Safety devices. Safety shut-off valves PKN and PKV
According to existing safety requirements, no machine, machine or equipment can be considered suitable for performing work if it does not have safety protective devices in case of emergency conditions. Safety devices are based on the principle of turning off equipment when a controlled parameter (pressure, temperature, force, movement, etc.) goes beyond acceptable limits.
The fundamental solutions and design of safety devices are varied and depend on the characteristics of the equipment and the technological process.
Depending on the nature of the occurrence of a hazardous production factor, all safety devices can be divided into four groups:
Fuses against mechanical overloads;
Fuses to prevent movement of machine parts beyond the established dimensions;
Fuses against excess pressure and temperature;
Fuses to prevent electric current from increasing beyond permissible limits.
To protect against mechanical overloads and prevent related accidents, couplings, load limiters, speed controllers, shear pins and studs are used. Friction clutches are widely used in agricultural machines, in which the pressure between the friction surfaces is created by springs adjusted to transmit the maximum torque. The clutch is activated when the working body is overloaded. Lifting mechanisms are equipped with load limiters, which eliminates dangerous overload during lifting and moving cargo.
Simplest type load lever limiter is shown in Figure 3.4.
Figure 3.4 – Diagram of operation of the load lever load limiter
When the crane is overloaded, the force P from pressing the branches of the cargo rope 1 will exceed the value of the balancing moment from the load 4. Lever 3 will turn, and its right end will press the limit switch lever 5 and open the control circuit of the electric motor. The actuation moment is regulated by moving the load G along the lever. The mechanism is triggered if the following condition is met:
If the pulleys and gears are secured to the drive shaft using safety pins or studs, then when the permissible loads they are cut off and the pulley (gear) rotates on the shaft idle. To resume operation of the mechanism, it is necessary to replace the cut pin (pin).
Speed controllers operate on the principle of automatically limiting the supply of fuel to the engine cylinder and preventing a dangerous increase in speed in the event of malfunctions of fuel supply devices in internal combustion engines.
To protect moving parts of a machine from going beyond the established limits and to prevent associated machine breakdowns, limit switches (travel limiters), stops, grips and stops are used. Limit switches are widely used in lifting mechanisms to limit the path of movement of the load both horizontally and vertically. vertical planes, on metal cutting machines– to turn off the movement of the caliper, to change the direction of movement of the working body, etc.
To prevent accidents (explosions), mechanisms operating under pressure of steam, gas or liquid above atmospheric pressure are equipped with safety devices in the form of valves and membranes. All steam boilers, hydraulic and pneumatic systems are equipped with safety valves, which, if the pressure exceeds established standards open and thereby relieve excess pressure of steam, liquid or gas (air).
The designs of the valves are different, but they have one purpose - to prevent an accident and prevent accidents with operating personnel.
If we neglect the masses of the valve levers, then the condition under which the lever valve begins to open will look like:
(3.7)
and for a spring valve:
(3.8)
where a is the coefficient of steam flow through the valve; N – limit operating pressure in a vessel, Pa; G – mass of moving cargo, kg; T – spring force, N; , – lever arms, m; d – hole diameter, m.
Safety valves can effectively protect equipment only if the pressure builds up relatively slowly, does not require a greater degree of tightness, and there is no corrosive effect of the environment. In conditions where the performance of the safety valve is insufficient, safety membranes are used. To manufacture the membrane, a thin metal plate is used, the thickness of which must be such that when pressure exceeds permissible limits, it ruptures and a shock wave escapes into the atmosphere.
Safety devices of this design are installed on some models of foam fire extinguishers. For boiler installations, the membrane is made from sheet asbestos. The design and dimensions of the membrane must be such that after its rupture the possibility of a further increase in pressure in the vessel is excluded.
Figure 3.5 shows a diagram of the operation of the safety water seal low pressure installed on acetylene generators to prevent their explosion. During the reverse impact, the explosive mixture enters the gate, and some of the water is displaced along the gas outlet pipe 4. When the end of tube 5 is detected, the gas will begin to escape into the atmosphere. After excess gas escapes through tube 5 and the pressure drops, the valve will begin to operate normally.
A great danger is the appearance of electric current on parts of equipment that are not energized under normal conditions. To prevent current from increasing to dangerous values, fuses are used on parts of equipment. When the current exceeds the established limits, the fuse melts and interrupts the electrical circuit. At more critical installations, circuit breakers are used for protection.
