The principle of operation and types of valves for pipelines

Pipe fittings - what is it

The connecting elements of the pipeline include valves, adapters, plugs and other elements that allow you to control the activity of the system. The devices have different fields of application, made of cast iron, metal or plastic. The simplest designs are manually operated, the more complex ones are equipped with a mechanical or automatic drive.

The choice depends on the characteristics and performance of the lines. The working environment (degree of heating, chemical or physical processes), pressure (normal, maximum, minimum) are taken into account. In addition, the possible external influence is calculated - mechanical loads, temperature drops.

Pipeline fittings performing control functions

This class of devices is designed to regulate the parameters of the working environment. This type includes a part of the valves, which are inherently shut-off valves. For this reason, all classifications described for locking devices apply to adjusting devices.

A separate type of control devices is a pressure reducing valve. The purpose of these devices is to reduce the pressure of the medium, which is carried out by changing the value of the hydraulic resistance. Pressure regulating devices are sometimes referred to as reducers.

What materials is it made of

Various materials are used for the production of pipe fittings. GOST R 55509-2013 indicates the requirements for the composition of the metals used. Cast iron used:

• gray СЧ15, СЧ20;
• malleable KCH30-6;
• with spheroidal graphite VCh40, VCh45.

Of metal alloys used:

• carbon steel, alloyed, high-alloyed;
• non-ferrous metals and alloys - bronze, brass, titanium alloy, aluminum, nickel.

Plastic products are widely used, these are polyvinyl chloride, polyvinyl chloride, polyethylene. Used to transport aggressive substances.

Tip: Recently, the plastic Walraven star Quick clips with a ratchet actuator that speed up the installation process are becoming more common.

Types of wear of valves and ways to minimize it

Rebar parts can be subject to various types of wear:

• Mechanical
• Erosive
• Thermal
• Chemical, etc.

Mechanical wear of reinforcement is the result of mutual friction of parts, for example, sealing rings of valves, a spindle and a spindle in their threaded connection, shafts in plain bearings, etc. surfaces. A decisive role in the intensity of mechanical wear can be played by oxidative processes occurring in the surface layer of the metal (oxidative wear), microcutting with abrasive particles (abrasive wear), metal seizure, etc.

The mechanical wear of parts can be reduced by increasing the hardness of the material from which they are made. For this purpose, various methods are used: surface hardening by high-frequency currents, chemical-thermal treatment (carburizing), nitriding, diffusion chromium plating, etc.

To protect against damage and corrosion, the threaded elements of the valves are galvanized or coated with special antifriction materials based on solid lubricants.

Antifriction coatings are gaining more and more popularity today, since, in comparison with galvanic coatings, they are more resistant to wear and tear and continue to operate after multiple cycles of assembly and dismantling of valves.

In Russia, antifriction solid lubricating coatings (ATSP) are produced under the MODENGY brand. For threaded fasteners of shut-off valves, the ATSP line with the addition of polytetrafluoroethylene is used - MODENGY 1010, MODENGY 1011 and MODENGY 1014 (the latter coating also contains molybdenum disulfide). These materials help protect the metal from corrosion and wear, stabilize the twist ratio, and avoid thread biting.

The coatings have been successfully tested for chemical resistance, therefore they can be used in aggressive pumped media.

Valve parts that throttle the fluid are exposed to erosive wear: plungers and seats of control valves.

Distinguish between crevice and impact erosion, as well as the process of cavitation destruction of metal. With crevice erosion, the surfaces of the parts are washed out under the action of a jet of wet steam passing at high speed through the gap between the seat and the plunger. With impact erosion, the material is destroyed due to the impact of water droplets on the surface of the part. During the cavitation mode of movement in the flow of the medium, bubbles (voids) are formed. When they collapse, they create local hydraulic shocks that destroy metal surfaces.

It is possible to reduce the intensity of erosional wear by changing the operating modes of the reinforcement and using erosion-resistant materials.

Thermal wear (aging) of a material is the result of a change in its structure when heated. Aging is most typical for rubber - it loses its elasticity, becomes brittle and brittle. The stuffing box packing burns out and hardens under the influence of high temperature.

Chemical wear is nothing more than corrosion to which parts of valves are exposed under the influence of working media.

