02232017Thu
Last updateTue, 21 Feb 2017 8pm

i

Human Factors Can Cause a Disaster—or Prevent One

Human Factors Can Cause a Disaster—or Prevent One

Process industry plants are complex and ...

Improving Valve Sealing Performance and Reliability

Improving Valve Sealing Performance and Reliability

From time to time, we are re-posting wel...

A Primer on Fugitive Emissions

A Primer on Fugitive Emissions

Fourscore and seven years ago, no one ha...

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Industry Headlines

Powell Valve Approves Flotech as Authorized Repair Facility

1 DAY AGO

The Wm. Powell Company recently approved Flotech as an authorized modification and repair facility for Powell Valves.

“Flotech has been manufacturing and repairing valves for over 40 years. Adding another high quality valve manufacturer to the list of valve companies Flotech represents speaks vol...

Readmore

CIRCOR Reports Fourth Quarter 2016 Financial Results

1 DAY AGO

CIRCOR International, Inc. reports revenue of $158 million, GAAP EPS of ($0.12) and adjusted EPS of $0.48 in the fourth quarter of 2016 . CIRCOR had an operating cash flow of $20 million and free cash flow of $17 million for the quarter. Cost control and restructuring actions continued to drive bottom...

Readmore

Southern California Updating Natural Gas Pipeline Infrastructure

1 DAY AGO

Southern California Gas Company (SoCalGas) will upgrade or replace 50 to 60 pipeline valves in 2017 to further enhance the safety of its system. The effort is part of SoCalGas' Pipeline Safety Enhancement Plan (PSEP), a multi-billion-dollar program that tests and updates the natural gas pipeline infra...

Readmore

How New U.S. Policies Will Affect the Chemical Industry

7 DAYS AGO

“In 2017, barring a recession in the U.S. and Europe or a slowdown in China, Moody’s Investor Service expects EBITDA in the chemicals industry to slip by 1 or 2% year-over-year.”

A new report from PwC predicts that the Trump administration “is likely to embrace policies that are...

Readmore

Empire State Manufacturing Expands at Fastest Rate Since 2014

1 DAY AGO

Business activity expanded at a solid clip in New York State, according to firms responding to the February 2017 Empire State Manufacturing Survey. The headline general business conditions index rose twelve points to 18.7, its highest level in more than two years. The new orders index climbed to 13.5,...

Readmore

Philly Fed Manufacturing Conditions Continued to Improve in February

6 DAYS AGO

The index for current manufacturing activity in eastern Pennsylvania, southern New Jersey and Delaware increased from a reading of 23.6 in January to 43.3 this month and has remained positive for seven consecutive months. The share of firms reporting growth continues to increase: More than 48% of the ...

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