Figure 3.5 – Scheme of operation of a low pressure drop water seal: a) during normal operation; b) during a reverse impact; 1 – body; 2 – funnel; 3 – stop valve; 4 – gas exhaust pipe; 5 – safety tube; 6 – control valve
Safety devices include pulse safety devices (IPD) and safety valves direct action. Safety devices are designed to ensure safe work equipment and systems of power plants by protecting them from overpressure working environment(saturated or superheated water vapor) above the permissible value.
Safety devices operate automatically and, when opened, release excess working fluid from the protected vessel or system into the atmosphere. IPUs are designed for installation on drums and outlet manifolds of boiler units with a nominal steam pressure of 10.0, 14.0 and 25.5 MPa, on the “cold” and “hot” lines of pipelines for intermediate superheating of steam, as well as on pipelines of reduced and cooled steam ( behind reduction-cooling units) with conditional pressure 6.3 MPa.
The main difference between the pulse valves (PV) included in the IPU, supplied for the protection of coglobin units, from those supplied for pipelines for intermediate superheating, as well as reduced and cooled steam, is their equipment with an electromagnetic drive, which ensures high accuracy of operation (opening and closing ) of these valves and the IPU as a whole. Such an electromagnetic drive is based on two electromagnets or one double-acting electromagnet, which ensure timely opening and closing of the device.
The IPU is adjusted to the specified opening and closing pressure using only a pulse valve. This is achieved by installing the weight on the IR lever in a position that ensures the valve opens at the set pressure. The IR and IPU as a whole closes at a pressure lower than the nominal one. If electrical power is lost in the control circuit, the safety device is activated by the weight on the pulse valve lever.
The hydraulic valves are equipped with a hydraulic damper to soften the impact of the chassis parts when the valve opens and closes. Brake fluid is process water, the constant supply of which to the damper is provided by the device shown in the wiring diagram.
The choice of one or another direct-acting valve or IPU from the nomenclature given in this catalog is carried out depending on the parameters of the working environment in the protected vessel or system, as well as on the required throughput, i.e. steam flow through the valve per unit time.
Number of safety valves and their capacity for power plants general purpose must be selected by calculation in accordance with the normative and technical documentation agreed with the technical supervision of the Republic of Belarus.
Technical requirements include structural strength requirements for given energy parameters of the working environment (pressure, temperature); corrosion resistance of the material against chemical exposure of the working environment; compliance of the dimensions of the nominal diameter of the passage and connecting (main) pipes with the corresponding dimensions of the pipeline; compliance with the device design functional purpose; ensuring the required hydraulic parameters and characteristics (throughput); ensuring the required speed; compliance of the type of energy used to control the device with the available energy sources (electric, compressed air, mineral oil under pressure, working fluid transported through a pipeline). Also assessed dimensions devices that determine the size of the room or space required for its placement, convenience and method of control, reliability parameters.
Economic requirements include: cost of construction; cost of operation, repair, replacement of worn parts, Maintenance, the cost of the required premises; the cost of products (working environment) lost through possible leaks in the shut-off organ, gland and through the destroyed membrane after its rupture; the cost of equipment downtime caused by the need to repair or replace an installed device.
If several designs can satisfy the requirements, the final decision is made based on a comparative assessment of competing options. The first stage is to establish the possibility of using a design that is mass-produced by industry, and only if the required one is not available, data is prepared for its design and production on a special order.
On pipelines transporting flammable, flammable petroleum products or active gases and liquids with toxic properties, it is recommended to use designs specifically designed for these environments under specified operating conditions. The use of general-purpose structures is permitted only if they, as well as the materials of the parts, comply with the requirements of reliable and safe operation. For aggressive environments, it is allowed to use parts with corrosion-resistant metal and non-metallic coatings applied to their surfaces. Nominal diameter passage in the vast majority of cases is equal to the diameter of the pipeline passage.
For explosive and fire hazardous, toxic or highly pure environments, designs with bellows sealing of the rods are used; it is also provided if the system requires evacuation. On mobile installations (tanks), it is not recommended to use safety valves and fill limiters (level regulators) of general technical structures, since they are not designed to operate in vibration conditions. Devices operating on lines with toxic, fire- and explosive atmospheres are subject to increased requirements for the tightness of the shut-off valve, gland (bellows) and detachable connections covers with housing and connecting pipes.
