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Views: 13 Author: Site Editor Publish Time: 2022-04-08 Origin: Site
The gate valve is the main tool of the pipeline, which is able to block the flow of matter. There are many varieties of this device on the pipe fittings market. Some are intended for public utilities, others for gas and oil workers. Third…
To make a choice, you need to know:
what types of valves are;
in what working environments it is allowed to operate them;
how to install them;
and store.
You will learn about all the nuances by reading this review.
The gate valve belongs to shutoff valves. It is used to completely shut off the flow of the working medium in the pipe.
In the technology of work of various enterprises that have pipeline systems on their balance sheets, there are processes that cannot be carried out without the use of a valve.
But in which industries the valve is used:
city utility networks;
oil and gas industry;
shipbuilding;
food and construction industries.
Practically any producing and operating production, which has the smallest pipeline network, needs stop valves. The valve is its most common representative.
To work with different substances circulating through pipes, gate valves are manufactured in different designs. They differ in:
case material;
spindle type;
the material of the sealing surfaces of the valve;
drive type;
method of connection to the pipe.
According to the material of body parts, cast iron and steel gate valves are produced. Cast iron is designed for non-aggressive media such as fresh water and steam. The maximum pressure in the pipe at which the valve operates under normal conditions is not high here - up to 1.6 MPa (or 16 atmospheres).
Steel gate valves are divided into high carbon and alloy steel products. High-carbon alloys are designed to work with water, steam, oil products.
But valves made of alloyed alloys are allowed to be operated in pipelines through which aggressive media (acids, alkalis, etc.) circulate. The maximum system pressure is up to 250 MPa.
When determining permissible working environments, one must be guided by GOST 9.908-85g. According to this document, the corrosion rate of valve body parts during operation should not exceed 0.1 mm/year.
According to the type of spindle, gate valves come with a rising and non-rising spindle. This classifier also affects the scope of reinforcement. For example, gate valves with a non-rising stem are installed only for clean water, steam and oils. But devices with a sliding spindle are used for a wide range of working environments.
The material of the valve seals also affects the scope of the valve. For municipal needs, as well as for highways where water and steam are transported, rubber-coated gates are used. But for petroleum products and other substances, manufacturers use steel valves with stainless steel surfacing.
According to the type of valve drive, there are:
manual (steering wheel);
mechanical (reducer);
and electrical (electric motor).
Valve bodies are equipped with 2 types of connections - flanged and welded (for welding, with cutting of connecting pipes).
Each modification of the valve has its own advantages and disadvantages, as well as the scope.
The valve is designed to stop the flow of matter in the line. The main moving part is a gate located perpendicular to the flow axis.
Gate valves are mounted in pipelines through which :
water;
steam;
gas;
oil products;
chemical substances.
With the help of the handwheel (1) and the running nut (2), the spindle (6) is set in motion, fixed in a T-shaped way with the shutter (9). The rotation of the nut is transmitted to the spindle, which, by means of a rotational-translational movement, opens / closes the shutter.
The section on the right shows that the valve and a part of the spindle are located directly in the working space, in contact with the substance circulating in the pipe. In order to prevent the substance from escaping into the environment, the moving part is hermetically sealed by means of the stuffing box swing bolts (4).
The stuffing box itself is completed with a packing tightly wound on the smooth part of the spindle (stem), which is a seal. In addition, the seal is placed in a special groove of the flange connection of the cover (5) and body (7).
To fix the valve, connecting flanges (8) are used, which are also sealed with a gasket - paronite.
On fig. 2 shows a steel rising stem gate valve. When the steering wheel is rotated, the spindle extends upwards, opening the shutter, for the full output of which the device has a yoke assembly (3). The height of this node is not less than 1 nominal bore diameter.
Gate valves are available in various modifications.
Most Popular:
30ch6br ;
30s41nzh;
30s15nzh ;
30s64nzh.
After manufacturing, each valve is subjected to factory tests for the strength of body parts and the tightness of the valve.
In addition to the rising stem valve shown in fig. 2, devices with a non-rising spindle are manufactured. Their main feature is a lower building height.
Gate valves with a non-rising spindle are installed in cramped conditions, mainly for operation in pipelines through which water (which does not have impurities), oil and oil products, oils circulate. This type of reinforcement is widely used for shipbuilding.
The principle of operation of a non-rising spindle is that when the handwheel is rotated, it (the spindle) performs only rotational movement. The wedge in this case is wound onto the spindle, which is “hidden” in a special hole (groove) formed in the body of the wedge.
Gate valves with a non-rising stem are mostly made of cast iron.
The model range is represented by the following products:
30h39r ;
M3B ;
M3VG .
Like steel, cast iron gate valves, they are subjected to factory tests before being sold, with the obligatory affixing of the results in the product passport.
