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Last updateTue, 28 Mar 2017 8pm

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Valves Help Enable Net-Zero Water Use

Valves Help Enable Net-Zero Water Use

With drought and climate change affecting ...

Valve Selection in Pulp and Paper Operations

Valve Selection in Pulp and Paper Operations

Over the centuries, the pulp and paper i...

How to Improve Control Valve Performance with Positioners

How to Improve Control Valve Performance with Positioners

As the final control element in most pro...

VMA Technical Event: Engineering Valves in the Extreme

VMA Technical Event: Engineering Valves in the Extreme

While much the 2017 VMA Technical Semina...

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Industry Headlines

Colorado Seeing Surge in Oil & Gas Investments

Tuesday, 28 March 2017  |  Chris Guy

“Drilling applications and investments by oil and gas companies are surging in Colorado after crude prices partially rebounded from their collap...

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Industry Headlines

Emerson Opens Second Additive Manufacturing Center

1 DAY AGO

With the goal of spurring innovation to address customers’ engineering design challenges and accelerating speed to market for new, rigorously-tested products, Emerson opened an advanced additive manufacturing center at its Singapore campus. This is Emerson’s second location to have additiv...

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GE Oil & Gas Expands with New Sub Saharan Africa Facility

5 DAYS AGO

GE Oil & Gas opened a new facility in Takoradi Port, Ghana, expanding its global footprint and supporting local investment. The facility, which will be the primary service center for deep-water offshore projects in Ghana, has a 1,600 square meter indoor test area with capability for testing thre...

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Colorado Seeing Surge in Oil & Gas Investments

6 HOURS AGO

“Drilling applications and investments by oil and gas companies are surging in Colorado after crude prices partially rebounded from their collapse in recent years, pushing the industry deeper into residential communities largely unaccustomed to drilling,” the Associated Press is reporting .

&...

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U.S. Specialty Chemicals Markets Accelerated in February

1 DAY AGO

The American Chemistry Council (ACC) reported that U.S. specialty chemicals market volumes rose a strong 0.6% in February. This follows an upwardly revised 0.4% gain in January. Volumes have generally been moving up since May. All changes in the data are reported on a three-month moving average (3MMA)...

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Four Out of Ten Jobs Could be Lost to Automation by 2021

7 HOURS AGO

Automation is the new norm across sectors and will affect the bottom of pyramid so much so that four out of every 10 jobs globally would be lost due to this by 2021, experts say. As automation adoption increases, all high transaction and labor intensive jobs will take a hit. According to PeopleStrong...

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U.S. Durable Goods Orders Rose 1.7% in February

1 DAY AGO

New orders for manufactured durable goods in February increased $3.9 billion or 1.7% to $235.4 billion, the U.S. Department of Commerce announced . This increase, up two consecutive months, followed a 2.3% January increase. Excluding transportation, new orders increased 0.4%. Excluding defense, new or...

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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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