A safety valve is a valve that functions as a fail-safe. An example of a safety valve is a pressure relief valve (PRV), which automatically releases substances from boilers, pressure vessels, or other systems, when pressure or temperature exceeds a predetermined threshold. Pilot-operated release valve is a special type of pressure-safety valve. Rigorous leakage, lower costs, single emergency use option will be a broken disk.
The safety valve was first developed for use on boilers during the Industrial Revolution. Early boilers that operate without them are prone to explosion unless operated with caution.
Safety vacuum valves (or combined pressure/vacuum safety valves) are used to prevent tanks from collapsing while being emptied, or when cold rinse water is used after CIP heat (spot-in-place) or SIP (sterilization-in-place) procedures. When measuring the vacuum safety valve, the calculation method is not defined in any norm, especially in CIP/cold water scenarios, but some manufacturers have developed a size simulation.
Video Safety valve
Functions and design
The earliest and simplest safety valves are used on 1679 steam digester and use weight to maintain steam pressure (this design is still commonly used in pressure cookers); However, this is easily damaged or accidentally released. In Stockton and Darlington Railways, safety valves tend to be extinguished when a machine crashes into a lump on the track. The less sensitive valves accelerate suddenly using a spring to withstand the vapor pressure, but this (based on Salter spring balance) can still be locked to increase pressure beyond the design boundary. This dangerous practice is sometimes used to slightly improve the performance of the steam engine. In 1856, John Ramsbottom invented the tamper-proof spring springs valve that became universal on the train. The Ramsbottom valve consists of two plug-type valves connected to each other by a spring-spun pivot arm, with one valve element on either side of the pivot. Any adjustment made to one of the valves in an attempt to increase its operating pressure will cause another valve to be lifted from its seat, regardless of how the adjustment is attempted. The pivot point on the arm is not symmetrical between the valves, so the firming of the spring will cause one of the valves to lift. Only by removing and separating all valve assemblies, the operating pressures can be adjusted, so the 'valve' thrust from the valve by the locomotive crew seeks a more unlikely power. Rotating arms are generally extended into grip leads back into the locomotive cabin, allowing the crew to 'swing' both valves from their seats to ensure that they are installed and operating properly.
Safety valves also evolve to protect equipment such as pressure vessels (fired or not) and heat exchangers. The term safety valve must be limited to the application of a compressible liquid (gas, steam, or vapor).
The two common types of protection faced in the industry are heat protection and stream protection.
For liquid-filled vessels, the heat release valve is generally characterized by the relatively small size of the valve required to provide protection against excess pressure caused by thermal expansion. In this case a small valve is adequate because most of the fluid is nearly incompressible, so a small amount of liquid discharged through the release valve will result in a large pressure reduction.
The flow protection is marked with a safety valve much larger than that installed for heat protection. They are generally sized for use in situations where large amounts of gas or high volume of liquids must be immediately disposed to protect the integrity of ships or pipelines. This protection can be done alternatively by installing a high integrity pressure protection system (HIPPS).
Maps Safety valve
Technical terms
In petroleum refining, petrochemical, chemical manufacturing, natural gas processing, power generation, food, beverages, cosmetics and pharmaceutical industries, the term safety valve is associated with the provision of pressure relief valves PRV), pressure safety valve (PSV) and release valve . The generic term is Pressure relief valve (PRV) or pressure safety valve (PSV). It should be noted that PRVs and PSVs are not the same thing, regardless of what many people think; the difference is that PSV has a manual lever to open the valve in an emergency.
- Relief valve (RV): automatic system driven by static pressure in a liquid filled vessel. This is particularly open in proportion to the increased pressure.
- Safety valve (SV): an automated system that reduces the static pressure on the gas. Usually fully open, accompanied by a popping sound.
- Safety relief valve (SRV): an automated system that reduces static pressure on gases and liquids.
- Pilot relief valve operated (POSRV): an automated system that reduces remote commands from a pilot, in which static pressure (from equipment to protect) is connected.
