On the fire safety valve

First, the importance of fire safety control valve

    In the chemical, oil and other automation systems in the event of a fire, if the system, certain devices can be cut off flammable fluid in a timely manner throughout the road leading to the fire, it would be possible to avoid the fire spreading directly from the fire zone around the plant caused by losses.

    Regulating valve is an automated system is an important integral part of the installed on-site control flow path, so somewhere in the fire when it was cut off to prevent flammable fluid flow path leading to the fire throughout the territory of major equipment. In the fire case, it is open or closed is very critical. As the control valve from the control room of the regulator to conduct self-control, not manually, so fire the main features of the valve should be: able to withstand the thermostat while the short-term work, or turn off when put up with hardships so that leakage should be minimal. The fire safety of the valve should be seen to be a great need to consider the performance, hoping to rise to the persons concerned attention.

Second, the standard fire control valve

    What kind of valve is the fire valve then? Abroad, referred to the fire valve (fire-safe valve), right valve of the definition of a lot of fire instead of unity, such a definition in the industry is still a lack of clear requirements. So far, still no single test or definition can clearly determine whether a valve fire.

    Large number of industrial society, oil companies, insurance companies, valve manufacturers, as well as the United Kingdom, the United States, the provisions of the relevant agencies have a variety of testing methods. However, the measured valve types and the main test specifications with the test methods differ. Debate on the combustion valve testing continues, and some tried to approach two or more integrated as a complete way, but still not conclusive. How can we be accurate to the fire damper subglottic defined? This is what we need to study the issue, first of all should study the soft valve seat standards.

    Some people think that the fire will not melt the metal gate valve and ball valve (globe valve) is the fire dampers. The design and structure of these valves can guarantee it on fire before and after are metals and metal (metal-to-metal) contact, which avoids the flammable fluid into the fire that in the. However, the metal valve seat at the fire before the operation, the seal is not good. As the leakage is very small, so most of the established fire safety standards are also permitted.

    User requirements during normal operation the valve is both a fine seal, but also has fire resistant. Many valve manufacturers as early as 15 to 20 years ago to try to resolve this complex issue, they have developed a variety of "soft" or "hard" seal components, all of which caught fire two types of components, the latter can keep metal face contact seal.

    Hard seat is made of metal or alloy, and its own can withstand high temperatures. Soft seat with rubber, plastic or melting point lower than 700 � (about 370 ℃) of elastic material, soft seat can be destroyed after the fire, then by virtue of the system pressure, the valve plate rotate, spring force or the role of self-gravity to maintain contact with metal surface. However, many soft-seat valve in the safety of combustion is not ideal. If the elasticity of the valve seat can not be totally destroyed in the fire, it can not form a metal surface contact. The following table summarizes the soft seat, including several fire test, from the table view, the various tests have different standards for the valve test specifications for analysis and comparison, you can learn which five kinds of standards are more stringent. Must be pointed out, the American Petroleum Institute Standard API607 "soft-sealing valve combustion test (1977)" is a provisional standard, it has all of 16 inches below the ball apply. Later, the second edition of the standard API RP6F was amended to require more stringent.

    Provided by different manufacturers of valves can only be consistent with one or two described in the following table the fire safety standards, such as Rockwell (Rock well) provided by the company fire plunger valve and ball valves can only be consistent with API607 and API RP6F 2 kinds of standards, others can only be provided in line with some other standard valves.

Third, specific measures for fire control valve

    1, valve body of fire

    Although the fire safety valve and some have different views and formulate the specifications of different test methods are also different, but how to fire the valve should have a more consistent view. The valve body, it should have the following three properties, but also to ensure the performance of these three points should be taken to a variety of specific measures.

    (1) The minimum amount of internal leakage. To ensure this performance, we should first take into account the valve core and valve seat of the metal surface contact, in the fire, or fire it, the valve being in heat, regardless of their enclosed structure, the spring force and applied pressure on how these changes are should ensure that, should think that this is the key to ensure its precision closed.

    (2) The minimum amount of external leakage. In order to minimize the external leakage, the methods being considered are: use of stem sealing material can be fire, avoid using large valve gasket-style links.

    (3) a continuous operational. Still work properly after combustion valve, naturally, with anti-deformation capability, resistant to damage.

