07012016Fri
Last updateThu, 30 Jun 2016 6pm

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Fugitive Emissions—Issues and Opportunities

Fugitive Emissions—Issues and Opportunities

Fugitive emissions, ppm, consent decrees...

Problem-Driven Innovation

Problem-Driven Innovation

Developing Alternative Technology to Imp...

Valve Repair Takes Center Stage in Houston

Valve Repair Takes Center Stage in Houston

Attendees gathered June 2-3 in Houston t...

What Internal Best Practices Can Do for Valve Selection

What Internal Best Practices Can Do for Valve Selection

As time goes by, technology moves forwar...

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Industry Headlines

Watson Valve Upgrades Oxygen Clean Room

Thursday, 30 June 2016  |  Chris Guy

In an effort to ensure proper cleaning procedures are performed on valves intended for oxygen service, Watson Valve Services has upgraded its existing...

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Industry Headlines

Watson Valve Upgrades Oxygen Clean Room

8 HOURS AGO

In an effort to ensure proper cleaning procedures are performed on valves intended for oxygen service, Watson Valve Services has upgraded its existing clean room within its manufacturing plant in Houston. Watson Valve Services’ clean room is operated by trained technicians, and is constructed wi...

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Emerson Selected to Upgrade SE Virginia Wastewater Utility

1 DAY AGO

Emerson Process Management is replacing an outdated supervisory control and data acquisition (SCADA) system as well as remote terminal units (RTUs) used throughout Hampton Roads Sanitation District’s (HRSD) wastewater collection system. Currently, HRSD serves about 1.7 million people over an are...

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U.S. Natural Gas Making Up for Coal Plant Closures

11 HOURS AGO

"Five years ago, opponents of newly proposed clean-air rules sounded dire warnings of blackouts and surging electricity prices if coal-burning plants were shuttered,"  Bloomberg  reports .

"Instead of rising, the price of electricity in the nation’s largest grid is now 40% lower than it ...

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U.S. Crude Storage Capacity Utilization Rises Even as Capacity Grows

1 DAY AGO

Weekly U.S. commercial crude oil inventories have increased by more than 71 million barrels (15%) since the end of September, pushing crude oil storage capacity utilization to a near record high of 73% for the week ending June 10.

The U.S. Energy Information Administration (EIA) measures crude oil stor...

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Trump Comes Out Against Trade, Draws Pushback

1 DAY AGO

GOP presidential candidate Donald Trump, speaking Tuesday near Pittsburgh, expressed fierce opposition to free-trade agreements and criticized Hillary Clinton for supporting them. Trump blamed Clinton and her husband for the loss of millions of manufacturing jobs and threatened to pull the U.S. out ...

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Consumer Confidence Climbs to 8-Month High

2 DAYS AGO

The Conference Board Consumer Confidence Index, which had decreased in May, improved in June. The Index now stands at 98.0 , up from 92.4 in May. Those stating business conditions are “good” increased slightly from 26.1% to 26.9%, while those saying business conditions are “bad&rdquo...

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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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