A safety valve is a type of pipeline fittings, an automatic mechanism designed to protect closed channel (pipeline) systems, devices installed in them, machines and containers from damage by excessively high or low (vacuumized) pressure. Protection of a closed thermodynamic system with a safety valve is carried out by dumping (during vacuuming - suction) of a part of the working medium.
Unlike irretrievably collapsing safety (bursting) diaphragms, the automatic mechanism of the safety valve ensures that the discharge of the working medium is stopped when the emergency pressure in the circuit is normalized to a safe (operating) value. Thus, functional safety valves simultaneously maintain:
- valuable work equipment from accident damage;
- the working environment from an unjustifiably large discharge, which is very important in situations where the working environment itself is of great material value;
- supported technological and business processes from abnormal interruption.
Device and principle of action
The classic design is the design of a spring-loaded direct-acting safety valve. Its mechanism is carried out in its own casing, with the inlet and outlet pipes assembled. The valve body has an internal flow channel, as a rule, of an angular shape (but there is also a direct-flow design). The valve mechanism consists of a spool (plug) with a guiding stem, which is pressed by a driver spring (adjuster) against a seat on the inlet channel of the body. The response pressure of the safety valve is determined by the clamping force of the set spring, which can be adjusted:
- an adjusting mechanism (usually a screw);
- selection of springs with the required force (in the simplest designs).
In the working position, under the influence of the force of the reference spring, the safety valve is always closed (its shutter is pressed against the seat). The pressure of the working medium through the inlet channel acts on the valve disc, but cannot overcome the clamping force of the driver spring.
As the pressure in the system rises, its resistance to the downforce of the spring increases. When the pressure in the system reaches the threshold (emergency) value, it overcomes the force of the master spring, the spool (valve) rises above the seat, opening the passage slot through which a massive discharge of the working medium (and, accordingly, excess pressure in the system) begins through the outlet channel and branch pipe , into the discharge system. After the overpressure in the system is relieved and normalized to a safe value, the force on the valve plug from the side of the working medium decreases, and under the influence of the actuating spring, the spool (plug) disc is again pressed against the seat, thereby closing the valve and stopping the mass discharge of the medium.
It should be borne in mind that the closing pressure of the safety spring-loaded valve (direct acting) will always be 10 - 15% less than the threshold value of its operation (opening). This is due to the need to overcome the dynamic (kinetic) resistance from the flow of the discharged medium by the force of the driving spring.
In some cases, the safety valve can be equipped with a forced opening mechanism (usually a lever type), which is used to check its functionality. This forced valve check is used to prevent sticking, sticking, freezing, as well as for preventive purging. But in cases of duct systems with high working pressures and temperatures, aggressive and toxic working fluids, activation of the forced opening mechanism of the valve can be dangerous. For such systems, safety valves with a positive opening mechanism are not used.
Types of safety valves
According to the principle of operation, safety valves are:
- Direct action - when the opening and closing of the valve occurs as a result of a direct effect on its mechanism from the side of excess pressure in the system. The classic spring-loaded valve is of this type.
- Indirect action - when the opening and closing of the valve occurs from a controlled servo (usually electromagnetic), which receives signals for opening and closing from third-party sensors.
By the type of the shutter lifting mechanism, safety valves are distinguished:
- cargo (lever-cargo);
- combined lever-spring;
- combined magnetic-spring.
Depending on the lift height of the valve disc above the seat, safety valves are distinguished:
- low-lift, where the height of the valve disc lift does not exceed 1/20 of the bore diameter of the seat;
- full-lift, where the lift height of the valve disc reaches ¼ and more of the bore diameter of the seat;
- medium-lift, where the lift of the valve disc is in the range from 1/20 to ¼ of the bore diameter of the seat.
By the nature of the operation of the lifting mechanism, safety valves are:
- proportional action - when the lift of the valve disc is proportional to the degree of exceeding the pressure threshold;
- two-position action - when triggered, such valves immediately open to the entire flow area, thereby accelerating the discharge of the working medium and the normalization of the pressure in the system.
