05232017Tue
Last updateTue, 23 May 2017 4pm

i

The Future of Coal: Efficiency Over Politics?

The Future of Coal: Efficiency Over Politics?

Many changes in the power industry have ...

Valve World Americas Event Set for June 20-21

Valve World Americas Event Set for June 20-21

End users, distributors, EPC/AEC personn...

Water Hammer

Water Hammer

Water hammer is a shock wave transmitted...

Turning the Tables on Valve Corrosion

Turning the Tables on Valve Corrosion

Multiple valve manufacturers and users w...

Subscribe vmspr17

FREE SUBSCRIPTION*

•  Print magazine
•  Digital magazine
•  VALVE eNews
Read the latest issue

*to qualified valve professionals in the U.S./Canada

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Roger Fix Named Chairman of Flowserve

Tuesday, 23 May 2017  |  Chris Guy

In its most recent annual meeting, Flowserve announced that Bill Rusnack and Lynn Elsenhans have retired as members of the board of directors. Flowser...

Readmore

Loading...
Advertisement
i

Industry Headlines

Roger Fix Named Chairman of Flowserve

4 HOURS AGO

In its most recent annual meeting, Flowserve announced that Bill Rusnack and Lynn Elsenhans have retired as members of the board of directors. Flowserve also announced that board member Roger Fix has been elected to replace Rusnack as chairman.

"Bill and Lynn provided years of distinguished service to ...

Readmore

MRC Global Opening Gulf Coast Regional Distribution Center

1 DAY AGO

MRC Global (US) Inc. is opening a new regional distribution center (RDC) and operational hub for the Gulf Coast area in La Porte, TX. The new facility will house over 400,000 square feet of warehouse space, have over 75,000 square feet of office space and an extensive pipe yard. MRC Global expects t...

Readmore

ExxonMobil, SABIC Agree on Proposed Petrochemical Project

5 HOURS AGO

Affiliates of Exxon Mobil and SABIC (Saudi Basic Industries Corporation) signed an agreement to conduct a detailed study of the proposed Gulf Coast Growth Ventures project in Texas and begin planning for front-end engineering and design work. The agreement was signed during the Saudi-US CEO Forum in R...

Readmore

Report Shows Potential for Appalachian Petrochemical Industry

5 HOURS AGO

An economic report released by the American Chemistry Council (ACC) shows that the Appalachian region could become a second center of U.S. petrochemical and plastic resin manufacturing, similar to the Gulf Coast.

ACC's report presents a hypothetical scenario that includes the development of a storage ...

Readmore

ISM: Manufacturing Growth Should Continue Through 2017

6 HOURS AGO

According to the Institute for Supply Management (ISM), 64% of respondents from the panel of manufacturing supply management executives predict their revenues will be 8.5% greater in 2017 compared to 2016, 12% expect a 9.6% decline, and 24% foresee no change in revenue. This yields an overall averag...

Readmore

Labor Secretary Pushes Public-Private Apprenticeships

1 DAY AGO

Speaking at the G-20 labor and employment ministers' meeting on May 19, U.S. Secretary of Labor Alexander Acosta emphasized his support for fostering the growth of apprenticeships, a major priority for President Trump and the Department of Labor. The secretary's remarks reinforce the U.S.’s comm...

Readmore

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.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association