Corrosion can be general (over the entire surface of the metal), crevice, intergranular, pitting (point). The greatest danger is corrosion cracking of steel, which occurs under the simultaneous action of the environment and mechanical stress.

Steel and its alloys are most susceptible to corrosion cracking.

It is possible to reduce the intensity of chemical wear by using alloy steels, corrosion-resistant metallic and non-metallic coatings. Some of them - for example, the MODENGY already mentioned above - have very high anticorrosive properties and are easy to use.

Unlike passivation, electrochemical protection and other processes that require specialized equipment, working with ASTP involves the use of standard painting tools.

Types of pipeline fittings

Reinforcement products are classified according to the method of application, purpose, design. The types of fittings on pipelines are as follows:

• flanged;
• connecting;
• for pipes made of different materials;
• for nuclear power plants.

Let us dwell on these types in more detail.

Flanged

A flange is a flat disc with a specified number of mounting holes. The flanges of adjacent elements fit snugly against each other. The connection is made by tightening the fastening bolts with nuts. Gaskets ensure tightness. Flanged fittings are installed in systems operating at different pressures and temperatures. The flange is welded to the pipe.

The flange mount is collapsible, which simplifies repair work, inspection and replacement of elements. It is made of cast iron or steel, it is used for pipelines from 50 mm in diameter, it can withstand temperatures up to 400 ° C, can be placed in a horizontal and vertical position.

Connecting

Pipeline fittings are used when connecting elements of different materials and diameters. At the point of joining of pipes made of steel and plastic, where the diameters of the connected elements differ, connecting fittings are used.

Couplings, plugs and other fittings are installed as additional parts, in the design of which there is no locking and adjusting mechanism. Such elements provide quick installation and replacement of pipeline parts. Connecting elements are produced with a section of 25-2020 mm, for pressure from 1 to 4 MPa from cast iron, steel, plastic.

Stainless

Stainless steel pipe fittings form a compound that does not react chemically with the working medium, which ensures the longevity of the system. Elements such as valves, taps, adapters, gate valves are used for stainless pipelines when transporting food liquids, alcoholic and non-alcoholic beverages.

Corrosion-proof elements form a strong connection that is resistant to corrosion and aggressive media, which ensures its use in the petrochemical and gas industries, pharmacology, and nuclear power plants. The parts do not interact with the transported products, do not change it and their structure.

NPP fittings

A nuclear power plant is a highly hazardous energy facility. Its design includes a large number of pipelines, industrial pipeline fittings are installed. The following requirements are imposed on the elements:

1. The direction of movement of the working fluid must match the direction of the arrow on the body.
2. You cannot use parts that do not correspond to the purpose.
3. Access to all types of fittings must be free.
4. The connecting elements of the pipeline heated during operation should be closed with a removable structure with thermal insulation fixed by means of a thread.

Individual parts of the pipeline, which are under high or medium pressure, are connected by welding or flanged fittings, which reduces the possibility of leaks. The material for the products must be high quality metals.

Important: to ensure the safety of the steam generators, safety valves are installed - main and auxiliary. To remove drainage from the circuit of the station, first a shut-off, then an adjustment one.

Reinforcement of metal-plastic pipes

Reinforced-plastic pipes are used for indoor installation. This is internal plumbing and heating. The connection of the sections is carried out by valves, shut-off and transition valves and other elements. They are used at a coolant temperature up to 95 ° C and a pressure of 16 atm.

Metal-plastic pipelines are used in everyday life, have a neat appearance, threaded or press connection. The fittings are made of nickel-plated brass. The products have standard dimensions and are marked on their surfaces.

Fittings for polyethylene and polypropylene pipes

Fittings for plastic pipes are distinguished for pressure and non-pressure systems. For polyethylene pipes, a welded joint is considered the most reliable. As a result, we get a single cast sealed pipe.

Type of fittings by type of connection to the system

The type of connection is one of the key parameters in the design of pipeline fittings. The most popular types are compounds:

• flanged;
• threaded coupling;
• choke;
• welded.

For the existing pipeline, this issue is not relevant, since there are no options, they are dictated by the system itself.

Flanged type of connection

All flanged fittings differ in one thing - the shape of the flanges. They are round, square, triangular. The first two are the most common. Round flanges are universal, they are suitable for all pressures.The limitation for the use of square flanges is pressure above 20 atmospheres.

