PTEC 132 - Exam 5 - Spring 14 - Chapter 11

An actuator is a device that responds to an instrument signal by generating linear or rotational motion. It converts the input signal into physical movement, allowing it to control various mechanical systems or components. Actuators are commonly used in industries such as robotics, automotive, and aerospace to control valves, pumps, motors, and other equipment.

A butterfly valve is opened with a rotary motion because it operates by rotating a disc or vane within the valve body. This disc is attached to a shaft, which can be turned to either open or close the valve. As the shaft rotates, the disc also rotates, allowing or blocking the flow of fluid through the valve. This rotary motion is an effective way to control the flow rate and pressure in a system, making it the correct answer.

In the context of actuators and valves, the term "reverse acting" refers to the opposite action or movement compared to direct acting. Direct acting actuators and valves respond to a signal or input by moving in the same direction as the input, while reverse acting ones move in the opposite direction. This distinction is important in various applications where different types of actuation are required for specific purposes or control mechanisms.

If a spring and diaphragm actuator loses air, it means that there is no air pressure to keep the actuator in its normal operating position. In this case, the spring inside the actuator will push the diaphragm into its fail-safe position, which is typically a fully closed or fully open position depending on the design of the actuator. This fail-safe position ensures that the actuator does not cause any unintended operation or damage to the system in the absence of air pressure. Therefore, the statement is true.

The pushing rod that transfers the motion of the actuator to the valve plug is called a stem. The stem connects the actuator to the valve plug and allows for the opening and closing of the valve. It is responsible for transmitting the force and motion from the actuator to the valve plug, controlling the flow of fluid or gas through the valve.

An I/P or valve positioner is a device that is used to control the position of a control valve based on the input signal from a controller. In this case, the increasing signal from the controller is reversed by the I/P or valve positioner to a decreasing signal, which is then used to control the position of the control valve. This allows for precise and accurate control of the system by adjusting the flow of fluid through the control valve based on the input from the controller.

A double acting cylinder type actuator always requires a positioner because it is designed to operate in both directions, meaning it can extend and retract. A positioner is necessary to accurately control the position of the actuator and ensure it reaches the desired endpoints. Without a positioner, the actuator may not be able to accurately stop at the desired positions, leading to potential issues or inaccuracies in the system it is being used for.

The most common control valve body style in the processing industry is the Globe valve.

The possible combinations of actuator and valve actions include direct/direct, direct/reverse, reverse/direct, and reverse/reverse. This means that the actuator and valve can both move in the same direction (direct), or they can move in opposite directions (reverse). Therefore, all of the given options are correct.

A handwheel is a type of actuator accessory that allows for manual control and override of an actuator. It is used to manually operate the actuator or to limit its motion. By turning the handwheel, the operator can directly control the movement of the actuator, providing a convenient and reliable way to adjust or override its automated functions.

When a stem on a control valve is sticking, it means that it is not able to move smoothly. Instead, it will jump or jerk as it tries to move. This jumping motion is a clear indication that there is an issue with the valve, such as dirt or debris causing it to get stuck. The other options, twist, pivot, and bend, do not accurately describe the movement of a sticking stem.

In a control valve with a spring and diaphragm actuator, the term "air-to-close" means that the valve requires air pressure to close. In the event of a power loss or loss of actuating energy, there will be no air pressure to keep the valve closed. As a result, the spring in the actuator will force the valve to open completely. Therefore, the correct answer is that the valve will be forced completely open by the spring.

The stationary part of the valve trim connected to the body that comes in contact with the valve plug is called the seat. The seat provides a tight seal when the valve is closed, preventing any leakage. It is usually made of a durable material such as metal or synthetic material to withstand the pressure and flow of the fluid passing through the valve.

The correct answer is "actuator, valve". In this context, the term "ATC" refers to the actuator, which is a device responsible for controlling or moving a mechanism or system. On the other hand, "atc" represents the valve, which is the component that regulates the flow or direction of a fluid or gas. Therefore, the ATC tag represents the actuator, and the atc tag represents the valve.

Valve positioners are used for multiple purposes. They can be used to accurately position the valve, reverse the action of the valve, and mimic a valve trim type. Additionally, they can provide split-range control. Therefore, the correct answer is "all of the above."

The final control element is considered to be the device that directly controls the manipulated variable. It is responsible for adjusting the process variable based on the feedback received from the comparing and controlling element. The final control element is typically a valve, actuator, or motor that regulates the flow, pressure, or temperature in a system to maintain the desired setpoint.

