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Thermal binding methodology and model description in wedge gate valves

Thermal binding is generally associated with a wedge gate valve that is closed while the system is hot and then is allowed to cool before attempting to open the valve. Mechanical interference occurs because of different expansion and contraction characteristics of the valve body and disk materials. Thus, reopening the valve might be prevented until the valve and disk are reheated. Solid-wedge gate valves are most susceptible to thermal binding. However, flexible-wedge gate valves experiencing significant temperature changes or operating with significant upstream and downstream temperature differences may thermally bind. Thermal binding occurs as a result of the valve design characteristics (wedge and valve body configuration, flexibility, and material thermal coefficients) when the valve is subjected to specific temperature during various modes of plant operation.
The main objectives are: -
• Study the occurrence of thermal binding in the sample valves, including the magnitude of temperature difference across the valve and the thrust needed to unseat a thermal bounded valve.
• Evaluate the operational configurations of safety-related power-operated (i.e., motor-operated, air-operated, and hydraulically operated) gate valves in its plant to identify valves that are susceptible to thermal binding.
• Perform further analyses as appropriate, and take needed corrective actions (or justify longer schedules), to ensure that the susceptible valves identified in 1 are capable of performing their intended safety function(s) under all modes of plant operation, including test configuration.

Mostra/Nascondi contenuto.
3 CHAPTER 1 INTRODUCTION 1.1 Gate Valve Gate valves are named after a wedge-shaped internal barrier, called a gate which rises and falls inside the valve as a handle is turned (the handle does not rise or fall, only the gate). Gate valves effectively regulate flow rates from zero to full flow, they work well with solids- laden water, and these valves can be serviced in place if necessary. Gate valve plays a major role in virtually every refinery, chemical plant and industrial facility in the world. The most popular style of valve in the world of flow control is the gate valve. They are the on/off switches of the fluid control industry and they are found in every refinery, chemical plant, power plant and industrial facility. Gate valves exist for one primary purpose- to stop flow. Because of this, they are often referred to as �stop� or �block� valves. The chief advantage of a gate valve is that it offers virtually no resistance to flow in the open position. Gate valves can be used to stop flow from either direction. They are available in every material from the shiny brass construction of the diminutive �� water valves on the hardware store shelf, to the exotic high alloy models found in nuclear power installations. Gate valves have been an important piece of fluid control equipment for over 150 years. In fact, the very first valve patent issued in the United States was for a �gate valve�. Since those humble beginnings in the 19th century. From the outside, most gate valves look somewhat similar. However, inside there are a host of different design possibilities.

International thesis/dissertation

Autore: Dr Gurudutt Sahni Contatta »

Composta da 39 pagine.


Questa tesi ha raggiunto 277 click dal 18/04/2007.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.