IN apartment buildings Residents mainly use the services of the central heating network for space heating. The quality of these services is influenced by many factors: the age of the house, wear and tear of equipment, the condition of the heating main, etc. In the heating system, a special scheme is also essential, according to which the connection to the heating network is carried out.

Connection types

Connection schemes can be of two types: dependent and independent. Connecting by dependent method is the simplest and most common option. An independent heating system has gained its popularity recently, and is widely used in the construction of new residential areas. What solution is more effective for providing warmth, comfort and coziness to any room?

dependent

Such a connection scheme, as a rule, provides for the presence of in-house heating points, often equipped with elevators. IN mixing unit At the heat station, superheated water from the main external network is mixed with the return one, while acquiring a sufficient temperature (about 100 ° C). Thus, the internal heating system of the house is completely dependent on external heat supply.

Advantages

The main feature of such a scheme is that it provides for the flow of water into the heating and water supply systems directly from the heating main, while the price pays off rather quickly.

Flaws

Along with the advantages, this connection also has some disadvantages:

• inefficiency;
• adjustment temperature regime significantly difficult during weather changes;
• overexpenditure of energy resources.

Connection methods

The connection can be made in several ways:

Independent

The heat supply system of an independent type allows you to save consumed resources by 10-40%.

Operating principle

The connection of the heating system of consumers occurs with the help of an additional heat exchanger. Thus, heating is carried out by two hydraulic isolated circuits. The circuit of the external heating main heats the water of the closed internal heating network. In this case, mixing of water, as in the dependent variant, does not occur.

However, such a connection requires considerable costs for both maintenance and repair work.

water circulation

The movement of the coolant is carried out in the heating mechanism thanks to the circulation pumps, due to which there is a regular supply of water through the heating devices. An independent connection scheme may have an expansion vessel containing a supply of water in case of leaks.

Components of an independent system.

Scope of application

Widely used to connect to the heating system of multi-storey buildings or buildings that require advanced level reliability of the heating mechanism.

For objects that have premises available, where access by unauthorized service personnel is undesirable. Provided that the pressure in the reverse heating systems or heating networks is above the permissible level - more than 0.6 MPa.

Advantages

Negative points

• high price;
• complexity of maintenance and repair.

Comparison of two types

The quality of heat supply according to a dependent scheme is significantly affected by the operation of the central heat source. This is a simple, cheap, low maintenance and repair cost method. However, the advantages of a modern independent connection scheme, despite the financial costs and complexity of operation, are obvious.

The main methods are flanged, coupling, trunnion, welded (one-piece). Flanged fittings are more often used, the advantages of which are obvious: the possibility of multiple installation and dismantling on the pipeline, the reliability of sealing joints and the possibility of tightening them, greater strength and suitability for a wide range of pressures and passages. The disadvantages include the possibility of loosening and loss of tightness, the relative complexity of assembly and disassembly, big sizes and mass.

For small cast fittings with nominal bores up to 50 mm (especially cast iron), coupling joints are often used, the main scope of which is low and medium pressure fittings. For small high-pressure fittings made of forgings or rolled products, a trunnion connection with an external thread for a union nut is used.

Valve types

Welded joints provide absolute long-term tightness of the joint, reducing total weight fittings and pipelines. The disadvantage of welded joints is the difficulty of dismantling and replacing fittings. Common types of valves.

Depending on the nature of the movement of the locking elements, the valves are divided into the following types:

gate valves;

valves;

Locks are rotary.

Gate valves are locking devices that block the passage by moving the gate in a direction perpendicular to the flow of the transported medium.

Compared to other types of valves, gate valves have the following advantages:

Insignificant hydraulic resistance with a fully open passage;

The absence of flow turns;

Possibility of application for overlapping;

Flows of medium of high viscosity;

Ease of maintenance;

The possibility of supplying the medium in any direction.

The disadvantages common to all valve designs include:

Inability to use for media with crystalline inclusions;

Small allowable pressure drop across the gate (compared to valves);

Slow shutter speed;

The possibility of obtaining a hydraulic shock at the end of the stroke;

Great height;

Difficulties in repairing worn sealing surfaces during operation;

The impossibility of applying permanent lubrication of the sealing surfaces of the seat and valves.

