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Description of the functions and terminology of various regulating valves

Intrinsic die pressure range: When the pressure inside the valve body is atmospheric pressure, it acts on the diaphragm to generate high and low pressures for the rated spool stroke. This range is usually referred to as the spring setpoint range, as this range will be the valve's range of motion when the valve is set to this operating range.
Various regulating valve functions and terminology
Spring setting range: regulating valve (control valve) actuator spring adjustment range to balance the actual process force.
Flow 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 pressure range of the diaphragm. This can be considered an inherent or installation feature.
Double acting actuator: An actuator that can provide power in either direction.
Dynamic Imbalance Force: The net force generated on the spool at any specified opening due to the pressure of the process fluid.
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 as it moves, usually at the beginning of the stroke, and at the end of the stroke. The molded diaphragm has a smaller effective area change than the flat diaphragm, so it is recommended to use a molded diaphragm.
Equal percentage flow characteristics: (see "Process Control Terminology": "Equivalent Percentage Flow Characteristics".)
Loss of Gas - Off: A state in which the valve shutoff element moves to the closed position when the drive energy is lost.
Loss of gas - Open: A state in which the valve shutoff element moves to the open position when the drive energy is lost.
Loss of gas - safety: a type of valve and its actuator
Features: When the drive energy supply is interrupted, the valve shut-off element is moved to fully closed, fully open, or left in the last position, and any position is considered necessary for the protection process. The fail-safe mode of operation 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 stroke when the percentage rated stroke changes from 0 to 100%. This term should always be expressed as an inherent flow characteristic or an installation flow characteristic.
Flow coefficient (CV value): A constant (C V value) for a given stroke associated with the geometry of the valve that can be used to measure flow capacity. It is the US gallon of 60°F water flowing through the valve at a pressure drop of 1 pound per square inch.
High Pressure Recovery Valve: A valve construction that disperses relatively little fluid energy due to the streamlined internal profile and minimal fluid turbulence. Therefore, the pressure downstream of the valve diversion section will return to a very high percentage of the inlet pressure. DC-type valves, such as rotary ball valves, are typical high pressure recovery valves.
Intrinsic die pressure range: When the pressure inside the valve body is atmospheric pressure, it acts on the diaphragm to generate high and low pressures for the rated spool stroke. This range is usually referred to as the spring setpoint range, as this range will be the valve's range of motion when the valve is set to this operating range.
Intrinsic flow characteristics: The relationship between flow and the travel of the shut-off element as the pressure drop across the valve is constant as the valve moves from the closed position to the nominal stroke. Install diaphragm pressure range: Under the specified operating conditions of the valve body, it acts on the diaphragm to produce high and low pressures for the rated spool stroke. 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: The relationship between flow and shut-off components as the pressure drop across the valve is affected by changing process conditions as the valve moves from the closed position to the nominal stroke.
Leakage: (see "Seat Leakage".) Linear Flow Characteristics: (see "Process Control Terminology": "Linear Characteristics".)
Low Pressure Recovery Valve: A valve structure that dissipates a significant portion of the fluid energy due to turbulence created by the contour of the fluid passage. As a result, the pressure downstream of the valve diversion section will return to a smaller inlet pressure percentage value than the valve with more streamlined passages. Although each valve has a different structure, conventional straight-through valves typically have low pressure recovery capabilities.
Modified parabolic flow characteristics: A flow characteristic that provides an equal percentage of characteristics at the lower stroke of the shut-off element and linearity at the high travel of the shut-off element.
Normally closed valve: (see "Gas-off".)
Normally open valve: ("See Lost - Open".)
Push down to close the structure: a straight-through valve structure with a shut-off element between the actuator and the seat ring so that the push-out of the actuator pushes the shut-off element toward the seat ring and finally closes the valve. This term can also be used for rotary valve construction. In a rotary valve configuration, 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 such that the push-out of the actuator pushes the shut-off element away from the seat, thus opening the valve. This term can also be used in rotary valve construction. 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).
Quick-on flow characteristics: (see "Process Control Terminology": "Quick-Open Characteristics".)
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 rate is increased to 100 times the minimum controllable flow, 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 flows.
Rated flow coefficient (CV value): The flow coefficient (CV value) of the valve at rated stroke.
Rated stroke: The distance the valve shut-off element moves from the closed position to the fully open position. The rated 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 flowing through the valve when it is in the fully closed position at the specified differential pressure and temperature.
Spring factor: The change in spring force as the length of the spring changes. In membrane actuator regulators (control valves), the spring rate is typically expressed in pounds per inch of compression.
Valve stem imbalance force: The net force generated on the valve stem at any position due to fluid pressure.
Shrinkage section: the part of the stream where the flow rate is the largest, the hydrostatic pressure, and the cross-sectional area are the smallest. In a regulating valve (control valve), the contraction section is usually located downstream of the actual physical limit.

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