly fitting. The second is used when installing connections that have a sufficiently large gap between the parts.

The effect of this sealant is limited by the time of its contact with air. Most often, literally 5-7 minutes after application, the process of active polymerization of the gel begins, and it first begins to form a film, and then the process moves to the inner layers.

The process is usually completed 15 minutes after contact with air. This time is enough to not only apply, but also fix both parts.

The disadvantage of this technology is the need to work with clean, fat-free material. In addition, if a mistake is made and the connection is made incorrectly, after disassembly, considerable effort will be required to clean the threaded areas from glue residues.

Options for repairing holes in a plastic pipeline

When carrying out repairs, it is not always possible to use high-temperature connection technology and therefore it is necessary to use other methods:

Using a clamp clamp. A temporary measure to solve the problem of how to eliminate a leak in a polypropylene pipe is the use of clamps (for more details: “Types of repair clamps for pipes and rules for their use”). The part with screw clamps is supplemented with a layer of plastic waterproof material, thanks to which it is possible to almost completely eliminate leakage. This method does not interfere with the liquid moving through the system, so there is no need to turn off the water supply. But it also has a drawback - over time, the fastening points of the clamp weaken and the connection loses its tightness.
Cold welding technology. Before repairing a leak in a plastic pipe, you should prepare the required amount of the component for the work: knead it in your hands or mix it in a certain proportion. Then the composition is applied to the damaged area, the crack in the pipeline is sealed and the required time is waited until the mixture completely hardens.
Application of adhesive bandage. Using a pair of clamping clamps together with a material that is impregnated with glue will help you quickly deal with a leak with your own hands. This can be a two-component composition plus rubber for polypropylene pipe products or a bandage plus cement for sewer pipes. The advantage of this method is that there is no need to shut off the water flow. But for systems operating under high pressure, the use of such a bandage is not allowed.
Sealing tape overlay. The method allows for quick repairs if it is not possible to seal a small leak with sealant. Several layers of adhesive tape are wrapped around the damaged area.
Using a special sealant. It will be possible to eliminate a leak if a plastic pipe bursts quickly. But this solution is temporary.

There are three types of sealant on sale:

In cases where the water supply or heat supply system is partially laid using a hidden installation method, before proceeding with the repair of the plastic pipeline, you should find out exactly where the damage to the line occurred. To do this, unfortunately, you will have to either dismantle the decorative trim or open the wall covering.

Which seal is best to choose for installing a heating system?

Today, the main criteria for choosing the best technology for sealing threads in heating system connections are experience and materials to work with.

So, when working with cast iron radiators and shut-off valves, the best option for them is to use flax strands with plumbing paste or silicone heat-resistant sealant.

For small diameter connections up to 25 mm from branded fittings, it is recommended to use FUM tape or adhesive sealant.

To install taps or connect steel, aluminum or bimetallic radiators, you can use the entire arsenal of methods for sealing connections.
The only point that you need to pay attention to is that when installing copper pipelines, you must carefully study the instructions for the sealant in order to exclude incompatibility between the composition of the adhesive and the non-ferrous metal.

First actions

What to do if a hot water pipe, a cold water pipe or a heating system that is under pressure is leaking? First of all you need to:

turn off the liquid supply to the pipes if the leak is located after installing an individual shut-off valve, or find any rag, wrap it around the leak site, leaving one end long enough, and place the long end in any collection container (basin, bucket, tank, etc. ). This will help avoid flooding of premises;

If the leak is small, then you can limit yourself to installing a collection tank.

Collecting water to avoid flooding

report the accident to the management company or emergency service. Telephone numbers of all service organizations, as a rule, are indicated on receipts for payment of utility services.

Why is tightness needed?

Brick stoves and fireplaces are prone to cracking due to uneven heating of the masonry, especially if it is not protected by a layer of plaster or tiles. If the cracks in the body of the heating unit turn out to be through, this entails unpleasant consequences

fuel is consumed faster because it burns under conditions of additional oxygen;
soot may enter the room and settle on the walls and ceiling;
combustion products enter the room, primarily carbon dioxide, which can cause poisoning.

Cracks in a brick chimney, cracks in a metal pipe for removing combustion products reduce draft, and the heating unit cannot operate in optimal mode. This causes the fuel to burn at lower temperatures, producing a lot of ash and more soot deposited on the inside of the chimney.

A large amount of soot and a leaky chimney is a dangerous combination. The intake of air causes the soot to ignite, and it burns at temperatures above 1500°C, causing the chimney to heat up. An insufficiently thick layer of thermal insulation around the pipe will not save wooden structures from charring; there is a serious risk of fire.

For gas boilers, a leak in the chimney results in gusts of wind extinguishing the burner.
To avoid the need to regularly check the operation of the boiler, the gaps in the chimney duct are sealed with a special sealant. Date: September 25, 2021