When closing valves, the shut-off element does not encounter any noticeable resistance from the medium, since it moves perpendicular to the flow, that is, only friction must be overcome. The area of ​​the sealing surfaces of the gate valves is small, and due to this, the gate valves provide reliable tightness.

A variety of designs of gate valves can be generally divided into two types: wedge and parallel. In turn, wedge gate valves are divided into gate valves with solid, elastic and composite wedges, and parallel - into single-disk (gate) and double-disk. In gate valves designed to operate at high pressure drops across the gate, in order to reduce the opening / closing forces, the total passage area is made smaller than the cross-sectional area of ​​the inlet pipes (narrowed passage).

Depending on the design of the "screw-nut" systems, gate valves with rising and non-rising stems are distinguished. The latter should have indicators of the degree of opening.

The gate of wedge gate valves has the form of a flat wedge, and the seats or sealing surfaces parallel to the sealing surfaces of the gate are located at an angle to the direction of movement of the gate. This design ensures the tightness of the passage in the closed position and the insignificance of the sealing force.

In parallel valves, the sealing surfaces are parallel to each other and are located perpendicular to the direction of flow of the working medium. The advantages of gate valves of this design are the ease of manufacture of the gate (disk or gate), ease of assembly and repair, and the absence of jamming of the gate in the closed position. However, parallel gate valves require significant closing/opening forces and are characterized by severe wear of the sealing surfaces. Most valves can be installed in horizontal and vertical gas pipelines in any position other than spindle down. The position of valves with pneumatic and electric actuators is regulated specifically. Cranes are shut-off devices in which the movable part of the shutter (plug) has the shape of a body of revolution with a hole to pass the flow and, when the flow is blocked, rotates around its axis.

Depending on the shape of the sealing surfaces of the valve, valves are divided into three types: conical, cylindrical (not used for gas equipment) and ball valves (with a spherical valve). In addition, the design of valves may vary in other parameters, for example, in the method of pressurizing the sealing surfaces, in the shape of the porthole, in the number of passages, in the type of control and drive, in construction materials, etc.

The taper of the plug (body) of conical valves is set depending on the anti-friction properties of the materials used and is equal to 1:6 or 1:7. According to the method of creating a specific pressure between the body and the plug to ensure the required tightness in the gate, taps with a conical gate are divided into the following types: tension, stuffing box with lubrication and with plug clamping.

The group of tension valves includes widely used socket valves with threaded tightening, simple in design and easy to adjust the tightening force. Stuffing valves are characterized by the fact that the specific pressures necessary for tightness on the conical sealing surfaces of the body and the plug are created when the gland is tightened. The tightening force is transferred to the plug, pressing it against the seat. Lubricated stuffing box valves are used to reduce control forces at medium and large nominal diameters, specific pressures on sealing surfaces and prevent galling of contacting surfaces.

Ball valves, which have all the advantages of conical valves (simplicity of design, direct flow and low hydraulic resistance, constant mutual contact of sealing surfaces), are widely used, while at the same time favorably differing:

Smaller dimensions;

Increased strength and rigidity;

An increased level of tightness due to the design (the contact surface of the sealing surfaces of the body and the plug completely surrounds the passage and seals the valve gate);

Less labor-intensive manufacturing (lack of labor-intensive machining and lapping of the sealing surfaces of the body and plug).

Ball valves, despite the variety of designs, can be divided into two main types: floating plug valves and floating ring valves.

Valves - shut-off pipeline valves with translational movement of the shutter in the direction coinciding with the direction of the flow of the transported medium. The movement of the shutter is carried out by screwing the spindle into the running nut. Basically, valves are designed to shut off flows, but often throttling devices with any flow characteristics are created on their basis.

Compared to other types of valves, valves have the following advantages:

Ability to work at high pressure drops across the spool and at high operating pressures;

Simplicity of design, maintenance and repair;

Small spool stroke (compared to gate valves) necessary to close the passage (usually no more than 1/4Dy);

Small overall dimensions and weight;

The tightness of the overlap of the passage;

Possibility of use as a regulating body and installation on the pipeline in any position (vertical/horizontal);

Safety against the occurrence of water hammer.

For shutting off the flow in pipelines with a small conditional passage and high pressure drops, valves are the only acceptable type of shut-off valves. The advantage of valves over gate valves is that in them the spool seal can easily be made of rubber or plastic, while the sealing force is significantly reduced, and the corrosion resistance of the seal is increased.

