Regulator Function and Characteristics

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

Gap flow: The flow below the minimum controllable flow when the closure element is not seated.

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

Double Acting Actuator: An actuator that provides power in either direction.

Dynamic imbalance force: Due to the pressure of the process fluid, it is generated on the valve core at any specified opening

Effective area: In a 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, it is minimal. The molded diaphragm has a smaller effective area change than the flat diaphragm, so it is recommended to use a molded diaphragm.

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, it will make the valve closure element move fully closed, fully open, or remain 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-rated travel when the percentage-rated travel changes from 0 to 100%. This term should always be expressed as an inherent flow characteristic or an installed flow characteristic.

Flow coefficient (Cv value): A valve related to the geometry of the valve, for a given trip constant (Cv value), can be used to measure the flow capacity. It is under the pressure drop per pound of inch per square inch per minute flow American gallons of 60°F water for valves.

High Pressure Recovery Valve: A valve structure that disperses relatively little fluid energy due to the streamlined internal contour and minimal fluid turbulence. Therefore, the pressure downstream of the valve contraction section will return to a very high inlet pressure. The percentage value of the DC valve, such as rotary ball valve is a typical high pressure recovery valve.

Intrinsic die pressure range: The pressure in the valve body at atmospheric pressure acting on the diaphragm to produce the nominal spool stroke pressure high and low values. This range usually refers to the spring set value range, because when the valve is set in the On the working range, this range will be the range of action of the valve.

Intrinsic flow characteristics: When the pressure drop across the valve is constant, as the valve moves from the closed position to the rated stroke, the relationship between flow and shut-off element stroke.

Diaphragm pressure range: In case the valve body is subjected to the specified working conditions, the pressure acting on the diaphragm to produce the nominal valve core stroke is high and low. Due to the force acting on the shut-off element, the inherent diaphragm pressure range may be different. Install 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 large portion of the fluid energy due to the turbulence created by the contour of the fluid passage. As a result, the pressure downstream of the valve contraction section recovers more streamlined than with the valve. A smaller inlet pressure percentage for the valve of the channel. Although each valve structure 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 lower stroke of the shut-off element and linear characteristics 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. Can also be used for rotary valve structure. In the rotary valve structure, the actuator rod linear extension will move the ball or valve plate to the closed position. Also known as positive action.

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 actuator push rod will remove the shut-off element from the valve seat, so open the valve. The term can also be used for rotary valve structures. In a rotary valve structure, the linear extension of the actuator stem moves the ball or valve plate to 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 characteristic does not exceed the specified limit. When the flow increases to the next 00 times, the minimum can be controlled. At flow rate, a valve that is still well controlled 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 closing 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 length of the spring. In a diaphragm actuator valve, the spring constant is usually expressed in terms of pound-force per inch of compression.

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

Condensed flow section: The portion of the stream where the flow rate is at a maximum and where the hydrostatic pressure and cross-sectional area are at a minimum. In a regulating valve, the reduced flow 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 the American Society of Mechanical Engineers.

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

Automatic control system: A control system that can work 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 represented as a function of its steady-state input. This curve is usually expressed as a percentage of the output range versus the percentage of the input range.

Calibration cycle: In the range of the instrument, in the direction of ascending and then descending, 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. Get. It is usually expressed as a percentage of the output range as a percentage of the input range. It provides a measure of backlash.

Clearance flow: When the closure element is not seated, it is below the minimum controllable flow rate.

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 heat 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 regulating valve with a positioner, the feedback signal is usually a mechanical indication of the position of the connecting element of the shut-off element fed back 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 control device. Dynamic behavior.

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

Oscillation: After the external excitation has disappeared, there is still a vibration with significant amplitude. Oscillation is sometimes referred to as a cycle or limit cycle. Oscillation is evidence of working at or near the stability limit. In the regulator, the control system or valve The instability of the positioner will cause fluctuations in the loading pressure of the actuator and the oscillation will follow.

ISA: Abbreviation of the American Instrument Society. Now known as 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 the valve positioner is not used, the loading pressure can be the instrument pressure.

NACE: used to represent the American Society of Corrosion Engineers. With the increasing internationalization of the organization, 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.

Working limit: The range of operating conditions that a device can withstand without causing permanent damage to the operating characteristics.

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

Repeatability: The degree of closeness of a series of consecutive output measurements over the entire range of travel, in the same direction, under the same operating conditions, for the same input value. It is usually measured as non-reproducible. , but expressed as a percentage range. 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 that the signal represents.

Signal amplitude ordering (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, each terminal control element is continuous, with With or without overlap, it responds to the amplitude of the input signal.

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

Air supply pressure: The pressure at the air supply port of a device. Commonly used valve air supply pressure values ​​are set to 20 Psig for springs from 3 to 15 Psig, and 35 Psig for springs from 6 to 30 Psig.

Zero error: When the input is a low range value, the error of a device under the specified conditions of use, it is usually expressed as a percentage of the ideal range.