4AE3 U7 C2 Review
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Questions and Answers

What percentage of the overall system costs do valves typically represent?

  • A considerable percentage of the costs (correct)
  • A small percentage of the costs
  • All of the costs
  • A majority of the costs

    • What is the primary purpose of using valves for isolation?

  • To change the fluid flow speed
  • To reduce the pressure
  • To isolate the flow completely (correct)
  • To change the fluid flow direction

    • What type of valve has a gate-like disc that is actuated by a threaded stem and a handwheel?

  • Gate valve (correct)
  • Ball valve
  • Globe valve
  • Needle valve

    • What is the purpose of the valve wheel in a gate valve?

    <p>To mesh with threads in the valve stem</p> Signup and view all the answers

    What is a key consideration when selecting a valve?

    <p>The type of fluid being used</p> Signup and view all the answers

    What is the primary function of the disc in a gate valve?

    <p>To shut off the flow</p> Signup and view all the answers

    What happens to the pressure on the outlet side when the demand for fluid increases?

    <p>It drops slightly</p> Signup and view all the answers

    What is the purpose of the adjusting screw in the spring-operated reducing valve?

    <p>To adjust the outlet pressure</p> Signup and view all the answers

    What happens when the demand for fluid decreases in the spring-operated reducing valve?

    <p>The valve closes more</p> Signup and view all the answers

    Why is the diaphragm mounted outside the valve housing in the spring-operated reducing valve?

    <p>To protect the diaphragm from overheating</p> Signup and view all the answers

    What should be installed on either side of the reducing valve?

    <p>Isolating valves</p> Signup and view all the answers

    What type of valve should be used as the by-pass valve in the reducing valve?

    <p>Globe valve</p> Signup and view all the answers

    What is the purpose of gaskets in valve installations?

    <p>To prevent leakage at the flanges</p> Signup and view all the answers

    What is the primary advantage of butterfly valves?

    <p>Relatively light weight and ease of operation</p> Signup and view all the answers

    What is the characteristic of the spherical plug in ball valves?

    <p>It provides precise control of the flow and a tight shutoff</p> Signup and view all the answers

    In which industry are ball valves commonly used due to their ability to handle slurries and fluids with high solid content?

    <p>Paper industry</p> Signup and view all the answers

    What is the purpose of the packing box in plug valves?

    <p>To prevent leakage along the valve stem</p> Signup and view all the answers

    What is the primary function of check valves?

    <p>To prevent reversal of flow in piping</p> Signup and view all the answers

    What is the characteristic of the disc in swing check valves?

    <p>It moves upward to allow flow and downward to close</p> Signup and view all the answers

    What is the advantage of plug valves in terms of pressure drop?

    <p>They have a very low pressure drop across the valve</p> Signup and view all the answers

    Which type of valve is commonly used in gas supply lines?

    <p>Plug valve</p> Signup and view all the answers

    What is the problem associated with tapered plugs in plug valves?

    <p>They have a tendency to jam in the tapered seat and cause scoring</p> Signup and view all the answers

    What is the primary function of a dashpot in larger check valves?

    <p>To cushion the action of the disc</p> Signup and view all the answers

    What is the main advantage of a lift check valve?

    <p>Its simplicity</p> Signup and view all the answers

    What is the primary concern when using a lift check valve with a metal seat?

    <p>It may not be suitable for applications where a small amount of leakage is not acceptable</p> Signup and view all the answers

    What is the purpose of the stop valve in a boiler system?

    <p>To provide a means of shutting off the steam supply</p> Signup and view all the answers

    What is the advantage of an outside-screw-and-yoke type stop valve?

    <p>The operator can see whether the valve is open or closed from a distance</p> Signup and view all the answers

    What is the purpose of the non-return stop valve in a boiler system?

    <p>To prevent backflow of steam</p> Signup and view all the answers

    When is the disc in a non-return stop valve forced down onto the seat?

    <p>When the outlet steam pressure is greater than the inlet steam pressure</p> Signup and view all the answers

    What is the purpose of the spring in some lift check valves?

    <p>To hold the plug on its seat</p> Signup and view all the answers

    What is the main limitation of the lift check valve?

    <p>It is only suitable for horizontal pipelines</p> Signup and view all the answers

    What is the type of valve that is typically used in the boiler discharge outlet?

    <p>Stop valve</p> Signup and view all the answers

    What is the advantage of a gate valve with a non-rising stem?

    <p>It requires less room between the valve handle and a fixed surface.</p> Signup and view all the answers

    What is the primary function of a gate valve?

    <p>To serve as a stop or isolation valve.</p> Signup and view all the answers

    What is the disadvantage of a partially opened gate valve?

    <p>It causes excessive wear to the valve disc and seats due to erosion forces.</p> Signup and view all the answers

    What is the primary advantage of a globe valve?