Common disadvantages of valves include:

High hydraulic resistance;

The impossibility of their application on the streams of heavily polluted media;

Large construction length (compared to gate valves and butterfly valves);

Medium flow only in one direction, given by the design of the valve;

Relatively high cost.

However, for the control of flows with high operating pressures and low or high medium temperatures, there are no alternatives to valves.

The classification of numerous valve designs can be carried out according to several criteria:

By design - straight, angular, direct-flow and mixing valves;

By appointment - shut-off, lock-regulating and special;

By design of throttle devices - with profiled spools and needle;

According to the design of the shutters - poppet and diaphragm;

According to the method of sealing the spindle - stuffing box and bellows.

The word "flange" came into Russian from German language together with the flange itself, and was not assigned on the basis of some analogies. In German, the noun Flansch means exactly the same thing as its derivative Russian word“flange”, ─ a flat metal plate at the end of a pipe with holes for threaded fasteners (bolts or studs with nuts). It is more usual when this plate is round, but the shape of the flanges is not limited to one disk. For example, square and triangular flanges are used. But round ones are easier to make, so the use of rectangular or triangular flanges can be justified for really good reasons.

The material, types and design features of the flanges are determined by the nominal diameter, pressure of the working medium and a number of other factors.

For the manufacture of flanges of pipeline fittings, gray and malleable cast iron, different grades of steel are used.

Ductile iron flanges are designed for higher pressures and a wider temperature range than gray iron flanges. Cast steel flanges are even more resistant to these factors. Steel welded, just as easy to transfer high temperatures, are inferior to cast flanges in the maximum allowable pressure.

The design features of the flanges may be the presence of protrusions, chamfers, spikes, annular selections, etc.

The prevalence of flanged pipe fittings is due to their many inherent advantages. The most obvious of them is the possibility of multiple assembly and disassembly. The temptation to add the adjective “easy” to the noun “installation” is somewhat reduced if we remember how many bolts will need to be unscrewed and tightened when disassembling and joining flanges of large diameters (flanged connections are usually used for pipes with a diameter of 50 mm or more). Although in this case the complexity installation work will not go beyond reason.

Flange connections are durable and reliable, which allows them to be used to complete pipeline systems operating under high pressure. Under a number of conditions, flanged connections provide very good tightness. To do this, the butted flanges must have similar connecting dimensions that do not go beyond the permissible error. Another of the conditions is the mandatory periodic tightening of the joints, which allows maintaining the "grip" of bolted joints at the proper level. This is especially important when they are constantly exposed to mechanical vibrations or there are significant fluctuations in temperature and humidity of the environment. And the larger the diameter of the pipeline, the more relevant it is, because as it increases, the force on the flanges increases. The tightness of flange connections largely depends on the sealing ability of the gaskets installed between the flanges.

Deformations cannot be discounted. Moreover, flanges made of different materials, are subject to them to an unequal degree, therefore the material from which it is made is the most important parameter of the flange. Thus, ductile steel flanges deform more easily than those made of more brittle, but much better shape-holding cast iron.

The disadvantages of flanged fittings are a continuation of its advantages. High strength results in significant overall dimensions and weight, which, in turn, mean increased metal consumption (in the manufacture of large-sized flanges, you have to use a thick metal sheet or large-diameter round profiles) and labor-intensive production.

Weld fittings

Reinforcement welding is resorted to when the reliability and tightness of other types of joints is considered unsatisfactory. Welding is especially in demand in the construction of pipeline systems in which the working medium is toxic, poisonous or radioactive liquids and gases. In this case, a welding joint that, when properly designed, provides 100% tightness, may be the optimal, and often the only acceptable solution. It is only important that such a section of the system does not need frequent dismantling of the equipment, the implementation of which every time will lead to the complete destruction of the welded joints.

Thanks to welding, which combines fragments of the pipeline system into a single whole, it is possible to ensure harmony, or, in technical terms, structural compliance between all its elements ─ pipes and pipe fittings. The main thing is that due to differences in the mechanical properties of the welded joint and other components of the pipeline system, it does not become its weak link.

The connecting ends of the reinforcement are prepared for welding by leveling and grinding the surface of the fragments to be welded, removing the required chamfers.