Fastening of protective and safety devices to the pipeline is most often provided by flange connections, which allow for quick replacement or removal for repairs. The type of flange connection and gasket material are selected depending on the operating conditions of the product, pressure, temperature and corrosive properties of the working environment. In pipelines of small passage diameter (DN<80 p="">
However, its scope of application is limited by a number of inherent disadvantages, which include the following: the difficulty of installing the product on a pipeline due to the need to screw together a section of pipe, a fitting or the product itself; the possibility of forming a permanent connection as a result of corrosion of surfaces in contact in the thread; the difficulty of making threads large diameter and the large torque required when assembling a large diameter threaded connection. Threaded connection chosen only when dismantling the product is unlikely. The flange connection is universal and is often used if it is expected that the product will need to be removed for repair or replacement. The most reliable and tight connection is achieved by welding, and it is widely used for steel in all cases where this is permissible.
In flange connections with ru<2,5 300="">2.5 MPa (regardless of temperature) and at temperatures above 300 °C (regardless of pressure) studs with nuts are used.
To assess the operating conditions of protective and safety devices important have physical and Chemical properties working environment. The viscosity of liquid petroleum products can be in a wide range of values. The dynamic viscosity of a liquid is measured in pascal seconds (Pahs). To assess the viscosity of petroleum products, the values of conditional viscosity are used, which are defined as the ratio of the time of flow of 200 ml of the tested petroleum product from an Engler viscometer at the test temperature (the viscosity of petroleum products depends on temperature) to the time of flow of the same volume of distilled water at 20 °C, which is the water number of the device. This ratio, expressed in conventional degrees, is denoted by VU.
Of great importance for mechanisms operating in petroleum products is the oiliness of the liquid, which helps reduce friction. Gasoline, as a solvent for mineral lubricants, exposes metal and creates conditions for friction without lubrication in moving joints. Increased viscosity creates difficulties when transporting petroleum products through pipes and through safety valves due to the high internal friction of the fluid and, as a consequence, the high hydraulic resistance of local hydraulic obstacles. Very viscous petroleum products are transported heated. The viscosity of petroleum products is determined by paraffin, the content of which in oil ranges from tenths to 15%. Based on the paraffin content, oils are divided into three types: low-paraffin (up to 1.5%); paraffinic (1.51-6.0%) and highly paraffinic (more than 6%).
The operating conditions of protective and safety devices, for example the SMDK valve, are influenced by the corrosive effect of petroleum products associated with the content of acids, water, sulfur and hydrogen sulfide in them. The acidity of petroleum products is assessed by the acid number, which is determined by the number of milligrams of KOH required to neutralize 1 ml of petroleum product. Usually it does not exceed 0.02-0.07.
1. classification of safety devices
2 Certification of labor protection work:
3. joint operation of fans: For ventilation, two and larger number fans. The effectiveness of their joint work depends on the pressure characteristics and location in the ventilation network, as well as on the aerodynamic resistance of the network. There are three possible schemes for joint operation of fans in a network: serial, parallel and combined. The energy of air movement in a passive ventilation network using two or more fans is supported by their useful power.
4.Air-mechanical foam as a fire extinguishing agent: foams are colloidal systems consisting of gas bubbles, the shell of which contains a 3-5% aqueous solution of a foaming agent. Foams are used for extinguishing solid and liquid flammable substances that do not interact with water, and primarily for extinguishing oil products. The fire extinguishing effect of foam is based on cooling the fire with water, as well as partially isolating the combustion zone from access fresh air. The advantages of foam as a fire extinguishing agent include:
Duration of foam retention of its structure and volume, which allows for both area and volumetric fire extinguishing
Possibility of remote influence on the source of fire
The ability of foam to move over significant distances and penetrate into hard to reach places
The fire extinguishing properties of foam are largely determined by its expansion rate and durability. Multiplicity is the ratio of the volume of foam to the volume of the liquid phase. Durability is the resistance of foam to the destruction process and is assessed by the duration of the release of 50% of the liquid phase from the foam. As the foam ratio increases, the durability decreases. The durability of medium expansion foam is about 2 hours. Resistance can be increased by introducing stabilizing additives. Foam is electrically conductive, so it is prohibited to extinguish live installations with it.
