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Is Your Company Ready for The New Reality?

Is Your Company Ready for The New Reality?

Since August, 2015, when VMA’s 201...

Offshore Oil Extraction and Transportation

Offshore Oil Extraction and Transportation

Offshore oil facilities come to the fore...

Back to Basics: Pressure Relief Devices, Part 2

Back to Basics: Pressure Relief Devices, Part 2

In Part 1 of Pressure Relief Devices, wh...

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Industry Headlines

Watson Valve Announces Watson Valve Services, Australia

3 DAYS AGO

Watson Valve Services Inc. announces Watson Valve Services, Australia. Watson Valve will now have the ability to support the supply of its severe service valve products to non-U.S. domestic sites from its Australian based service agent, Process Plants International (PPi) under the name, Watson Valve...

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Velan Makes Changes to Management Team

3 DAYS AGO

Velan recently announced that Executive Vice-President (EVP) Ivan Velan has decided to reduce his work scope, but will remain with the company as Special Advisor to the President, Yves Leduc. Ivan will lead key projects and continue to support the management team.

Martin Allen joined Velan’s ...

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U.S. Oil Inventories Now at Record High

3 DAYS AGO

Several factors have played a part in pushing U.S. crude oil prices below $30 per barrel, including high inventory levels of crude oil, uncertainty about global economic growth, volatility in equity and non-energy commodity markets, and the potential for additional crude oil supply to enter the mark...

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FERC Approves $3.2B Sabal Trail Pipeline Project

3 DAYS AGO

Sabal Trail Transmission, LLC, a joint venture of Spectra Energy Partners, LP, NextEra Energy, Inc. and Duke Energy, received a certificate of public convenience and necessity from the Federal Energy Regulatory Commission (FERC) to construct and operate the Sabal Trail interstate natural gas pipelin...

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Labor Productivity Down More Than Expected in Fourth Quarter

-1 DAYS AGO

U.S. labor productivity decreased at a 3.0-percent annual rate during the fourth quarter of 2015, the U.S. Bureau of Labor Statistics reported, as output increased 0.1% and hours worked increased 3.3%.

Manufacturing sector labor productivity decreased 0.4% in the fourth quarter of 2015, as output i...

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U.S. Adds 151,000 Jobs, Unemployment Rate Down to 4.9%

2 DAYS AGO

Total nonfarm payroll employment rose by 151,000 in January, and the unemployment rate dropped 0.1% to 4.9%, the lowest since Feb. 2008. Job gains occurred in several industries, led by retail trade, food services and drinking places, health care and manufacturing. Employment declined in private edu...

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Don't Overlook Linear Actuators on Gate Valves

At a recent sales meeting in California, I was surprised to discover the lack of awareness regarding linear valve actuators. In fact, one veteran of the valve industry remarked, "I didn't know you could operate a gate valve using compressed air and a linear actuator." Most folks in the valve industry are familiar with operating globe valves in this manner, but typically, multi-turn electric actuators have been used when automating gate valves. However, if the control application calls for faster stroke speed, mechanical failure position, precise positioning, or higher thrust, linear pneumatic or hydraulic actuators may be preferred.

The basic principle behind linear actuators is simple: a piston in a cylinder. This type of actuator is very simple and reliable; after all, it only has one moving part. Such a mechanical device has been around for more than 200 years. Pistons in cylinders first saw use in steam engines. Scotland's James Watt crafted the first good ones during the 1770s.

Attaching a linear actuator to a gate valve is fairly straightforward. First, the handwheel and drive nut comes off, exposing the threaded stem. Then, a coupling is used to connect the stem to the piston rod. This allows the linear actuator to move the stem up and down directly. The before-and-after pictures on the left and right, respectively, show the change from a manual valve to an automatic valve with the linear actuator.

Of course, the actuator is now producing "thrust" not "torque," and this is a critical specification for linear actuator design. As it turns out, the size of the cylinder is a function of the required valve thrust and the available supply (pressure x area = force). The cylinder is larger for a higher required thrust and a lower supply pressure. And since the actuator price increases as the cylinder size increases, engineers must verify that the supply pressure given is the highest available at the project site.

Moreover, if the calculated thrust is based on the maximum differential pressure rating across the valve (as defined by ANSI) and not actual operating design conditions, the specified thrust might be much higher than actual, which would require a larger cylinder and thus a higher price. Therefore, it is best to specify thrust based on actual design conditions to get the best price.

Linear actuators can be an effective automation solution for gate valves. As automation increases, so should our choices. That the linear actuator has proven reliable in many applications outside of the valve industry is testament to the enduring design of the pneumatic and hydraulic cylinder.

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