Welded joints can be made in the socket and butt. In the first case, the weld is located on the outside of the pipe. This option is usually used for steel fittings of relatively small diameter, mounted in pipelines operating at high pressure and temperature of the working medium.

In the second case, the connection can be supplemented with a backing ring, which excludes distortion of the connected parts. It is these connections, characterized by reliability and absolute tightness, that are used in the installation of pipeline systems of hazardous production facilities, for example, power units of nuclear power plants.

Important advantages of welded joints, especially in comparison with flanged ones, are minimal weight, compactness and space saving.

Coupling fittings

One of the most common in technology is the coupling connection of reinforcement.

It is used for various types fittings of small and medium diameter, operating at low and medium pressures, the body of which is made of cast iron or non-ferrous metal alloys. If the pressure is high, then it is preferable to use a pin fitting.

In the connecting pipes of coupling fittings, the thread is on the inside. As a rule, this is a pipe thread ─ inch thread with fine pitch. It is formed in various ways ─ knurling, cutting, stamping. It is important that with a fine thread pitch, the height of the teeth does not depend on the diameter of the pipeline.

Outside, the connecting ends are designed in the form of a hexagon, so that it is convenient to use the key.

The word "coupling" came into Russian from German, and possibly from Dutch, where mouw means sleeve. A coupling, like a valve, is an example of how tailoring and the production of pipeline fittings each use words that sound the same in their special terminology, but carry a different semantic load. In technology, a sleeve is not called a sleeve, but a short metal tube that provides connections for the cylindrical parts of machines.

The fine thread of the coupling joint plus the use of special viscous lubricants, linen strands or fluoroplastic sealing material (FUM tape) guarantee its high tightness. The sleeve connection does not require the use of additional fasteners (for example, bolts or studs, as in a flange connection). But it must be taken into account that screwing the coupling onto a thread with a seal requires considerable effort, the greater the greater the diameter of the pipeline.

Choke fittings

The German origin of the term "fitting" from the verb stutzen (cut, cut) even betrays its sound. So because of the presence of a rifled barrel, the muskets used to arm armies were called until the 19th century. In modern technology, this noun is used to define a short piece of pipe (in other words, bushings) with threads at both ends, which serves to connect pipes and pipeline fittings to units, installations and tanks. In a union connection, the connecting end of the fitting with an external thread is pulled to the pipeline by means of a union nut. It is used for fittings of small and extra small (with a nominal diameter up to 5.0 mm) diameters. As a rule, these are laboratory or other special fittings. For example, gearboxes mounted on compressed gas cylinders. With the help of a nipple connection, various control and measuring instruments (CIP) are “implanted” into pipeline networks, evaporators, thermostats, and many types of equipment that are part of chemical production process lines are mounted.

Tie-down fittings

The term "trunnion connection" came into wide use at the end of the 19th century. Its main attributes for pipeline fittings are connecting pipes with external thread and the presence of a shoulder. The end of the pipeline with a collar is pressed against the end of the valve branch pipe with a union nut.

The pin connection is used for high pressure fittings small size in particular instrumentation. It is effective when screwing fittings into the body of vessels, apparatuses, installations or machines. Its tightness is ensured by the presence of gaskets and special lubricants.

An example of a pin connection is the connection of a fire hose to a fire hydrant.

All threaded connections are characterized by such advantages as the minimum number of connecting elements, low metal consumption and, accordingly, low weight, manufacturability. Efficient Installation threaded connections require the matching of internal and external threads, the use of soft or viscous materials for sealing. But it should be borne in mind that threading reduces the thickness of the pipe wall, so this type of connection is not well suited for thin-walled pipes.

In addition to those listed, there are other ways to attach reinforcement. So, in pipeline systems, durite compounds can be used. These are connections by means of cylindrical couplings, consisting of several layers of rubberized fabric (speaking in simple terms─ fragments of hoses), pushed onto the protrusions made on the nozzles and fixed with metal clamps.

Another way to attach reinforcement is soldering, which is used to copper pipes with small diameter. The end of the pipeline treated with solder is inserted into the groove made in the branch pipe.

The functionality, performance and reliability of the pipeline system is determined not only by the parameters of the fittings included in it, but also by how welldone rebar connection , the selection and implementation of which should always be given increased attention.