5. Vibration, vibration disease and its prevention: vibration occurs as a result of mechanical vibrations and is a periodic movement with different amplitudes and frequencies. Harmful vibration occurs involuntarily during operation Vehicle, engines, turbines, hammers, etc. It can lead to destruction of structures, parts, and buildings. According to the impact on a person, vibration is divided into local (vibrations of tools, equipment applied to individual parts of the body) and general (the entire workplace). Under the influence of vibration, neurovascular disorders of the hands appear, expressed in changes in the blood supply to tissues, as well as changes in the viscoelastic state and vascular reactivity. Vibration affects endocrine system, on metabolism, on blood composition, on vegetative-vascular regulation. The first degree of manifestation of the effects of vibration is tingling of the fingertips, the second is episodic vibration of the phalanges of the fingers when exposed to cold, the third is acrocyanosis with impaired blood circulation, the fourth is necrosis of the phalanges of the fingers. Vibration disease is divided into 3 degrees. Vibration protection - technical, organizational and use of PPE.
1. Classification of workplaces and premises according to the risk of injury electric shock: category 1 - premises without increased risk of injury to people - dry, dust-free with an insulated floor.
a. Presence of humidity>75%
b. Presence of conductive dust
c. Presence of conductive bases
d. Availability elevated temperature
e. Possibility of simultaneous human contact with metal structures and electrical equipment housings connected to the ground
Presence of dampness (rain, snow, etc.)
The presence of a chemically active environment (aggressive vapors, gases, liquids that form deposits and mold, which are destructive to the insulation and live parts of electrical installations)
The presence of two or more high-risk conditions.
2. General hygienic assessment of working conditions: assessment of the actual state of working conditions in terms of the degree of harmfulness and danger of working environment factors is carried out in accordance with Hygienic criteria
Classes of working conditions are established based on an integral assessment of the combined effect, taking into account the predominance of certain parameters for 14 hazardous and harmful factors:
· Chemical
· Biological
Aerosols with fibrinogenic action
· Infrasound
Ultrasound
General vibration
Local vibration
Non-ionizing radiation, ionizing radiation
Microclimate
· Lighting
· Difficulty of work
· Work intensity
The assessment results are included in the final table for assessing the working conditions of workers according to the degree of harmfulness and danger. The general hygienic assessment of working conditions is established on the basis of data on classes of working conditions for 14 harmful and dangerous factors
· According to the most high class and degree of harm
· In the case of a combined effect of three or more factors related to 3.1, the overall rating corresponds to class 3.2
· When combining 2 or more factors 3.2, 3.3, 3.4, the conditions are assessed one step higher.
If there are no dangerous and harmful production factors in the workplace or their actual values correspond to optimal or permissible values, as well as when the requirements for injury safety and the provision of workers with personal protective equipment are met, it is considered that the working conditions in the workplace meet hygienic and safety requirements, workplace is considered certified. Otherwise, working conditions are classified as harmful or dangerous. When working conditions are assigned to class 3, the workplace is considered conditionally certified, indicating the class and degree of harmfulness; when classified as class 4, the workplace is not certified and is subject to liquidation.
3. Mine self-rescuers - principle of operation, storage, testing: mine self-rescuers are designed to protect the respiratory organs of miners in mines and mines who find themselves as a result of an accident in an atmosphere unsuitable for breathing (suffocating), and are used to remove them from emergency areas into mine workings with fresh a stream of air. Mine rescue units use self-rescuers as one of the means of assistance delivered to gas-polluted workings by the department for victims. According to the principle of operation, self-rescuers are divided into isolating and filtering. Isolating self-rescuers completely isolate the human respiratory system from the atmosphere, which may contain no more than 10% CO, 2% sulfur dioxide, 1% hydrogen sulfide or nitrogen oxide, and 15% CO2. Oxygen may be completely absent. Filtering self-rescuers are used if there is confidence in sufficient quantity oxygen in the surrounding air. Insulating self-rescuers contain chemically bound oxygen, which, when turned on, is released for breathing within 30 seconds, after which the exhaled air is purified. The operating principle of filter self-rescuers is based on the chemical absorption of harmful gases by an absorber. Self-rescuers are checked for leaks using the PGS device quarterly. The self-rescuer does not lose its properties within 2 years from the moment it is issued to the worker or 3 years of storage. Self-rescuers are stored in a vertical position on racks or in boxes in a dry room. Self-rescuers must be protected from direct sun rays and be at a distance of at least a meter from heat-emitting devices.
4.Sprinkler and deluge installations automatic fire extinguishing: sprinkler installations, water sprinklers, protected by an individual low-fusible lock that melts when the temperature rises. Available in various thermal designs at 72, 93, 141, 182 degrees. They operate directly above the fire.
Deluge sprinklers that are switched on centrally. They extinguish the entire room at once. Turned on manually or automatically by signal automatic detector. They are used in rooms where fire can spread very quickly or to create water curtains.
