By Luke Biermann, Mechanical Seal Engineering
Pumps are essential components in a wide range of industries, including mining, water supply and treatment, power generation, food and beverage etc. The sealing mechanism of a pump is crucial in maintaining its efficiency and reliability. There are two primary options for sealing a pump: mechanical seals and gland packing. Each of these options has its unique advantages and disadvantages, and the choice depends on several factors.
Mechanical seals are a great choice for many industrial applications due to their superior sealing capabilities. Unlike gland packing, which relies on compression to create a seal, mechanical seals use a rotating and stationary element to create a barrier that can withstand higher pressures and temperatures. The reduced friction on the shaft leads to lower energy consumption and reduced maintenance costs.
Additionally, mechanical seals can handle a wide range of fluids, including corrosive and abrasive substances, making them more versatile than gland packing. The downside of mechanical seals is that their initial setup costs can be more than gland packing and require more specialized knowledge and equipment for installation and maintenance. This is why finding a reliable mechanical seal company is important.
Gland packing is an older sealing technology that is still in use in many applications. Gland packing consists of a braided rope or cord that is compressed into a stuffing box to create a seal. The advantage of gland packing is that it is cheaper and easier to install than mechanical seals. Gland packing is also more forgiving of misalignment and vibration, making it a better option for older or less efficient pumps.
However, gland packing is less efficient than mechanical seals and requires more frequent replacements due to wear and tear. Additionally, gland packing is not suitable for handling corrosive or abrasive substances, making it less versatile than mechanical seals.
How to choose between them
When choosing between mechanical seals and gland packing, several factors should be considered. The first is the type of fluid being pumped. If the fluid is corrosive or abrasive, mechanical seals are a better choice as they can handle a wider range of substances. Additionally, if energy efficiency is a priority, mechanical seals should be used as they provide less resistance on the shaft. However, if the pump is older or less efficient, gland packing may be a better option as it is more forgiving of misalignment and vibration.
Another factor to consider is the cost. Mechanical seals are more expensive initially than gland packing, but they also last longer and require less frequent replacements, leading to cost savings over time. Additionally, if the pump is being used in an application where downtime is critical, mechanical seals are a better option as they require less maintenance and can be replaced more quickly.
Finally, the expertise and knowledge of the maintenance team should be considered. Mechanical seals require more specialized knowledge and equipment for installation and maintenance than gland packing. If the maintenance team is not experienced in working with mechanical seals, gland packing may be a better option. A good mechanical seal supplier will provide support for installation and troubleshooting.
In conclusion, the choice between mechanical seals and gland packing for pump sealing depends on several factors, including the type of fluid being pumped, energy efficiency, cost, and the expertise of the maintenance team. Mechanical seals offer superior sealing capabilities and are more versatile, making them a preferred option in many industrial applications. However, gland packing is cheaper and easier to install and maintain, making it a better option for older or less efficient pumps. Ultimately, the choice should be based on a careful assessment of the specific needs and priorities of the application.
For more information, please visit mechsealengineering.com.au.
The environment a seal will be exposed to is crucial when selecting the design and material.
There are a number of key properties that seal materials need for all environments, including creating a stable seal face, able to conduct heat, chemically resistant, and good wear resistance. In some environments, these properties will need to be stronger than in others. Other material properties that should be taken into account when considering the environment includes hardness, stiffness, thermal expansion, wear and chemical resistance. Keeping these in mind will help you to find the ideal material for your seal.
The environment can also determine whether cost or quality of the seal can be prioritised. For abrasive and harsh environments, seals may be more expensive due to the materials needing to be strong enough to withstand these conditions. For such environments, spending the money for a highquality seal will pay itself back over time as it will help prevent the costly shutdowns, repairs, and refurbishment or replacement of the seal that a lower quality seal will result in. However, in pumping applications with very clean fluid that has lubricating properties, a cheaper seal could be purchased in favour of higher quality bearings.
Carbon used in seal faces is a mixture of amorphous carbon and graphite, with the percentages of each determining the physical properties on the final grade of carbon. It is an inert, stable material that can be self-lubricating. It is widely used as one of the pair of end faces in mechanical seals, and it is also a popular material for segmented circumferential seals and piston rings under dry or small amounts of lubrication.
