06202018Wed
Last updateWed, 20 Jun 2018 6pm

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From Cannon Balls to Pressure Seals: Graphite for Sealing

From Cannon Balls to Pressure Seals: Graphite for Sealing

From time to time, we re-publish well-re...

Gaskets Are Not Created Equal

Gaskets Are Not Created Equal

Gaskets are near the bottom of the food ...

Your Valves May Be Weaponized

Your Valves May Be Weaponized

The advent of the Internet of Things (Io...

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Industry Headlines

Global LNG Trade Growing, Led by Australia and the U.S.

Wednesday, 20 June 2018  |  Chris Guy

Global trade in liquefied natural gas (LNG) reached 38.2 billion cubic feet per day (Bcf/d) in 2017, a 10% (3.5 Bcf/d) increase from 2016 and the larg...

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Industry Headlines

Metso Receives Major Valve Orders in China

1 DAY AGO

Metso has received two valve orders totaling 8,200 valves from major pulp and paper customers in China. The orders are booked in Metso's first quarter 2018 orders received. The total value of the orders and the company names are not being disclosed. Broadly covering China's mid and high-end customers ...

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A-T Controls Names Andy Cheney Southwest Regional Manager

4 DAYS AGO

A-T Controls recently announced the addition of Andy Cheney as the company’s new southwest regional manager, effective immediately.

Cheney’s new role will cover California, South Nevada, Arizona and New Mexico. He has over twenty years in the valve and automation business and is very famil...

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Global LNG Trade Growing, Led by Australia and the U.S.

-1 DAYS AGO

Global trade in liquefied natural gas (LNG) reached 38.2 billion cubic feet per day (Bcf/d) in 2017, a 10% (3.5 Bcf/d) increase from 2016 and the largest annual volume increase since 2010, according to the Annual Report on LNG trade by the International Association of Liquefied Natural Gas Importers...

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U.S. Natural Gas Production Could Grow 60% Over Next 20 Years

-1 DAYS AGO

A decade since the start of a shale gas revolution that unlocked new supplies and resulted in a “wholesale turnaround” in U.S. production, the overall size of recoverable gas reserves continues to increase and the pace of production growth is only accelerating, a new report by IHS Markit s...

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Texas Economy Continues to Expand at “Solid Pace”

2 HOURS AGO

The Texas economy is expanding at a solid pace. Employment has grown at a 3.6% annualized rate through May, driven by job gains in the goods-producing sector. Unemployment remains near its historical low, and labor markets are tight. The Dallas Fed’s Texas Business Outlook Surveys (TBOS) suggest...

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Consumer Sentiment Climbs to Three-Month High

1 DAY AGO

Consumer sentiment rose slightly in early June due to consumers' more favorable assessments of their current financial situation and more favorable views of current buying conditions for household durables. The Expectations Index declined to its lowest level since the start of the year due to less f...

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A Case for Mechanical Temperature Control

vmwnt12_beyond_valves_fig1Instrument, mechanical or project engineers may see a multitude of temperature applications cross their desks. Their immediate reaction might be to employ a temperature control loop. But could a mechanical, self-operated temperature regulator be a better solution for the valve application?

When approaching a temperature control application, the engineer usually considers:

  • The degree of accuracy needed
  • Whether the application requires feedback (Are limit switches/output signals used?)
  • Whether the application needs to be controlled through a DCS, PLC or other type of controller
  • The budget for the application.

The answer to whether a mechanical temperature regulator might be a cost-effective and reliable solution for the application depends on those considerations.

In almost any process facility, a variety of temperature control applications can be found. As with any controlled variable, both the accuracy and criticality of those applications can vary widely. Often, non-critical temperature applications become instrumented control loops even when a self-operated or mechanical regulator could provide the desired accuracy along with a substantial cost savings.


WHAT’S CONSIDERED

vmwnt12_beyond_valves_fig1Figure 1. Temperature regulatorA typical temperature control loop ­(Figure 1) requires:

  • a temperature sensor
  • wiring and conduit
  • connection to a controlling device
  • a control valve (and sometimes a positioner and/or I/P converter, and an air-filter regulator)
  • plant air

A self-contained temperature regulator requires no power, no air supply or other expensive compo­nents to operate. Representative costs based on a 1-inch line size would be:

  • Temperature transmitter: $300-1,000
  • Temperature controller: $400-1,000
  • Control valve and actuator: $1,500-3,000
  • I/P converter: $200-350
  • Air set regulator: $100-150
  • Positioner: $500-2,000
  • Control loop total: $3,000-7,500
  • Temperature regulator: $500-2,500

Although designs may vary from manufacturer to manufacturer, most temperature regulators operate on the same principle. A premeasured amount of “fill” is drawn into the thermal system filling the upper diaphragm chamber, the capillary tube and most of the bulb. As the controlled temperature increases, the fill in the sensing bulb begins to vaporize and creates pressure on the sealed system. This pressure drives the valve stem, closing direct-acting valves or opening reverse-acting valves. By using different fill fluids, many different temperature control ranges can be offered for both cooling and heating applications—temperature ranges are readily available from -20° F (-29° C) to 500° F (260° C).

Applications for which these devices might be ideal include tank farms, large heat exchangers, heat exchangers with slow temperature changes, area heating/cooling (warehouse/maintenance shops) and steam tracing.

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