02182018Sun
Last updateFri, 16 Feb 2018 8pm

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Putting Servo Valves Back to Work

Putting Servo Valves Back to Work

Industries as varied as paper production...

Corrosion and Fouling: Is There a Solution?

Corrosion and Fouling: Is There a Solution?

According to a 1998 study released by the ...

Valves with All the Trimmings

Valves with All the Trimmings

The term valve trim has been around for ...

VMA Chair Mark Nahorski: Industry Has Many Pathways to Success

VMA Chair Mark Nahorski: Industry Has Many Pathways to Success

Part of the discussion today about what ...

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Industry Headlines

ValvTechnologies ITC 2018 Recap

Friday, 16 February 2018  |  Chris Guy

The biennial ValvTechnologies’ International Technical Conference and Users Group (ITC) was held on February 8-9 in Houston. Seeking to educate,...

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Putting Servo Valves Back to Work

Putting Servo Valves Back to Work

Monday, 12 February 2018  |  Christopher Valiquette

Industries as varied as paper production, steelmaking and power generation rely on servo valves for precise motion control. A servo valve can last wel...

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Industry Headlines

ValvTechnologies ITC 2018 Recap

2 DAYS AGO

The biennial ValvTechnologies’ International Technical Conference and Users Group (ITC) was held on February 8-9 in Houston. Seeking to educate, inspire and engage attendees over a two-day period, the event brought together hundreds of attendees from across the globe to share valuable insight ...

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Matthew Davis Named Field Service Manager at Weir

3 DAYS AGO

Weir Valves & Controls USA (WVC USA) has appointed Matthew Davis to the position of field service manager. In his new role, Davis will be responsible for managing the WVC USA Field Service crew and organizing WVC Service jobs for power plants worldwide.

Davis joins WVC USA with over 20 years of ex...

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TransCanada Turns Attention to Natural Gas System

3 DAYS AGO

TransCanada Corp. will move forward with a $1.9 billion expansion of its NGTL System to connect incremental supply and expand basin export capacity by one billion cubic feet of natural gas per day at the interconnection with its Canadian Mainline. NGTL expects to begin construction in 2019.

The increme...

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U.S. Oil Output Surge Reminiscent of Run-Up to 2014 Dive

4 DAYS AGO

According to the International Energy Agency (IEA), fast rising production in non-OPEC countries, led by the U.S., is likely to grow by more than demand in 2018. For now, the upward momentum that drove the price of Brent crude oil to $70/bbl has stalled; partly due to investors taking profits, but a...

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U.S. Industrial Production Fell 0.1% in January

2 DAYS AGO

Industrial production edged down 0.1% in January following four consecutive monthly increases. At 107.2% of its 2012 average, total industrial production was 3.7% higher in January than it was a year earlier.

Manufacturing output was unchanged in January for a second consecutive month; the index has i...

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U.S Business Inventories Rose 0.4% in December

3 DAYS AGO

Manufacturers’ and trade inventories, adjusted for seasonal variations but not for price changes, were estimated at an end-of-month level of $1,902.2 billion, up 0.4% from November 2017 and were up 3.2% from December 2016.

A poll of economists “had forecast inventories, a key component of...

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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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