Electric actuators are produced with the highest torques from 0.5 to 850 kgf-m in normal and explosion-proof versions with different explosion protection categories. These and other parameters of electric drives are reflected in the symbol of the drive, which consists of nine characters (numbers and letters). The first two characters (numbers 87) designate an electric drive with an electric motor and a gearbox. The next sign is the letter M, A, B, C, G or D, indicating the type of connection of the electric actuator to the valve. Type M connection is shown in fig. II.2, types A and B - in fig. II.3, types C and D in - fig. II.4, type D - in fig. P.5. The dimensions of the connecting elements are given in table. 11.106.

11.106. Dimensions of connecting elements of unified electric actuators of valves

All actuators are attached to the valve with four studs. The diameters of the studs and the dimensions of the support areas for different types of connections are different. With an increase in the torque developed by the drive, they increase. Types C, D and D connections are provided with two keys in order to unload the studs from shearing forces created by the torque transmitted from the drive to the valve.

The next figure conditionally indicates the torque of the electric drive. In total, seven gradations are provided for the total range of torques from 0.5 to 850 kgf-m (Table 11.107). Within the prescribed interval, the adjustment to the required torque is made by adjusting the torque limiting clutch.

11.107. Conventions parameters of electric drives

The next figure conventionally denotes the speed (in rpm) of the drive shaft of the electric drive, which transmits rotation to the valve stem nut or spindle. Eight frequencies of rotation of the drive shaft of the electric drive are provided - from 10 to 50 rpm (Table 11.107).

Then, conditionally, the total number of revolutions of the drive shaft is indicated, which it can make, depending on the version of the box of limit and torque switches. In total, six gradations are provided (Table 11.107).

This limits the first group of characters. The second group consists of two letters and a number. The first letter of the second group of designations indicates the version of the drive according to climatic conditions: U - for a temperate climate; M - frost-resistant; T - tropical; P - for elevated temperature. The second letter indicates the type of connection of the control cable to the electric drive box; Ш - plug connector; C - gland entry. The last digit indicates the explosion protection version of the actuator. The number 1 indicates the normal version H; the remaining numbers from 2 to 5 indicate the explosion protection categories: 2 - VZG category; 3 - category B4A; 4 - category V4D; 5 - category РВ. Thus, the electric drive under the designation 87V571 US1 has the following data: 87 - electric drive; B - type of connection; 5 - torques from 25 to 100 kgf-m; 7 - frequency of rotation of the drive shaft 48 rpm; 1 - total number of revolutions of the drive shaft (1 - 6); U - for a temperate climate; C - gland entry of the control cable; 1 - explosion protection standard N.

Below are brief specifications and dimensional data of electric drives of the unified series.

Electric actuators of normal execution with type M connection with a two-way torque limiting clutch (Fig. A.6). Symbols 87M111 USh1 and 87M113 USh1. Designed to control pipeline valves in structures with a maximum torque of up to 2.5 kgf-m. Torque control limits from 0.5 to 2.5 kgf-m. The total number of revolutions of the drive shaft 1 - 6 (87M111 USh1) and 2 - 24 (87M113 USh1). Drive shaft speed 10 rpm. The drive is equipped with an AV-042-4 electric motor with a power of 0.03 kW and a rotation speed of 1500 rpm. The gear ratio from the handwheel lever to the drive shaft = 1. A force of up to 36 kgf can be applied to the flywheel rim. Electric drives have a built-in box! travel and torque switches. The mass of the electric drive is 11 kg. The overall dimensions of electric drives 87M111 USh1 and 87M113 USh1 are shown in fig. P.6.

11. 108. Symbols of electric drives

11.109. Brief technical characteristics and mass of electric drives

11.110. Symbols of electric drives

Electric actuators of normal execution with type A connection with a two-way torque limiting clutch (Fig. II.7). The maximum torques created by the drives are 6 and 10 * kgf-m. Eight modifications of electrical appliances are provided (Table 11.108). Specifications and mass of electric drives are given in Table. 11.109. Rotational speed of the electric motor shaft 1500 rpm Gear ratio from the flywheel of the handwheel to the drive shaft i = 3. The electric drives have a built-in box of travel and torque switches. The overall dimensions of the electric drives are shown in fig. P.7.