5. The influence of high and low atmospheric pressure on humans
1. General requirements safety to lifting devices: 2.1.1. All lifts must be manufactured in full compliance with these Rules and regulatory documents approved in in the prescribed manner. The development of regulatory documents is carried out by leading specialized organizations, and the development of projects is carried out by specialized organizations that have a license (permit) from the territorial bodies of the State Mining and Technical Supervision of Russia*.
2.1.2. Lifts and their assembly units purchased abroad must comply with the requirements of these Rules and have a certificate of conformity (certified copy) indicating the serial number of the lift. Possible deviations from these Rules must be agreed upon with the Gosgortekhnadzor of Russia before concluding a supply contract. Copies of the approval and certificate of conformity must be attached to the passport, made in accordance with Appendix 4.
When delivering the lift, technical documentation must be attached, written in Russian and meeting the requirements of these Rules.
2.1.3. Electrical equipment of lifts, its installation, current supply and grounding must comply with the Rules for Electrical Installations.
2.1.4. Operation electrical equipment lifts must be carried out in accordance with the requirements of the Rules for the operation of consumer electrical installations regarding cranes and the Safety Rules for the operation of consumer electrical installations.
2.1.5. Lifts intended for operation in indoor and outdoor installations in which an explosive and fire hazardous environment may occur must be designed and manufactured in accordance with the requirements of the Electrical Installation Rules and other regulatory documents.
The possibility of operating the lift in an explosive and fire hazardous environment (indicating the category of the environment) must be reflected in the passport, as well as in the operating manual of the lift.
2.1.6. Lifts, except those intended for operation in heated rooms, must be manufactured to operate at temperatures from minus 40 °C to plus 40 °C and wind speeds of no more than 10 m/s at a height of up to 10 m.
2.1.7. Lifts intended for operation at temperatures below minus 40 °C must be manufactured in the UHL (HL) climatic design in accordance with GOST 15150.
2.1.8. All changes in drawings or calculations, the need for which may arise during the manufacturing or repair of the lift, must be agreed upon between the development organization, manufacturer or customer.
2.1.9. .Before putting into operation, lifts must be registered and technical examination in the manner prescribed by these Rules.
2.1.10. Basic specifications, including load capacity, must comply state standards, technical specifications or others regulatory documents.
2.1.12. Lift designs must include:
1) ease of management, maintenance and repair;
2) towing capability: smooth start and stop of mechanisms;
3) replacement of elements of the hydraulic system of lifts without draining working fluid from the entire hydraulic system.
2.1.13. Lifts must be equipped with a device for recording operating hours.
2.1.14. Elevator mechanisms equipped with mechanical devices for their activation must be designed in such a way as to exclude the possibility of their spontaneous activation.
2.1.15. In the assemblies of lift mechanisms that transmit torque, in order to avoid rotation of the mating parts, it is necessary to use splined, keyed, bolted and other connections, which must be protected from arbitrary unscrewing or disconnection. The use of spring washers for fastening the slewing bearing is prohibited.
2.1.16. Fixed axles that support individual lift components must be securely fastened to prevent them from moving.
2.1.17. For lifts with telescopic extendable knee sections, reliable fixation of the extended sections in the working position must be provided.
2.1.18. Guides for ropes, chains and rods of the tracking system for orienting the cradle floor in a horizontal position must be arranged in such a way as to exclude the possibility of them spontaneously falling off the rollers, sprockets, drums and jamming of rods.
They operate successfully abroad. The issue of delimitation of the rights of labor collectives and trade unions in production is relevant. This problem is not new to labor law Ukraine. 1. SUBJECT OF LABOR LAW. The industry is distinguished in the legal system according to the criteria of the subject and method of legal regulation. The state is interested in specific legal management. Subject Composes: labor...
...: labor and collective; - internal rules labor regulations organizations, liability for violation of these rules; -organization of work on labor protection management; -control and supervision of compliance with labor protection requirements in the organization; -main dangerous and harmful production factors, characteristic of this production; -PPE, procedure and standards for issuing them and terms of wearing; - ...
Obliges to provide the employee with work according to the specified labor function, to ensure working conditions provided for by law, agreements, local regulations, containing labor law norms, pay the employee’s salary in a timely manner and in full, and the employee undertakes to personally perform the labor function defined by this agreement, to comply with the existing ones in the organization...
