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Last updateWed, 22 Nov 2017 2pm

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Unique Operating Dynamics of Trunnion-Mounted Ball Valves

Unique Operating Dynamics of Trunnion-Mounted Ball Valves

For a very long time, the idea has exist...

Adopting the IIoT: Are Results Matching the Hype?

Adopting the IIoT: Are Results Matching the Hype?

Many valve, actuator and control manufac...

Where Valves Are Used: Everywhere!

Where Valves Are Used: Everywhere!

Valves can be found just about anywhere ...

Oxygen Cleaning: A Validated Process is Critical for Safety

Oxygen Cleaning: A Validated Process is Critical for Safety

From time to time, we re-publish well-re...

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Industry Headlines

Conference Board Economic Index Rose in October

Tuesday, 21 November 2017  |  Chris Guy

The Conference Board Leading Economic Index (LEI) for the U.S. increased 1.2% in October to 130.4 (2010 = 100), following a 0.1% increase in September...

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Industry Headlines

VanAire Celebrates Manufacturing with ‘Industry After Hours’

1 DAY AGO
VanAire Celebrates Manufacturing with ‘Industry After Hours’

On Nov. 8, Delta County, MI K-12 students and parents attended Industry After Hours at VanAire to learn more about the high tech, high skilled manufacturing jobs that are available. Over 276 participants were treated to a fun, entertaining and informative event that exceeded expectations and inspired ...

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Emerson Opens Solutions Center in Singapore

4 DAYS AGO

As part of its drive to make Singapore a hub for the delivery of Industrial Internet of Things (IoT) technologies and services for customers across Asia Pacific, Emerson opened a customer-focused Solutions Center at the regional headquarters of its Automation Solutions business in Singapore. To mark...

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Nebraska Approves Keystone XL Pipeline Route

1 DAY AGO

By a vote of 3-2, the Nebraska Public Service Commission approved an order giving TransCanada the go ahead to build the Keystone XL Pipeline utilizing the proposed Mainline Alternative Route. This is one of three proposed routes included in the application filed by TransCanada Keystone Pipeline. L.P...

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Energy Outlook Shows a World in Transformation

7 DAYS AGO

The resurgence in oil and gas production from the United States, deep declines in the cost of renewables and growing electrification are changing the face of the global energy system and upending traditional ways of meeting energy demand, according to the World Energy Outlook 2017 . A cleaner and more...

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Conference Board Economic Index Rose in October

22 HOURS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 1.2% in October to 130.4 (2010 = 100), following a 0.1% increase in September, and a 0.4% increase in August.

“The U.S. LEI increased sharply in October, as the impact of the hurricanes dissipated,” said Ataman Ozyildi...

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U.S. Industrial Output Up 0.9% in October

4 DAYS AGO

Industrial production rose 0.9% in October, and manufacturing increased 1.3%. The index for utilities rose 2.0%, but mining output fell 1.3%, as Hurricane Nate caused a sharp but short-lived decline in oil and gas drilling and extraction. Even so, industrial activity was boosted in October by a return...

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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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