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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 ...

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Industry Headlines

Leading Economic Indicators Rose in January

Friday, 23 February 2018  |  Chris Guy

The Conference Board Leading Economic Index (LEI) for the U.S. increased 1.0% in January to 108.1, following a 0.6% increase in December, and a 0.4% i...

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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...

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Industry Headlines

MRC Global Announces Fourth Quarter 2017 Results

2 DAYS AGO

MRC Global’s sales were $903 million for the fourth quarter of 2017, which was 26% higher than the fourth quarter of 2016 and 6% lower than the third quarter of 2017 due to seasonality. As compared to 2016, all sectors increased driven primarily by midstream and upstream.

MRC Global's fourth qu...

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Curtiss-Wright Acquires Dresser-Rand Government Business

3 DAYS AGO

Curtiss-Wright has entered into an agreement to acquire the assets that comprise the Dresser-Rand Government Business (Dresser-Rand), a business unit of Siemens Government Technologies, for $212.5 million in cash.

Dresser-Rand designs and manufactures mission-critical, high-speed rotating equipment sol...

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U.S. Refiners Increasingly Turning to Export Markets

2 DAYS AGO

“U.S. gasoline consumption has leveled off as the stimulus provided by low and falling oil prices between 2014 and 2016 has faded, so refiners are increasingly turning to diesel and customers in emerging markets,” Reuters  reports .

“In geographical terms, the fastest growth in co...

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$900M Power Plant Planned for Indiana

2 DAYS AGO

Vectren Energy Delivery of Indiana is proposing to install an additional 50 megawatts (MW) of universal solar and build an 800 to 900-MW natural gas-fired generation facility in addition to other critical investments that will significantly change the way the company generates power for the region .

Th...

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Leading Economic Indicators Rose in January

16 HOURS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 1.0% in January to 108.1, following a 0.6% increase in December, and a 0.4% increase in November.

“The U.S. LEI accelerated further in January and continues to point to robust economic growth in the first half of 2018. Whi...

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IHS Markit Manufacturing Index Rose in February

1 DAY AGO

U.S. manufacturers reported a strong upturn in business conditions during February, which continued the positive trend seen at the start of 2018. At 55.9, up from 55.5 in January, the seasonally adjusted IHS Markit Flash U.S. Manufacturing Purchasing Managers’ Index (PMI) pointed to the fastes...

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Hydraulic Actuators Gaining in Use

vmsum11_actuatorsHydraulic actuators (in black) for flow control valves in a distribution terminal of a pipeline help control gasoline, diesel and other products.

Although the actuator market is dominated by pneumatic and electromechanic products, a growing number of niches require the performance levels of electrohydraulic actuators.

Pneumatics have been the mainstay of control valve manufacturers for the better part of the last century—just imagine how large the installed base has grown to be. Electromechanical designs, on the other hand, date back almost as far as pneumatics, but have only recently been seriously considered for throttling control applications.

But what about hydraulics? The basic technology also has been around a long time, but the technology was never considered mainstream because of the complexity, maintenance requirements and costs. Still, some people argue that today, hydraulically driven actuators are among the highest performing modulating designs with the widest range of thrusts and torques. And, over the last 20 years, advances in hydraulic actuator technologies have opened doors to applications previously categorized as either pneumatic or electromechanical opportunities.


THE DIFFERENCES

So, what changes have we seen over the last few decades? Here are some thoughts on that issue.

Operation has changed from “continuous” to “discrete”: Conventional hydraulic technology, whether a central hydraulic reservoir power unit or a valve-mounted individual reservoir, is based on a servo system that uses a continuously running unidirectional motor and pump. This technology has superior frequency response (small spool valves for directional changes) and offers extremely tight positioning control with high available stroking speeds. A potential drawback is that these systems use gravity-fed reservoirs that communicate with the atmosphere. This can lead to ingress of condensate and particulates, requiring significant filtration and maintenance.

Discrete operating technology utilizes a bidirectional motor and pump in a truly self-contained, sealed hydraulic system. This eliminates the need for an active reservoir. It also means the oil volume is a small fraction of what would be required for a continuous system. The motor and pump operate discretely, only running when required to make a position change. Power consumption is lower than any other control actuator technology.

While the frequency response available with a discrete system is high, it can’t compare to the continuous system. However, the hydraulic fluid filtering and maintenance are eliminated, and the positioning accuracy and control remains as good as a continuous system.

“Self contained, discrete” technology has gained more acceptance in the control actuator market: What this really describes is a form of electromechanical actuator with a hydraulic transmission instead of a gear train. Electromechanical actuators use reversible motors and operate discretely (just like the discrete type of hydraulic actuator). Most traditional electromechanical actuators are designed for isolating duty and as such lock in position and power down when set point position is satisfied. Unlike the self-contained hydraulics, traditional electromechanical actuators are usually limited to fail-in-last-position on loss of motor power. Some newer designs of electromechanical actuators can replicate the functionality of the hydraulic or pneumatic actuators; however, most traditional electromechanical actuators have limitations on duty cycle and life cycle when compared to hydraulics or pneumatics.


A COMPARISON

So what does the self-contained discrete hydraulic technology have in common with pneumatics? Pneumatics are revered by most control valve manufacturers as the foundation of control valve positioning. They are the puppet controlled by the puppet master, which is the smart positioner. Pneumatics have been proven performers, with about 100 years as the staple of control valve actuation. That’s why it’s hard to stack up this younger, self-contained discrete hydraulic technology against the legend that is pneumatics.

However, both types are capable of continuous movement. They both have a variety of failure modes—through the use of simple springs or stored energy devices such as accumulators and volume tanks. However, pneumatics is more akin to conventional hydraulic technology regarding the power source. Just as a conventional hydraulic uses a continuously running unidirectional motor and pump to maintain pressure, the pneumatic has stored energy (supply pressure) from a central air compressor. Both approaches consume much more power than either the electromechanical or the discrete electrohydraulic technologies.

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