Material Selection

Its very difficult to choose the right gasket for the job these days, there are just so many styles. There are many different packings with similar properties and prices. And with the ban on asbestos-based materials, there are many more styles being made to replace them. The four basic things you have to keep in mind when selecting a material are as follows: • Operating Pressure

• Bolt Load

• Resistance to chemical attack (Corrosion)

• Operating temperature

The corrosion resistance can vary based on a couple different factors: • The concentration of the corrosive agent: Higher concentrations dont always mean the fluid will be more corrosive.

• The temperature of the corrosive agent: Higher temperatures tend to speed the effects of corrosion.

• Dew Point: When the fluid moves through the dew point when in the presence of sulfer and water can result in the formation of highly corrosive condensates. The formation of sulfer and water are commonly found in gases resulting from combustion. In critical applications it is common practice to test materials in a lab to determine their chemical resistance to corrosive media under service conditions. In order to design a gasket, an evaluation is required, starting with the type of flange, bolt load, setting stress, etc. Attention to detail is key in this process and every step must be followed in order to get maximum use out of your material. Gasket selection can be simplified by using the Pressure x Temperature Factor.

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Styles of PTFE

Molded and Sintered PTFE: This type of PTFE was the first to be introduced to the market. This style is made from virgin or reprocessed PTFE resin, without fillers, which is then molded, compressed and sintered. As with any other type of plastic, PTFE has a high creep factor when compressed. The creep factor is detrimental and can lead to having to re-tighten the bolts to maintain seating pressure and prevent leakage. The higher the temperature in the application it is used for, the more the creep factor will increase. Even with these drawbacks, PTFE is affordable, easily available and highly chemical resistant.

Skived PTFE: This style is similar to molded and sintered PTFE as it is also make of virgin or reprocessed PTFE without fillers. Instead of molding an individual sheet, the sheets are taken from a billet of PTFE with a process called skiving. The skiving process was developed to overcome manufacturing deficiencies of the molding process. Skived PTFE shares the same creep characteristics as molded and sintered PTFE.

Molded or Skived Filled PTFE: In order to correct the creep characteristics of molded and skived PTFE, manufacturers started adding mineral fillers or fibers in order to reduce creep factor. This indeed reduced the creep characteristics but not by a significant amount.

Restructured Filled PTFE: Besause the addition of fillers in the molding process was not enough to significantly reduce creep, a new manufacturing process was developed to produce filled PTFE sheets. In this new process the material is laminated before being sintered, which yeilds a highly fibrillated structure with significantly less creep. The different fillers used in this process are as follow: • Barite: Added for use in strong caustic service. Also FDA compliant.

• Mineral Silica: Used for strong acidic service.

• Hollow Glass Microshperes: Used to increase compressibility.

• Synthetic Silica: Used as subsitute for glass microspheres.

Expanded PTFE: This style of PTFE is made by heating and stretching PTFE before sintering it. Lke all PTFE it has strong chemical resistance, but unlike molded or skived PTFE, this material has a high compressibility and is good for use in flanges made from fragile materials. The only drawback to this material is that its floppy and difficult to install, especially if the flanges cannot be separated.

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GS (General Service) Metal Bellows

Metal Bellows seals can seal with Flexible Graphite instead of a rubber boot or o-ring Elastomers allowing it to be used in higher temperature applications No Springs to clog. Metal Bellows seals are a very effective method of maintaining seal face pressure on the seal face.

Metal Bellows seals that do use o-rings only require one static o-ring to seal off any leakage along the shaft in Chemical Service this o-ring can be Aflas, EPDM, Nitrle, Viton, Encapsolated PTFE, Ameri-rez, or PTFE Because the o-ring is static it will not wear on the shaft.

When installed correctly metal bellows seals will provide exceptionally long service. Metal bellows seals are and excellent solution on chemical applications where Kalrez, Chemrez,Viton, FKM, Buna, Aflas or EPDM are not compatible.

For many years an inexpensive form of metal bellows seals have been used very successfully in the waste water / sewage industry and in the agricultural fields pumping irrigation water. These seals were generally made of a formed bellows rather than a welded bellows. Welded bellows seals are much stronger and have superior flex and recovery characteristics which are more ideal to holding seal faces together but cost more to manufacture. Welded metal bellows seals are less prone to metal fatigue and are available in single and double ply.

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ASP Type 9 Mechanical Seal

Mechanical seals often need to be used in chemical applications. When confronted with some harsh chemicals, mechanical seals containing elastomers made of Viton, Kalrez or Chemrez can't hold up. Because PTFE (polytetrafluoroethylene)or as most people know it Teflon ® , has a 0-14 ph range it usually will hold up.

