The flanged spring safety valve 17s28nzh is one of the main types that is used to protect pipeline equipment. The spring safety valve 17s28nzh is designed to protect equipment and pipelines from unacceptable excess pressure in the system. Ensuring safe pressure values is carried out by automatically discharging excess working fluid into a specially installed outlet pipeline or into the atmosphere, and when the operating pressure is restored, safety valve 17s28nzh stops discharging the working medium.
The spring safety valve 17s28nzh is mounted with the equipment and using a flange connection. The flanged spring safety valve 17s28nzh has a service life of more than 11 years, and the manufacturer provides a guarantee for it for 18 months from the date the valve is put into operation. Safety valve 17s28nzh is not sealed in relation to the external environment.
Material of the main parts from which the 17s28nzh safety spring valve with flange connection is made:
- Housing, cover - Steel 25L
- Disc, seat - Steel 20Х13
- Rod - Steel 20Х13/Steel 40
- Gasket - AD1M
- Spring - 50HFA
Safety device spring valve 17s28nzh
1 .Cap
2 . Adjustment screw
3 . Spring
4 . Lid
5 . Stock
6 . Manual detonation unit
7 . Spool assembly
8 . Saddle
9 . Frame
Overall and connecting dimensions of safety valve 17s28nzh
|
DN, mm |
Dimensions, mm |
||||||||||||
| 4 | |||||||||||||
Technical characteristics of safety valve 17s28nzh
|
Name |
Meaning |
|||
|
Nominal diameter, DN, mm |
||||
|
Seat hole diameter dc, mm |
||||
|
Allowable leakage in the valve, cm 3 /min |
5-for air 1-for water |
10-for air 2-for water |
||
|
Seat cross-sectional area Fс, mm 2, not less |
||||
|
Nominal inlet pressure РN, MPa (kgf/cm2) |
||||
|
Nominal outlet pressure РN, MPa (kgf/cm2) |
||||
|
Full opening pressure Рп.о. MPa (kgf/cm 2), no more |
For gaseous media: pH+0.05 (0.5) for pH<0,3 МПа; 1,15 Рн для Рн>0.3 MPa For liquid media: pH+0.05 (0.5) for pH<0,2 МПа; 1,25 Рн для Рн>0.2 MPa |
|||
|
Closing pressure Рз |
not less than 0.8 pH |
|||
|
Spring setting pressure limits, pH MPa (kgf/cm2), not less |
0,05-0,15 (0,5-1,5); 0,15-0,35 (1,5-3,5); 0,35-0,7 (3,5-7,0); 0,7-1,0 (7-10); 1,0-1,6 (10-16) |
|||
|
Temperature environment, RS |
from minus 40 to 40 |
|||
|
Working environment temperature, °С |
from minus 40 to 450 |
|||
|
Characteristics of the working environment |
Water, steam |
|||
|
Flow rate? |
0.8 for gaseous; 0.5 for liquid media |
|||
|
Connecting dimensions and dimensions of housing sealing surfaces |
according to GOST 12815-80 version 1 row 2 |
|||
|
Weight without flanges (kg) |
||||
All vessels operating under increased pressure must be equipped with safety devices against increased pressure. For this we use:
lever-load PCs;
safety devices with collapsible membranes;
Lever-load PCs are not allowed for use on mobile vessels.
Schematic diagrams of the main types of PCs are shown in Figures 6.1 and 6.2. Weight on lever-weight valves (see fig. 6.1,6) must be securely fixed in the specified position on the lever after calibration of the valve. The design of the spring PC (see Fig. 6.1, c) must exclude the possibility of tightening the spring beyond the established value and provide a device for
Rice. 6.1. Schematic diagrams of the main types safety valves:
checking the proper operation of the valve in working condition by forcing it to open during operation. The design of the spring safety valve is shown in Fig. 6.3. Number of PCs, their sizes and throughput must be calculated so that in Fig. 6.2. The bursting safety membrane did not exceed more than 0.05 MPa for vessels with pressure up to 0.3 MPa, at
15% - for vessels with pressure from 0.3 to 6.0 MPa, by 10% - for vessels with pressure more than 6.0 MPa. When operating PCs, it is allowed to exceed the pressure in the vessel by no more than 25%, provided that this excess is provided for by the design and is reflected in the vessel passport.
PC throughput is determined according to GOST 12.2.085.
