06272017Tue
Last updateTue, 27 Jun 2017 5pm

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Lubricants: Always Important—Sometimes Essential

Lubricants: Always Important—Sometimes Essential

Most valve professionals take more notic...

Why Air Valves are Needed in Water Applications

Why Air Valves are Needed in Water Applications

Air valves are hydromechanical devices d...

Achieving Profitability Through Maintenance Management

Achieving Profitability Through Maintenance Management

One of the distinctions between maintena...

Control Valve Positioner Performance Diagnostics

Control Valve Positioner Performance Diagnostics

There has been discussion for some years...

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Industry Headlines

Emerson in Talks to Acquire Software Company Paradigm Ltd.

1 HOUR AGO

According to Bloomberg , Emerson is in talks to acquire software company Paradigm Ltd. for approximately $1.5 billion.

“Paradigm specializes in seismic data interpretation and imaging equipment to help oil and gas companies know where to drill. The logic of such a deal seems sound and will help Eme...

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VMA Members Lead MDM Top Industrial PVF Distributors List

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Modern Distribution Management (MDM) recently published its Top Distributors list for 2017. Four of the top 5 distributors in the Industrial PVF category ; MRC Global, NOW Inc., Wolseley Industrial Group and FloWorks International; are currently VMA members.

“While oil & gas markets have start...

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Mountain Valley Pipeline Gets Environmental Approval

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The Federal Energy Regulatory Commission (FERC) determined that construction and operation of the Mountain Valley Pipeline would result in some adverse environmental impacts, but the majority of these impacts would be reduced to less-than-significant levels. This determination is based on a review o...

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Delta Chemical Plant Planned for Houston Area

23 HOURS AGO

Braskem will commit up to $675 million in investment capital towards the design and construction of a new facility, named Delta, located next to Braskem's existing production facilities. Construction is expected to begin mid-summer, with the final phase of main construction targeted for the first qu...

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U.S. Durable Goods Orders Fell the Most in 18 Months

3 HOURS AGO

New orders for manufactured durable goods in May decreased $2.5 billion or 1.1% to $228.2 billion, the U.S. Department of Commerce announced. This decrease, down two consecutive months, followed a 0.9% April decrease. Excluding transportation, new orders increased 0.1%. Excluding defense, new orders...

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Texas Manufacturers See 12th Consecutive Month of Growth

4 HOURS AGO

Texas factory activity increased in June, according to the Texas Manufacturing Outlook Survey. The production index, a key measure of state manufacturing conditions, fell 11 points to 12.3, indicating output grew but at a slower pace than in May.

Other measures of current manufacturing activity also i...

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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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