Shut-off valves and their application in pipeline systems

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.

Purpose of pipeline valves

Since in the open state of the shut-off unit, pipeline shut-off valves pass through the flow of the working medium without any changes in its characteristics, and in the closed state of these elements completely cuts off the pipeline section, these products are used to solve the following problems:

• a set of gas / liquid in a container, a reservoir;
• draining the working medium from the vessel;
• opening of the elbow / branch pipe with instrumentation to determine the parameters of the medium;
• cutting off a part of a local pipeline or a section of a pipeline for its repair / maintenance;
• sampling of the medium, air bleeding.

There is a category of pipeline shut-off valves - control shut-off valves. That is, the valve assembly has been modernized to be able to regulate the pressure or pressure of the working medium flow. Some products of the shut-off type can simultaneously belong to two categories of shut-off valves. For example, a swing check valve is essentially a butterfly valve.

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 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 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.

For pipelines

Products are pumped over long distances at high pressure and at high speed to be an efficient means of transport. Therefore, special requirements are imposed on the selection of pipes and valves - valves, valves, rotary valves.

It is selected in accordance with technical standards, with design pressure, viscosity of the medium, differences in internal and external temperatures.The degree of pumping automation is also important.

In the systems of main water supply systems, the pumped liquid always contains a certain amount of aggressive components. Therefore, chemically resistant materials are used for reinforcement. These properties are fully possessed by cast iron, from which all types of valves for pipelines are made.

They are used in high and low pressure pipelines and for pumping various media. The same material is most popular in the manufacture of pipeline fittings for oil pipelines.

On main pipelines, shut-off valves with dimensions of 8 - 2000 millimeters are used.

The valves are controlled manually using handwheels, and in hard-to-reach places - using an electric drive remotely.

Most cast iron gate valves are designed with flanged mechanisms and can be produced in various designs:

1. Gate - with a movable or fixed rod;

The gate valve is a cast iron body, in which a flat gate with a hole corresponding to the pipe size is located. Two types of drive are used for control: manual for units located in an accessible place, and remote, if the valve is installed in a closed space.

The manual drive consists of a handle in the form of a handwheel, a screw pair and a stem attached to the gate. When the handle rotates, the screw pair converts the rotational motion into translational motion, which drives the gate in the desired direction through the stem. When the hole in it matches the hole in the pipe, fluid flow resumes.

1. Wedge - a highly effective type of valves for pipelines. The shape of the locking element allows to ensure the maximum tightness of the closure of the lock and the seat, which increases the quality of the overlap.

The lift of the shutter provides movement of the wedge in relation to the seat, as a result of which its hole is aligned with the hole in the stationary part, providing the passage of the working medium. Rotation can be done manually or using a remote control.

1. Parallel.

Such devices are designed to operate at a pressure of 2 - 200

atmospheres.

The working medium and the locking elements of the device in the form of two plates are located in the chamber. The valve plates are attached to the actuator stem. When it rotates, they open up, letting water or steam through the pipeline.

All presented valves have a number of common parameters, including:

1. Connection to the product pipeline is made using flanges, couplings or welding.
2. Gate valves are not used to adjust the pressure in the pipeline, but only close or open it in extreme positions.
3. Gate valve bodies are made of cast iron by casting, less often from steel.
4. All types of these fittings use sealing devices made of rubber, paronite, cardboard, etc.
5. Depending on the accessibility of the device, a manual handwheel drive or remote control using an electric drive is used.

Flanged valves for pipelines are used not only in water supply networks, but also when pumping oil products or other liquid media.

In distribution networks on pipelines DN100 and less water supply, valves and taps with coupling joints are often used. Such devices are smaller and more technologically advanced during installation. Connections are made by screwing onto the thread of the mating part.

The tightness of such a joint is ensured by the use of various seals: flax fiber, FUM tape (fluoroplastic sealing material), sealing cords and special-purpose silicone sealant.Such a connection is less reliable than a flanged one, but the elimination of leaks on it is faster and easier.

Shut-off couplings for pipelines are used on in-house distribution networks with dimensions less than DN 50 at a pipeline pressure of 0.6 atmospheres.

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.

Rebar classification

Pipe fittings are products classified by application, sealing methods, design features. Let's take a look at 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 nozzles are used; when coupling, internal threads and additional nozzles 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.

Go to the catalog of valves

Gate valves

The simplest design solution with minimal water loss is a shut-off valve with vertical movement of the working body at right angles to the flow - a gate valve. The main nuances of the gate valve design are:

• minimum length compared to taps, valves and dampers;
• no hydro loss;
• rapid wear of seals;
• large mass and height of the reinforcement;
• long time of transfer of the spindle from one extreme position to another;
• most often, valves of this type are made full bore;

The reducing valve has an inner diameter that is one size smaller than DN, which makes it possible to slightly reduce the tightening force at the handwheel. However, already at DN 300 mm, the shut-off valves are equipped with a gearbox or an actuator.

Depending on the design, shut-off valves are divided into categories:

• pinch valve - the spindle pinches the elastic hose located inside the body in the closed position;
• gate valve - lamellar working body of the shut-off unit;
• parallel valve - the elements of the locking unit do not have a narrowing, that is, the sealing surfaces are parallel to each other;
• wedge valve - a cone valve overlaps a saddle with mating surfaces of a similar shape.