- Low pressure safety valve (LPSV): an automatic system that reduces the static pressure on the gas. Used when the difference between ship pressure and ambient atmospheric pressure is small.
- Air vacuum safety valve (VPSV): an automated system that reduces static pressure on the gas. Used when the pressure difference between the vessel pressure and ambient pressure is small, negative and close to atmospheric pressure.
- Low-pressure and vacuum safety valves (LVPSV): an automated system that reduces static pressure on the gas. Used when the pressure difference is small, negative or positive and close to atmospheric pressure.
RV, SV, and SRV are operated with springs (even springs). LPSV and VPSV are operated with springs or heavy loads.
Legal and industry code requirements
In most countries, industries are legally required to protect pressure vessels and other equipment using the release valve. In addition, in most countries, equipment design codes such as those provided by ASME, APIs, and other organizations such as ISO (ISO 4126) must be obeyed. These codes include design standards for the release valve and schedules for periodic checks and after valve testing have been issued by the company's engineers.
Nowadays, food, beverages, cosmetics, pharmaceuticals, and fine chemical industries are calling for a hygienic, fully-fledged and cleanable-In-Place safety valve. Most are made of stainless steel; especially 3A hygiene norms in the United States and EHEDG in Europe.
Development of safety valve
The deadweight weighing valve
The first safety valve was created by Denis Papin for its steam steering machine, an initial pressure stove and not a machine. The weights that work through the lever push the plug valves around the steam jar. By using a smaller "steel" lever the required load, also the pressure can be easily adjusted by shifting the same weight back and forth along the lever arm. Papin maintains the same design for its 1707 steam pump. The initial safety valve is regarded as one of the controls of the engineman and requires continuous attention, in accordance with the load on the machine. In a famous early blast in Greenwich in 1803, one of Trevithick's high-pressure stationary engines exploded when a boy trained to operate the engine left him to catch a eel in the river, without first removing the safety valve from his workload. In 1806, Trevithick was a safety valve fitting pair, an external valve for driver adjustment and one sealed inside a fixed-weight boiler. It can not be repaired and released at higher pressure, which is intended as a guarantee of safety.
When used on locomotives, this valve will beat and leak, releasing steam wastes continuously.
Direct-acting deadweight valves
Although the lever safety valve was comfortable, it was too sensitive to steam locomotive movement. The early steam locomotive therefore uses a simpler weight arrangement that is stacked directly above the valve. This requires a smaller valve area, thus keeping the weight manageable, which sometimes proves inadequate to vent the unattended boiler pressure, which causes an explosion. The greater danger is the ease with which such valves can be bonded, thereby increasing the pressure and thus engine power, at the risk of further explosion.
Although the dead weight safety valve has a short life span in steam locomotives, they are still used on a stationary boiler as long as steam power remains.
Direct spring valve
The weighted valve is sensitive to reflections from early locomotive riders roughly. One solution is to use a lighter spring than heavy. This was the discovery of Timothy Hackworth at George George in 1828. Due to limited metallurgy during that period, Hackworth's first spring valve was using a pile of leaf springs that resembled an accordion.
This direct-acting spring valve can be adjusted by tightening the nut that holds the spring. To avoid interference, they are often covered with a high brass sheath that also releases steam from the locomotive crew.
Salter spring balance valves
Salter coil spring spring balance for weighing, first made in England around the year 1770. It uses newly developed spring steel to create a strong but compact spring in one piece. Again using the lever mechanism, the spring balance can be applied to the strength of the boiler safety valve.
The spring balance valve also acts as a pressure gauge. This is useful because the previous pressure gauge is a heavy mercury manometer and the Bourdon gauge has not been found.
Lockable Valves
The risk of firefighters binding on the safety valve remains. This is driven by those equipped with easily adjusted nut wings, the practice of adjusting the boiler's working pressure through the safety valve to a well-accepted behavior into the 1850s. It is then common with Salter valves for them to be paired in, one adapted and often calibrated for use as a tester, the other sealed inside a locked lid to prevent disturbance.
