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The Challenges of Slurry Valve Packing

The Challenges of Slurry Valve Packing

Because of the difficulties of dealing w...

The Many Layers of Valve Qualification

The Many Layers of Valve Qualification

While there has been much rhetoric from ...

Valves Help Achieve Net-Zero Water Use

Valves Help Achieve Net-Zero Water Use

With drought and climate change affecting ...

Valve Selection in Pulp and Paper Operations

Valve Selection in Pulp and Paper Operations

Over the centuries, the pulp and paper i...

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Industry Headlines

Industry Headlines

Wolseley Announces Name Change, CEO Succession

19 HOURS AGO

Wolseley plc is officially changing its name to Ferguson plc, subject to shareholder approval. Ferguson is the most significant brand in the Wolseley Group of companies and accounts for 84% of the Wolseley Group’s profitability.

The company also announced that CEO Frank Roach will retire on July ...

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Spirax Sarco Employees Build Prosthetic Hands for Children

1 DAY AGO

Spirax Sarco hosted their annual charity event at the Westin Hotel in Savannah, GA on Saturday, March 11, 2017 where participants built prosthetic hands for children in third-world countries who are missing limbs.

There are 300,000 landmine rated amputees globally and 20% of those are children. Emplo...

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Permian Drillers Acquiring Slivers of Land for Horizontal Drills

2 HOURS AGO

With horizontal drilling in the Permian Basin allowing producers to “drill longer wells than ever before, companies such as Pioneer Natural Resources Co., Parsley Energy Inc. and Double Eagle Energy Permian LLC are increasingly haggling with other producers for slivers of land that allow them ...

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In Blow to Nuclear Industry, Westinghouse Files for Bankruptcy

1 DAY AGO

“The Westinghouse unit of Japanese technology giant Toshiba plunged into Chapter 11 bankruptcy Wednesday as the Cranberry Township, Pa.-based division faces cost overruns and delays with its U.S. nuclear plant projects,” reports USA Today .

“The company said the bankruptcy does not aff...

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Richmond Fed: Manufacturing Grows at Fastest Rate in Nearly Seven Years

2 HOURS AGO

Manufacturers in the fifth district were generally upbeat in March, according to the latest survey by the Federal Reserve Bank of Richmond. The index for shipments and new orders both rose and employment gains were more common. This improvement led to a composite index for manufacturing that rose from...

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Consumer Confidence Reaches 16-Year High in March

2 HOURS AGO

The Conference Board Consumer Confidence Index, which had increased in February, improved sharply in March. The Index now stands at 125.6, up from 116.1 in February. The Present Situation Index rose from 134.4 to 143.1 and the Expectations Index increased from 103.9 last month to 113.8.

“Consum...

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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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