02212018Wed
Last updateWed, 21 Feb 2018 7pm

i

Achieving Predictable Valve Performance for Safety Applications

Achieving Predictable Valve Performance for Safety Applications

A focus on having the proper specificati...

Putting Servo Valves Back to Work

Putting Servo Valves Back to Work

Industries as varied as paper production...

Corrosion and Fouling: Is There a Solution?

Corrosion and Fouling: Is There a Solution?

According to a 1998 study released by the ...

Valves with All the Trimmings

Valves with All the Trimmings

The term valve trim has been around for ...

SubscribeWNT18

FREE SUBSCRIPTION*

• Print magazine
Digital magazine
• VALVE eNews
Read the latest issue

*to qualified valve professionals in the U.S./Canada

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

MRC Global Announces Fourth Quarter 2017 Results

Wednesday, 21 February 2018  |  Chris Guy

MRC Global’s sales were $903 million for the fourth quarter of 2017, which was 26% higher than the fourth quarter of 2016 and 6% lower than the ...

Readmore

Loading...
Advertisement
i

Web Only

Valve Positioners Offer Improved Control Valve Performance

Valve Positioners Offer Improved Control Valve Performance

Monday, 19 February 2018  |  David Matherly

From time to time, we are re-posting well-received or particularly valuable articles that have previously run on VALVEMagazine.com so that those who m...

Readmore

Loading...

Industry Headlines

MRC Global Announces Fourth Quarter 2017 Results

-1 DAYS AGO

MRC Global’s sales were $903 million for the fourth quarter of 2017, which was 26% higher than the fourth quarter of 2016 and 6% lower than the third quarter of 2017 due to seasonality. As compared to 2016, all sectors increased driven primarily by midstream and upstream.

MRC Global's fourth qu...

Readmore

Curtiss-Wright Acquires Dresser-Rand Government Business

23 HOURS AGO

Curtiss-Wright has entered into an agreement to acquire the assets that comprise the Dresser-Rand Government Business (Dresser-Rand), a business unit of Siemens Government Technologies, for $212.5 million in cash.

Dresser-Rand designs and manufactures mission-critical, high-speed rotating equipment sol...

Readmore

U.S. Refiners Increasingly Turning to Export Markets

-1 DAYS AGO

“U.S. gasoline consumption has leveled off as the stimulus provided by low and falling oil prices between 2014 and 2016 has faded, so refiners are increasingly turning to diesel and customers in emerging markets,” Reuters  reports .

“In geographical terms, the fastest growth in co...

Readmore

$900M Power Plant Planned for Indiana

-1 DAYS AGO

Vectren Energy Delivery of Indiana is proposing to install an additional 50 megawatts (MW) of universal solar and build an 800 to 900-MW natural gas-fired generation facility in addition to other critical investments that will significantly change the way the company generates power for the region .

Th...

Readmore

Survey Finds Surge in Confidence of Small Business Owners

-1 DAYS AGO

CNBC and SurveyMonkey recently announced the results of their quarterly Small Business Survey. According to the findings, 47% percent of small-business owners say overall business conditions are good , up from 44% in the fourth quarter of 2017. Also, 32% of small business owners expect to increase the...

Readmore

Construction Starts in 2017 Decline 7%

1 DAY AGO

Many of the leading U.S. metropolitan areas for commercial and multifamily construction starts showed reduced activity in 2017 compared to levels reported during 2016, according to Dodge Data & Analytics. Of the top ten markets ranked by the dollar amount of construction starts, seven registered...

Readmore

Advertisement

Soft Goods in Actuators and Valves

vmsum12_beyone_valves_o-ringsSoft goods such as rings, gaskets, bushings, washers, seals and packing sets are widely used in valves and actuators. Manufacturers specify fillings and percentages for compounds for these soft goods to ensure they will operate properly with their valve and actuator products.

End users, on the other hand, operate the products and processes that use them. They change soft goods at certain frequencies to maintain smooth operations and assure reliability of the products as well as plant processes.


IN THE DESIGN

During the design phase for valves and actuators, manufacturers require specific fillings and compounds for soft goods. They specify those soft goods in the bill of materials (BOM) for their products to ensure that end users order the right soft goods for use with their manufactured valve or actuator. Usually, the part numbers do not show compound percentages and other details such as the filling type specified by the manufacturer. Instead, part numbers just show the part name and a short description of the materials. This is done because manufacturers usually work with specialized soft goods companies to manufacture those parts for them. In most cases, those soft goods companies also do not provide the detailed recipes of their products—they only provide a part number with a general size and base material description.