Spring splash balance valve
Paired valves are often adapted to slightly different pressures as well, small valves as control measures and locked valves are made larger and permanently set to higher pressure, as a safety. Some designs, such as those done by Sinclair for the Eastern Railway in 1859, have valve springs with a pressure scale behind the dome, facing the cab, and the valve locked in front of the dome, beyond the range of interference.
Ramsbottom safety valve
In 1855, John Ramsbottom, LNWR locomotive supervisor in the future, described a new form of safety valve intended to improve reliability and especially to damage tamper. A pair of plug valves are used, pressed by a spring-loaded lever between them with a single central spring. These levers are characteristically extended to the rear, often reaching into the cabin in the original locomotive. Instead of shrinking the use of spring levers by firefighters, the Ramsbottom valve encouraged this. Shake lever frees the valve alternately and checks that nothing is stuck in the seat. Even if the fireman holds the lever down and increases the force in the back valve, there is an appropriate reduction of force on the forward valve.
Various forms of Ramsbottom valves are produced. Some separate fittings to the boiler, through separate penetration. Others contained in U-shaped housing are tied to one hole in the boiler shell. As the boiler diameter increases, some shapes are even set inside the boiler shell, with the springs placed in the recess and only the protruding valve and balance lever outside. It has a clear disadvantage for easy maintenance.
- GB 1299 Ã, 1299: June 7, 1855: Safety valve, cutlery for steam-boilers.
The lack of Ramsbottom type is its complexity. Poor or incorrect maintenance of connections between springs and valves may cause valves that are no longer being opened properly under pressure. Valves can be retained in their seats and fail to open or, even worse, to allow the valve to open but not enough to vent the steam at an adequate level and not be a clear and obvious mistake. This only natural mis-assembly caused a fatal boiler explosion in 1909 in Cardiff on the Rhymney Train, although the boiler was almost new, at only eight months old.
Naylor valve was introduced around 1866. The bellcrank setting reduces spring extension (spring extension percentage), thus maintaining a more constant force. They are used by L & amp; Y & amp; NER.
"Pop" Valves
All previous safety valve designs are gradually opened and have a tendency to leak "vapor" steam as they approach "blowing", although this is under pressure. When they open, they also do it partly at first and do not release the vapor quickly until the boiler is over pressure.
A quick open "pop" valve is the solution to this. Their construction is simple: the existing circular plug valve is converted to an inverted "cap" shape, with an enlarged top diameter. They are mounted on a chair trampled with two suitable diameters. When closed, the vapor pressure only applies to the top crown of the cap, and is balanced by the spring force. After the valve is opened slightly, the steam can pass through the lower seat and start acting on the larger edge. This larger area defeats the spring force and the fully-open flying valve with "pop". Flowing steam in this larger diameter also holds the valve open until the pressure drops below initially opened, giving hysteresis.
These valves coincide with changes in firing behavior. Rather than showing their manhood by always showing feathers on the valve, firefighters are now trying to avoid noise, especially around the station or under the main roof of the main station. This was largely at the behest of station chiefs, but firefighters also realized that every blow through the pop valve dumped a few pounds of boiler pressure; estimated at 20% lost and 16 pounds or more of shoveled coal.
The pop valve comes from Adams's patent design in 1873, with long lips. Valve RL Ross patented in 1902 & amp; 1904. They were more popular in America at first, but were widespread from the 1920s.
Although the polished brass cover over the safety valve has been a feature of steam locomotives since Stephenson's day, the only railway to maintain this tradition to the pop valve era is GWR, with their distinctive tapered brass valve hoods and chimney-lined chimneys copper.
Sea elevation lifting valve and Cockburn
The development of high-pressure water tube boilers for marine use places more demand on safety valves. A larger capacity valve is required, to securely release the high-vapor producing capacity of this large boiler. As the force on their valves increases, the problem of increasing the stiffness of the spring as its load increases (such as the valve Naylor) becomes more critical. The need to reduce the feather valve becomes more important with high-pressure boilers, as this represents the loss of distilled water feed and also the scouring of the valve seat, which causes wear.