    <p>It is suitable for throttling or regulating flow with minimal wire drawing and seat erosion.</p> Signup and view all the answers

    What is the purpose of a needle valve?

    <p>To allow precise flow control.</p> Signup and view all the answers

    What is the characteristic of a butterfly valve that allows it to provide a bubble-tight seal?

    <p>The disc is lined with a resilient material.</p> Signup and view all the answers

    What is the difference between a lug body and a wafer body butterfly valve?

    <p>The presence or absence of flanges.</p> Signup and view all the answers

    What is the primary advantage of a gate valve over a globe valve?

    <p>It offers the lowest resistance to flow.</p> Signup and view all the answers

    What is the disadvantage of an unbalanced, single disc globe valve in larger sizes?

    <p>It is difficult to open and close against high fluid pressure.</p> Signup and view all the answers

    What is the purpose of the threads on the stem of a gate valve?

    <p>To mesh with threads inside the disc.</p> Signup and view all the answers

    What is the primary purpose of a non-return valve in a boiler system?

    <p>To prevent flow reversal into the boiler</p> Signup and view all the answers

    What happens to the pressure in the boiler if it trips during normal operation?

    <p>The pressure in the boiler drops quickly</p> Signup and view all the answers

    What is the purpose of a pressure reducing station (PRS)?

    <p>To reduce the pressure of the process fluid to a controlled lower pressure</p> Signup and view all the answers

    What is the function of the sensing line in a pressure reducing station?

    <p>To feed the low pressure to the regulator</p> Signup and view all the answers

    What is the purpose of the strainer in a pressure reducing station?

    <p>To prevent foreign particles from entering the regulator</p> Signup and view all the answers

    What is the function of the pressure relief valve in a pressure reducing station?

    <p>To protect the system if the regulator fails</p> Signup and view all the answers

    What is the common feature of the two spring-operated reducing valve designs described?

    <p>They use a compressed spring and a diaphragm</p> Signup and view all the answers

    What happens to the valve in a spring-operated reducing valve with internal diaphragm when the outlet pressure reaches a set value?

    <p>The valve holds open a certain distance, allowing a proportional flow</p> Signup and view all the answers

    What is the purpose of the steam separator and steam trap in a steam PRS?

    <p>To remove free water from the steam before the regulator</p> Signup and view all the answers

    What is the requirement of ASME B31.1 122.1.7 (A.3) for boiler connections to a common header?

    <p>Two stop valves with an ample free-blow drain between them</p> Signup and view all the answers

    What is the primary reason why valves must be carefully selected?

    <p>Because they represent a considerable percentage of the overall system costs</p> Signup and view all the answers

    What is the main function of the stem in a gate valve?

    <p>To move the disc up and down at right angle to the flow path</p> Signup and view all the answers

    What is the purpose of the valve characteristics in valve selection?

    <p>To determine the percentage valve travel to flow rate</p> Signup and view all the answers

    What is the primary advantage of using valves in power plants?

    <p>They are an essential element of any power plant</p> Signup and view all the answers

    What is the primary function of the handwheel in a gate valve?

    <p>To move the stem up and down</p> Signup and view all the answers

    What is the consideration that must be given when selecting a valve for a particular application?

    <p>The type of fluid, working pressure and temperature, and flow rate</p> Signup and view all the answers

    What is the effect of turning the adjusting screw downward on the outlet pressure in a spring-operated reducing valve?

    <p>The outlet pressure increases</p> Signup and view all the answers

    Why is the diaphragm in a spring-operated reducing valve with an external diaphragm not affected by the temperature of the fluid?

    <p>Because the fluid in the control line and diaphragm casing become the same temperature as the surrounding air</p> Signup and view all the answers

    What is the purpose of installing a by-pass valve and line with a spring-operated reducing valve?

    <p>To allow the valve to be removed for repairs without interrupting the fluid supply</p> Signup and view all the answers

    What type of valve is preferred for isolating valves on either side of a spring-operated reducing valve?

    <p>Gate valve</p> Signup and view all the answers

    What happens to the valve disc in a spring-operated reducing valve when the demand for fluid increases?

    <p>The valve disc opens more</p> Signup and view all the answers

    Why is it necessary to fill the lines and casing with distilled water when using a spring-operated reducing valve with an external diaphragm in steam lines?

    <p>To protect the diaphragm from damage</p> Signup and view all the answers

    What is the primary advantage of a gate valve over a globe valve?

    <p>It offers less resistance to flow</p> Signup and view all the answers

    What is the purpose of the stem threads in a gate valve?

    <p>To move the disc up or down</p> Signup and view all the answers

    What is the characteristic of a butterfly valve that allows it to provide a bubble-tight seal?

