01172017Tue
Last updateTue, 17 Jan 2017 4pm

i

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

IMF Raises U.S. Economic Growth Forecast

Tuesday, 17 January 2017  |  Chris Guy

After a lackluster outturn in 2016, economic activity is projected to pick up pace in 2017 and 2018, especially in emerging market and developing econ...

Readmore

Loading...

Industry Headlines

David Paradis Named President of Weir Flow Control Division

3 DAYS AGO

The Weir Group PLC has appointed David Paradis to its group executive as president of the Weir Flow Control Division. He will take up this new role on January 23, 2017. Paradis succeeds John Heasley who was appointed Weir Group CFO in October 2016.

Paradis is currently president of Weir Oil & Gas&r...

Readmore

GE, Transocean Announce Performance-Based Service Agreement

5 DAYS AGO

GE Oil & Gas has secured a new contractual service agreement (CSA), valued at approximately $180 million, with Transocean. Under the agreement , GE will provide condition-based monitoring and maintenance services for pressure control equipment on seven of Transocean’s rigs over the next 10 t...

Readmore

PA Town Approves $6B Shell Ethane Cracker Plant

19 HOURS AGO

Potter Township in western Pennsylvania has granted a conditional use permit for a $6 billion petrochemical plant to be built by Shell Chemicals. The location was chosen because more than 70% of North American polyethylene customers are within a 700-mile radius of Pittsburgh, PA. More state and fede...

Readmore

$4.17B Canadian Trans Mountain Pipeline Expansion Approved

4 DAYS AGO

Kinder Morgan’s Trans Mountain Expansion Project has received its environmental certificate from British Columbia, Canada. The proposed $4.17 billion Trans Mountain Expansion Project would increase the capacity of the pipeline to 890,000 barrels per day. The current capacity of the pipeline is 3...

Readmore

IMF Raises U.S. Economic Growth Forecast

-1 DAYS AGO

After a lackluster outturn in 2016, economic activity is projected to pick up pace in 2017 and 2018, especially in emerging market and developing economies. However, the International Monetary Fund (IMF) noted in its new World Economic Outlook, there is a wide dispersion of possible outcomes around ...

Readmore

Texas Economy Poised to Shift into ‘Second Gear’ in 2017

19 HOURS AGO

Texas job growth should increase slightly from 1.6% in 2016 to about 2% in 2017, says Federal Reserve Bank of Dallas assistant vice president and senior economist Keith Phillips.

“Job growth picked up in the second half of 2016 due to a stabilization of the energy sector,” Phillips said. ...

Readmore

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.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association