The three pressure gauges on a pneumatic valve positioner are Signal, Output, and Supply. These gauges are used to monitor and measure different aspects of the valve positioner system. The Signal gauge measures the input signal from the controller, the Output gauge measures the output pressure to the actuator, and the Supply gauge measures the supply pressure to the positioner. These gauges are essential in ensuring that the valve positioner is functioning properly and that the appropriate pressures are being maintained for optimal valve operation.

The top portion of the valve that connects the valve to the actuator and can be removed to allow entry into the valve body cavity is called a bonnet. The bonnet acts as a cover for the valve body and houses the stem and packing. It is designed to provide a secure connection between the valve and the actuator while also allowing for maintenance and repair by providing access to the valve internals.

The actuator is the device that provides motion to the valve. It is responsible for opening and closing the valve, controlling the flow of fluid or gas. The actuator can be operated manually or automatically, depending on the application. It converts a control signal into mechanical motion, allowing the valve to be adjusted or regulated as needed. The spring, bonnet, and body are all components of the valve itself, but they do not directly provide motion to the valve.

If an actuator does not have a spring, it will fail in place. This means that it will remain in its current position and will not be able to move or perform any action. Without a spring, the actuator does not have the ability to return to a default or neutral position in case of failure. Therefore, it will simply stop functioning and remain in the position it was in when the failure occurred.

A back pressure regulator is a device used to control the pressure of a fluid flowing through a system. It maintains a constant pressure upstream by adjusting the flow rate downstream. This is achieved by sensing the pressure downstream and adjusting the valve accordingly to maintain the desired pressure. In other words, a back pressure regulator ensures that the pressure in the system does not exceed a certain limit by regulating the flow rate.

During a power failure, the valve needs to stop the flow of material to the tank. An air-to-open valve is designed to open when air pressure is applied, so when the power fails and the air pressure drops, the valve will close and stop the flow. On the other hand, an air-to-close valve is designed to close when air pressure is applied, so it would remain closed during a power failure and not stop the flow. Fail-in-place valves are designed to maintain their current position even during a power failure, so it would not stop the flow. Therefore, the best option is an air-to-open valve.

Spring and diaphragm actuators provide excellent modular control with or without a positioner. These actuators use a combination of a spring and a diaphragm to control the movement of the valve. The spring provides the necessary force to open or close the valve, while the diaphragm acts as a flexible barrier between the actuator and the valve. This design allows for precise control of the valve's position, making spring and diaphragm actuators a reliable choice for controlling flow in various applications.

These symbols represent different types of regulators used in various industrial processes. A pressure reducing regulator is used to reduce the pressure of a fluid or gas to a desired level. A back pressure regulator is used to maintain a constant pressure in a system by adjusting the flow rate. A reverse valve positioner is a device that controls the position of a valve in the opposite direction to its normal operation. A forward valve positioner, on the other hand, controls the position of a valve in the same direction as its normal operation.

A valve positioned is used to provide split range control, position the valve, mimic a valve trim type, and reverse the action. However, it does not send a signal back to the controller. This means that the valve positioned does not communicate with the controller to provide feedback or relay information about its position or status.

If the tag on a pneumatically actuated control valve identifies it as air-to-open, it means that the valve is designed to open when air pressure is applied. However, if the positioner has been configured to reverse the signal, it means that the valve will actually close when air pressure is applied. Therefore, if the valve fails, it will fail to open, resulting in it being closed.

A controller's output signal can be reversed by the valve positioner. A valve positioner is a device that is used to control the position of a valve based on the input signal from a controller. It can modify the output signal to reverse the direction of the valve movement. This allows for precise control and adjustment of the valve position, which is essential in many industrial processes.

A valve positioner is a device that is used to accurately position the valve stem based on the instrument signal. It ensures that the valve is in the correct position to regulate the flow of fluid or gas. Additionally, a valve positioner can also reverse the action of the signal received from the controller, meaning it can change the valve's position based on the inverse of the signal received. Therefore, the correct answer is "Both a and c" because a valve positioner can both position the valve stem in reference to the instrument signal and reverse the action of the signal received from the controller.

If a control valve and its spring and diaphragm actuator are both direct acting, it means that the valve will open when the actuator receives a signal to open. Therefore, if air is lost to the valve, the actuator will not receive the signal to close the valve, causing it to fail in the open position.