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Last updateFri, 24 Mar 2017 2pm

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Valve Selection in Pulp and Paper Operations

Valve Selection in Pulp and Paper Operations

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

How to Improve Control Valve Performance with Positioners

How to Improve Control Valve Performance with Positioners

As the final control element in most pro...

VMA Technical Event: Engineering Valves in the Extreme

VMA Technical Event: Engineering Valves in the Extreme

While much the 2017 VMA Technical Semina...

FEL: The Preferred Phase for Valve Technical Definition

FEL: The Preferred Phase for Valve Technical Definition

A typical oil and gas capital project cy...

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Industry Headlines

Kansas City Fed Shows Manufacturing At 6-Year High

Friday, 24 March 2017  |  Chris Guy

Tenth District manufacturing activity strengthened further in March, and many indexes of expectations for future activity were at or near record highs...

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Industry Headlines

GE Oil & Gas Expands with New Sub Saharan Africa Facility

21 HOURS AGO

GE Oil & Gas opened a new facility in Takoradi Port, Ghana, expanding its global footprint and supporting local investment. The facility, which will be the primary service center for deep-water offshore projects in Ghana, has a 1,600 square meter indoor test area with capability for testing thre...

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Metso Launches Digital Program to Accelerate Growth

2 DAYS AGO

Metso has set up a Digital Program to accelerate the company’s digital capabilities, which are required to succeed in the future of minerals processing and flow control. Metso's ambition is to become one of the digital leaders in the industries it serves. This means for example turning custome...

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Shell Looking to Lower Cost of Offshore Projects

1 DAY AGO

“With oil prices hovering around $50 a barrel or less, and a rising amount of renewable energy chipping away at market share, Shell is going lean on its deepwater projects to make sure it can eke out a profit from all of its operations,” writes ChemInfo .

For example, Shell is attempting to ...

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Report Says PA Can Support Four More Ethane Crackers

1 DAY AGO

A new report from IHS Markit, commissioned by the state of Pennsylvania, forecasts $2.7 to 3.7 billion in investments in natural gas liquid (NGL) assets as well as the opportunity to attract additional cracker plants, and petrochemical and plastics manufacturing. IHS Markit believes the Marcellus an...

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Kansas City Fed Shows Manufacturing At 6-Year High

2 HOURS AGO

Tenth District manufacturing activity strengthened further in March, and many indexes of expectations for future activity were at or near record highs. Most price indexes increased moderately. The month-over-month composite index was 20 in March , its highest reading since March 2011, up from 14 in Fe...

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Consumer Sentiment Reaches Highest Level Since 2000

3 DAYS AGO

The overall level of consumer sentiment remained quite favorable in early March due to renewed strength in current economic conditions as well as the extraordinary influence of partisanship on economic prospects. The current economic conditions component reached its highest level since 2000, largely...

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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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