Flanged fittings.

The connecting flanges must fit snugly against the counter flanges on the pipeline. They are pulled together with bolts or studs. For this, both elements have holes. For better clamping, the fasteners are tightened with nuts. Increase the tightness of the gaskets placed between the flanges. This is a detachable connection, so there are no problems during installation and dismantling. The advantages of products include:

• strength and reliability;
• high pressure resistance;
• good tightness.

The main disadvantages of this installation method are the possible weakening of fasteners, impressive dimensions, considerable weight, and high price.

Flanges are made of steel or cast iron - ductile or gray. Ductile iron is better than gray cast iron withstands high temperature drops and high pressure. Cast steel flanges are very durable, but they are adversely affected by plastic deformation.

Threaded connection

This type of connection is used for pipelines with the largest diameter - up to DU-50 and for pressures up to 1.6 MPa. In this case, threads are present both on the pipe and on the fittings. Even if there is no thread on the pipeline, it can always be cut. There is a hexagon at one end of this type of fittings for the possibility of using an adjustable wrench for tightening.

Threaded fittings.

Threaded connections come in two versions - with an internal thread and an external one. There can be different threads on both sides of the product - internal on one and external on the other, or identical on both sides. Thread standards are also different.

Strengthen the threaded connection by using seals - linen thread, FUM tape, thick lubricants. Such a connection is used for the installation of a wide variety of shut-off valves - valves, gate valves, flow dividers.

The advantages of threaded connections include the absence of additional elements for installation, low price, ease of installation and replacement. Minus - unsuitability for high pressure lines.

Nipple connection

This type is used to connect fittings of very small diameters - up to DU-5. In this case, the connecting end has an external thread and is pressed against the pipe with a union nut. Various measuring devices are introduced into the line by means of a choke connection.

Fittings with choke connection.

Use it for a small list of specific pipes such as laboratory ones.

Welded connection

A welded connection is necessary on those lines that carry fluids that are hazardous to health. Perfect tightness is needed here, since even the smallest leaks are unacceptable. The main condition is that the weld should not be weaker than the pipe wall.

Welded fittings.

Connections are made in two ways:

1. Butt, when the clutch is supplemented with a backing ring to prevent misalignment of the parts.
2. In the bell. In this case, the weld seam is on the outside of the pipe.

A competent welding connection is the most reliable, 100% tight. Welding is preceded by the preparation of the pipe ends. The advantages of a welded joint include low cost, low weight, small dimensions.

The disadvantages are that the use of such a connection method is impossible without the involvement of qualified personnel. Dismantling the fittings is very time consuming.

Toilet flush valve

Toilet fittings.

In everyday life, very often you have to deal with fittings for a toilet bowl flush. More details about it, its types, correct installation and adjustment can be found in a separate article: drain fittings for a toilet barrel.

Types of locking devices

The shut-off structures of pipelines can be regulating. They are divided into four types:

1. The gate valve has two mutually perpendicular positions relative to the pipe axis. Closes and opens the passage for the transported product.
2. The valve is equipped with a closing or regulating mechanism, the movement of which is parallel to the direction of movement of the flow of the transferred substance.
3. At the crane, the mechanism rotates around its own axis, moving up or down at different angles to the pipe axis.
4. The valve is required to shut off and regulate the product flow in the pipeline. It can serve as a safety valve, condensate drain. It happens ball and valve.

Gate valves are more often used as a shut-off structure, valves are installed as control mechanisms. They work quickly, are characterized by high hydraulic resistance and tightness.

Purpose of valves

Shut-off valves for a pipeline are a set of engineering units, the main purpose of which is to shut off or restore the flow of a working fluid or gas. The devices are designed for installation on pipelines for various purposes. The medium can be either liquid or gaseous. The products provide a high level of reliability and tightness.

Rebar classification

Pipe fittings are products classified by application, sealing methods, design features. Let's consider some of them.

Scope of application

Based on performance characteristics, there are: vacuum, cryogenic, shut-off valves. Depending on the purpose, these are control, reduction, anti-surge devices. The transported product determines their tightness, resistance to chemical and aggressive media.

Connection type

The method of connecting to the pipeline subdivides fittings into flanged, interflanged, coupling, threaded, and welded. When welding fittings with pipes, connecting pipes are used; when coupling, internal threads and additional pipes are used.