It is possible to distinguish a cast-iron product from a steel one in several ways.
1. The name of the reinforcement according to the table of figures.
2. Case color.
3. Scope.
4. Material of wedge sealing surfaces.
Let's compare the designation of steel ( 30s41nzh ) and cast iron ( 30ch39r ) fittings.
30s41nzh - steel valve with stainless steel sealing surfaces. The letter "c" in the designation indicates the material of the body parts. In this case, "c" is high-carbon steel. Marking "nzh" indicates stainless steel overlays. Such seals are mainly used for petroleum products, oils, gasoline, kerosene and some gases.
30h39r - cast iron gate valve with a rubberized wedge. The designation "h" indicates the material of the body parts. The letter "h" is cast iron. Marking "r" means that the wedge is made of rubber. Rubberized closures are used to transport water and steam.
The color of the body, steel and cast iron fittings also differ. Carbon steel products are painted grey. But cast iron valves can be black, red and blue.
Do not confuse the blue and light blue reinforcement markings. Blue color means that the body is made of alloy steel.
If the passport for the product indicates that only water and steam can be used as a working medium, this is cast iron fittings. If it is possible to operate in pipelines through which gases, oil products and other substances circulate, this is a steel valve.
The shutter in the gate valves according to the type of formation is represented by 3 types.
1. Wedge. The sealing surfaces are at an angle to each other.
2. Disk. Seals are parallel.
3. Sheet (gate). The shutter is made of solid metal sheet.
Wedge valves are divided into designs with a rigid, elastic and double-disk wedge. Each type has its own advantages and disadvantages. For example, a rigid wedge has high tightness values, but the process of adjusting the geometry of the seals is difficult.
According to the type of sealing surfaces, the shutter is of 2 types.
1. With EPDM rubber coating (shown in Fig. 3). Rubber wedge is used for installation in pipelines of utility systems. The rubberized wedge resists corrosion and has excellent abrasion resistance in hard water.
2. With built-up surfaces on the wedge and on the body rings. Stainless steel wire is used as the weld material. Stainless steel is used on highways with high pressure and temperatures up to +425 0 C, as well as in the chemical industry.
Figure 5 shows a valve with a stainless steel overlay. A wedge (2) is attached to the stem (1) using a T-connection. The body rings (3) have a welded part in contact with the welded part (5) of the discs (4).
The quality of surfacing and grinding of seals of rings and disks directly affects the tightness class of the gate valve, determined in accordance with GOST 9544-2015. test method.
According to GOST 5762-2002, gate valves are manufactured for pipelines with bore diameters from 15 to 1600 mm. Demanded in production are devices with a nominal diameter of 50 to 800 mm.
Such a variation in standard sizes causes a large difference in the dimensions of each model. For example, the mass of a gate valve with a bore diameter of DN 50 is no more than 40 kg. But the 800 mm model weighs about 3.5 tons. Accordingly, it is inconvenient to use such a device with a manual mechanism.
Therefore, manufacturing plants complete fittings with different drives.
There are:
manual;
mechanical;
electrical;
electromagnetic;
pneumatic;
hydraulic.
Visually, the hydraulic drive is similar to the pneumatic drive. They differ only in the control medium: in the first one, a liquid is used, in the second, respectively, gas (air).
The control medium is a way of influencing the shutter. In our case, it is a liquid or a gas.
Demanded drives are manual, with a mechanical gearbox and electric.
Marking of models equipped with a mechanical gearbox: 30s564nzh , 30s527nzh . The number "5" indicates the type of drive - gearbox.
Models on which the electric drive is installed are marked with the number "9". For example: 30s964nzh , 30s941nzh .
Cast iron fittings are marked in a similar way. Example: 30h906br .
Installation of electric actuators is also carried out on small diameter gate valves. This is due to the length of pipeline systems. In this case, the highway is divided into sections controlled by a single console.
When installing an electric drive, you must be guided by the type of drive connection specified in GOST R 55510-2013. The product data sheet indicates the maximum torque. For each model it is individual. Failure to comply with these requirements may result in damage to the wedge or leakage of the working fluid to the atmosphere.
Body parts of gate valves, which include the body, cover and handwheel, can be made of;
cast iron grade GGG40;
steel grade 25/35L;
alloy steel 20GL;
stainless steel grades 20X5ML, 12X18H9TL or 12X18H12M3TL.
Each metal has its own strength characteristics and structure.
Cast iron bodies are cast for fittings used in municipal systems, for heating and water supply, mainly for water and steam. Additionally, the body is coated with an epoxy-powder composition.
Cast iron GGG40 is a ductile cast iron with nodular graphite in its crystal lattice, which has a lower surface to volume ratio. This factor has a positive effect on the continuity of the metal, which receives a greater resistance to corrosion.