Electric drives of normal execution with type B connection with two-way torque limiting clutch (Fig. II.8). The maximum torque on the drive shaft is 25 kgf-m (regulation interval from 10 to 25 kgf-m). There are twelve modifications of electric drives (Table 11.110). Technical characteristics of electric drives are given in table. 11.111. The frequency of rotation of the motor shaft is 1500 rpm. The overall dimensions of the electric drives are shown in fig. II.8. The mass of the electric drive is 35.5 kg.

11.111. Brief technical characteristics of electric drives

Electric actuators of standard execution with type B connection with a two-way torque limiting clutch (Fig. II.9). The highest torque on the shaft is 100 kgf m (regulation interval from 25 to 100 kpm). There are twelve modifications of electric drives (Table 11.112). Technical characteristics and mass of electric drives are given in Table. II. 113. The frequency of waxing the motor shaft is 1500 rpm. The overall dimensions of the electrical wires are shown in fig. II.9.

Electric actuators of standard design with G-type connection with a two-way torque limiting clutch (Fig. 11.10). The highest torque on the shaft is 250 kgf-m (regulation interval from 100 to 250 kgf). There are twelve modifications of electric drives (Table 11.114). Technical characteristics and mass of electric drives are given in Table. 11.115. The frequency of rotation of the motor shaft is 1500 rpm. The overall dimensions of the electric drives are shown in fig. UFO.

11.112. Symbols of electric drives

11.113. Brief technical characteristics and mass of electric drives

11.114. Symbols of electric drives

11.115. Brief technical characteristics and mass of electric drives

Electric actuators of standard design with type D connection with a two-way torque limiting clutch (Fig. 11.11). The highest torque on the drive shaft is 850 kgf-m (regulation interval from 250 to 850 kgf-m). Drive shaft speed 10 rpm. There are six modifications of electric drives (Table 11.116). The gear ratio from the flywheel to the drive shaft i = 56. Permissible force on the rim of the handwheel flywheel 90 kgf. The electric drives are equipped with an AOC2-42-4 electric motor with a power of 7.5 kW and a shaft speed of 1500 rpm. The mass of the electric drive is 332 kg. The overall dimensions of the electric drives are shown in fig. 11.11.

Rice. 11.12. Electrical control circuit for electric drives of a unified series:

D - asynchronous electric motor with a squirrel-cage rotor; KVO, KVZ - travel microswitches MP 1101 opening and closing; KV1, KV2 - additional travel microswitches MP 1101; VMO, VMZ - moment microswitches MP 1101 opening and closing; O, 3 - magnetic starters for opening and closing; LO, LZ, LM - signal lamps "Open", "Closed" and "Clutch"; KO, KZ, KS - control buttons "Open", "Closed" and "Stop"; 7 - potentiometer PPZ-20, 20 kOhm; Pr - fuse; A - automatic; 1 - 4 - contacts of microswitches

Explosion-proof electric drives are also provided:

11.116. Symbols of electric drives

The electrical circuit for controlling electric drives (same for all) is shown in fig. Item 12. In the “Open” position, the LO signal lamp is on, in the “Closed” position, the LZ and LM lamps are on, in the “Emergency mode” position, the LM lamp is on. The operation of the microswitches is clear from the table. 11.117.

11.117. Operation of microswitches (Fig. 11.12)

The connections of fittings to the pipeline (Fig. 13.2) are detachable (flanged, coupling, pin) and one-piece (welded and soldered). The most common flange connection. The advantages of flange connection of fittings are the possibility of multiple installation and dismantling on the pipeline, good sealing of joints and the convenience of tightening them, high strength and applicability for a very wide range of pressures and passages. The disadvantages of a flange connection are the possibility of loosening and loss of tightness over time (especially under vibration conditions), increased laboriousness of assembly and disassembly, large overall dimensions and weight. These disadvantages of flanges are especially affected by pipelines of large diameters, designed for medium and high pressures.

When assembling such a connection, dozens of large-diameter studs are tightened with a special tool. Tightening these flange connections often requires a team of locksmiths. With an increase in the nominal pressure and flow area of ​​the flanges, the mass of both the valve itself and the entire pipeline (including mating flanges) increases and the metal consumption increases. In connection with the indicated disadvantages of flanged connections, as well as an increase in the diameters of pipelines and their working pressures, fittings with butt welds are becoming more common. Such fittings, in particular, equip the main gas and oil pipelines.

