Valve function and characteristic terminology

Spring setting range: Adjustment valve actuator spring adjustment range to balance the actual process force.

Circulation capacity: The rated flow through the valve under specified conditions.

Gap flow: The flow below the minimum controllable flow when the shut-off element is not seated.

Diaphragm pressure range: The difference between the high and low diaphragm pressure range. This can be considered an inherent or installation feature.

Double-acting actuator: An actuator that provides power in either direction.

Dynamic imbalance force: Due to the pressure of the process fluid, it is produced on the spool at any specified opening

Effective area: In a thin film actuator, the effective area is the area of ​​the diaphragm that effectively produces the output force. The effective area of ​​the diaphragm may change with its movement, usually at the beginning of the stroke, and at the end of the stroke. Molded diaphragms have a smaller effective area change than flat diaphragms, so molded diaphragms are recommended.

Loss of gas - Closed: A state in which the valve closure element moves to the closed position when the drive energy is lost.

Loss of gas - open: A state in which the valve closure element moves to the open position when the drive energy is lost.

Loss of gas - safety: A characteristic of the valve and its actuator: When the drive energy supply is interrupted, the valve closing element is moved to fully closed, fully open, or left in the last position, any position is considered It is necessary to protect the process. Failure-safe action may require the use of auxiliary controls connected to the actuator.

Flow characteristics: The relationship between the flow through the valve and the percentage of rated travel when the percentage-rated travel changes from 0 to 100%. This term should always be expressed as inherent flow characteristics or installation flow characteristics.

Flow coefficient (CV value): A constant (CV value) related to the geometry of the valve for a given stroke can be used to measure the flow capacity. It is the United States gallon of 60° F water flowing through the valve per minute at the pressure drop per square inch.

High pressure recovery valve: A valve structure that disperses relatively little fluid energy due to its streamlined internal profile and minimal fluid turbulence. Therefore, the pressure downstream of the valve contraction section will return to a very high percentage of the inlet pressure. DC type Valves, such as rotary Ball Valves, are typically high pressure recovery valves.

Intrinsic die pressure range: When the pressure in the valve body is atmospheric, the pressure acting on the diaphragm to produce the nominal spool stroke is high and low. This range usually refers to the spring setpoint range, because when the valve is set on the working range, this range will be the valve's range of motion.

Inherent Flow Characteristics: The relationship between flow and shut-off element stroke as the valve moves from the closed position to the rated stroke when the pressure drop across the valve is constant.

Install diaphragm pressure range: Under the condition that the valve body bears the specified working conditions, the pressure acting on the diaphragm to produce the rated valve core stroke is high and low. Due to the forces acting on the shut-off element, the inherent diaphragm pressure range may differ from the installed diaphragm pressure range.

Installation flow characteristics: When the pressure drop across the valve is affected by changing process conditions, the relationship between the flow and the shut-off element as the valve moves from the closed position to the rated stroke.

Low pressure recovery valve: A valve structure that disperses a significant portion of fluid energy due to the turbulent flow path profile. As a result, the pressure downstream of the valve contraction section returns to a smaller inlet pressure percentage than a valve with more streamlined passages. Although the structure of each valve is not the same, the ordinary straight-through valve usually has a low pressure recovery capability.

Modified Parabolic Flow Characteristics: A flow characteristic that provides equal percentage characteristics at the low stroke of the shut-off element and linearity at the high stroke of the shut-off element.

Push-down closure structure: A straight-through valve structure whose shut-off element is located between the actuator and the seat ring so that the push-out of the actuator pushes the shut-off element towards the seat ring and finally closes the valve. This term can also be used for rotary valve structures. In rotary valve configurations, the linear extension of the actuator stem moves the ball or valve plate toward the closed position. Also known as positive effect.

Push down to open the structure: a straight-through valve structure. Its seat ring is located between the actuator and the shut-off element, so that the introduction of the push rod of the actuator moves the shut-off element away from the valve seat, thus opening the valve. This term can also be used for rotary valve structures. In a rotary valve configuration, the linear extension of the actuator stem moves the ball or valve plate toward the open position. (also known as reaction).

Adjustable ratio: The ratio between the maximum flow coefficient (CV value) and the minimum flow coefficient (CV value) when the deviation from the specified flow characteristics does not exceed the specified limit. When the flow rate is increased to the next 00 times the minimum controllable flow rate, a still well-controlled valve has a 100:1 adjustable ratio. The adjustable ratio can also be expressed as the ratio between the maximum and minimum controllable flow.

Rated stroke: The distance from the closed position of the valve closing element to the fully open position. The full open position is the maximum opening recommended by the manufacturer.

Relative flow coefficient: The ratio between the flow coefficient (CV value) at the specified stroke and the flow coefficient (CV value) at the rated stroke.

Seat leakage: The amount of fluid that flows through the valve when the valve is in the fully closed position at the specified pressure differential and temperature.