Continuity - the properties of the metal to fill the entire space (volume) without voids and defects. The higher the continuity, the better the alloy.
Treatment of the internal cavities and the outer body of the cast iron gate valve with epoxy-powder composition allows to increase the corrosion resistance, significantly increasing the service life.
Some models of valves are processed by nickel plating.
Nickel plating is the process of applying a layer of nickel to a surface. The layer thickness is 50 µm.
The nickel layer protects the metal from corrosion damage, extending the life of the product.
Steel cases from 25/35L are wide-profile. They are successfully used both for water / steam, and for oil and gas pipelines, nuclear power plant systems and energy.
Alloy 25L is widely used in mechanical engineering. It is used to make bearing housings, pistons and cylinder covers. The operating temperature range for 25L is from -40 0 C to +450 0 C. The use of 25L alloy for gate valves is an indicator of strength and reliability.
Manufacture of housings from alloyed and stainless steels is carried out for highways operated in cold regions (temperatures up to -60 0 C), as well as for highly aggressive environments. Such gate valves are manufactured by order of a particular production.
High demands are placed on drive components. For example, a spindle at one end is in the working environment, and at the other it is a member of a threaded pair, where it is affected by a friction force.
The spindle is made of steel:
20X13;
14X17H2;
12X18H9T.
The increased content of chromium ensures the normal operation of the fittings in difficult conditions with constant friction.
The requirements for the drive nut are lower because it is not affected by the working medium. It uses brass LS59-1, resistant to friction. For cold regions, nuts are available in 40X steel.
In some models, the spindle is made of bronze BrAZhMts10-3-1.5.
In cast iron gate valves, ethylene-propylene rubber (EPDM, VITON, Silicon) is used as a wedge seal. The body of the wedge is cast from GGG40/50 cast iron. To improve the resistance of the wedge to corrosion, a nickel layer is applied to its surface.
In steel reinforcement, the requirements for the wedge and disks are higher than in cast iron products. Therefore, they are made from steel grades 25L, 20GL, or from alloys containing stainless additives of chromium and nickel (for operation in harsh climatic conditions).
Surfacing on the sealing parts of the body rings is carried out using corrosion-resistant wire:
07X25H13;
08X21N10G6.
Since surfacing occurs at a high temperature (up to 3500 0 C), there are certain additives in the surfacing wire that help preserve the crystal lattice of metals.
Wedge seals are welded with steel 13X25T or 10X17T.
Nickel, chromium, titanium and copper are present in these alloys. Due to these metals, the weld surfaces have excellent strength, toughness, abrasion resistance and corrosion resistance.
Basically, at modern valve manufacturing plants, TRG rings are used as stuffing box seals.
TRG is thermally expanded graphite reinforced with various materials.
As a reinforcing substance TRG is used:
stainless steel wire;
cotton thread;
fiberglass;
lavsan;
inconel wire.
Also, AGI asbestos cord is used to seal the stuffing box. It is impregnated with special graphite.
The use of one or another sealant determines the branch of use of reinforcement. For example, when sealing a TRG reinforced with stainless steel wire, it is allowed to operate gate valves in aggressive environments of the chemical industry.
The gate valve is mounted in the pipeline using a flange connection. In addition to this method, a welded joint is used. But the flange is more common.
For an exact match of the holes of the flanges of the fittings and pipes, they are made in response. The process is regulated by GOST 33259-2015.
The fastening of overall fittings in the pipeline occurs with the use of lifting structures (gantry, portal or other cranes). In order not to spoil the body parts, the slings are installed in the places indicated in the instruction manual for a particular model.
Grooves are provided in the flanges of the valve and pipe. They are needed for laying a seal - paronite.
Paronite can be used in 4 types:
ordinary (general purpose);
reinforced (holds high pressure);
oil-petrol resistant (for oil, liquid gas);
electrolysis (for acids).
The body and cover of the valve are also connected by a flange and have the corresponding reciprocal grooves. A specific seal gasket is selected for each area of use.
Gate valves are produced for specific operating conditions, and are divided according to:
nominal diameter DN;
nominal pressure PN;
climatic performance;
maximum temperature of the working environment;
spatial arrangement in the pipeline;
seal tightness class.
The nominal diameter is the nominal diameter measured in the valve. Gate valves can be produced with full or partial bore. The second option means that the diameter in the gate will be smaller than the diameter of the pipe for which the valve is intended.
Nominal pressure is the maximum pressure in the line at which the valve will work normally according to the tightness class declared in the passport. Note that the value of the nominal pressure indicated in the passport determines the maximum pressure of the working medium at its temperature equal to 20 0 C.
This parameter characterizes the limiting ambient temperature at which the valve can be operated.
