02192018Mon
Last updateMon, 19 Feb 2018 3pm

i

Achieving Predictable Valve Performance for Safety Applications

Achieving Predictable Valve Performance for Safety Applications

A focus on having the proper specificati...

Putting Servo Valves Back to Work

Putting Servo Valves Back to Work

Industries as varied as paper production...

Corrosion and Fouling: Is There a Solution?

Corrosion and Fouling: Is There a Solution?

According to a 1998 study released by the ...

Valves with All the Trimmings

Valves with All the Trimmings

The term valve trim has been around for ...

SubscribeWNT18

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

Philly Fed: Manufacturing Activity Expanded Solidly

Monday, 19 February 2018  |  Chris Guy

The index for manufacturing activity in the Philadelphia Federal Reserve region increased 4 points in February to a reading of 25.8. The index has sta...

Readmore

Loading...
Advertisement
i

Web Only

Valve Positioners Offer Improved Control Valve Performance

Valve Positioners Offer Improved Control Valve Performance

Monday, 19 February 2018  |  David Matherly

From time to time, we are re-posting well-received or particularly valuable articles that have previously run on VALVEMagazine.com so that those who m...

Readmore

Loading...

Industry Headlines

ValvTechnologies ITC 2018 Recap

2 DAYS AGO

The biennial ValvTechnologies’ International Technical Conference and Users Group (ITC) was held on February 8-9 in Houston. Seeking to educate, inspire and engage attendees over a two-day period, the event brought together hundreds of attendees from across the globe to share valuable insight ...

Readmore

Matthew Davis Named Field Service Manager at Weir

3 DAYS AGO

Weir Valves & Controls USA (WVC USA) has appointed Matthew Davis to the position of field service manager. In his new role, Davis will be responsible for managing the WVC USA Field Service crew and organizing WVC Service jobs for power plants worldwide.

Davis joins WVC USA with over 20 years of ex...

Readmore

TransCanada Turns Attention to Natural Gas System

3 DAYS AGO

TransCanada Corp. will move forward with a $1.9 billion expansion of its NGTL System to connect incremental supply and expand basin export capacity by one billion cubic feet of natural gas per day at the interconnection with its Canadian Mainline. NGTL expects to begin construction in 2019.

The increme...

Readmore

U.S. Oil Output Surge Reminiscent of Run-Up to 2014 Dive

4 DAYS AGO

According to the International Energy Agency (IEA), fast rising production in non-OPEC countries, led by the U.S., is likely to grow by more than demand in 2018. For now, the upward momentum that drove the price of Brent crude oil to $70/bbl has stalled; partly due to investors taking profits, but a...

Readmore

Philly Fed: Manufacturing Activity Expanded Solidly

-1 DAYS AGO

The index for manufacturing activity in the Philadelphia Federal Reserve region increased 4 points in February to a reading of 25.8. The index has stayed within a relatively narrow range over the past nine months. Nearly 41% of the firms indicated increases in activity this month, while 15% reported...

Readmore

U.S. Industrial Production Fell 0.1% in January

2 DAYS AGO

Industrial production edged down 0.1% in January following four consecutive monthly increases. At 107.2% of its 2012 average, total industrial production was 3.7% higher in January than it was a year earlier.

Manufacturing output was unchanged in January for a second consecutive month; the index has i...

Readmore

Advertisement

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
BUYERS GUIDE 300x220

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