    <p>Its use of a resilient material for the disc and seat</p> Signup and view all the answers

    What is the primary disadvantage of an unbalanced, single disc globe valve in larger sizes?

    <p>It is difficult to open and close against high fluid pressure</p> Signup and view all the answers

    What is the primary function of a needle valve?

    <p>To allow precise flow control</p> Signup and view all the answers

    What is the main difference between a lug body and a wafer body butterfly valve?

    <p>The way they are installed in the piping system</p> Signup and view all the answers

    Why is the gate valve not suitable for flow throttling purposes?

    <p>Erosion forces associated with high velocity flow can cause excessive wear</p> Signup and view all the answers

    What is the primary advantage of a globe valve?

    <p>It is suitable for throttling purposes</p> Signup and view all the answers

    What is the purpose of the internal threads in the valve body of a globe valve?

    <p>To mesh with threads on the valve stem</p> Signup and view all the answers

    What is the primary function of a gate valve with a non-rising stem?

    <p>To provide a visual indication of the valve position</p> Signup and view all the answers

    What is the primary reason why lift check valves are limited to water applications?

    <p>Because of the potential for leakage under reverse flow conditions</p> Signup and view all the answers

    What is the primary advantage of an outside-screw-and-yoke type stop valve?

    <p>The operator can see whether the valve is open or closed from a distance</p> Signup and view all the answers

    In which situation does the disc in a non-return stop valve remain closed?

    <p>When the boiler is being started and brought on line with other boilers</p> Signup and view all the answers

    What is the primary function of a stop valve in a boiler system?

    <p>To isolate the boiler from the rest of the system</p> Signup and view all the answers

    What is the primary advantage of butterfly valves in terms of operation?

    <p>Ease of operation</p> Signup and view all the answers

    What is the characteristic of a lift check valve that makes it robust and requires minimal maintenance?

    <p>The plug is the only moving part</p> Signup and view all the answers

    What is the function of the valve cover in a plug valve?

    <p>To prevent leakage along the valve stem</p> Signup and view all the answers

    What is the primary purpose of a non-return stop valve in a boiler system?

    <p>To prevent a reversal of steam back to the boiler</p> Signup and view all the answers

    What is the requirement of ASME B31.1 122.1.7(A) for boiler connections to a common header?

    <p>Each boiler discharge outlet must be fitted with a stop valve</p> Signup and view all the answers

    What is the primary advantage of ball valves in terms of handling fluids?

    <p>Ability to handle fluids with high solid content</p> Signup and view all the answers

    What is the primary function of the disc in a swing check valve?

    <p>To prevent reversal of flow in piping</p> Signup and view all the answers

    What is the primary advantage of a lift check valve?

    <p>It is simple and robust</p> Signup and view all the answers

    What is the primary function of the disc in a non-return stop valve?

    <p>To prevent a reversal of steam back to the boiler</p> Signup and view all the answers

    What is the disadvantage of tapered plugs in plug valves?

    <p>They are prone to jamming in the tapered seat</p> Signup and view all the answers

    Why is the lift check valve only suitable for applications where a small amount of leakage under reverse flow conditions is acceptable?

    <p>Because it is designed to operate with a metal seat</p> Signup and view all the answers

    What is the primary advantage of plug valves in terms of operation?

    <p>Quarter-turn operation</p> Signup and view all the answers

    What is the primary function of the valve body in a ball valve?

    <p>To house the spherical plug</p> Signup and view all the answers

    What is the characteristic of the spherical plug in ball valves?

    <p>It allows for precise control of fluid flow</p> Signup and view all the answers

    What is the primary advantage of butterfly valves in terms of design?

    <p>They are relatively light in weight</p> Signup and view all the answers

    What is the primary function of the packing box in plug valves?

    <p>To prevent leakage along the valve stem</p> Signup and view all the answers

    What is the primary purpose of the piping arrangement between the boiler and the header?

    <p>To prevent flow reversal into the boiler</p> Signup and view all the answers

    What is the difference between the spring-operated reducing valve with internal diaphragm and the spring-operated reducing valve with external diaphragm?

    <p>The internal diaphragm is more sensitive to pressure changes</p> Signup and view all the answers

    What is the purpose of the adjustable screw in the spring-operated reducing valve?

    <p>To adjust the outlet pressure</p> Signup and view all the answers

    What is the function of the bypass line in a pressure reducing station?

    <p>To allow manual control of the outlet pressure</p> Signup and view all the answers

    What is the primary concern when using a lift check valve with a metal seat?

    <p>The risk of corrosion</p> Signup and view all the answers

    What is the purpose of the strainer in a pressure reducing station?

    <p>To filter out contaminants from the process fluid</p> Signup and view all the answers

    What is the primary advantage of a pressure reducing station?