This carbon/graphite mixture can also be impregnated with other materials to give it different characteristics such as reduced porosity, improved wear performance or improved strength.
A thermoset resin impregnated carbon seal is the most common for mechanical seals, with most resin impregnated carbons capable of operating in a wide range of chemicals from strong bases to strong acids. They also have good frictional properties and an adequate modulus to help control pressure distortions. This material is suited to general duty to 260°C (500°F) in water, coolants, fuels, oils, light chemical solutions, and food and drug applications.
Antimony impregnated carbon seals have also proven to be successful due to the strength and modulus of antimony, making it good for high pressure applications when a stronger and stiffer material is needed. These seals are also more resistant to blistering in applications with high viscosity fluids or light hydrocarbons, making it the standard grade for many refinery applications.
Carbon can also be impregnated with film formers such as fluorides for dry running, cryogenics and vacuum applications, or oxidation inhibitors like phosphates for high temperature, high speed, and turbine applications to 800ft/ sec and around 537°C (1,000°F).
Ceramic
Ceramics are inorganic non-metallic materials made from natural or synthetic compounds, most commonly alumina oxide or alumina. It has a high melting point, high hardness, high wear resistance and oxidisation resistance, so it is widely used in industries such as machinery, chemicals, petroleum, pharmaceutical and automobile. It also has excellent dielectric properties and is commonly used for electrical insulators, wear resistant components, grinding media, and high temperature components.
In high purities, alumina has excellent chemical resistance to most process fluids other than some strong acids, leading it to be used in many mechanical seal applications. However, alumina can fracture easily under thermal shock, which has restricted its use in some applications where this could be an issue.
Silicon carbide is made by fusing silica and coke. It is chemically similar to ceramic, but has better lubrication qualities and is harder, making it a good hard-wearing solution for harsh environments. It can also be re-lapped and polished so a seal can be refurbished multiple times over its lifetime.
It is generally used more mechanically, such as in mechanical seals for its good chemical corrosion resistance, high strength, high hardness, good wear resistance, small friction coefficient and high temperature resistance. When used for mechanical seal faces, silicon carbide results in improved performance, increased seal life, lower maintenance costs, and lower running costs for rotating equipment such as turbines, compressors, and centrifugal pumps.
Silicon carbide can have different properties depending on how it has been manufactured. Reaction bonded silicon carbide is formed by bonding silicon carbide particles to each other in a reaction process. This process does not significantly affect most of the physical and thermal properties of the material, however it does limit the chemical resistance of the material. The most common chemicals that are a problem are caustics (and other high pH chemicals) and strong acids, and therefore reaction-bonded silicon carbide should not be used with these applications.
Self-sintered silicon carbide is made by sintering silicon carbide particles directly together using non-oxide sintering aids in an inert environment at temperatures over 2,000°C. Due to the lack of a secondary material (such as silicon), the direct sintered material is chemically resistant to almost any fluid and process condition likely to be seen in a centrifugal pump.
Tungsten carbide is a highly versatile material like silicon carbide, but it is more suited to high pressure applications as it has higher elasticity which allows it to flex very slightly and prevent face distortion. Like silicon carbide, it can be re-lapped and polished.
Tungsten carbides are most often manufactured as cemented carbides so there is no attempt to bond tungsten carbide to itself. A secondary metal is added to bind or cement the tungsten carbide particles together, resulting in a material that has the combined properties of both tungsten carbide and the metal binder. This has been used to an advantage by providing greater toughness and impact strength than possible with tungsten carbide alone. One of the weaknesses of cemented tungsten carbide is its high density.
In the past, cobalt-bound tungsten carbide was used, however it has gradually been replaced by nickel-bound tungsten carbide due to it lacking the range of chemical compatibility required for industry. Nickel-bound tungsten carbide is widely used for seal faces where high strength and high toughness properties are desired, and it has good chemical compatibility generally limited by the free nickel.
As Buna is a synthetic rubber copolymer, it performs well in applications requiring metal adhesion and abrasion-resistant material, and this chemical background also makes it ideal for sealant applications. Furthermore, it can withstand low temperatures as it is designed with poor acid and mild alkali resistance.