    In order to ensure that fire prevention valve performance, many manufacturers have been various attempts. For example, they bandaged the valve on the cover of the multi-layered mat, using refractory bricks box, so that the valve separating the outside world. However, the above methods are less likely to be considered satisfactory because each time the valve repair should be apart, build on. The same day, due to valve installation location restrictions, it may not be this way.

    At present a more satisfactory way is to use a fire bag, it can be put on within a few minutes, maintenance can easily be opened. Bags of material containing multi-layered ceramic fiber (eramic fiber) or glass fiber (fiberglass) bind tightly tied with nylon and used vinyl coated stainless steel wires are properly tied in the device. In general questions, does not need to change the location of pipelines, installation space is small, through the test in 2000 � flame burning for 30 minutes, the valve is still not damaged, the performance is satisfactory.

    2, the executing agency of the fire

    As the implementing agency and direct control over the location of the valve, so need careful study. In order to close the valve to maintain a timely manner, and therefore easier to fire occasions are often used in pneumatic diaphragm spring steel (iron) executing agencies, mainly the use of low melting point, this feature patch. Fire, due to the low melting point membrane damage very quickly, so spring movement, so that the valve in the closed position. The use of heat-sensitive fusible plug-type holes to reduce the pressure of pneumatic system, particularly suitable for reciprocating piston-type spring executing agency.

    A serious fire can change the characteristics of metal parts, there is cause metal tempering features softened and lost, and some metal actually melted. Spring force of the size and tempering characteristics are directly related to whether the burning of residual spring force sufficient to keep the valve position, the need for implementing agencies to conduct combustion tests can prove.

    Right valve, the combustion is often necessary to keep the remainder of spring torque valve closed position, closing the force required to appear much smaller than the original output power of the implementing agencies. In the spherical valve body on the implementation of the remaining spring force is very important. In the same pipeline pressure, balanced than the unbalanced ball valve ball valve spring force required to be smaller, so use fire-prone places, people are willing to use a balanced-type ball valve.

    To make operation even after burning of the implementing agencies on the need to protect the springs, to make it from the flame annealing effects. Protection of springs can be used three kinds of methods: thermal insulation material, using sprinklers or fire protection coating. Including the multi-layer insulated the tropics, the use of thermal insulation cover or use fire bag, so that implementing agencies in the running for half an hour after the fire. But this trick and sealing method is more cumbersome and inconvenient, accounting for a large space. In the implementing agencies at the top fitted with sprinklers, which has increased the installation and maintenance costs; and often without water due to fire, nor to the sprinkler water supply. Enforcement bodies may be coated with a epoxy-based (epoxy-based) expansion of thin material, so that normal operation of the executing agency. In a combustion experiment, due to the protection of paint, although the fire temperatures as high as 1400 ~ 1700 �, implementing agencies able to work 42 minutes. Test of the spring-loaded with 1600 pounds of cast iron implementing agencies, about 7 feet long, 12-inch cylinder bore, using nine propane torch to burn spray. Throughout the combustion process in the executive body of the spring back and forth once every minute, after the spring burn to reduce the output torque is only 6%, and was mainly due to decreased precision bearings, the friction caused by the increase. Tests showed that burning flame springs are not subject to the impact of the piston and rod seals also remain, such as old, sealed well. After the completion of the pilot, the executive body immersed in cold water. Simulate the role of high-temperature shell suddenly cold. Tests showed that the executing agency of the housing and internal parts are not due to a sudden cooling by the harmful effects.

    Expansion coating is cast with me, like using concrete, as when wiping in the field, we must be careful not to wipe seals live in parts, this would allow maintenance of inconvenience. When the coating when it dries to form a hard, impermeable sealing layer. Jamesbury company also built the main body of the disk board and cabinet, respectively, coated, so that maintenance can be opened to move board. If the executing agency is the aluminum body, that the use of paint is difficult to fire because of the low melting point of aluminum (1033 ~ 1150 �), higher than the melting point of the hydrocarbon mixture flame, parts will be failure, the valve can not be closed.

    Finally, we need introduce a link protection method. Reciprocating spring-loaded devices from different manufacturers supply valve, these spring-loaded devices in a "pending attack" position, it can only fire when the firing, firing an automatic when the valve to move to the insurance position. There will be holding components can be used fusible link, connecting rod or electric rod brittle. Electric rod and easy to link the role of melting, as heat can be started. Dangerous moment in the fire, which was immediately smoke servo rod device is disconnected, so that the valve is in the insurance bit. 

 

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