The advantages of joining fittings to a pipeline by welding are great, which is, first of all, complete and reliable tightness of the connection, which is especially important for pipelines transporting explosive, toxic and radioactive substances. In addition, the welded joint does not require any maintenance and tightening, which is very important for main pipelines, where a minimum of maintenance is desirable. A welded joint saves metal and reduces the weight of fittings and pipelines. Especially effective is the use of fittings with ends for welding on such pipelines, where the pipeline itself is assembled entirely by welding.

The disadvantage of welded joints is increased complexity dismantling and replacing fittings, since for this it has to be cut out of the pipeline.

For small fittings, especially cast iron, the coupling connection is most often used. In this case, the ends of the reinforcement have the form of couplings with an internal thread. Since flanges for small reinforcement have a relatively large mass (often of the same order of magnitude as the mass of reinforcement without flanges), the use of flanges in such conditions leads to an unjustified increase in metal consumption. In addition, tightening bolts for small diameter flanged joints is more labor intensive than tightening a box joint and requires the use of special torque wrenches.

Rice. 13.2. The main types of connection of fittings to the pipeline:

a - flanged (cast flanges with a connecting ledge and a flat gasket); b - flanged (steel welded flanges end-to-end with a protrusion-cavity seal with a flat gasket); V- flanged (cast flanges with a spike-groove seal with a flat gasket); g - flanged (steel flat welded flanges with a flat gasket); d - flanged (cast steel flanges with a lens gasket); e- flanged (cast steel flanges with oval section gasket); and - coupling; h - tsapkovoe.

A coupling connection is usually used in cast fittings, because it is easiest to obtain an external coupling configuration (turnkey hexagon) by casting. In this regard, the main area of ​​application of coupling joints is fittings for low and medium pressures. For small high-pressure fittings, which are usually made from forgings or rolled products, the pin connection with an external thread for a union nut is most often used.

Flange connections of pipelines and fittings, designed for a nominal pressure of 1-200 kgf / cm 2, are standardized. At the same time, the types of flanges (GOST 1233-67), their connecting dimensions (GOST 1234-67), designs, performance dimensions and technical requirements are standardized. In special, technically justified cases (with shock or increased load, short service life, specific properties of the environment - toxicity, explosiveness, chemical aggressiveness, etc.), the standard allows the manufacture of flanges according to industry standards or drawings deviating from GOST, but with the obligatory implementation of connecting sizes according to GOST 1234-67.

Flanges are usually round. The only exceptions are cast-iron flanges, tightened with four bolts, designed for pressure p y not higher than 40 kgf / cm 2. They are allowed to be square.

Standard valve flanges are divided into several types according to the design of the gasket connection. The simplest of them - with a smooth front surface (with or without a connecting protrusion), unprotected type, without a groove for a gasket. These flanges are the easiest for mounting and dismantling fittings and for replacing gaskets, however, the tightness of the connection they create is the least reliable.

Flanges designed for high pressures (from 40 to 200 kgf / cm 2) are used with toothed steel gaskets, for low ones - with soft or soft-core gaskets. To protect soft gaskets from being knocked out by the pressure of the working medium in fittings, flanges with a cavity for the gasket are used. In this case, the counter flanges are made with a ledge, so that the flanges outside the gasket form a lock protecting it. Such flanges are used with soft gaskets or metal ones with a soft core. The third type of valve flanges, designed for the same gaskets as the previous one, are flanges with a gasket groove. Reciprocal flanges have a spike. Thus, the gasket is protected by a flange lock both from the outside and from the inside, which increases the reliability of the connection. However, installation, dismantling of fittings and replacement of gaskets are somewhat difficult here compared to flanges of the first type.

For high pressures, starting from p y \u003d 64 kgf / cm 2, seals of two more standard types are used in flanges - for a lens gasket and for an oval gasket. These seals are more economical and reliable in high pressures than conventional flat gaskets. In such flanged connections, the gaskets touch the sealing surfaces of the flanges theoretically along a line, but practically along a very narrow ring. This allows for equal overall dimensions flanges and tightening forces create high specific pressures on the seal. Thus, it becomes possible to use massive steel gaskets of high strength and durability in place of conventional soft ones.