1. T1 - from -10 0 С to +50 0 С.
2. TpU1 - from -29 0 C to +40 0 C.
3. U1 - from -40 0 С to +40 0 С.
4. HL1 - from -60 0 С to +40 0 С.
Climatic version is classified according to GOST 15150-69g.
For gate valves, the bodies of which are made of stainless steel, the temperature limits of the media are wider than for steel and cast iron.
For stainless steel cases, the temperature range is from -40 0 C to +550 0 C. For steel products - from -10 to +425 0 C.
But for cast iron, these figures are much lower:
from -5 0 C to +90 0 C when using an EPDM shutter;
from -5 0 C to +150 0 C when using their VITON and Silicon shutter.
Operation of gate valves at maximum temperature is carried out with a mandatory decrease in the pressure of the working medium. This is due to a decrease in the strength of body parts.
Basically, cast iron and steel gate valves are designed to operate in a vertical spindle position. When installed in a pipeline, it is allowed to place fittings with a deviation of up to 90 degrees in any direction. In doing so, the location requirements of the drive must be taken into account.
There are no spatial restrictions for manual and mechanical drives. But for an electric drive, pneumatic or hydraulic, manufacturers can set restrictions that are indicated in the product passport.
When installing gate valves with a large diameter (from 400 mm), as well as those equipped with an electric drive, it is additionally necessary to provide a support for the drive (when mounting with a deviation of up to 90 degrees).
Support is also required under the valve if the pipeline is not reinforced in this place.
Before you buy a batch of gate valves, you must select the required tightness class of the gate. At factories, this parameter is determined by experimental (acceptance) tests on special installations.
The procedure for testing and the tightness class are determined by GOST 9544-2015. According to this document, valves are tested with liquid or gas.
If the valve is to be installed in a pipeline for transporting liquid and non-hazardous substances, tests can be carried out with a liquid (water, kerosene).
When installing on pipelines in which the working medium is gas or a hazardous chemical - tests are carried out only with gas (air, nitrogen).
In each specific case, by agreement between the factory and the customer, tests can be carried out with liquid and gas, only gas or only liquid.
The test requirements for liquid and gas are different. So, when water is supplied to the pipe, its pressure rises to the PN mark indicated in the passport for the valve, and increases by 10%. In this state, the valve is kept for some time and the leakage volume is measured.
The time to start measuring leakage after a steady pressure is different for each valve.
1. For DN up to 50mm, the holding time is 1 minute.
2. DN from 65mm to 150mm - 2 minutes.
3. For DN from 200mm and more - 3 minutes.
These standards apply to both water and air tests. For air, the pressure in the system is brought to 0.6 MPa, regardless of the diameter of the passage.
Valves produced can have a tightness class from A to G. Class A is the highest and is assigned to valves that have no leakage in the valve.
Since the pipelines operate under high pressure, the installer's mistake will result in victims. Therefore, the installation of valves should only be carried out by trained personnel who have access and permission to carry out this type of work.
Before installation it is necessary:
carry out re-preservation, in compliance with the requirements of GOST 9.014-78;
lubricate the spindle with special grease;
remove the factory plugs from the nozzle;
check the cavities of the nozzles for the presence of foreign objects and dirt;
check the operation of the shutter by opening and closing it.
Installation in the highway is carried out using lifting mechanisms (cranes). It is possible to hang the valve only by the nozzles or by the method specified in the operating instructions.
It is necessary to depreserve the fittings immediately before installation.
When the valve is connected to the pipeline, it is not allowed to collide with the connecting pipes. Hangers can only be removed after all bolts, nuts and studs have been installed in the flange holes (or after welding has been completed). Failure to comply with this paragraph will lead to distortion of the flange connection and loss of tightness.
Bolts and nuts are tightened with a special torque wrench with a built-in dynamometer. This device provides tightening of fasteners with the established norms of effort, preventing overtightening.
After installation of fittings, hydraulic tests (pressure testing) are carried out. This procedure is carried out with a working medium, with an increase in maximum pressure by 25%.
When pressing, check:
the tightness of the connection of the flanges of the valve and the pipeline;
tightness of the gasket connection between the body and the cover;
seal tightness.
Crimping is carried out with a mandatory open passage. Movement of the valve when the test pressure is reached is not allowed.
The results of hydraulic tests are recorded in the product passport.
If, after purchasing a batch of fittings, it is not planned to install it in the pipeline in the near future, or the removed valve must be removed for long-term storage, conservation measures are taken.
The conservation procedure is specified in GOST 9.014-78g. It is necessary to store the device in its original packaging with the nozzles cleaned of residual medium and plugged. The spindle must be lubricated with special grease VNIINP-232.
The shutter closes during storage without fail.
Transportation of preserved fittings is carried out in the original packaging. The box must be secured with transportation fasteners that do not allow longitudinal and transverse displacements during movement. Loading and unloading operations are carried out without shocks and shocks.