    <p>It allows for more precise control of the outlet pressure</p> Signup and view all the answers

    What is the purpose of the steam separator and steam trap in a steam pressure reducing station?

    <p>To remove free water from the steam</p> Signup and view all the answers

    What is the primary function of the sensing line in a pressure reducing station?

    <p>To sense the pressure of the system</p> Signup and view all the answers

    What happens to the pressure in the boiler if it trips during normal operation?

    <p>The pressure drops quickly</p> Signup and view all the answers

    What is the main consideration when selecting materials for valve bodies?

    <p>Pressure, temperature, and type of fluid in the application</p> Signup and view all the answers

    Which material is used for valve bodies in high-pressure applications and temperatures up to 650°C?

    <p>Alloy steel</p> Signup and view all the answers

    What is the importance of proper identification of valves?

    <p>To prevent accidents and ensure safety</p> Signup and view all the answers

    What is the material used for valve trim in moderate pressure and temperature applications?

    <p>Bronze</p> Signup and view all the answers

    What is the purpose of valve packing in a valve?

    <p>To ensure proper sealing of the valve</p> Signup and view all the answers

    Which type of valve requires special alloy steels for temperatures in excess of 650°C?

    <p>Any type of valve</p> Signup and view all the answers

    What information must be indicated on the valve markings according to ASME standards?

    <p>The manufacturer's name, service designation, and material designation</p> Signup and view all the answers

    What is the primary cause of wear on stem packing in valves?

    <p>The rising and turning motion of the valve stem</p> Signup and view all the answers

    What is the result of neglecting to stop flange leaks in valves?

    <p>Wire drawing on the faces of the flanges</p> Signup and view all the answers

    What is the purpose of lubricating the external thread of the valve stem?

    <p>To reduce friction and wear</p> Signup and view all the answers

    What is the recommended procedure for repairing damaged valve discs and seats?

    <p>Refacing the valve disc and seat using a grinding compound</p> Signup and view all the answers

    What is the purpose of internal inspection of valves?

    <p>To prevent damage to the valve disc and seat</p> Signup and view all the answers

    What is the recommended frequency for inspecting valve discs and seats?

    <p>Periodically</p> Signup and view all the answers

    What is the purpose of applying a few drops of oil to the valve stem?

    <p>To reduce friction and wear</p> Signup and view all the answers

    What is the result of over tightening the packing nut in valves?

    <p>Extra friction and wear</p> Signup and view all the answers

    What is the primary purpose of valve maintenance?

    <p>To prevent damage to the valve and surrounding equipment</p> Signup and view all the answers

    What is the primary material used for valve bodies in high-pressure applications and temperatures up to 650°C?

    <p>Alloy steel</p> Signup and view all the answers

    What is the primary purpose of identifying valves in a pipeline?

    <p>To prevent accidents caused by incorrect material usage</p> Signup and view all the answers

    What is the primary material used for valve trim in low-pressure and temperature applications?

    <p>Cast iron</p> Signup and view all the answers

    What is the primary characteristic of valve packing materials?

    <p>Combinations of various materials</p> Signup and view all the answers

    What is the primary consequence of using a valve made of the wrong material in a pipeline?

    <p>Accidents and safety risks</p> Signup and view all the answers

    What is the primary requirement for valves in a pipeline?

    <p>They must be properly identified and labeled</p> Signup and view all the answers

    What is the minimum information required to be indicated on the valve markings according to the standards?

    <p>Manufacturer's name, service designation, and material designation</p> Signup and view all the answers

    What is the primary cause of wear on stem packing in valves?

    <p>Rising and turning motion of the valve stem</p> Signup and view all the answers

    What is the recommended procedure to repair slightly damaged valve discs and seats in globe valves?

    <p>Grind the valve disc in on the valve seat with a grinding compound</p> Signup and view all the answers

    What is the effect of neglecting to stop flange leaks in valves?

    <p>Wire drawing on the faces of the flanges</p> Signup and view all the answers

    What is the purpose of lubricating the external thread of the valve stem?

    <p>To reduce the effort required to open and close the valve</p> Signup and view all the answers

    What is the benefit of applying a few drops of oil occasionally to the valve stem?

    <p>It extends the life of the packing</p> Signup and view all the answers

    What is the procedure for renewal of packing in stuffing boxes of valve stems?

    <p>Similar to that of pump shafts, with the same amount of lubricant</p> Signup and view all the answers

    What is the result of over-tightening the packing nut in valves?

    <p>Extra friction resulting in wear and added effort</p> Signup and view all the answers

    What is the recommended frequency for inspecting valve discs and seats?

    <p>Periodically, during routine maintenance</p> Signup and view all the answers

    What is the purpose of internal inspection of valves?

    <p>To inspect the valve disc and seat for damage</p> Signup and view all the answers

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