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Industry Headlines

Velan Announces New Sales Structure

2 HOURS AGO

Velan is re-designing its sales structure to be better aligned with customers’ market approach. This change is intended to focus Velan’s resources on maximizing impact and competitiveness in today’s challenging economy.

Paul Dion has been appointed as vice-president of sales, process ...

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MSS Revises Standards for Instrument Valves, Sealing of Rising Stem Valves

1 DAY AGO

The Manufacturers Standardization Society (MSS) is pleased to announce the publication of the following revised Standard Practices:

  • MSS SP-99-2016a, Instrument Valves (replaces 2016 edition)
  • MSS SP-105-2016a, Instrument Valves for Code Applications (replaces 2016 edition)
  • MSS SP-120-2017, Flexible Grap...

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Construction Underway on Atlantic Sunrise Pipeline

1 DAY AGO

Construction is officially underway in Pennsylvania on the greenfield portion of the Atlantic Sunrise pipeline project – an expansion of the existing Transco natural gas pipeline to connect Marcellus gas supplies with markets in the Mid-Atlantic and Southeastern U.S.

Construction broke ground in ...

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EIA Projects 28% Increase in World Energy Use by 2040

1 DAY AGO

The U.S. Energy Information Administration (EIA) projects that world energy consumption will grow by 28% between 2015 and 2040. Most of this growth is expected to come from countries that are not in the Organization for Economic Cooperation and Development (OECD), and especially in countries where d...

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U.S. Manufacturers Seeking More Renewable Energy

5 HOURS AGO

A new report from David Gardiner and Associates finds that 83% of the largest manufacturing companies with a U.S. footprint have established greenhouse gas reduction targets and 25% of manufacturers have established renewable energy targets. The analysis also finds that enabling access to renewable en...

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Harvey Caused Steep Drop in U.S. Industrial Output

3 DAYS AGO

Industrial production declined 0.9% in August following six consecutive monthly gains. Hurricane Harvey is estimated to have reduced the rate of change in total output by roughly 0.75%. The index for manufacturing decreased 0.3%; storm-related effects appear to have reduced the rate of change in facto...

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Selection Considerations for Control Valves vs. Regulators

In any control system, the option potentially exists to select either a control valve or a regulator, so it is useful to compare the respective performance and economics of these approaches to arrive at some general selection guidelines.

Unlike regulators, control valves are not standalone products. A control valve is the final control element in a control system and needs to be evaluated in that context. A control valve is most frequently used in the control of the following parameters: temperature, pressure, flow and level.

However, in principle, any continuously varying system parameter that can be measured and compared to a set point can be controlled. Also, keep in mind that regardless of the parameter being controlled (the controlled variable), the control valve itself can only change the flow rate.

All control is to a set point, and the control system can be diagrammatically illustrated as shown in Figure 1.

spr09_bv_fig1

The essential feature of the controller (whether acting as a single-loop controller or as a component within a PLC or within a DCS or fieldbus device) is the incorporation of proportional and integral control modes capable of returning the measured variable to the set point following load changes or system disturbances. Control is generally within 5%, often within 1 to 2%.

Rising stem control valves are typically globe valves commonly used to the 2-inch size. However, globe valves can extend to at least 24 inches in size with special trims and cages for severe service and high-noise applications.

For economic reasons, rotary control valves are generally applied as line sizes increase above 2 inches and a variety of ball valves, eccentric plug and segmented ball valves, and butterfly valves exist in this segment of the market. The segmented ball valve is used in many applications and the largest size rotary control valves, such as butterfly valves, can extend to 72 inches in diameter.

Globe-style valves offer advantages in that the plug and/or cage can be more readily characterized to optimize the installed flow characteristic. Most rotary valves have an inherent flow coefficient characteristic that increases approximately exponentially with the increase in travel.

Although a range of actuators can be used, pneumatic actuation predominates. The diaphragm actuator is generally the style of choice due to minimized resistance and hysteresis for small changes in travel associated with control to within 1 to 2%. For improved control and minimized deadband, positioners are generally specified. It is also common practice for the current-to-pneumatic conversion to occur at the positioner. There is also a continuing increase in the use of intelligent or smart positioners, thereby providing automatic commissioning, higher accuracy, tight shut off, customizable characteristics and diagnostic capabilities.

There are obvious economic considerations associated with the choice of a control valve, which, at a minimum, require the incorporation of sensors and transmitters, controllers, positioners, instrument valves, tubing, wiring, calibration, tuning, etc. Generalized cost estimates can only be considered representative, at best, and can vary significantly depending upon application, size, material, accuracy and commercial circumstances.

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