By sealing method

Depending on the used sealing elements, fittings are distinguished:

• stuffing box;
• membrane;
• bellows;
• hose.

The stuffing box uses a fiber packing impregnated with sealant for sealing. The diaphragm seal is an elastic disc that is clamped at the junction.

The bellows is a corrugated tube that folds when clamped. The hose design uses a flexible hose that is pinched, cutting off or reducing the fluid flow.

By the design of the connecting pipes

Allocate the device through passage, angular, partial bore, full bore. In a partial bore, the inner section of the connecting pipe is less than the diameter of the pipe entering the fitting. In full bore fittings, all diameters are the same.

Classification of shut-off valves according to the flow control method

Depending on how the flow of the working medium is controlled, shut-off valves are divided into the following types:

1. Cranes.
2. Shut-off valves.
3. Dampers.
4. Gate valves.

Crane characteristics

They are ball and cork. The first ones are used mainly in household pipelines. The second - in the highways transporting oil fractions, gas, water. In the first case, the element that cuts off the flow is a ball, in the second - a cone in the form of a plug.

The design of the shut-off valve is extremely simple. The main parts are the body and the locking element. Depending on capacity, valves are divided into full bore (90 - 100%), partial bore (40 - 50%), standard (70 - 80%). The adjustment is carried out by means of a flywheel or an electric drive. There are remote controlled cranes.

Crane.

The main element of the ball valve is a lock, which looks like a chrome-plated ball, along one of its axis there is a hole.It is located between two O-rings (seats) in the center of the body. The constipation parameters depend on the section of the pipe.

Ball grain device.

Opening / closing occurs when the steel ball is displaced during the rotation of the lever. When the hole is oriented along the longitudinal line of the pipe, the working medium is supplied. When the hole is perpendicular, the flow is shut off. There are no rubbing elements in the design of this reinforcement, which is why water losses are insignificant.

The most popular ball valves are brass and steel made of carbon steel, stainless steel and molybdenum. There are plastic ball valves resistant to aggressive chemicals. The tightness of such products is low; they are highly sensitive to solid inclusions in the flow and high temperatures.

They are introduced into the systems of both cold and hot water supply, but with a temperature not higher than 65⁰. Stainless steel taps are built into lines with a diameter of more than 50 mm. The products are designed to function in conditions of high temperatures and pressures. These taps are too expensive for home use.

Shut-off valves

These are valves designed for both shut-off and flow control. They are manipulated by means of a flywheel or an electric drive. Different specimens are designed for a specific temperature regime. Large models are most often flanged, and small ones are connected with couplings.

The device is a shut-off straight valve.

The valves maintain the required pressure in the line, and also mix liquids in a given ratio. The shut-off assembly regulates the flow as follows:

1. The flywheel transmits its rotational motion to the spindle.
2. He begins to move, making movements of a reciprocating nature.

The spindle is started manually, or by means of a servo drive. The most popular type of valve is straight through. They cut it into flat sections of the highway. The main disadvantage of this type of valve is considerable hydraulic resistance.

Diagram of a straight-through vent.

Direct-flow valves are devoid of this drawback. They are installed in areas where it is impossible to reduce the flow rate of the liquid medium at its outlet. Valve bodies are cast iron, steel, bronze, brass. The first ones belong to general technical shut-off valves, they are connected by means of flanges and couplings.

In high-tech processes, where the requirements for the working environment are particularly stringent, steel valves are used. Their connection is flanged.

The following video shows the appearance of various valves, as well as their design.

Bronze and brass valves are used in water supply and heating systems of buildings. Attach them using flanges, by welding or coupling. The direction of movement of the fluid is indicated on the body. The flow is regulated by means of a spool located on the stem.

Features of dampers

Locking elements of this type are installed in systems with low pressure, since they do not provide great tightness. These are sewer lines and with chemical liquids. The dampers are connected using flanges or welded. The locking piece is a disc rotating around an axis. Most often, the body is cast iron, and the disc is steel.

Damper device.

Gate valves

These shut-off assemblies represent an extremely simple design that blocks the free movement of the medium. They can withstand heat and pressure. They are used in highways that allow non-aggressive compounds to pass through. Their locking element is a wedge, disc or sheet. It carries out reciprocating movements, vertical in relation to the axis of the moving avalanche.

