01172018Wed
Last updateWed, 17 Jan 2018 9pm

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Young Valve Professionals: Logan Moore

Young Valve Professionals: Logan Moore

In 2014, VMA's leadership created the Va...

VALVE Magazine: Readers' Choice 2017

VALVE Magazine: Readers' Choice 2017

Happy New Year to our VALVE Magazine rea...

Educational Opportunities Abound at New VMA Knowledge Forum

Educational Opportunities Abound at New VMA Knowledge Forum

From technical to manufacturing to human...

Offshore Production in a Low Oil-Price Environment

Offshore Production in a Low Oil-Price Environment

Three years ago, The Washington Post publi...

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Interior Coatings for Waterworks Valves

Interior Coatings for Waterworks Valves

Monday, 15 January 2018  |  John V. Ballun, P. E.

Since the 1990s, two types of epoxy coatings have been commonly specified and used for iron valves in the waterworks industry: fusion-bonded epoxy and...

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Industry Headlines

ASCO Valve and Numatics Now Doing Business as ASCO, L.P.

1 DAY AGO

Effective January 1, 2018, ASCO Valve, Inc. and Numatics, Inc. began doing business as ASCO, L.P. This change in legal entities affects neither current channel alignment nor purchasing processes—everything will remain the same, including product authorizations. Within ASCO, a business unit of Em...

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Union Tech Names Chris Mayo Director for Global Power

1 DAY AGO

Union Tech recently announced that Chris Mayo has joined the valve sales team as director for global power. He will be primarily responsible for power markets, which include Union Tech’s Z1 Unibody Power Valve amongst other valve products in the Z-Series line.

Mayo is an industry veteran who bri...

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Natural Gas Prices, Production, Exports Increased in 2017

3 HOURS AGO

Overall, natural gas prices at key regional trading hubs were less volatile in 2017 than in previous years, as pipelines that came online throughout the year eased some infrastructure constraints that affect regional prices, according to the U.S. Energy Information Administration . In the Northeast, w...

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Pipeline Capacity Expansions Accelerating in U.S. Northeast

2 DAYS AGO

With projects such as Columbia Gas Transmission’s Leach Xpress and Energy Transfer Partners’ Rover pipeline, “[t]he U.S. northeast should realize an increase of more than 3 Bcf/d of natural gas pipeline capacity by the end of this quarter, compared with an increase of 2.3 Bcf/d in ...

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House Unanimously Passes Miscellaneous Tariff Bill

59 MINS AGO

The House of Representatives voted unanimously this week to pass H.R. 4318 , the Miscellaneous Tariff Bill (MTB) Act of 2018. This bipartisan, bicameral legislation was written to increase the competitiveness of American manufacturers by temporarily reducing tariffs on nearly 1,700 different products ...

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Manufacturing Technology Orders Increased in November

1 DAY AGO

Orders for manufacturing technology climbed year over year and year to date in November 2017 according to the Association for Manufacturing Technology (AMT). Orders totaled $425.97 million for the month, up 19.0% compared to November 2016. At a cumulative total of $4.06 billion for the year, orders we...

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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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