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Cameron Signs Two Long-Term Transocean Service Agreements

14 HOURS AGO

Cameron, a Schlumberger company, has signed two 10-year pressure control equipment management service contracts on behalf of Transocean valued at greater than $350 million.

The first contract calls for Schlumberger to manage Transocean’s Cameron risers in the Gulf of Mexico. This comprehensive ag...

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Total Valve Systems, Continental Disc/Groth Sign Distributorship Deal

14 HOURS AGO

Total Valve Systems (TVS) announces a new distributorship with Continental Disc (CDC) and Groth Corporation. The two companies will provide customer service and relief & vacuum products to customers worldwide. Total Valve Systems will be responsible for sale and distribution to Oklahoma, Kansas, T...

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Plains All American Expanding Cactus Pipeline Capacity

13 HOURS AGO

Plains All American (PAA) Pipeline, L.P. is expanding the capacity on its Cactus pipeline from McCamey to Gardendale, TX to approximately 390,000 barrels per day. The expansion will allow PAA to move increasing production volumes from the Permian Basin to Corpus Christi and other delivery points along...

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New Investments Spur Permian Oil Production Increase

1 DAY AGO

The Department of Energy (DOE) said on Tuesday that oil production in the Permian Basin could increase by 53,000 bpd by next month. According to the Energy Information Administration (EIA), that is the largest monthly increase in the region in a year.

“The EIA’s first shale oil forecast o...

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Industrial Production Sees Largest Rise in More Than Two Years

1 DAY AGO

Industrial production rose 0.8% in December, the largest increase since November 2014, after falling 0.7% the previous month. For the fourth quarter as a whole, the index slipped 0.6% at an annual rate.

Manufacturing output moved up 0.2% in December, as an increase in durable manufacturing outweighed d...

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IMF Raises U.S. Economic Growth Forecast

2 DAYS AGO

After a lackluster outturn in 2016, economic activity is projected to pick up pace in 2017 and 2018, especially in emerging market and developing economies. However, the International Monetary Fund (IMF) noted in its new World Economic Outlook, there is a wide dispersion of possible outcomes around ...

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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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