05282016Sat
Last updateFri, 27 May 2016 2pm

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Industry and Regulatory Changes in Offshore Operations

Industry and Regulatory Changes in Offshore Operations

On May 13, 2016, the offshore oil and ga...

Strategies for Successful SIS Valve Diagnostic Implementation

Strategies for Successful SIS Valve Diagnostic Implementation

End users and contractors alike strive t...

Stop Check Valves

Stop Check Valves

Stop check valves are vital to several i...

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Industry Headlines

ValvTechnologies Names Garcia, Mermelstein to New Positions

3 DAYS AGO
ValvTechnologies Names Garcia, Mermelstein to New Positions

ValvTechnologies, Inc. has named David Garcia director of manufacturing and Steve Mermelstein as regional director, Americas and director, channel management.

Previously, West Point graduate Garcia served as director of operations for Merla Wellhead Solutions and held plant manager positions at Hallib...

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Emerson Automating UK Waste-to-Energy Plant

3 DAYS AGO

Emerson will provide control systems and project services for a new waste-to-energy power plant near Knaresborough Allerton, North Yorkshire, UK. Construction is expected to be completed in 2017, with the plant fully operational in 2018.

The plant , which will also incorporate biogas and recycling faci...

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U.S. Still Top Producer of Petroleum, Natural Gas Hydrocarbons

1 DAY AGO

The U.S. remained the world's top producer of petroleum and natural gas hydrocarbons in 2015, according to U.S. Energy Information Administration estimates . U.S. petroleum and natural gas production first surpassed Russia in 2012, and the U.S. has been the world's top producer of natural gas since 20...

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Why $50/Barrel Oil Means Stability to U.S. Producers

2 DAYS AGO

The rise to $50-per-barrel oil means a return to stability, particularly for domestic shale producers, according to Dan K. Eberhart, CEO, Canary, LLC. At this level , companies that saw the value of their product drop more than 75% in less than two years might have the confidence to resume drilling ac...

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Survey: Manufacturing Execs Investing in Advanced Tech

2 DAYS AGO

 A convergence of disruptive factors such as new technologies, increasing competition, and pricing pressures, is forcing manufacturers to increase investment in new products and services as they seek to innovate manufacturing capabilities, according to the 2016 KPMG Global Manufacturing Outlook ...

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Durable Goods Orders Surge 3.4%, But Demand Soft

2 DAYS AGO

New orders for manufactured durable goods in April increased $7.7 billion or 3.4% to $235.9 billion, the U.S. Census Bureau announced today. This increase, up three of the last four months, followed a 1.9% March increase. Excluding transportation, new orders increased 0.4%. Excluding defense, new or...

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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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