When determining the size of the flow sections and the number of safety valves, it is important to calculate the valve capacity per G (in kg/h). It is performed according to the methodology outlined in the SSBT. For water vapor, the value is calculated using the formula:
G=10B 1 B 2 α 1 F(P 1 +0.1)
Rice. 6.3. Spring device
safety valve:
1 - body; 2 - spool; 3 - spring;
4 - outlet pipeline;
5 - protected vessel
Where bi - a coefficient that takes into account the physicochemical properties of water vapor at operating parameters in front of the safety valve; can be determined by expression (6-7); varies from 0.35 to 0.65; coefficient taking into account the pressure ratio in front of and behind the safety valve, depends on the adiabatic index k and indicator β, with β<β кр =(2-(k+1)) k/(k-1) коэффициент B 2 = 1, показатель β вычисляют по фор муле (6.8); коэффициент B 2 varies from 0.62 to 1.00; α 1 - flow coefficient indicated in the safety valve data sheets, for modern designs of low-lift valves α 1 = 0.06-0.07, high-lift valves - α 1 = 0.16-0.17, F- valve flow area, mm 2; R 1 - maximum excess pressure in front of the valve, MPa;B 1 =0.503(2/(k+1) k/(k-1) * 
Where V\ - specific volume of steam in front of the valve at parameters P 1 and T 1, ) m 3 /kg - temperature of the medium in front of the valve at pressure Pb °C.
(6.7)β = (P 2 + 0.1)/(P 1 +0.1), (6.8)
Where P2 - maximum excess pressure behind the valve, MPa.
Adiabatic exponent k depends on the temperature of the water vapor. At a steam temperature of 100 °C k = 1.324, at 200 "C k = 1.310, at 300 °C k= 1.304, at 400 "C k= 1.301, at 500 ° Ck= 1,296.
The total throughput of all installed safety valves must be no less than the maximum possible emergency flow of medium into the protected vessel or apparatus.
Safety diaphragms (see Figures 6.2 and 6.4) are specially weakened devices with a precisely calculated pressure failure threshold. They are simple in design and at the same time provide high reliability of equipment protection. The membranes completely seal the discharge hole of the protected vessel (before actuation), are cheap and easy to manufacture. Their disadvantages include the need for replacement after each actuation, the inability to accurately determine the actuation pressure of the membrane, which makes it necessary to increase the safety margin of the protected equipment.
Diaphragm safety devices can be installed instead of lever-load and spring safety valves if these valves cannot be used in a particular environment due to their inertia or other reasons. They are also installed in front of the PC in cases where the PC cannot operate reliably due to the peculiarities of the influence of the working environment in the vessel (corrosion, crystallization, sticking, freezing). The membranes are also installed in parallel with the PC to increase the capacity of pressure relief systems. The membranes are also installed in parallel with the PC to increase the throughput of pressure relief systems. Membranes can be bursting (see Fig. 6.2), breaking, tearing (Fig. 6.4), shearing, snapping out. The thickness of bursting discs A (in mm) is calculated by the formula:
P.D./(8σ vr K t )((1+(δ/100))/(1+((δ/100)-1)) 1/2
Where D - working diameter; R- membrane response pressure, σ BP - tensile strength of the membrane material (nickel, copper, aluminum, etc.); TO 1 - temperature coefficient varying from 0.5 to 1.8; δ is the relative elongation of the membrane material at rupture, %.
For tear-off membranes, the value determining the response pressure is
is the diameter D H (see Fig. 6.4), which is calculated as
D n =D(1+P/σ time) 1/2
It is not allowed to install any shut-off valves between the vessel and the safety device, as well as behind it. In addition, safety devices must be located in places convenient for their maintenance.
Safety devices. Safety devices (valves) must automatically prevent pressure from increasing above the permissible level by releasing the working fluid into the atmosphere or disposal system. At least two safety devices must be installed.
On steam boilers with a pressure of 4 MPa, only pulse safety valves should be installed.
Passage diameter (conditional) installed on lever-type boilers; load and spring valves must be at least 20 mm. The tolerance is to reduce this passage to 15 mm for boilers with a steam capacity of up to 0.2 t/h and a pressure of up to 0.8 MPa when installing two valves.
The total capacity of safety devices installed on steam boilers must be no less than the rated capacity of the boiler. Calculation of the capacity of limiting devices of steam and hot water boilers must be carried out according to 14570 “Safety valves of steam and hot water boilers. Technical requirements".
