Week 11 of 15 – Terms	Name: Answer Sheet

In your own words, write a definition for each of the following terms. Plagiarism will be checked and not tolerated.

Points: 5 pts/each = 33 * 5 = 165 pts

Rangeablity

1. Describes the relationship between the range and the minimum quantity that can be measured. 2. The ratio of the maximum flow rate to the minimum flow rate of a meter. 3. The ratio of the largest flow coefficient (Cv or Kv) to the smallest controllable flow coefficient (Cv or Kv) within which the deviation from the specified flow characteristic does not exceed the stated limits. [ANSI/ISA-75.05.01-2000]

Turndown ratio

The ratio from the maximum operating conditions to the minimum operating conditions, which provides a controllable or measurable span. The device must perform over this range. [ANSI/ISA-77.13.01-1999]

Throttling valve

A device for regulating the flow of a fluid by alternatively opening up or closing down a restriction in a passage or inlet.

Globe valve

1. A valve with a linear-motion closure member, one or more ports, and a body that is distinguished by a globular shaped cavity around the port region. [ANSI/ISA-75.05.01-2000] 2. A type of flow-regulating valve that consists of a movable disc and a stationary-ring seat in a generally spherical body. In the general design, the fluid enters below the valve seat and leaves from the cavity above the seat. 3. A valve with a linear motion closure member whose seal is perpendicular to the stem motion, that has one or more ports, and that has a body distinguished by a globular-shaped cavity around the port region. (See figure.) [ANSI/ISA-75.05.01-2000]

Angle valve

A valve design in which one port is collinear with the valve stem or actuator, and the other port is at a right angle to the valve stem. [ANSI/ISA-75.05.01-2000]

Butterfly valve

1. A valve with a circular body and a rotary motion disk closure member, pivotally supported by its stem. [ANSI/ISA-75.05.01-2000]. 2. A valve that consists of a disk inside a valve body, which operates by rotating about an axis in the plane of the disk in order to shut off or regulate flow in a piping system. A similar device used in heating or ventilating ductwork is called a butterfly damper.

Ball valve

A valve that has a rotary motion closure member consisting of a full ball or a segmented ball. [ANSI/ISA-75.05.01-2000]

Actuator

1. A pneumatic, hydraulic, or electrically powered device that supplies force and motion so as to position a valve’s closure member at or between the open or closed position. [ANSI/ISA-75.05.01-2000] 2. A part of the final control element that translates the control signal into action by the final control device in the process. Typical examples are motors, solenoids, cylinders, and so on. 3. A device responsible for actuating a mechanical device such as a control valve. 4. A device that actuates.

Positioner

A position controller that is mechanically connected to a moving part of a final control element or its actuator. It automatically adjusts its output to the actuator in order to maintain a desired position for the closure member in proportion to the input signal. Double-acting positioner: a positioner with two outputs, suited to a double acting actuator. Single- acting positioner: a positioner with one output, suited to a spring-opposed actuator. [ANSI/ISA-75.05.01-2000]

Regulator

A device for controlling pressure or flow in a process. See also controller, self-operated (regulator).

Control valve

1. Any valve that controls pressure, rate of flow, or flow direction in a fluid- or gas-filled system. 2. A final controlling element, through which a fluid or gas passes, that adjusts the size of a flow passage in order to modify the rate of flow of the fluid, as directed by a signal from a controller. [ANSI/ISA-51.1-1979 (R1993)] 3. A device, other than a common, hand-actuated on–off valve or self-actuated check valve that directly manipulates the flow of one or more fluid process streams. Use of the term hand control valve is limited to hand-actuated valves that (a) are used for process throttling or that (b) require identification as an instrument. 4. A power-actuated device that modifies the fluid flow rate in a process control system. It consists of a valve that is connected to an actuator mechanism (including all related accessories) and that is capable of changing the position of a closure member in the valve in response to a signal from the controlling system. [ANSI/ISA-75.05.01-2000]

Modulating valve

A valve which can be positioned anywhere between fully on and fully off to proportion the rate of flow in response to a modulating controller. Modulating control valves are used in variable-flow systems in which flow must be adjusted to slow, moderate, or full stream. Due to batch process changes, regulate flow or other control applications, the actuator is adjusted often and its control accuracy of modulating service actuators must remain consistent and not deteriorate.

Installed characteristics

Pressure losses in a system change the valve manufacturer’s characteristics as specified on the manufacturers specification sheet. When process losses change the specified characteristics it is called installed characteristics.

Cv

The valve-sizing coefficient. This coefficient is the number of U.S. gallons per minute of water at 60-degrees F, that can flow through the valve when it is wide open and the pressure drop is one psi.

