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Last updateFri, 29 Jul 2016 2pm

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Basics of Elastomeric Seal Design

Basics of Elastomeric Seal Design

Engineers need critical design informati...

Wastewater Treatment

Wastewater Treatment

Society’s desire for a clean envir...

Controlling Our Water Systems, Part II

Controlling Our Water Systems, Part II

To better understand the actuators and c...

Controlling Our Water Systems

Controlling Our Water Systems

Actuators and controls are a critical pr...

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Industry Headlines

Pentair Reports Second Quarter 2016 Results

1 DAY AGO

Pentair plc announced second quarter 2016 sales of $1.7B. Sales were up 4% compared to sales for the same period last year. Excluding the unfavorable impact of currency translation and the positive contribution from acquisitions, core sales declined 3% in the second quarter . Second quarter 2016 earni...

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ValvTechnologies Names Bryant Holt Industry Director, Fossil Power

2 DAYS AGO
ValvTechnologies Names Bryant Holt Industry Director, Fossil Power

ValvTechnologies, Inc. has appointed Bryant Holt as industry director for the company’s fossil power division. Holt will succeed George Stover, who has served in this role since 2014.

Based in Houston, Holt will have global management responsibility for ValvTechnologies’ fossil power group ...

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ExxonMobil Expanding Beaumont, TX Facility

1 DAY AGO

ExxonMobil has plans to increase production of ultra-low sulfur fuels at its Beaumont, TX refinery by approximately 40,000 barrels per day, representing an investment of approximately $450 million.

Construction is scheduled during the second half of 2016 to install a selective cat naphtha hydrofining u...

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LNG’s Surge from Decade-Low Seen Fizzling as Supply Ramps Up

2 DAYS AGO

“LNG’s surge is running out of gas. Liquefied natural gas in Asia, which was in such over-supply that prices in Japan fell to a decade-low in April, has risen by almost half in the past three months as production outages stifled supply, demand rose in places like China and India and a co...

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Second Quarter GDP Grew Only 1.2% in Second Quarter

21 HOURS AGO

Real GDP in the U.S. increased at an annual rate of 1.2% in the second quarter of 2016, according to the advance estimate released by the U.S. Department of Commerce. In the first quarter, real GDP increased 0.8%.

The increase in real GDP in the second quarter reflected positive contributions from cons...

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U.S. Durable Goods Orders Down 4% in June

2 DAYS AGO

New orders for manufactured durable goods in June decreased $9.3 billion or 4.0% to $219.8 billion, the U.S. Department of Commerce announced. This decrease , down two consecutive months, followed a 2.8% May decrease. Excluding transportation, new orders decreased 0.5%. Excluding defense, new orders d...

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The Human Factor in Valve Operation

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Worker safety, efficiency and the cost of operations, and most recently, new methods of control, are key focal points in operating valves. One factor that affects all areas is the role and level of human involvement in the processes.

THE CHOICES

Opening or closing valves can be completed either by manual input or automated devices driven by various energy sources. Manual operators are simple, inexpensive and require little peripheral planning beyond the installation and orientation of operators in the process line. Automated devices, on the other hand, require input energy systems, control systems, additional installation space and infrastructure for support, operation and maintenance.

Two concerns considered during selection of manual operators are the effort required to operate the valve and the number of turns some valves require. A lot of effort and a high number of turns can result in personnel fatigue, safety concerns, excessive time for operation and the need for multiple personnel. Also under consideration in selecting manual operators are the valve’s expected frequency of operation and the physical location of the operation, such as whether it might be high in a superstructure or situated in an inhospitable environment. Both also present challenges to humans.

Designers have to weigh all of these factors in their decision matrix to receive the most productive yet acceptable selection of how a valve should be operated. Two aspects that primarily define operator selection are human factors and economic factors. Human factors can be defined as the human capability to cycle the valve in a safe, timely and economically sound manner. These factors require considerations such as the work needed to be done (turns and rim pull) to operate the valve, the environment in which the valve is located, the time required to complete the task, and the health and safety of the personnel involved. Economic factors include the cost of the actuator as well as the cost of infrastructure, which could include wiring, controls system, power required and ongoing maintenance to support automated solutions.

THE SPECS INVOLVED

Specifications for the highest values personnel should exert on levers or handwheels to operate a valve are defined in the industry, with current API specifications limiting pull to 360 newtons (80 pounds-force). Mechanical advantage can be used to decrease the pull required to open or close the valve by increasing the length of the lever or diameter of the handwheel mounted on the valve. How­ever, the maximum lever length or handwheel diameter is also limited by industry specifications.

As valve torque increases, maximum limits imposed by industry standards result in levers transitioning to gear units to increase mechanical advantage. However, this increase in mechanical advantage comes with the disadvantage of increasing the number of turns to move the valve across the full stroke distance.

The higher number of turns results in longer time required to cycle the valve at a constant number of revolutions per minute. With significant gear reduction, the number of turns required for full cycle can number in the hundreds. This increased number of turns leads to a greater opportunity for accidents or injury to personnel due to repetitive motion and fatigue. Companies will limit the rim pull and number of turns to reduce the risk. Once established limits are exceeded for turns, the valve is generally required to be automated.

Communicating what human factor limits might be imposed on valves can provide suppliers the opportunity to recommend the best value of operator for manual valves. Until recently, the valve industry was limited to levers, bevel gears and traditional worm gears for manual cycling. Once these devices exceeded worker safety limits, a valve purchaser’s only choice was to select an automated solution. However, new devices available in the marketplace extend the range of manual operators. These devices can reduce initial capital costs, reduce site design complexity and minimize operating expenditures. The devices include high-efficiency gear operators and portable drivers coupled with well-designed arrestors.


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