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Industry Headlines

Poll: U.S. Economy to Grow 2.2% in 2017

Wednesday, 07 December 2016  |  Chris Guy

National Association for Business Economics’ (NABE) December 2016 Outlook Survey forecasts 2.2% growth in real GDP for 2017. The annualized grow...

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Industry Headlines

GE Oil & Gas Signs Agreement with TAG GmbH

14 HOURS AGO

GE Oil & Gas has signed an agreement with TAG (Trans Austria Gasleitung) GmbH, a pipeline operator with stations across Austria, to install its new Tuning Maintenance Software (TUMAS) across TAG’s fleet of 16 PGT25 gas turbines. This is the first time this solution has been rolled out across...

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Apollo Valves Combining with Shurjoint Mechanical Groove Systems

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In October, 2016, The Pipeline and Hazardous Materials Safety Administration (PHMSA) announced a final rule that expands safety requirements for excess flow valves (EFVs) to multi-residential and commercial applications. That version of the rule covered the installation of EFVs in new or replaced se...

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New Wastewater Rules Preceded Reduction in Seismic Activity

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“The rate of earthquakes in Oklahoma has dropped dramatically since late May, when the state limited wastewater injections into energy wells,” according to a statistical analysis from the Associated Press .

“This year, before the new rules went into effect on May 28, Oklahoma averaged 2...

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Poll: U.S. Economy to Grow 2.2% in 2017

9 HOURS AGO

National Association for Business Economics’ (NABE) December 2016 Outlook Survey forecasts 2.2% growth in real GDP for 2017. The annualized growth rate forecasted for 2017 inched downward to 2.2% in the current survey from 2.3% in September. Both projections illustrate the panel’s expectat...

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U.S. Factory Orders Rose 2.7% in October

14 HOURS AGO

New orders for manufactured goods in October, up four consecutive months, increased $12.5 billion or 2.7% to $469.4 billion, the U.S. Department of Commerce reports . This followed a 0.6% September increase.

New orders for manufactured durable goods in October, up four consecutive months, increased $10...

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Accessories for Control Valves

spr11_b2b_introHigh-pressure, angle-style control valves with high-pressure piston actuators are equipped with digital valve positioners, airsets and volume boosters, along with other accessories.While control valves are an essential part of most flow processes today, they cannot accomplish their key tasks without help from the many accessories that aid in smooth operation.

Control valves are a ubiquitous essential in today’s industrial facilities. Whether they are managing flow or controlling process conditions such as temperature or pressure, they are key to maximizing production, maintaining product quality and ensuring safety.

However, they cannot accomplish these tasks on their own. Equally important to the processes are the accessories that work with a control valve—helping ensure accuracy, boosting output, making various control system components compatible with one another and providing added layers of safety.

In this article, we will review some of these devices, the roles they play in a control system and factors that should be considered when specifying these devices.


VALVE POSITIONER

Positioners are required in almost all control valve applications. Many positioner types and communication protocols are available, but a positioner’s primary function is always the same: to accurately position the throttling element within a control valve as directed by a signal from the process control system.

The positioner receives a sign from an external process controller, compares the valve’s actual position to the desired position, and sends a command change to the actuator to correct the valve position in a controlled feedback loop. The process controller measures the change in the process and sends further changes to the position signal as necessary.

Without a positioner, a control valve position is an open loop; the valve moves in response to the signal but nothing is providing feedback to ensure the valve is in the desired position.

Four factors make positioners vital components in today’s process control systems:

Higher-pressure actuators: Positioners make it possible to use today’s higher-pressure actuators in traditional pneumatic control systems, which can reduce costs and make the valve more responsive.

Most pneumatic control systems use an output signal range of 3 to 15 psig or 6 to 30 psig. Traditional spring-diaphragm actuators are widely available in these ranges, but the output force from a given actuator size is significantly limited. And, piston actuators almost always require higher air pressures to perform optimally.

As a result, most actuators are designed and sized to operate at air pressure ranges well above the 3 to 15 or 6 to 30 psig delivered by the control system. Therefore, a positioner or other amplifying device is required to make them compatible with the control system’s lower output pressure. The higher air pressure allows selection of smaller actuators reducing overall equipment cost.

spr11_b2b_schematicTypical placement of some of the most commonly used control valve accessories
Forces within the control valve: Friction from valve stem sealing systems (packing) can be significant, particularly in higher-temperature applications in which graphite-based materials must be used. Unbalanced forces or flow-induced forces within the valve also will affect the actuator’s ability to consistently position the throttling element or plug within the valve.

A positioner continually monitors the effects of these forces and sends the appropriate feedback to the controller, ensuring that necessary adjustments are made quickly to keep the control valve performing as expected.

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