136 Questions
What percentage of the overall system costs do valves typically represent?
A considerable percentage of the costs
What is the primary purpose of using valves for isolation?
To isolate the flow completely
What type of valve has a gate-like disc that is actuated by a threaded stem and a handwheel?
Gate valve
What is the purpose of the valve wheel in a gate valve?
To mesh with threads in the valve stem
What is a key consideration when selecting a valve?
The type of fluid being used
What is the primary function of the disc in a gate valve?
To shut off the flow
What happens to the pressure on the outlet side when the demand for fluid increases?
It drops slightly
What is the purpose of the adjusting screw in the spring-operated reducing valve?
To adjust the outlet pressure
What happens when the demand for fluid decreases in the spring-operated reducing valve?
The valve closes more
Why is the diaphragm mounted outside the valve housing in the spring-operated reducing valve?
To protect the diaphragm from overheating
What should be installed on either side of the reducing valve?
Isolating valves
What type of valve should be used as the by-pass valve in the reducing valve?
Globe valve
What is the purpose of gaskets in valve installations?
To prevent leakage at the flanges
What is the primary advantage of butterfly valves?
Relatively light weight and ease of operation
What is the characteristic of the spherical plug in ball valves?
It provides precise control of the flow and a tight shutoff
In which industry are ball valves commonly used due to their ability to handle slurries and fluids with high solid content?
Paper industry
What is the purpose of the packing box in plug valves?
To prevent leakage along the valve stem
What is the primary function of check valves?
To prevent reversal of flow in piping
What is the characteristic of the disc in swing check valves?
It moves upward to allow flow and downward to close
What is the advantage of plug valves in terms of pressure drop?
They have a very low pressure drop across the valve
Which type of valve is commonly used in gas supply lines?
Plug valve
What is the problem associated with tapered plugs in plug valves?
They have a tendency to jam in the tapered seat and cause scoring
What is the primary function of a dashpot in larger check valves?
To cushion the action of the disc
What is the main advantage of a lift check valve?
Its simplicity
What is the primary concern when using a lift check valve with a metal seat?
It may not be suitable for applications where a small amount of leakage is not acceptable
What is the purpose of the stop valve in a boiler system?
To provide a means of shutting off the steam supply
What is the advantage of an outside-screw-and-yoke type stop valve?
The operator can see whether the valve is open or closed from a distance
What is the purpose of the non-return stop valve in a boiler system?
To prevent backflow of steam
When is the disc in a non-return stop valve forced down onto the seat?
When the outlet steam pressure is greater than the inlet steam pressure
What is the purpose of the spring in some lift check valves?
To hold the plug on its seat
What is the main limitation of the lift check valve?
It is only suitable for horizontal pipelines
What is the type of valve that is typically used in the boiler discharge outlet?
Stop valve
What is the advantage of a gate valve with a non-rising stem?
It requires less room between the valve handle and a fixed surface.
What is the primary function of a gate valve?
To serve as a stop or isolation valve.
What is the disadvantage of a partially opened gate valve?
It causes excessive wear to the valve disc and seats due to erosion forces.
What is the primary advantage of a globe valve?
It is suitable for throttling or regulating flow with minimal wire drawing and seat erosion.
What is the purpose of a needle valve?
To allow precise flow control.
What is the characteristic of a butterfly valve that allows it to provide a bubble-tight seal?
The disc is lined with a resilient material.
What is the difference between a lug body and a wafer body butterfly valve?
The presence or absence of flanges.
What is the primary advantage of a gate valve over a globe valve?
It offers the lowest resistance to flow.
What is the disadvantage of an unbalanced, single disc globe valve in larger sizes?
It is difficult to open and close against high fluid pressure.
What is the purpose of the threads on the stem of a gate valve?
To mesh with threads inside the disc.
What is the primary purpose of a non-return valve in a boiler system?
To prevent flow reversal into the boiler
What happens to the pressure in the boiler if it trips during normal operation?
The pressure in the boiler drops quickly
What is the purpose of a pressure reducing station (PRS)?
To reduce the pressure of the process fluid to a controlled lower pressure
What is the function of the sensing line in a pressure reducing station?
To feed the low pressure to the regulator
What is the purpose of the strainer in a pressure reducing station?
To prevent foreign particles from entering the regulator
What is the function of the pressure relief valve in a pressure reducing station?
To protect the system if the regulator fails
What is the common feature of the two spring-operated reducing valve designs described?
