A11 Flashcards
What typically measures the variable (e.g., pressure, flow, temperature) in a control valve system?
A) Controller
B) Valve positioner
C) Transmitter
D) Actuating device
Transmitter
In a control valve system, what does the valve positioner do?
A) It measures the variable being controlled
B) It acts as the actuator to move the valve stem
C) It converts an electronic control signal into an air signal to control the valve stem position
D) It supplies air pressure to the valve body
It converts an electronic control signal into an air signal to control the valve stem position
Which type of application might require a valve positioner for control valves?
A) On-off valve operation
B) Open-loop control
C) Remote flow rate setting
D) High-temperature fluid shutoff
Open-loop control
In more sophisticated applications, control valves are used to respond to deviations in which of the following?
A) Temperature
B) Pressure
C) Level
D) All of these
All of these
What is the primary function of a valve positioner in an open-loop control system?
A) To regulate the temperature of the valve
B) To provide a power source to the valve
C) To ensure that the valve plug or ball moves the required amount
D) To increase the noise level during operation
To ensure that the valve plug or ball moves the required amount
What is one feature of the most sophisticated modulating control valves?
A) High-friction packing and actuating devices
B) High noise generation
C) Simple on-off functionality
D) Linear or equal percentage flow characteristic
Linear or equal percentage flow characteristic
What are the typical signal ranges for pneumatic and electronic controllers used in control valves?
A) 3 to 15 psi; 4 to 20 mA
B) 0.2 to 1.0 bar; 3 to 15 psi
C) 4 to 20 psi; 10 to 15 dBA
D) 0.2 to 1.0 bar; 10 to 15 dBA
3 to 15 psi; 4 to 20 mA
How do three-way valves function in a mixing application?
A) By reducing pressure at all ports
B) By diverting fluid to a single outlet
C) By combining fluids from two ports into one discharge
D) By separating fluids into different exits
By combining fluids from two ports into one discharge
What feature makes eccentric rotary plug valves suitable for modulating control?
A) Low or constant operating torque
B) High flow velocity
C) Multi-port design
D) Adjustable orifices
Low or constant operating torque
Which of the following is a characteristic of ball valves?
A) They are unsuitable for high-temperature applications.
B) Metal-seated ball valves are used for normal liquid or gaseous fluids up to 82°F.
C) Ball valves have a good shutoff characteristic and high flow capacity, making them ideal for on-off or sequencing control.
D) They are only available with welded connections.
Ball valves have a good shutoff characteristic and high flow capacity, making them ideal for on-off or sequencing control.
What is the most common type of actuator used in control valves?
A) Electric actuators
B) Pneumatic actuators, either spring-opposed diaphragm or piston actuated
C) Hydraulic actuators
D) Manual actuators
Pneumatic actuators, either spring-opposed diaphragm or piston actuated
Why is the spring/diaphragm actuator the most popular choice for control valves?
A) It is the most cost-effective option but lacks fail-safe functionality.
B) It is simple and has the ability to fail-safe, driving the valve to either fail-close or fail-open based on safety requirements.
C) It is more complex but provides superior control compared to other actuators.
D) It does not rely on spring force and operates only with constant air pressure.
It is simple and has the ability to fail-safe, driving the valve to either fail-close or fail-open based on safety requirements.
What happens when air pressure is lost in a spring/diaphragm actuator?
A) The valve remains in its current position until air pressure is restored.
B) The valve opens partially to relieve pressure in the system.
C) The actuator loses functionality, requiring manual operation of the valve.
D) The spring force drives the valve to either fail-close or fail-open based on process safety requirements.
The spring force drives the valve to either fail-close or fail-open based on process safety requirements.
What is an advantage of piston actuators compared to spring-opposed diaphragm actuators?
A) They provide more dynamic stiffness and are more compact due to higher air pressures.
B) They are less compact but have lower air pressure requirements.
C) They are more cost-effective and simpler than spring-opposed diaphragm actuators.
D) They are primarily used for special applications requiring electric power.
They provide more dynamic stiffness and are more compact due to higher air pressures.
Why are electric and hydraulic actuators used less frequently than pneumatic actuators?
A) They require higher air pressures to function.
B) They are less reliable and more expensive than pneumatic actuators.
C) They lack dynamic stiffness and fail-safe functionality.
D) They are only suitable for low-pressure applications.
They are less reliable and more expensive than pneumatic actuators.
What materials are used for valve housings in highly corrosive applications?
A) Carbon steel and 316 stainless steel
B) Brass and aluminum
C) Cast iron and forged steel
D) Teflon-lined housings and exotic alloys like Hastelloy®, monel, or titanium
Teflon-lined housings and exotic alloys like Hastelloy®, monel, or titanium
What is the pressure at the thermodynamic critical point of water in psia?
A) 21,370 kPa
B) 1000 kPa
C) 14.7 psia
D) 3206 psia
3206 psia
What is the significance of providing simplified equations for gas and steam service?
A) To eliminate the need for complex calculations.
B) To ensure accurate results in all conditions.
C) To provide reasonable accuracy despite the non-linear relationship.
D) To simplify the design of control valves for gas and steam systems.
To provide reasonable accuracy despite the non-linear relationship.
What is the main factor influencing the non-linear relationship between Δp and flow for gases?
A) Temperature
B) Pressure
C) Density
D) Viscosity
Density
In the context of Application Guide for Modulating Control Valves, what is the recommended minimum valve size relative to the pipe diameter?
A) Equal to the pipe diameter
B) Half of the pipe diameter
C) One-third of the pipe diameter
D) One-fourth of the pipe diameter
Half of the pipe diameter
What is the gas specific gravity of air?
A) 0.5
B) 0.8
C) 1.0
D) 1.2
1.0
Which of the following statements accurately describes the typical range for low pressure drops in a system?
A) Low pressure drops are typically less than 10% of the inlet pressure.
B) Low pressure drops are typically less than 20% of the inlet pressure.
C) Low pressure drops are typically less than 30% of the inlet pressure.
D) Low pressure drops are typically less than 40% of the inlet pressure.
Low pressure drops are typically less than 20% of the inlet pressure.
