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What is Valve Live Loading?
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Posted On :
Feb-04-2013
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Article Word Count :
551
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Over the past few years, valve live loading has been a trending topic in many articles and papers. Some have recommended it while other people see no value for it altogether. Actually, the two situations can be correct.
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Over the past few years, valve live loading has been a trending topic in many articles and papers. Some have recommended it while other people see no value for it altogether. Actually, the two situations can be correct. It’s all determined by the application.
How Valve Live Loading Works
Valve live loading refers to the application of a spring load to gland follower of a packed valve. Disc springs between gland followers and their fastening studs and nuts provide an effective means of establishing and maintaining a controlled amount of stress in packing sets. The stress levels can be controlled by the size of the disc spring used and how far it is deflected or compressed.
In valve live loading systems, the follower keeps on pushing against the packing despite loss of packing volume through friction, consolidation or other factors. Though the expansion of the springs will reduce the spring load, the load reduction will be significantly less than the lost load if the packing set wasn’t live loaded. The remaining load helps to minimize packing stress, which enables the packing to be free of leaks.
What Valves Can Be Live Loading?
Several factors determine if a valve is a candidate for live loading including:
If the valve is packed
The valve cycle frequency
Whether the valve uses a motor
Ease of accessing the valve
Subjectivity to high temperatures and pressure
If the valve is in a critical application
History of packing leaks
If the valve should be monitored under EPA rules
If a valve has any of the features listed, there could be a high probability that the valve is a live loading candidate.
Packing Materials
Live loading applies in various packing materials. However, one material used in many live loading applications is graphite based materials. Other names used to refer to valve live loading washers arespecialized bellevilles and disc springs among others. This type of spring is conical in shape. It has a special design, material thickness, height and can be made from various spring materials.
Valve live loading washers can handle high temperatures from 400-12000 degrees Fahrenheit. The disc springs are made from a variety of materials such as stainless steel, alloy steel, tool steel and temper phosphor bronze among others.
Benefits of Specialized Bellevilles
Straight line load
Deflection curves
Efficient space use
Durable
Self-damping
High spring force
The disc spring material to select is determined by the application, temperature and environment to which the spring will be subjected. It is very important to consider the right spring material because specialized bellevilles are subject to stress corrosion cracking if used in the wrong application.
Though stainless steel disc springs are used in most applications, it is not a suitable material for chloride and fluoride applications. This includes areas with salt air such as around a coast. Consider plating stainless steel disc springs used in coastal applications.
Disc spring materials have different tensile strengths and elasticity. Disc springs with the same dimensions but made from different materials may not have the same load characteristics. Specialized belleviles can be stacked together to achieve deflection, spring load or both. The springs can be used in four different ways:
Single
Parallel
Series
A combination of parallel and series
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Article Source :
http://www.articleseen.com/Article_What is Valve Live Loading?_248916.aspx
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Author Resource :
The author has an immense knowledge on valve live loading washers. Know more about specialized bellevilles related info in his website.
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Keywords :
valve live loading washers, specialized bellevilles,
Category :
Business
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Business
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