Buna is limited in applications with extreme factors such as high temperatures, weather, sunlight and steam resistance applications, and is not suitable with clean-in-place (CIP) sanitising agents containing acids and peroxides.
EPDM
EPDM is a synthetic rubber commonly used in automotive, construction and mechanical applications for seals and O-rings, tubing and washers. It is more expensive than Buna, but can withstand a variety of thermal, weather and mechanical properties due to its long-lasting high tensile strength. It is versatile and ideal for applications involving water, chlorine, bleach and other alkaline materials. Due to its elastic and adhesive properties, once stretched, EPDM returns to its original shape regardless of the temperature.
EPDM is not recommended for petroleum oil, fluids, chlorinated hydrocarbon or hydrocarbon solvent applications.
GFPTFE has good chemical resistance, and the added glass reduces the friction of the sealing faces. It is ideal for relatively clean applications and is cheaper than other materials. There are sub-variants available to better match the seal to the requirements and environment, improving its overall performance.
Buna
Buna (also known as nitrile rubber) is a cost-effective elastomer for O-rings, sealants and moulded products. It is well known for its mechanical performance and performs well in oil-based, petrochemical and chemical applications. It is also widely used for crude oil, water, various alcohol, silicone grease and hydraulic fluid applications due to its inflexibility.
Viton is a long-lasting, highperformance, fluorinated, hydrocarbon rubber product most commonly used in O-Rings and seals. It is more expensive than other rubber materials but it is the preferred option for the most challenging and demanding sealing needs.
Resistant to ozone, oxidation and extreme weather conditions, including materials such as aliphatic and aromatic hydrocarbons, halogenated fluids and strong acid materials, it is one of the more robust fluoroelastomers.
Choosing the correct material for sealing is important for the success of an application. While many seal materials are similar, each serves a variety of purposes to meet any specific need.
Shanfengyoufeng
·
Follow
2 min read
·
Aug 31, 2023
--
Nitrile rubber, also known as NBR or Buna-N, is a popular material used in the manufacturing of O-rings. O rings made from nitrile rubber offer several advantages and disadvantages. In this article, we will discuss the pros and cons of using nitrile rubber O-rings.
Firstly, one of the major advantages of nitrile rubber O-rings is their excellent resistance to oil, fuel, and other petroleum-based fluids. This makes them ideal for applications in the automotive and oil industries, where exposure to such fluids is common. Nitrile rubber O-rings also exhibit good resistance to water, hydraulic fluids, and many solvents, making them versatile for various industrial applications.
Another advantage of nitrile rubber o rings is their cost-effectiveness. Compared to other elastomers, nitrile rubber is relatively inexpensive to produce, making it a cost-efficient option for sealing applications. This affordability makes it a popular choice for industries where large quantities of O-rings are required.
Nitrile rubber O-rings also possess excellent mechanical properties. They have good tensile strength, tear resistance, and abrasion resistance, which contribute to their durability and long service life. These properties make nitrile rubber O-rings suitable for applications with high-pressure environments or those involving dynamic movements.
Furthermore, nitrile rubber o ring have a wide temperature range in which they can operate effectively. They can withstand temperatures ranging from -40°C to 120°C (-40°F to 248°F), making them suitable for both low and high-temperature applications. However, it is important to note that extreme temperatures can affect the performance and longevity of nitrile rubber O-rings.
Despite their numerous advantages, nitrile rubber O-rings also have some limitations. One of the main drawbacks is their limited resistance to ozone, sunlight, and weathering. Prolonged exposure to these elements can cause the rubber to degrade, leading to reduced sealing efficiency and shortened lifespan. Therefore, nitrile rubber O-rings may not be suitable for outdoor applications or those involving constant exposure to sunlight.
Additionally, nitrile rubber O-rings have relatively poor resistance to certain chemicals, such as acids, ketones, and aromatic hydrocarbons. Exposure to these substances can cause the rubber to swell or deteriorate, compromising its sealing properties. It is essential to consider the compatibility of nitrile rubber O-rings with the specific chemicals present in the application environment.
Overall, nitrile rubber O-rings are a reliable sealing solution, but it is important to consider the compatibility and environmental factors to ensure optimal performance and longevity.