08242016Wed
Last updateWed, 24 Aug 2016 5pm

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Valve Basics Training Helps Fill Industry Skills Gap

Valve Basics Training Helps Fill Industry Skills Gap

One of the most keenly felt needs in tod...

An End-User’s Perspective on Valve Selection and Risk

An End-User’s Perspective on Valve Selection and Risk

I am not a valve expert, although I ofte...

New Test Stamp and More Updates on Pressure Vessel Codes

New Test Stamp and More Updates on Pressure Vessel Codes

A new test organization program and stam...

The Role of Valves in HAZOP Studies

The Role of Valves in HAZOP Studies

Process hazard analysis (PHA) is require...

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ValvTechnologies Successfully Completes NUPIC Audit

5 HOURS AGO

ValvTechnologies, Inc. recently achieved NUPIC-approved suppliers list status, upon successful completion of the Nuclear Procurement Issues Committee (NUPIC) audit conducted at the Houston facility. NUPIC members include all domestic U.S. nuclear utilities as well as several international members.

Form...

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GE Oil & Gas Supporting ONGC’s Exploratory Drilling Campaign in India

8 HOURS AGO

GE Oil & Gas has been awarded a multi-million-dollar frame agreement by Oil and Natural Gas Corporation Limited (ONGC), India’s largest exploration and production company. Under the agreement , GE will provide an estimated 55 subsea wellheads (SG5) over next three years for the operator&rsqu...

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Chemical Activity Barometer Suggests Accelerated Business Activity

1 DAY AGO

The Chemical Activity Barometer (CAB) expanded 0.4% in August following an upward revision for July. This marks the barometer’s sixth consecutive monthly gain. Accounting for adjustments, the CAB is up 3.2% over this time last year, the strongest year over year growth since January 2015. All d...

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Innovation Could Lead to Significant Cuts in Chemical Manufacturing Energy Use

1 DAY AGO

Scientists from ExxonMobil and Georgia Tech have developed a new technology that could significantly reduce the amount of energy and emissions associated with manufacturing plastics. If brought to industrial scale, this breakthrough could reduce industry’s global annual carbon dioxide emissions ...

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Manufacturing Output Up, Firms Signal Softer Expansion in New Work

1 DAY AGO

U.S. goods producers saw a further upturn in overall business conditions during August, though the rate of improvement was softer than seen in July. While output continued to rise markedly, total new work rose at a slower pace and employment expanded at the weakest rate in four months. Meanwhile, co...

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Leading Economic Indicators Gained Ground in July

6 DAYS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 0.4% in July to 124.3, following a 0.3% increase in June, and a 0.2% decline in May.

“The U.S. LEI picked up again in July, suggesting moderate economic growth should continue through the end of 2016,” said Ataman Ozyi...

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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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