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Last updateTue, 24 May 2016 3pm

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Industry and Regulatory Changes in Offshore Operations

Industry and Regulatory Changes in Offshore Operations

On May 13, 2016, the offshore oil and ga...

Strategies for Successful SIS Valve Diagnostic Implementation

Strategies for Successful SIS Valve Diagnostic Implementation

End users and contractors alike strive t...

Stop Check Valves

Stop Check Valves

Stop check valves are vital to several i...

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Industry Headlines

MRC Global Expands Service to Chemours in the U.S. Gulf Coast

15 HOURS AGO

MRC Global Inc. announced that its subsidiary, MRC Global (US) Inc., has been awarded an agreement to be the primary provider of pipe, valve, fitting (PVF) products and services to all U.S. locations of The Chemours Company. The five-year agreement added the Gulf Coast region and also includes valve a...

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Sunbelt Supply Opens Shanghai Valve and Automation Center

3 DAYS AGO

Sunbelt Supply celebrated the grand opening of its new Valve and Automation Center with an open house on May 12, 2016 in Shanghai, China. The open house welcomed 80 customers and manufacturers. Attendees toured the newly stocked warehouse and automation center .

Sunbelt Supply Shanghai is a joint ventu...

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U.S. Chemical Production Stalled in April

18 HOURS AGO

According to the American Chemistry Council (ACC), the U.S. Chemical Production Regional Index (U.S. CPRI) was flat in April , following a 0.4% gain in March, and a 0.1% decline in February, as measured on a three-month moving average (3MMA). In April, the Gulf Coast was the only region to post a smal...

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Why the Sudden Surge in Chemical Industry M&A Deals?

5 DAYS AGO

“Earlier this year, ChemChina agreed to buy Syngenta in a $43 billion deal. And in another sign of the eat-or-be-eaten climate of the industry, this year Monsanto attempted and then ditched its own attempt at an acquisition, and has now become the target of a possible takeover by Bayer and BAS...

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Markit PMI Shows U.S. Manufacturers Stagnating in May

-1 DAYS AGO

The U.S. manufacturing sector crept closer to stagnation in May, with the seasonally adjusted Markit Flash U.S. Manufacturing Purchasing Managers’ Index (PMI) registering only slightly above the neutral 50.0 mark at 50.5. This was down from 50.8 in April and signaled only a marginal improvement...

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Why Innovation is the Key to U.S. Manufacturing Growth

20 HOURS AGO

Manufacturing may be facing some headwinds, but it’s undeniably in the midst of a technological renaissance that is transforming the look, systems and processes of the modern factory. Despite the risks — and despite recent history — industrial manufacturing companies cannot afford ...

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A Primer On Worm Gear Operators

vmsum12_worm_gears_1A remote gas pipeline installation in Pinedale, WyomingManual gear operators continue to provide a viable, age-old solution with a few 21st century twists. Understanding how these products work, as well as the tradeoffs and costs associated with manual operators, can help end users select the right technology for the application.

Over the past 30 years, valve automation has dominated the flow control industry. But even though power actuation captivates the attention, imagination and the lion’s share of growth in the market, manual valve actuation also continues to expand, receiving its own innovations. In this article, we provide an introduction to the basic principles behind these workhorse operators and discuss current trends in the market. We also consider the benefits and associated costs that come with manual worm gear designs. Please note that for ease of reference, a glossary of terms has been added; the definitions provided are industry specific and only intended to cover the depth and scope of this article (click here).


THE RANGE

Manual worm gear operators can be found in nearly every valve application throughout the world. Manual operators have no power requirements, no hydraulic or pneumatic pressure unit to maintain and can be used in the most remote locations. From submarine duty to mining, water works to oil and gas pipelines, if torque is required, manual worm gear operators are there.

To begin, it may help to view the world through the eyes of the application engineer. We push up our stylish horn rim glasses, open our 20-tab spreadsheet product selector and ask: “Torque or thrust?” The first consideration in selecting an actuator is the type of force required. Torque, that rotational or twisting force necessary to position ball valves, plug valves, butterfly valves, etc., will be the focus of this article.

Let’s look at the fundamental challenge our application engineer faces, which is: “How do we provide a means to safely and effectively position the valve?”

vmsum12_worm_gears_2Figure 1. A simple lever can work when just a small amount of torque is needed.If the valve torque is small enough, a wrench or lever of adequate length or a handwheel of the appropriate diameter provide simple solutions to our dilemma (Figure 1). Both the handwheel and the lever increase mechanical advantage by applying principles explained by Archimedes more than 2,000 years ago. Levers, while efficient and cost-effective, remain impractical or undesirable for many applications, however. At some point, the force required to position the valve exceeds the feasibility of a simple lever; this is where worm gear operators enter the picture.

We have used gears for thousands of years to harness energy from wind, water and beasts. Think of gear mechanisms as a series of interacting levers and screws. In our application, gears are used to amplify torque. In short, we use gears to convert force to work.


THE MECHANISM

vmsum12_worm_gears_3Figure 2. A simple cylindrical single-start worm and worm gear set.Worm gear operators are used for actuation because they offer high torque multiplication and load-carrying capability in a small, low-cost package. Figure 2 presents an example of a typical worm gear set found in a manual worm gear operator.

Following conventional American Gear Manufacturers Association (AGMA) (www.agma.org) gear design standards, if a single-start worm is the drive and an 80-tooth worm gear is the driven, the ratio would be expressed as 1:80 (the formula is available in the glossary). That’s a lot of ratio in a small package. But these numbers only tell us that it takes 80 worm revolutions (drive) to complete one revolution of the worm gear (driven). The ratio tells us about the mechanism’s effect on speed but little about torque. To understand the effect on torque, we need to know the mechanical advantage (MA). In a perfect machine, a 1:80 ratio would net an MA of 1:80 (expressed as 80), meaning that for 1 unit of force applied, 80 units of force are generated.

Does this mean free torque? Unfortunately, no. The energy of the universe is constant and as with everything, there is an associated cost.


THE COSTS

What are the costs associated with amplifying force through our manual actuator? The first cost is hard cash—the worm gear actuator will cost more than a lever or handwheel.

Second, machines are not perfect, which is demonstrated in efficiency losses through heat and wear. As it turns out, standard single-start metal worm gear sets are less than 35% efficient by design. Also, worm gear sets with a worm thread angle and design, which net an efficiency of approximately 35% and greater, are not typically self-locking, and without self-locking characteristics are not suitable for a number of applications. Based on a website sample of the top manufacturers, 32% is the approximate average efficiency for manual worm gear operators. This simple formula explains what happens to mechanical advantage in a 32% efficient gear train:

80 x .32 = 25.6 MA

The MA would be approximately 25, not 80. That is nearly 55 points of mechanical advantage lost to ­inefficiency.

Third, and not captured in manufacturer’s data sheets, is the cost in the exchange of force for distance. We increase force by simply making more trips, or more specifically, more turns on the handwheel to cycle the valve.

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