Like most materials every choice has an up and a down side. PTFE will handle most chemical applications, chemical attack is no longer an issue. On the down side PTFE wedges can cause fretting of your sleeve or shaft if you have not hard surfaced your shaft or sleeve (plasma coating).

The stationary element of your seal will require a PTFE gasket. It's not much good to have a PTFE on the rotary and then use an elastomer on the seat. We have seen it done, and because it is a static application some have gotten away with it, but it is not recommended. Most commonly the seat will be a L-shaped or Clamped mount style to allow space for a PTFE gasket to be used as the secondary sealing element.

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Style 615 Graphited Non-Asbestos Packing

Description:

Our Style 615 packing is manufactured from a synthetic yarn and impregnated with a petroleum and graphite lubricant. Due to its soft feel and composition, Style 615 adapts well to machinery that is out-of-spec due to wear and tear, such as with older pumps, valves, agitators and mixers.

Style 615 is a prime material for use in centrifugal and rotary pumps, as well as valves with applications involving water, steam, aqueous solutions, mild acids and alkalies, air and dry industrial gasses, and petroleum services.

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Technical parameter:
Temperature	-170 F (-110 C ) to +500° F (+260 C )
Speed	to 1500 fpm
Pressure	to 300 psi (rotary/centrifugal)
PH Value	4-10
Construction	Square Braid

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Style 649 Carbon/PTFE Packing

Description: Style 649 is a braided packing made of carbon fiber which is impregnated with PTFE dispersion. 649 is inert to almost all corrosive chemicals.

When it is used for pumps, frictional heat is freely conducted to the stuffing box metal because of its excellent thermal conductivity. As a result, no or little damage will be caused to the shaft sleeve or to the packing.

Although similar in cost, It can replace common non-asbestos (graphite/PTFE) packings, it will last longer and handle a wider range of applications.

This unique packing is an inexpensive version of high grade carbon packings. It can be used to replace both low cost graphited non-asbestos packings and in many cases can be used to replace the expensive carbon packings used as end rings in valve applications: (as long the temperature is less than + 662 degrees F).

It can be used to seal corrosive fluids except strong oxidizer acids, organic solvents. Ideal for use in centrifugal pumps, plunger pumps, mixers valves, etc.

Technical parameter:
Temperature	-328 F to +662 F
FPM	2500
PH Value	1-13

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What is O-Rings ? Learn Benefits of O-Rings

O-Rings

O-rings are also known as the toric joint and they are a type of seal used in industrial applications. The advantages of using these types of rings are many because they come with a rounded cross section and most machines used in an industry are circular in shape. Because of being circular by nature, they automatically match the shape of the device without much difficulty.

The origin of the o-rings dates back to the time in 1896 when it was first patented and was used in industries in the U.S. Later, sensing its versatile finish and usability in production, countries around the globe started purchasing it and now it is one of the most used accessories. The size of the rings are measured in different measurement scales. It is commonly measured in inches and sometimes in metric, based on the region around the globe. Irrespective of your location, you can easily purchase the material you need from any part of the globe as the size chart is the same wherever you go. The only region that varies drastically is in UK where it is referred using a BS scale which is almost the same but you may have to be careful when placing an order.

Common Uses The O-rings are best used as a joint within mechanical mounting. As they are made using metal bodies, they don’t easily give way and retain their shape irrespective of the pressure exerted on these items. The accessory acts as a reliable sealant even when high pressure liquid passes through it. It is also widely used in industries to contain gases, liquids and other types of items when they are transferred from one end of the manufacturing plant to another. They ensure that there is no leak in between which provides a loss free environment for investors to work in.

When inserting the ring in between two different metal casing, one has to make sure that the point of contact is not smooth because if it is too smooth, it may not exert the proposed pressure on the connecting bracelets. It could lead to unexpected leaks which is why they are always made with a surface finish that offers enough friction to keep the setup firmly in place during transfusions. Another widely used application for O-rings are in vacuum related applications where they are solid enough to not lose their shape. The best materials to create an o-ring for vacuum application is to make them using nickel, or copper materials. It is not advisable to use rubber because they could become hard when the temperature increases and brittle doesn’t withstand when the temperature goes really low.

Materials Used A wide range of materials are used to manufacture O-rings. The most common and the popular ones for every type of industrial purpose include butadiene rubber, butyl rubber, EPDM, Nitrile rubber, fluoro elastomer, Neoprene rubber and thermo plastic polyurethane. There are other types of rubber materials that are also used to make the rings. Sometimes, there are o-rings made using motor oils, even water and gasoline or hydraulic oil.

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