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VMA Sees Limited Valve Shipment Growth for 2017

VMA Sees Limited Valve Shipment Growth for 2017

After a year of little growth in 2016, U...

How to Improve Reliability and Safety of Solenoid Valves

How to Improve Reliability and Safety of Solenoid Valves

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Human Factors Can Cause a Disaster—or Prevent One

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Improving Valve Sealing Performance and Reliability

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Industry Headlines

ISM: Manufacturing Jumps to Two-Year High

Wednesday, 01 March 2017  |  Chris Guy

According to the Institute for Supply Management (ISM), manufacturing expanded in February as the Purchasing Managers Index (PMI) registered 57.7%, an...

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Industry Headlines

Flowserve Appoints Jay Roueche Interim CFO

-1 DAYS AGO

John E. (Jay) Roueche III, Flowserve’s vice president, investor relations and treasurer, will assume the role of interim chief financial officer (CFO), effective immediately. Mr. Roueche’s appointment follows Karyn Ovelmen’s departure from the company as executive vice president and ...

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GE Oil & Gas Selected for Louisiana LNG Export Facilities

1 DAY AGO

Venture Global LNG, Inc. has selected GE Oil & Gas as a strategic partner to provide a plant-wide technology solution for its liquefied natural gas (LNG) export facilities under development in Louisiana. Under the agreement, GE Oil & Gas will leverage advanced technologies to deliver a compr...

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Chemical Processing Industry Expects Growth in 2017

22 HOURS AGO

According to a recent Chem Show survey sent to more than 10,000 chemical and other processing manufacturers, equipment suppliers, and design/engineering firms, 2017 is expected to foster significantly elevated business prospects and sales throughout the chemical processing industry. Based on survey r...

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LNG Exports Expected to Drive Growth in U.S. Natural Gas Trade

1 DAY AGO

The U.S. is expected to become a net exporter of natural gas on an average annual basis by 2018, according to the recently released Annual Energy Outlook 2017 (AEO2017). The transition to net exporter is driven by declining pipeline imports, growing pipeline exports, and increasing exports of liquefie...

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ISM: Manufacturing Jumps to Two-Year High

-1 DAYS AGO

According to the Institute for Supply Management (ISM), manufacturing expanded in February as the Purchasing Managers Index (PMI) registered 57.7%, an increase of 1.7% from the January reading of 56%, indicating growth in manufacturing for the sixth consecutive month, and is the highest reading since ...

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Growth in Texas Manufacturing Activity Continues

22 HOURS AGO

Texas factory activity increased for the eighth consecutive month in February, according to business executives responding to the Texas Manufacturing Outlook Survey . The production index, a key measure of state manufacturing conditions, rose five points to 16.7, suggesting output growth picked up pac...

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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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