Spring Coefficient: The change in spring force per unit of spring length. In diaphragm actuator actuators, the spring constant is usually expressed in pounds per inch of compression.

Valve stem imbalance force: The net force generated on the valve stem at any position due to the fluid pressure.

Condensed flow section: The portion of the stream where the flow rate is maximum, hydrostatic pressure, and cross-sectional area are at a minimum. In a regulating valve, the contraction section is usually located downstream of the actual physical limit.

ANSI: Abbreviation for American National Standards Organization.

API: Abbreviation for the American Petroleum Organization.

ASME: Abbreviation for American Society of Mechanical Engineers.

ASTM: Abbreviation for the American Society for Testing and Materials.

Automatic Control System: A control system that works without manual intervention.

Bode plot: logarithmic amplitude scale and phase angle plots of a transfer function on a logarithmic base line. This is the most common form of graphical representation of frequency response data.

Calibration curve: Graphical representation of the verification result. The steady state output of a device is expressed as a function of its steady state input. This curve is usually expressed as a percentage of the output range to the percentage of the input range.

Calibration cycle: In the range of the instrument, in the direction of rising and then falling, use the known value of the measured variable, and record the corresponding output reading value. The verification cycle curve can be increased by first and then reduce the input of the device. obtain. It is usually expressed as a percentage of the output range as a percentage of the input range. It provides a measure of backlash.

Gap flow: The flow rate below the minimum controllable flow when the shut-off element is not seated.

Controller: A device that automatically operates to regulate a controlled variable.

ç„“: A thermal dynamic quantity, which is the sum of the product of the internal energy of the valve body and its volume and pressure: H = U + pVo (also called thermal capacity).

Entropy: A theoretical measure of energy that cannot be converted to mechanical work in a thermal dynamic system.

Feedback signal: The return signal obtained by measuring the directly controlled variable. For a control valve with a positioner, the feedback signal is usually a mechanical indication of the position of the shut-off element connecting rod to the positioner.

FCI: Abbreviation for Fluid Control Organization.

Frequency Response Characteristics: The frequency dependence of the steady-state sinusoidal input in terms of amplitude and phase and the resulting basic sinusoidal output. The magnitude and phase shift of the output can be seen as a function of the input test frequency and used to describe the dynamic behavior of the control device.

Hardness: The ability of a metal to resist plastic deformation (usually in the form of depressions). The ability of plastic and rubber to resist the tip of a penetrating surface.

Oscillation: After the external excitation disappears, there is still a vibration with obvious amplitude. Oscillations are sometimes called cycle or limit cycles. Oscillation is evidence of working at or near the stability limit. In control valves, instability of the control system or valve positioner can cause fluctuations in the loading pressure of the actuator, and oscillations will follow.

ISA: Abbreviation for American Instrument Society. It is now called the International Society for Measurement and Control.

Instrument pressure: The output pressure provided by an automatic regulator valve to operate the valve.

Loading pressure: The pressure used to position the pneumatic actuator. This is the actual pressure acting on the actuator diaphragm or piston. If no valve positioner is used, the loading pressure can be gauge pressure.

NACE: Used to represent the American Society of Corrosion Engineers. With the increasing internationalization of the organization's scope, the term has been changed to international NACE. NACE is no longer an abbreviation.

0SHA: Abbreviation for the Occupational Safety and Health Act (USA).

Working medium: This refers to the fluid, usually air or gas, used to power the positioner and automatic controller.

Operating Limit: A range of operating conditions that a device can withstand without causing permanent damage to operating characteristics.

Range: The area between two extremes, the spacing of which can be measured, accepted, or transmitted, and represented by upper and lower range values ​​(eg, 3 to 15 Psi; -4 to 212°F, -40 to 100°C).

Reproducibility: A series of consecutive measurements of the proximity of the same input value over the entire range of travel, in the same direction, under the same operating conditions. It is usually measured as non-reproducible, but expressed as a percentage scale. It does not include the return difference.

Sensitivity: After a steady state is reached, the change in output amplitude and the input change that caused the change

Signal: A physical variable whose one or more parameters carry information about another variable represented by the signal.

Sorting of signal amplitude (split range): An action mode in which two or more signals are generated, or two or more terminal control elements are driven by one input signal, and each terminal control element is continuously, with Or with no overlap to respond to the amplitude of the input signal.

Range: The arithmetic difference between upper and lower range values ​​(eg: range=0 to 150°F, span=150°F; range=3 to 15PSig, span=12PSig).

Air source pressure: The pressure at a device's air supply port. Commonly used regulator air supply pressure values ​​range from 20 Psig for springs from 3 to 15 Psig to 35 Psig for springs from 6 to 30 Psig.

Zero Error: The error of a device under specified conditions of use when the input is a low range value, which is usually expressed as a percentage of the ideal range.