The installation locations of safety devices are determined. In particular, in hot water boilers they are installed on the outlet manifolds or drum.
The method and frequency of regulation of safety valves on boilers is indicated in the installation instructions and instructions. Valves must protect vessels from exceeding the pressure in them by more than 10% of the calculated (permitted) pressure.
Short answer: All vessels operating under increased pressure must be equipped with safety devices against increased pressure. For this we use:
spring safety valves (SC);
lever-load PCs;
pulse safety devices consisting of a main PC and a direct-acting pulse control valve;
safety devices with rupture membranes;
other safety devices, the use of which has been approved by the Gosgortekhnadzor of Russia.
To relieve excess pressure into the atmosphere, spring safety valves are used, which are special pipeline fittings that provide reliable protection of the pipeline from malfunctions and mechanical damage. The device is responsible for automatically discharging excess liquids, steam and gas from vessels and systems until the pressure is normalized.
Purpose of a spring valve
Dangerous excess pressure in the system occurs as a result of external and internal factors. An increase is caused by both incorrect assembly of thermal-mechanical circuits, which causes malfunctions in the functioning of equipment, heat entering the system from extraneous sources, and intra-system physical processes that are not provided for by standard operating conditions that periodically occur in the system.
Safety products are an essential part of any domestic or industrial pressure system. Installation of safety mechanisms is carried out on pipelines in compressor stations, in autoclaves, and in boiler rooms. Valves perform protective functions on pipelines through which not only gaseous, but also liquid substances are transported.
Design and principle of operation of spring valves
The valve consists of a steel body, the lower fitting of which is used as a connecting element between it and the pipeline. If the pressure in the system increases, the medium is discharged through the side fitting. A spring adjusted depending on the pressure in the system ensures that the spool is pressed against the seat. The spring is adjusted using a special bushing, which is screwed into the top cover located on the body of the device. The cap located in the upper part is designed to protect the bushing from destruction as a result of mechanical stress. The presence of a special ear for sealing allows you to protect the system from outside interference.
For valves in which a spring acts as a balancing mechanism, the force of the working element is selected. If the parameters are selected correctly, in the normal state of the system, the spool responsible for releasing excess pressure from the pipeline should be pressed against the seat. When performance increases to a critical level, depending on the type of spring device, the spool moves up to a certain height.
The safety spring valve, which ensures timely release of pressure, is made of different materials:
- Carbon steel. Such devices are suitable for systems in which the pressure is in the range of 0.1-70 MPa.
- Stainless steel. Stainless steel valves are designed for systems in which the pressure does not exceed 0.25-2.3 MPa.
Classification and characteristics of spring valves
The spring safety valve is available in three versions:
- Low lift devices suitable for gas and steam pipeline systems, the pressure in which does not exceed 0.6 MPa. The lifting height of such a valve does not reach more than 1/20 of the seat diameter
- Mid-lift devices, in which the lifting height of the spool is from 1/6 to 1/10 of the nozzle diameter.
- Full lift devices, in which the valve lift height reaches up to ¼ of the seat diameter.
There is a known classification of valves based on the method of opening them:
- Non-return spring valve. To control spring check valves, an indirect external pressure source is used. Spring check valves, called impulse safety devices, can be operated by electrical power.
- Straight valve. In direct type devices, the operating pressure of the medium has a direct effect on the spool, which rises as the pressure increases.
Highlight valves open And closed type. In the case of using a direct type device, when the valve is opened, the medium is discharged directly into the atmosphere. Closed type valves remain completely sealed to the environment, releasing pressure into a special pipeline.
Advantages
There are various types of equipment that provide relief of excess pressure from the system, but spring safety valves are popular due to the presence of important advantages:
- Simplicity and reliability of design.
- Ease of setting operating parameters and ease of installation.
- Variety of sizes, types and designs.
- Installation of the safety product is possible in both horizontal and vertical positions.
- Relatively small overall dimensions.
- Large flow area.
The disadvantages of safety valves include the presence of restrictions in the lifting height of the spool, increased requirements for the quality of manufacturing of the spring for safety valves, which can fail when operating in an aggressive environment or constant exposure to high temperatures.
How to choose a spring valve?