Gate valve device.

Valves are divided into full bore and truncated.In the former, the seat diameter and the corresponding pipeline parameter are the same. Secondly, the saddle section is less than the pipe section. Install this shut-off valve on the lines, for which the connecting diameter exceeds 50 mm. The flow in them must be shut off smoothly so as not to provoke a water hammer.

The advantages of gate valves over other types of similar products are in simplicity of design and maintenance. They have small dimensions, low resistance. They are made from cast iron, steel, non-ferrous metals. They are controlled manually, by means of a hydraulic or electric drive.

Pipe fittings marking

For orientation in the types of fittings, special symbols are used. They indicate the main technical parameters of the products. Different manufacturers set their own markings. The most popular is the labeling of JSC Scientific and Production. It contains tables indicating the type of product, drive method, material of manufacture, and other designations.

As an example, we will decipher the following designation: 13br042nzh - a shut-off valve, brass, stainless steel seal, has a remote control, model 42. Sometimes letter marking is used: KSH - ball valve, KTS - three-way steel valve and others.

Aerospace

Aerospace shut-off valves are typically small, non-standard materials, and highly intelligent control systems.

The most common types of fittings here are solenoid valves, as well as small hydraulic valves used to act on control surfaces such as stabilizers, ailerons and rudders. Guided missiles use the same types of small valves.

Ground launch pads for orbiters are very complex and contain many pipelines. There are liquid fuel lines, which are usually loaded with cryogenic fittings. Other auxiliary lines contain different fluids at different pressures and temperatures, which also predetermines high demands placed on the valves used in them.

Testing of pipeline fittings

To ensure trouble-free operation of pipelines, a test of pipe valves and other connecting elements is carried out. The tests include the following steps:

1. Hydraulic loads to check the strength, impermeability of the material, the absence of shear of structural elements.
2. Checking the tightness of the shut-off elements.

At the first stage, industrial valves are tested under pressure from pumps. Test conditions are specified in the technical documentation.

Pressure is applied to an open working element with a closed hole in the pipe. If leaks are found in welds and other joints, the fittings are considered unusable.

When testing devices for tightness, liquid under pressure is supplied in turn from different directions to the device. Inspect the fitting on the opposite side of the pressure supply. Valves, dampers, valves are pressurized from one side.

Important: for the classification of products according to the sealing class, GOST R 9544 - 75 "Pipeline fittings" are followed. The standard specifies three classes of tightness, determined by the purpose of the pipelines.

Solar energy

Thermal solar installations (collectors) are major consumers of shut-off valves in the field of solar generation.

Solar collectors concentrate the thermal energy of the sun's rays and use it to generate steam. In other words, the water is heated by the sun and evaporates, circulating in a closed circuit.Accordingly, the fittings in such installations are divided into two segments - fittings for the heat carrier (water), and fittings for steam

The largest users of valves in solar energy are solar thermal installations, which concentrate the heat from the sun and use this energy to transfer a heating medium to create steam. In other words, the transfer fluid is heated and circulated in the receiver to produce steam. The valves for these installations are divided into two segments: heating medium piping and steam treatment piping systems.

Shut-off valves in the heat transfer system of solar collectors must withstand the pressure and temperature that occur during the heating process. In addition, it must be suitable for the medium used (hot water and heated steam). The characteristics of the elements here are similar to those used in steam turbine power plants.

Solar power plants that use the photovoltaic process to generate electricity do not have aggressive environments and harsh operating conditions, therefore, the requirements for the fittings used here are not so critical.

Benefits of valves

The advantages of shut-off pipeline valves include:

• The shut-off valves are made of wear-resistant materials of high hardness with an anti-corrosion coating.
• Control of valve assemblies is possible with pressure drops without additional efforts.
• The design of the assemblies ensures a high level of tightness class A.
• The conducted medium is different: steam, water, gaseous and liquid mixtures, water-gas-oil mixtures, associated and natural gas.
• Wide temperature range of the conducted medium.
• Use in a wide variety of conditions.
• Long service life.

The main requirements for shut-off valves are to optimally ensure the degree of tightness of shutdown in the closed state, while providing minimal resistance to the medium in the open state.