They use a compressed spring and a diaphragm
What happens to the valve in a spring-operated reducing valve with internal diaphragm when the outlet pressure reaches a set value?
The valve holds open a certain distance, allowing a proportional flow
What is the purpose of the steam separator and steam trap in a steam PRS?
To remove free water from the steam before the regulator
What is the requirement of ASME B31.1 122.1.7 (A.3) for boiler connections to a common header?
Two stop valves with an ample free-blow drain between them
What is the primary reason why valves must be carefully selected?
Because they represent a considerable percentage of the overall system costs
What is the main function of the stem in a gate valve?
To move the disc up and down at right angle to the flow path
What is the purpose of the valve characteristics in valve selection?
To determine the percentage valve travel to flow rate
What is the primary advantage of using valves in power plants?
They are an essential element of any power plant
What is the primary function of the handwheel in a gate valve?
To move the stem up and down
What is the consideration that must be given when selecting a valve for a particular application?
The type of fluid, working pressure and temperature, and flow rate
What is the effect of turning the adjusting screw downward on the outlet pressure in a spring-operated reducing valve?
The outlet pressure increases
Why is the diaphragm in a spring-operated reducing valve with an external diaphragm not affected by the temperature of the fluid?
Because the fluid in the control line and diaphragm casing become the same temperature as the surrounding air
What is the purpose of installing a by-pass valve and line with a spring-operated reducing valve?
To allow the valve to be removed for repairs without interrupting the fluid supply
What type of valve is preferred for isolating valves on either side of a spring-operated reducing valve?
Gate valve
What happens to the valve disc in a spring-operated reducing valve when the demand for fluid increases?
The valve disc opens more
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?
To protect the diaphragm from damage
What is the primary advantage of a gate valve over a globe valve?
It offers less resistance to flow
What is the purpose of the stem threads in a gate valve?
To move the disc up or down
What is the characteristic of a butterfly valve that allows it to provide a bubble-tight seal?
Its use of a resilient material for the disc and seat
What is the primary disadvantage of an unbalanced, single disc globe valve in larger sizes?
It is difficult to open and close against high fluid pressure
What is the primary function of a needle valve?
To allow precise flow control
What is the main difference between a lug body and a wafer body butterfly valve?
The way they are installed in the piping system
Why is the gate valve not suitable for flow throttling purposes?
Erosion forces associated with high velocity flow can cause excessive wear
What is the primary advantage of a globe valve?
It is suitable for throttling purposes
What is the purpose of the internal threads in the valve body of a globe valve?
To mesh with threads on the valve stem
What is the primary function of a gate valve with a non-rising stem?
To provide a visual indication of the valve position
What is the primary reason why lift check valves are limited to water applications?
Because of the potential for leakage under reverse flow conditions
What is the primary advantage of an outside-screw-and-yoke type stop valve?
The operator can see whether the valve is open or closed from a distance
In which situation does the disc in a non-return stop valve remain closed?
When the boiler is being started and brought on line with other boilers
What is the primary function of a stop valve in a boiler system?
To isolate the boiler from the rest of the system
What is the primary advantage of butterfly valves in terms of operation?
Ease of operation
What is the characteristic of a lift check valve that makes it robust and requires minimal maintenance?
The plug is the only moving part
What is the function of the valve cover in a plug valve?
To prevent leakage along the valve stem
What is the primary purpose of a non-return stop valve in a boiler system?
To prevent a reversal of steam back to the boiler
What is the requirement of ASME B31.1 122.1.7(A) for boiler connections to a common header?
Each boiler discharge outlet must be fitted with a stop valve
What is the primary advantage of ball valves in terms of handling fluids?
Ability to handle fluids with high solid content
What is the primary function of the disc in a swing check valve?
To prevent reversal of flow in piping
What is the primary advantage of a lift check valve?
It is simple and robust
What is the primary function of the disc in a non-return stop valve?
To prevent a reversal of steam back to the boiler
What is the disadvantage of tapered plugs in plug valves?
They are prone to jamming in the tapered seat
Why is the lift check valve only suitable for applications where a small amount of leakage under reverse flow conditions is acceptable?
Because it is designed to operate with a metal seat
What is the primary advantage of plug valves in terms of operation?
Quarter-turn operation
What is the primary function of the valve body in a ball valve?
To house the spherical plug
What is the characteristic of the spherical plug in ball valves?