For emergency servicing of installations of large unit power, safety valves with high throughput and high reliability. In some cases it is therefore necessary to install a large number of(dozens) of safety valves due to the insufficient capacity of each of them. Under these conditions, it is more appropriate to use pulse safety devices (IPD). which are indirect-acting safety valves and consist of a high-capacity main safety valve and a pulse valve that controls the piston drive of the main valve. They successfully serve systems and units with high energy parameters that require the discharge of large quantities of the working medium (the operating diagram of the IPU is shown in Fig. 2.151).
If there is a pressure in the system that exceeds the set one required for normal operation installation, the pulse safety valve opens and directs the working fluid to the main valve actuator. The main valve opens and releases excess fluid. The pulse safety valve is a direct-acting lever-weight safety valve that acts as a sensing element. Thanks to the presence of a piston drive, the control force on the main valve rod can be quite large, which ensures precise operation of the main valve and reliable sealing of the shut-off element when it is closed.
A pulse safety device is much more complex and more expensive than a safety valve, but with an increase in the energy parameters of installations, the difference in their cost quickly decreases. In some cases, indirect-acting safety valves are also used, controlled from an external energy source or electricity. To increase reliability, IPU pulse valves are equipped with electromagnets controlled by electric contact pressure gauges. Pulse valves are located in close proximity to the main valve and can be integrated into the main safety valve actuator. As a rule, they are independent design in the form of a lever-weight safety valve.
The classification of impulse safety devices is shown in diagram 2.15 (impulse valves) and diagram 2.16 (main valves).
Impulse and main valve designs
Rice. 5.1.
Rice. 5.2. Steel lever-load pulse safety valves: a -- Dy= 20 mm for water and steam (уОр = 4 MPa, /р< 550 °С); б -- Dy = = 25 мм для воды и пара (ру -- 6,4 МПа, < 570 °С)
Rice. 5.3. Safety valves made of corrosion-resistant steel with Dy = 25 mm and electromagnets: a - lever-load for water and steam (Рр = 0.27 MPa, Tr< 160°С); б -- для воды и пара (рр = 1,1 МПа, /р < 200 °С)
Rice. 5.4.
To operate in hazardous, such as radioactive and toxic media, bellows pulse valves are used.
According to the type of drive, IPUs are divided into two groups: with a loading drive, when when the pulse valve is activated, the drive piston is loaded with medium pressure and opens the main valve, and with an unloading drive, when the pulse valve, when activated, discharges the working medium from the main valve drive, unloads the piston and thereby opens the main valve.
According to the type of impact on the shut-off body of the main valve, IPU can be with a sealing valve, in which the pressure of the working environment presses the valve of the main valve to the seat (this type is used most often), and with a decompressing valve, in which the pressure of the working environment is supplied under the valve of the main valve ( usually used in combination with an unloading drive).
Impulse safety devices are widely used, for example, in high-power power plants.
Classification and scope of safety valves
General purpose safety valves are manufactured in two types: spring and lever-load . In spring-loaded valves, the poppet is pressed against the body seat by a spring. In lever-load valves, the force pressing the plate to the body seat is created by a load through a lever device. By design, safety valves are divided into full-lift and partial-lift, depending on the lift of the spool. Spring safety valves, depending on the type of springs and the design of the spool block, can be full-lift or partial-lift. Lever-weight safety valves are only of the partial lift type. According to the exhaust design, safety valves are divided into sealed and non-sealed. All spring safety valves designed by Giproneftemash are of the sealed valve type. All lever-weight valves do not have a sealed exhaust, so they are leaky. Sealed spring safety valves of the Giproneftemash system, depending on the design, are divided into balanced and unbalanced. Balanced valves include safety valves PPK and SPPK; for unbalanced valves - PPKD valves, which have a special diaphragm that protects the valve spring from direct contact with the medium. Installation of lever-load safety valves, which are leaky by design, in process installations with fire- and explosive-hazardous and toxic products is not allowed. Such valves can be used to protect devices and pipelines with compressed air and water vapor. Despite great importance safety valves, maintenance personnel often underestimate them. This is explained by ignorance of the design of safety valves and the features of their operation under operating conditions. Because of wrong choice and installation of safety valves, their capabilities are not fully used, and errors in handling them can lead to major accidents. The valve lift value is determined by the ratio of the spool lift height to the nozzle diameter. For partial-lift safety valves, the ratio of the spool lift height to the nozzle diameter is 1/20--1/40, i.e., the cross-section of the slot through which the medium passes will be significantly smaller than the cross-section of the nozzle. Such valves are mainly used in cases where large flow capacities are not required.