The high lifting valve is a spring type that is loaded directly, although the spring does not directly carry on the valve, but on the stem-rod valve rod. The valve below the base of the stem, the springs are resting at a height of some altitude above this. Increasing the space between the valve itself and the spring chair allows the valve to lift higher, further clear than the seat. It provides a steam flow through a valve equivalent to a valve one half or two times larger (depending on the detail design).
The enhanced Cockburn High Improvement design features similar to the Ross pop type. The exhaust vapors are partially trapped on the exit and act on the base of the spring chair, increasing the lift force on the valve and holding the valve more open.
To optimize the flow through the given valve diameter, full-bore design is used. It has a servo action, where steam through a narrow control path is allowed even if it passes through a small control valve. The vapor is then not depleted, but passed to the piston used to open the main valve.
There is a safety valve known as PSV and can be connected to a pressure gauge (usually with a 1/2 "BSP fitting), allowing the pressure resistance to be applied to limit the pressure imposed on the measuring tube, thus preventing more than air pressure, has been injected into the gauge, if over pressurized, will be diverted through a pipe in the safety valve, and should be kept away from the meter.
Type
There are a variety of safety valves that have many different applications and performance criteria in different fields. In addition, national standards are established for different types of safety valves.
United States
- ASME (American Society of Mechanical Engineers) Boilers & amp; Pressure Vessel Code, Part I
- ASME (American Society of Mechanical Engineers) Boilers & amp; Pressure Vessel Code, Part VIII, Division 1
- Best Practices API (American Petroleum Institute) 520 and API Standard 526, Standard API 2000 (low pressure - Storage tank)
European Union
- ISO 4126 (aligned with EU directives)
- EN 764-7 (previous CEN standard, synchronized with EU directives, replaced with EN ISO 4126-1)
- AD Merkblatt (Germany)
- PED 97/23/CE (Emergency Equipment Directive - EU)
Water heater
A safety valve is required on a water heater, where they prevent a disaster in a particular configuration if the thermostat should fail. There are still occasional, spectacular failures of older water heaters that do not have this equipment. The house can be flattened by the force of the explosion.
Pressure cooker
Pressure cooker is a cooking pot with a pressure-resistant lid. Cooking at pressure allows the temperature to rise above the normal boiling point of water (100 degrees Celsius at sea level), which speeds up cooking and makes it more thorough.
Pressure cookers usually have two safety valves to prevent the explosion. In older designs, one is a weighted nozzle. The other is a sealed rubber gromm issued in a controlled explosion if the first valve is blocked. In a new generation pressure cooker, if the steam vent is obstructed, the safety springs will exert excess pressure and, if failed, the gasket will expand and release the excessive pressure down between the lid and the pan. Also, the latest generation pressure cooker has a safety interlock that locks the lid when internal pressure exceeds atmospheric pressure, to prevent accidents from sudden release of steam, food and liquid, which would occur if the lid should be removed when the pan is still slightly pressurized inside , the lid will be very hard or impossible to open when the pot is still pressurized).
The term safety valve is also used metaphorically.
See also
- Ball valve
- Butterfly valve
- Control valve
- Stream delimiter
- Globe Valves
- Needle valve
- Pilot operated aid valve
- Release valve
- Security closing valve
Note
References
External links
- Working principle of schematic overview Safety Relief Valve
- Calculator pressure gauge pressure gauge size PSV gauge for a liquid-blocked outlet.
- PSV size calculator for blocked gas outlets. PSV size calculator for blocked gas discharge.
- PSV size calculator - fire box for gas container
- PSV size calculator - fire box for fluid container
- Safety release valve Size criteria, code requirements, pressure relief methods, general type of safety valve design.
Source of the article : Wikipedia
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