Pinch valves are marked with 33, for example 33a603p, and the valve body is most often made of aluminum. Rubber withstands a maximum of 120 ° C, therefore, gate valves with an internal hose are used for slightly aggressive media of high viscosity. The maximum DN is limited to 200 mm.

Gate valves are designated by the number 30, for example 30nzh36p (flanged, sliding spindle). The body is made of stainless, alloy and carbon steel (marking nzh, hp and s, respectively). The gate initially does not have absolute tightness, therefore, shut-off valves are used in drainage systems.

Parallel valves are designated by the numbers 30, they can have a steel and cast iron body, brass, bronze, stainless and even leather seals or not have them at all (marking bk). Lever and screw clamps, spacer wedges between the discs can be added to the design. There are pressure reducing and full bore versions of valves.

Wedge gate valve marking begins with number 30, there are several types of valves:

• sliding-type spindle - increased dimensions of the body and cover;
• non-rising spindle - the weight and dimensions of the body are reduced, but the resource is reduced;
• drive by hand wheel, by means of an electric motor reducer, hydraulic or pneumatic motor;
• cast or die-welded body of steel 20 / 20L, 25 / 25L, 35 / 35L, cast iron;
• the wedge is elastic, double-disk or rigid.

The stamped-welded body initially has no casting defects, has high strength and service life. However, the production cost of stamped and welded fittings is much higher.

Ball valves

Initially, a more complex gate assembly scheme was implemented in the valves:

• the saddle consists of rings;
• the plug is in the form of a ball or cone;
• the spindle rotates 90 degrees maximum.

These valves are initially referred to as shut-off and control valves, since in addition to completely cutting off the pipeline section, you can smoothly adjust the pressure and pressure of the medium, mix / separate the flows.

Valves are subdivided into conical and ball valves, test-and-run valves and conventional pipeline valves. Initially, valves with a tapered plug are more expensive, have a low resource, tightness and reliability. Therefore, ball valves with low torque, budget price, safety margin and convenient ergonomic control are more in demand.

The ball valve is the most demanded item of plumbing pipeline valves. Shut-off valves with a taper plug have a pull-type or stuffing box seal.

Cranes are designated according to GOST R 52720 and SP TsKBA 036 by numbers 10 and 11. The main nuances of the design are:

• all-metal or collapsible body;
• there are wafer valves with a minimum face-to-face length;
• taps are installed in the pipeline by all existing methods;
• plumbing taps are usually made in a polymer case (polypropylene, metal-plastic, polyethylene, vinyl plastic);
• the body of pipeline valves is made of brass, stainless steel, bronze, alloy or carbon steel;
• seat rings are cast from polymer, turned from stainless steel, composite material, ceramics.

In the engineering systems of buildings, fittings are used DN 12 - 50 mm, life support systems for settlements and local pipelines DN 50 - 400 mm, pressure lines DN 400 - 1200 mm.

Flaps (butterfly valve)

The official name for the valve is a butterfly valve that closes the internal section when rotated 90 degrees relative to the direction of flow. In axial butterfly valves, the axis of rotation coincides with the axis of the valve element, and in eccentric modifications it is shifted by an arbitrary angle.

Dampers are used in automatic fire extinguishing systems, pipelines for pumping sea water, oil products, abrasive media, air conditioning and ventilation. The only drawback of the butterfly valve is that it cannot be removed from the seat in the open position, which makes mechanical cleaning from the inside difficult.

The first digits in the butterfly valve marking are 32, and the body is often made of titanium, aluminum, and polymeric materials. In air ducts of small diameter, sealed valves are often used, which are analogous to disc dampers. For this category of pipeline fittings, there is no limitation on the nominal diameters of products.

There are modifications of valves with 1 - 4 eccentrics. The disc has a saddle-like, flat and biconvex shape in cross-section. Unlike the closest analogue - a ball valve, the butterfly valve handle has a complex design, and an original technology for installation into the pipeline:

• electric arc welding - beveled nozzles are used;
• flange - 4 holes are available in the cast body of the butterfly valve, studs are passed through them to pull the valve with pipes.

For pipeline sections, where it is possible to change the flow of the medium, modifications have been created to check butterfly valves - slammers. They are mounted exclusively on horizontal sections, the working body is spring-loaded to exclude the reverse movement of the working medium.

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.

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 "Pipe fittings" are followed. The standard specifies three classes of tightness, determined by the purpose of the pipelines.

Varieties of valves

By default, shut-off valves are a category of pipeline valves along with control, phase separation, safety, mixing and safety valves.Therefore, there is a general classification of pipe fittings and a smaller subdivision within the subcategory itself. In other words, pipeline fittings are classified according to the characteristics:

• type of installation in a pipeline rupture - welding, fittings, trunnions, couplings, flanges or any combination of these nozzles;
• drive - manual control wheel, mechanical gearbox with cylindrical, bevel or worm gear, electric, pneumatic or hydraulic drive;
• field of use - valves for tanks, plumbing, ships, steam and water, chemical, gas / oil, energy;
• type of seal - hose, stuffing box, diaphragm and bellows fittings;
• gate assembly design - gate, tap, valve and gate valve.

Within its subcategory, shut-off valves are subdivided into control and drain (drainage) valves. With the help of the control shut-off valves, the medium opens access to the section of the pipe with a measuring device (thermometer, manometer). Drainage fittings allow you to draw liquid into the container, bleed gas from the tank, drain the working environment after performing the technological process.