Diaphragm actuator

A fluid-powered device in which the fluid acts upon a flexible component, called the diaphragm. [ANSI/ISA-75.05.01-2000]

Fail-open

A condition in which the valve closure member moves into an open position when the actuating energy source fails. [ANSI/ISA-75.05.01-2000]

Fail-closed

Condition in which the valve closure member moves to a closed position when the source of actuating energy fails. [ANSI/ISA-75.05.01-2000]

Fail-safe

1. A characteristic of a particular valve and its actuator such that the loss of actuating energy supply will cause a valve closure member to be fully closed, fully open, or remain in the last position. [ANSI/ISA-75.05.01-2000] 2. Any protection against the effects of failure of equipment, such as a fuel shut-off when flame in a furnace is lost. 3. Referring to the capacity to go into a predetermined safe state when a specific malfunction occurs. [ANSI/ISA-84.01-1996; ANSI/ISA-77.13.01-1999]

Fail-locked

A term used to describe the ability of an actuator to stay at the same percent of travel it was in when it lost its air supply. On spring return actuators, this is accomplished by means of a lock up valve. On piston actuators a series of compressed air cylinders must be employed.

Fail-indeterminate

Fail indeterminate (FI) means when Instrument air goes off, the control valve will be in the position. It will not change its position. To remove the control valve for maintenance or replacement, we have to open the bye-pass valve and close two block valves one by one. For the worst case scenario if the control valve in closed position when the power goes off. To remove the fluid and also depressurize the system we need to drain the fluid both upstream and downstream of the control valve.

Piston actuator

A fluid-powered device in which the fluid acts upon a movable piston so as to provide motion to the actuator stem. [ANSI/ISA-75.05.01-2000]

Motor actuator

The electric actuator uses an electric motor to provide torque to operate a valve. They are quiet, non-toxic and energy efficient. However, electricity must be available, which is not always the case.Robust asynchronous three-phase AC motors are mostly used as the driving force, for some applications also single-phase AC or DC motors are used: These motors are specially adapted for valve automation as they provide higher torques from standstill than comparable conventional motors, a necessary requirement to unseat sticky valves. The actuators are expected to operate under extreme ambient conditions, however they are generally not used for continuous operation since the motor heat buildup can be excessive.

Solenoid actuator

A solenoid valve is an electromechanically operated valve. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed together on a manifold.

Booster relay or volume booster

A volume- or pressure-amplifying pneumatic relay that is used to reduce the time lag in pneumatic circuits by reproducing pneumatic signals that have high volume and/or high-pressure output. [ANSI/ISA-75.05.01-2000]

Pilot valve

A pilot valve is a small valve that controls a limited-flow control feed to a separate piloted valve. Typically, this valve controls a high pressure or high flow feed. Pilot valves are useful because they allow a small and easily operated feed to control a much higher pressure or higher flow feed, which would otherwise require a much larger force to operate; indeed, this is even useful when a solenoid is used to operate the valve.

Trim

The internal components of a valve, which modulate the flow of the controlled fluid. [ANSI/ISA-75.05.01-2000]

Cavitation

A two-stage phenomenon of liquid flow. The first stage is the formation of vapor bubbles within the liquid system because of the static pressure of fluid falling below the fluid vapor pressure. The second stage is the collapse or implosion of these cavities back into an all-liquid state as the fluid decelerates and static pressure is recovered. [ANSI/ISA-75.05.01-2000; ISARP75.23-1995]

Pressure relief valve

A mechanism that vents fluid from an internally pressurized system so as to counteract system overpressure. The mechanism may release all pressure and shut the system down (as does a rupture disk) or it may merely reduce the pressure in a controlled manner so as to return the system to a safe operating pressure (as does a spring-loaded safety valve).

Rupture disks

A diaphragm that is designed to burst at a predetermined pressure differential

Fusible plugs or links

A hollowed, threaded plug in which the hollowed portion is filled with a material with a low melting point. It is usually placed at the lowest permissible water level.

Excess-flow check valve

A valve that permits fluid to flow until the flow rate becomes excessively high. When flow rate becomes excessively high, the valve shuts off the flow. Shut off flow rates are usually 1-1/2 to 2 times the normal flow rate.

Proportioning pump (metering pump)

A plunger-type pump that is designed to control small-scale fluid-flow rates accurately. It is used to inject small quantities of materials into continuous-flow liquid streams. Also known as a proportioning pump.

Specific gravity

The ratio of the density of a material to the density of water at the same conditions. Specific gravity: Gf = liquid at flowing condition referred to water at 60°F. Gg = gas referred to air, both at standard temperature and pressure (STP).