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Check Valves in LNG Cryogenic Service

Check Valves in LNG Cryogenic Service

Because natural gas is currently conside...

Will Smart Machines Obsolete Human Resources?

Will Smart Machines Obsolete Human Resources?

Is artificial intelligence (AI) going to...

Is Valve Live Loading an Option?

Is Valve Live Loading an Option?

Valves leak. There’s no getting ar...

Managing Control Valve Reliability in the Arctic

Managing Control Valve Reliability in the Arctic

“A sow and polar bear cub are walk...

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Industry Headlines

U.S. Adds 228,000 Jobs in November

Friday, 08 December 2017  |  Chris Guy

Total nonfarm payroll employment increased by 228,000 in November, and the unemployment rate was unchanged at 4.1%, the U.S. Department of Labor report...

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Will Smart Machines Obsolete Human Resources?

Will Smart Machines Obsolete Human Resources?

Wednesday, 06 December 2017  |  Kate Kunkel

Is artificial intelligence (AI) going to take over manufacturing jobs and the jobs of human resources professionals? That is a question that concerns ...

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Industry Headlines

Classic Controls Certified by ITT Engineered Valves, REXA

3 DAYS AGO

Classic Controls is now certified by ITT Engineered Valves to repair Skotch brand FM approved and general purpose burner shut-off valves for oil and gas fired systems.

REXA, Inc. has also appointed Classic Controls as its exclusive authorized sales representative in the state of Florida. Classic Contr...

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Emerson Completes Paradigm Acquisition

6 DAYS AGO

Emerson has completed the purchase of Paradigm, a provider of software solutions to the oil and gas industry. Paradigm will be combined with Emerson’s Roxar software business to create a more comprehensive Exploration & Production (E&P) software portfolio offering.

Paradigm is headquarter...

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China to Become Second-Largest LNG Importer

3 DAYS AGO

The world’s no. 1 energy user, China, “is on the verge of passing South Korea to become the No. 2 buyer of LNG behind Japan, as environmental measures and winter heating needs boost demand,” Bloomberg reports .

“Tankers with total capacity of 33.6 million metric tons have visited...

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New Permian-Gulf Pipeline Proposed

5 DAYS AGO

Magellan Midstream Partners intends to develop an approximately 375-mile, 24-inch diameter pipeline from Crane to a location near Three Rivers, TX, providing shippers the option to ultimately deliver crude oil and condensate from the Three Rivers area to the Houston area via a new 200-mile pipeline or...

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U.S. Adds 228,000 Jobs in November

2 DAYS AGO

Total nonfarm payroll employment increased by 228,000 in November, and the unemployment rate was unchanged at 4.1%, the U.S. Department of Labor reported today. Employment continued to trend up in professional and business services, manufacturing and health care.

In November, manufacturing added 31,000...

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Manufacturing PMI at 58.2% in November

4 DAYS AGO

Manufacturing expanded in November as the PMI registered 58.2% , a decrease of 0.5% from the October reading of 58.7%. A reading above 50% indicates that the manufacturing economy is generally expanding.

"This indicates growth in manufacturing for the 15th consecutive month led by expansion in new orde...

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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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