Popular safety valve designs
Among the design options for the execution of industrial and household safety valves, the most common and demanded are:
- With high performance, these are, as a rule, full-lift, on-off valves, with a large flow area of the seat, which provide quick mass discharge of the medium and normalization of pressure in hydraulic systems with a large volume and flow rate of the working medium.
- For bypass (bypass) - it is used to maintain the pressure in the system at a constant level by continuously draining (overflowing) the medium into the drain (drainage) pipeline.
- Compact design - due to the use of modern materials and mechanisms, more compact dimensions of the valve are achieved, for use on small-sized and low-volume (low-performance) equipment, or in systems (devices) for household use.
- For sterile conditions - the design uses perfect systems and materials for sealing and sealing, in order to prevent leakage of the working medium into the surrounding space, and mix the environment into the working space.
- For aggressive media - in the design of such valves, in addition to ensuring a high degree of tightness, chemical resistant construction and sealing materials are used that can withstand the destructive (corrosive) effects of aggressive working media.
- API Valves - Designed to meet the specifications of the American Petroleum Institute (API). The application of the API standard technique will be required on samples of imported hydraulic equipment from the United States and other countries using this popular manufacturing standard.
- Pilot valves are of indirect action, with an electromagnetic servo drive for opening and closing, controlled by signals from third-party sensors. As a rule, they are used in complex hydraulic engineering systems with programmable (computer) control of operating modes. Pilot valves are usually provided with a direct spring actuator in addition to the pilot (servo) in case of power outages or servo power outages for other reasons.
Scope of application
The scope of application of safety valves can safely include all channel (pipeline) systems for industrial, economic or technical purposes, regardless of their size, technical parameters, location, man-made hazard. Since almost all of them need emergency protection equipment in case of possible work overloads, breakdowns of working equipment, third-party impact on the system, and other emergency situations.
The use of safety valves allows you to localize and limit, and often neutralize (prevent) the destructive impact of an emergency, and ultimately save valuable machinery, equipment, and partly the working environment. As a means of protection, safety valves have an advantage and priority in application over safety (bursting) diaphragms, thanks to their drive mechanism, which makes it possible not only to automatically open, but also to close the discharge channel. Typically, safety valves are used in conjunction with bursting discs. And in systems with a small volume or consumption of the working medium - and independently.
Safety valve specifications
The main technical requirements for safety valves are:
- ensuring the required degree of tightness of the system in a closed state;
- guaranteed reliability of the mechanism operation when the pressure in the system reaches the threshold value;
- provision of the necessary bandwidth for rapid mass discharge of the medium from the system, in order to maximize the limitation of the emergency situation (state) in terms of the time of action;
- ensuring timely closure of the valve when the pressure in the system is normalized to a safe (operating) level;
- guaranteeing the stability of the operating parameters of the valve (actuation and closing forces, tightness) throughout the standard service life.
Safety valves refer to the list of equipment that is subject to periodic checking in a specialized laboratory or organization (such as boiler inspection), periodic testing in action on a test bench.
Advantages of LESER safety valves
LESER safety valves are products of the well-known German engineering company LESER GmbH & Co. KG, which has specialized in this type of equipment for over 100 years. LESER GmbH & Co. KG has an undeniable reputation among industry professionals for the impeccable quality of its products.
The company has implemented a proprietary quality management system, which accompanies the entire process of manufacturing valves until their final assembly, including factory tests. LESER's proprietary quality management system is certified according to the most modern international and European industry standards:
- EN ISO 9001;
- Pressure Equipment Directive (PED) 97/23 / EC resp. 2014/68 / EU;
- EN ISO 4126-1;
- ASME VIII;
Safety valves TM LESER are characterized by:
- very accurate compliance with the declared technical parameters;
- excellent technical reliability;
- the use of modern high-quality materials and high-tech (high-precision) methods of their processing;
- availability and ease of setup / adjustment;
- compatibility with modern imported models of hydraulic equipment and machines of European production, as well as many samples of equipment manufactured in the USA, Russia and other countries of the world.