When choosing a fuse, you should be based on several important principles, the consideration of which determines the uninterrupted operation of the system and the ability of the fuse to perform the necessary functions:
- Spring safety valves have the smallest dimensions compared to other types of safety relief valves, so they should be chosen in cases where there is not enough free space.
- Features of the use of valves are associated with the presence of increased vibrations, which negatively affect the operational characteristics of the device and can quickly render it unusable. For example, lever-load type devices are more susceptible to breakdowns due to exposure to vibrations due to the presence of a long lever with weight and hinges in the design. Therefore, for systems in which significant vibration effects are observed, it is worth choosing a spring safety valve.
- Depending on the design features of the device, the spring may change the pressure force over time. This is due to the fact that the constant rise of the spool causes changes in the structure of the metal.
Installation nuances
A spring-type safety valve is installed at any point in the system that is subject to increased pressure and is at risk of mechanical damage. The device does not require a lot of free space, which is a significant advantage compared to other types of safety devices.
To avoid operational problems, do not install any shut-off valves in front of the safety valve. To discharge the gaseous medium, special devices are installed or the discharge occurs directly into the atmosphere. To alert personnel, a special whistle is mounted along with the spring valves, which is placed on the discharge pipe. When the valve is activated, a whistle will sound, indicating that the pressure in the system has increased and the valve has opened to release the medium.
Possible causes of safety valve failures
Safety valves are durable and reliable devices that provide constant protection of systems from overpressure. A direct or reverse spring valve fails for several reasons:
- The presence of increased vibrations;
- Constant exposure to an aggressive environment on the safety choke.
- Incorrect installation of safety spring throttle or valve.
In order to avoid accidents and malfunctions in the functioning of systems, safety valves undergo periodic checks for malfunctions. Valves are tested for strength and tightness before being put into operation. Periodic checks are also carried out to determine the tightness of sealing surfaces and gland connections.
With the correct selection of safety devices taking into account the system parameters, periodic inspections and timely troubleshooting, spring safety valves will ensure reliable operation of the system and trouble-free protection against overpressure for a long time.
A check valve is an element of a pipeline system that allows for the movement of the working medium in only one direction. Its use is mandatory for autonomous pumping stations and other equipment that may fail when the fluid flow moves in the opposite direction.
A spring check valve is one of the types of shut-off elements. It belongs to the category of direct-acting valves and is activated automatically by the energy of the working environment, which prevents equipment failure in the event of a power outage or other malfunctions.
Design features
The spring valve is structurally composed of three elements:
- A body usually made of brass and equipped with elements for fastening to the pipeline (coupling, thread). The body is also made of steel, cast iron and polypropylene. The choice of material is determined by the parameters of the working environment and the diameter of the pipeline.
- The working element, which represents a movable spool, includes two plates with a special sealed gasket between them and a rod.
- An actuator representing a spring located between the work element plates and the seat. Provides automatic shutoff of fluid flow when pressure decreases or changes its direction. The minimum pressure of the working medium at which the valve automatically opens depends on the stiffness of the spring.
Advantages of spring check valves:
- Possibility of installation in any position;
- simplicity of design;
- versatility.
At the same time, the valve is sensitive to contaminants in the water, which lead to wear of the sealing plates, so it is advisable to install a filter in front of it. It is also recommended that the valve be mounted in an easily accessible location to facilitate maintenance and replacement.
It is advisable to install the valve in a vertical position so that the blocking force of the spring coincides with the action of gravity. For correct installation, it is necessary to focus on the arrow marked on the valve body, which shows the direction of flow of the working medium through.
Scope of application
Spring check valves are widely used in autonomous water supply systems and intra-house networks of apartment buildings. They are installed on the suction lines of pumps, in front of storage tanks, boilers, water meters and other equipment.
Spring safety valve (PPV)– a type of pipeline fittings designed to automatically protect equipment and pipelines from excess pressure above a predetermined value by releasing excess working fluid and ensuring that the discharge stops when the closing pressure is restored and the operating pressure is restored.
Main valve assemblies and parts:
1 - body, 2 - seat, 3 - spool, 4 - cover, 5 - rod, 6 - nut, 7 - pin, 8 - spring, 9 - bellows (installed in bellows valves), 10 - locking screw, 11 - adjusting bushing, 12 - guide bushing, 13 - partition, 14 - adjusting screw, 15 - cap, 16 - threaded flange.
