Pump Shaft Seals

Pump shaft seals are actually mechanical seals which are used prevalently in pumps to solve a problem that persists in almost every industrial environment. When transferring liquids from one end of the factory to another, there are so many joints that it has to pass through. Leakage becomes an extremely persistent problem which is brought under control with the help of such powerful seals. However harsh the working conditions are, the devices are capable of withstanding such pressure and there are multiple types of products available designed to suit specific requirement. As time developed, newer and more advanced variants came into being.

Stuffing box seals isthe most primitive variant of the product and it is still being used in industries where they may not require any advanced devices. It is cheap, easy to use and is versatile enough to match many applications. One of the biggest weaknesses of the packing style is that because of being cheap and easy to create, it doesn’t last long. Industrial applications which require robust build and long lasting capability may have to skip this method of sealing.

The lip seals came into being which is a much better variant of pump shaft seals. For better durability and finish, the product is made using a rubber ring on the inside to keep the pressure levels intact. Based on the pressure the application requires, the thickness of the ring would vary. While rubber is the most preferred material to construct it, it is also built using polymer materials at times. Powered by a tight construction and limited space, this type of seal is more than capable of withstanding high pressure. The rubber material however will not stand against increased temperature conditions as it will easily melt.

The above mentioned models of pump shaft seals are used in industries where they can withstand only one type of liquid. If it has increased pressure, higher temperatures and corrosive in nature, such type of seals could never be used. It is in such a scenario that the stepped shaft metal components are used. Metal can easily overcome the corrosive nature of any liquid and it can also withstand increased temperatures without breaking a sweat. With such convenience and amazing robustness besides long lasting durability, they are obviously the most preferred models. They are often used in almost every industrial setup irrespective of the transfusion done.

While pump shaft seals are capable of transferring any type of liquid from one end to another, there could be leakage in the connecting edges. It is overcome by using o rings. They are made using rubber materials but when it comes to high temperature and pressure based liquids, they are made using different components that are capable of handling the demanding conditions.

It is important to buy the components from a reliable seller. It is supposed to help an industrial process run without any hiccups. Branded solutions are often preferred and online shopping has made it easier to find the right type of seal.

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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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