It allows for precise control of fluid flow
What is the primary advantage of butterfly valves in terms of design?
They are relatively light in weight
What is the primary function of the packing box in plug valves?
To prevent leakage along the valve stem
What is the primary purpose of the piping arrangement between the boiler and the header?
To prevent flow reversal into the boiler
What is the difference between the spring-operated reducing valve with internal diaphragm and the spring-operated reducing valve with external diaphragm?
The internal diaphragm is more sensitive to pressure changes
What is the purpose of the adjustable screw in the spring-operated reducing valve?
To adjust the outlet pressure
What is the function of the bypass line in a pressure reducing station?
To allow manual control of the outlet pressure
What is the primary concern when using a lift check valve with a metal seat?
The risk of corrosion
What is the purpose of the strainer in a pressure reducing station?
To filter out contaminants from the process fluid
What is the primary advantage of a pressure reducing station?
It allows for more precise control of the outlet pressure
What is the purpose of the steam separator and steam trap in a steam pressure reducing station?
To remove free water from the steam
What is the primary function of the sensing line in a pressure reducing station?
To sense the pressure of the system
What happens to the pressure in the boiler if it trips during normal operation?
The pressure drops quickly
What is the main consideration when selecting materials for valve bodies?
Pressure, temperature, and type of fluid in the application
Which material is used for valve bodies in high-pressure applications and temperatures up to 650°C?
Alloy steel
What is the importance of proper identification of valves?
To prevent accidents and ensure safety
What is the material used for valve trim in moderate pressure and temperature applications?
Bronze
What is the purpose of valve packing in a valve?
To ensure proper sealing of the valve
Which type of valve requires special alloy steels for temperatures in excess of 650°C?
Any type of valve
What information must be indicated on the valve markings according to ASME standards?
The manufacturer's name, service designation, and material designation
What is the primary cause of wear on stem packing in valves?
The rising and turning motion of the valve stem
What is the result of neglecting to stop flange leaks in valves?
Wire drawing on the faces of the flanges
What is the purpose of lubricating the external thread of the valve stem?
To reduce friction and wear
What is the recommended procedure for repairing damaged valve discs and seats?
Refacing the valve disc and seat using a grinding compound
What is the purpose of internal inspection of valves?
To prevent damage to the valve disc and seat
What is the recommended frequency for inspecting valve discs and seats?
Periodically
What is the purpose of applying a few drops of oil to the valve stem?
To reduce friction and wear
What is the result of over tightening the packing nut in valves?
Extra friction and wear
What is the primary purpose of valve maintenance?
To prevent damage to the valve and surrounding equipment
What is the primary material used for valve bodies in high-pressure applications and temperatures up to 650°C?
Alloy steel
What is the primary purpose of identifying valves in a pipeline?
To prevent accidents caused by incorrect material usage
What is the primary material used for valve trim in low-pressure and temperature applications?
Cast iron
What is the primary characteristic of valve packing materials?
Combinations of various materials
What is the primary consequence of using a valve made of the wrong material in a pipeline?
Accidents and safety risks
What is the primary requirement for valves in a pipeline?
They must be properly identified and labeled
What is the minimum information required to be indicated on the valve markings according to the standards?
Manufacturer's name, service designation, and material designation
What is the primary cause of wear on stem packing in valves?
Rising and turning motion of the valve stem
What is the recommended procedure to repair slightly damaged valve discs and seats in globe valves?
Grind the valve disc in on the valve seat with a grinding compound
What is the effect of neglecting to stop flange leaks in valves?
Wire drawing on the faces of the flanges
What is the purpose of lubricating the external thread of the valve stem?
To reduce the effort required to open and close the valve
What is the benefit of applying a few drops of oil occasionally to the valve stem?
It extends the life of the packing
What is the procedure for renewal of packing in stuffing boxes of valve stems?
Similar to that of pump shafts, with the same amount of lubricant
What is the result of over-tightening the packing nut in valves?
Extra friction resulting in wear and added effort
What is the recommended frequency for inspecting valve discs and seats?
Periodically, during routine maintenance
What is the purpose of internal inspection of valves?
To inspect the valve disc and seat for damage
Learn about the different types of valve operations, including manual and actuated valves, and the importance of selecting the right valve for a system based on factors such as working pressure, temperature, and fluid type. Understand the characteristics of valves and how they are used for isolation and control. Test your knowledge of valve selection and operation with this quiz!
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