Principle of operation. At normal operating pressure, the force of the compressed spring presses the spool against the seat (the passage for relieving the working medium is closed). When the pressure increases above the set value, an oppositely directed force begins to act on the spool, which compresses the spring, and the spool rises, opening a passage for discharging the working medium. After the pressure in front of the valve decreases to the closing pressure, the spool under the action of the spring is again pressed against the seat, stopping the discharge of the medium.
Installation position – vertical, cap up.
Shutter tightness– class “B” GOST R 54808. At the customer’s request, it is possible to manufacture with other classes of tightness.
Possible valve designs:
- A sealed cap with a forced opening unit, and without one.
- Balancing bellows.
- Thermal barrier.
- "Open" lid.
- A locking element that prevents the valve from operating.
Pipeline connection:
- flanged;
- for lens gasket (flange according to GOST 9399);
- fitting;
- tsapkovoe.
Valves with bellows.
The bellows is a mechanism that compensates for the effect of back pressure at the outlet of the valve. The bellows is designed to protect the valve spring from the harmful effects of an aggressive working environment under conditions of high or low temperatures. Bellows valves are made of steel grades 12Х18Н9ТЛ and 12Х18Н12МЗТЛ and are intended for working environments with temperatures from minus 60 °С and below. Designation of bellows valves: KPP4S, KPPS.
The design of the sealing surfaces and the connecting dimensions of the valve flanges are in accordance with GOST 12815-80, row 2, face-to-face lengths are in accordance with GOST 16587-71.
Valves DN 25 PN 100 kgf/cm2 can be manufactured with union ends for connection to a pipeline in accordance with GOST 2822-78, as well as with a flange connection in accordance with GOST 12815-80, row 2.
Safety valves with nominal pressure PN 250 kgf/cm2 and PN 320 kgf/cm2, like other models, are designed to protect equipment from unacceptable excess pressure by automatically releasing excess working fluid. Used on equipment with liquid and gaseous working media that do not cause corrosion of body parts greater than 0.1 mm.
Safety valves with a stamped-welded body can be manufactured with individual face-to-face length (L and L1), height (H) and flange mounting dimensions, which allows them to be used as substitutes for imported valves without changing already installed equipment and pipelines.
Calculation of valve capacity - according to GOST 12.2.085-2002.
Setting pressure, pH– the highest excess pressure at the inlet to the safety valve, at which the valve is closed and the specified tightness of the valve is ensured.
Opening start pressure, Рн.о.(starting pressure; set pressure) – excess pressure at the inlet to the safety valve, at which the force tending to open the valve is balanced by the forces holding the locking element on the seat. When the opening pressure begins, the specified tightness in the valve shutter is broken and the locking element begins to rise.
Full opening pressure, Рп.о.– excess pressure at the inlet to the safety valve, at which the valve moves and maximum throughput is achieved.
Closing pressure, Рз(reseating pressure) – excess pressure at the inlet to the safety valve, at which, after the working medium is discharged, the locking element is seated on the seat, ensuring the specified tightness of the valve. Valve closing pressure, Рз – not less than 0.8 Рн.
Back pressure– excess pressure at the outlet of the fittings (in particular, from the safety valve).
Back pressure is the sum of the static pressure in the exhaust system (in the case of a closed system) and the pressure arising from its resistance when the working fluid flows.
Mandatory minimum order information.
When ordering valves, you must fill out a questionnaire (Appendix B):
- product type, designation, type designation (according to the table of figures);
- nominal diameter of the inlet pipe, DN, mm;
- nominal pressure, PN, kgf/cm2;
- setting pressure (Рн, kgf/cm2) or spring number (when only the spring number is specified, the valve is adjusted to the minimum value from the range of the specified spring);
- body material;
- the presence of a manual detonation unit in the valve design;
- the presence of a bellows in the valve design.
Example of designation when ordering a spring safety valve:
An example of designation when ordering a spring safety valve DN 50 PN 16 kgf/cm2 made of steel 12Х18Н9ТЛ with a manual detonation unit, setting pressure – Рн=16 kgf/cm2, model KPP4R according to TU 3742-005-64164940-2013:
Safety valve KPP4R 50-16 DN 50 PN 16 kgf/cm2, pH=16 kgf/cm2, 17nzh17nzh. When placing an order, the need to complete the valves with matching parts (matching flanges, gaskets, studs, nuts; for valves DN 25 PN 100 - nipples with union nuts and gaskets) is specifically stated.