During the design phase, valve and actuator manufacturers usually consider several specifications when it comes to soft goods. They look at temperature ranges, operating media, service media and cycling frequency, depending on process conditions. For example, soft goods that are in contact with gases that are sour and have both moisture and particles would have different requirements from those in contact with gases that are sweet, dry and clean. Also, engineered soft goods designed for fluids might consider the presence of particles, gases and other contaminants.

The fillings and compounds that make up soft goods also have certain properties needed for valves and actuators in specific situations. The fillings might include glass fiber, carbon, bronze or graphite. The properties they may need include dielectric strength, hardness, coefficient of friction, total deformation, coefficient of thermal factor, wear, moisture absorption, temperature resistance and chemical resistance.1

End users typically catalog part numbers to ensure ordering “original” spare parts. However, there are situations where end users elect to go with local or nearby soft goods suppliers to get those spare parts. For example, an emergency may mean a valve or an actuator needs to be overhauled, but the end user’s spare parts warehouse does not have the required part in its stock. If placing an order for those spare parts from the original supplier or the manufacturer would take too long, an end user could elect to get the descriptions of those spare parts from the BOM, and then approach a local supplier for quick replacement parts.

But such a situation can be dicey—depending upon the criticality of the application, the location of the parts in the valve or the actuator, and the differences in properties between the “original” and the “fabricated” spare parts.


A CASE IN POINT

The following general example shows the major differences in properties, in this case between different polytetrafluoroethylene (PTFE) fillers. Non-filled PTFE or virgin PTFE is white in color and is capable of withstanding temperatures up to 450° F (232° C). Mineral-filled PTFE, meanwhile, is also white in color, but is capable of handling temperatures up to 550° F (288° C).2 If any of the mineral-filled PTFE soft goods on an actuator or a valve were replaced by a virgin PTFE, the probability of failure of those soft goods increases depending on the operating temperature of the application.

To carry this further, the following example shows how the same filler but with different percentages can affect the properties of a soft good. A 25%, glass-filled/75% virgin PTFE can handle a service temperature up to 550° F (288° C).3 Meanwhile, a 15% glass-filled/85% virgin PTFE can handle a service temperature up to 518° F (270° C).4 This means that if the normal operating temperature of a process is between 518° F (270° C) and 550° F (288° C), a failure can take place in that soft good if it was originally specified as a 25% glass-filled but was replaced by a 15% glass-filled.


SEALANTS

vmsum12_beyond_valves_fig1Figure 1. Influence of the acrylonitrile contentRubbers are very common and are widely used as sealants. Nitrile rubber is one example. The general term for such a seal is acrylonitrile butadiene copolymer. The percentage of acrylonitrile in nitrile rubber varies between 18% and 50%. This can have a significant influence on the physical properties of the finished nitrile rubber material.5

The higher the acrylonitrile percentage in nitrile rubber, the better the resistance to oil and fuel. At the same time, elasticity and resistance to ­compression set is adversely affected by that percentage. Figure 1 shows the different percentages of acrylonitrile and the effects on both the resistance to oil and the elasticity.6 This means that if a nitrile rubber with 50% acrylonitrile was replaced by a nitrile rubber with 20% acrylonitrile, the resistance to oil and fuel will increase and the prob­ability of swelling will increase rapidly.


IN CONCLUSION

Manufacturers select soft goods in valves and actuators to suit the applications for which they are designed. Replacing those soft goods with products that are locally fabricated can be risky because of the different properties of different filling percentages, a situation made more complicated because those filling percentages are not usually published and provided in the manufacturers’ BOM.

 


Gary Burrows is senior applications engineer for Emerson Process Management–Valve Automation–Bettis. He has 30 years of experience in actuator and valve design, field service and application engineering. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

Amr Atiah is an instrumentation engineer at Saudi Aramco–Ras Tanura Refinery. He has been in the instrumentation field 10 years and is currently on an 18-month internship assignment with Emerson Process Management. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

 


References

1. www.buckeyerubber.com/ProdDisc.htm#Teflon

2. http://www.darcoid.com/images/uploads/pdfs/Fluid Power Sealing Materials (PTFE - Filled & Non-Filled).pdf

3. www.k-mac-plastics.com/data%20sheets/teflon-25%25GF-Data-Sheet.htm

4. www.matweb.com/search/datasheet.aspx?matguid=313108f956a6497d8883d535c753dac5&ckck=1

5. www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

6. www.123seal.com/seal-gasket/wp-content/uploads/HYDRAULIC-GROUP_ resize1.jpg

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement
BUYERS GUIDE 300x220

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