Mechanical seal designs come in a wide variety. These designs differ in the way they are driven, the choice of secondary seals, and the location of the springs. Mechanical seals have all been designed to meet certain criteria in terms of application, cost, fit, ease of installation, and capability to seal. There are, however, a few basic characteristics that are common to any good mechanical seal design.
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Many early mechanical seal designs placed the spring inside the process fluid. Most products (process fluids) that are sealed are not very clean. When the spring mechanism of the mechanical seal is immersed in this unclean fluid, dirt collects between the springs. This situation eventually impacts the spring’s ability to respond to movements and vibrations, and the ability to keep the seal faces closed. Over time, clogging of the springs will cause premature seal failure.
The ideal design offers springs on the atmospheric side of the mechanical seals. The springs will be protected from the process fluid and their ability to work will not be impeded.
The pressure from both the seal springs (Ps) and the hydraulic pressure of the liquid in the pump (Pp) provide a compression force that keeps the seal faces closed. Balanced seals reduce the seal ring area (Ah) on which the hydraulic pressure of the liquid in the pump (Pp) acts.
By reducing the area, the net closing force is reduced. This allows for better lubrication that results in lower heat generation, face wear, and power consumption. Balanced seals typically have higher pressure ratings than unbalanced seals.
The balance ratio (B) of a mechanical seal is given by the ratio of the hydraulically loaded area (Ah) and the sliding surface area (As):
Mechanical seals can be designed with inserted seal faces or with monolithic seal faces. In both cases, the sacrificial seal face is often made from carbon/graphite. This material offers good running properties but is relatively weaker from a mechanical standpoint than other options. Inserted face designs use a metal rotary holder to transmit the shaft torque to the seal face.
The disadvantage of this inserted face design is that the face and holder material have different coefficients of thermal expansion. This changes the net interference force between both parts when they are exposed to heat from the process fluid or face friction. The seal face deforms, which results in leakage and accelerated wear.
More modern seals are equipped with monolithic seal faces that are made out of only the seal face material itself. The torque transmission is applied directly to the seal face. This is possible if the geometry of the seal face is designed in a particular shape to give it the strength to handle the torque through its geometric design. These monolithic seal face designs have been made possible through the use of Finite Element Analysis (computer modeling).
Monolithic seal faces provide a more stable fluid film between the faces, and they do not deform in operation compared to inserted faces (or to a much lesser degree). Therefore, they are more commonly used nowadays when reliability and low emissions are vital.
All mechanical seal designs have at least one secondary seal that interacts with the dynamic movement of the flexible mounted face. This secondary seal moves with the springs to keep the seal faces closed and is defined as the dynamic secondary seal. During operation of a rotary design, springs will keep the seal faces closed. They adjust with each rotation for any misalignment from installation and parts tolerances. As the springs compensate, the dynamic secondary seal moves back and forth, twice per revolution. This rapid movement prevents the protective chrome oxide layer (the layer that protects the metal) from forming. Erosion of this unprotected area under the dynamic secondary seal will cause a groove to develop. Eventually this groove becomes so deep that O-Ring compression is lost and the seal leaks. In most cases, fretted shafts must be replaced to achieve an effective seal.
Non-fretting seals are designed so that the dynamic secondary seal rides on a non-metallic surface, usually the sacrificial face.
A rotary mechanical seal has the spring mechanism in the rotating section (A) of the mechanical seal.
With rotary mechanical seals, it is important that the stuffing box face is perpendicular to the shaft for the faces to stay closed. There will always be some resulting misalignment from installation and parts tolerances. The springs must adjust with each rotation to keep the seal faces closed. This adjustment becomes more difficult at higher speeds.
In contrast, a stationary seal is a mechanical seal designed in such a way that the springs do not rotate with the pump shaft; they remain stationary. Because the springs do not rotate, they are unaffected by rotational speed. The springs do not need to correct or adjust with each rotation; they adjust for misalignment only once when installed.
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Rotary seals are simple in design which makes them inexpensive. They are suitable for lower speeds only. Stationary seals are more complicated to design but are suitable for all speed ranges. Because of design complexity, stationary seals are more commonly configured as cartridge seals rather than component seals.
In the current dynamic industrial landscape, selecting the appropriate material to seal components is vital to ensure the long-term durability and performance of machinery. When it comes to sealing components, industrial rubber is regarded as a strong, versatile, and reliable choice. At Ambassador Industrial, we are aware of the importance of seals in protecting machinery from leaking, contamination, or environmental changes.
In this article, we’ll look at the five key characteristics that make rubber the ideal material for sealing components and will convey the reasons why rubber used in industrial applications is a top choice.
The most sought-after characteristic that industrial rubber has is its exceptional toughness. The industrial environment is harsh, and equipment is exposed to high temperatures as well as continuous stress, friction, and chemicals. The inherent strength of rubber allows it to stand up to these challenges and provide long-term performance in the most demanding conditions.
We at Ambassador Industrial design and implement seals that are constructed to last. The long-lasting nature of industrial rubber helps reduce downtime as well as the requirement for regular repairs, a vital aspect for any business that strives to maintain a high level of efficiency.
Flexibility is a distinct feature of industrial rubber, making it the ideal material for seals. In industrial applications, seals typically have to adjust for motion, vibration, and pressure fluctuations. It doesn’t matter if you’re dealing with a spinning shaft, an erratic temperature, or a sporadic pressure increase; the rubber will be flexed, bent, and then returned to its original shape without losing its functionality.
At Ambassador Industrial, we exploit this flexibility naturally by creating seal components that are capable of adapting to different scenarios without losing their sealing capabilities. This versatility is crucial when accuracy and flexibility are essential to ensure that the systems are effective and leak-proof.
Chemical resistance is an essential quality of any sealant product used in difficult conditions. Industrial machinery frequently comes in contact with harsh chemicals, oil fuels, as well as other chemicals that are corrosive. Fortunately, it displays amazing resistance to a vast variety of environmental and chemical elements.
This quality is crucial in industrial applications, where exposure to liquids, different pH levels, or even sunlight can degrade other substances. Hence, you get a seal component that can handle everything from acidic solutions to high-temperature environments without degrading over time.
Consistent Performance: Since rubber is resistant to chemical corrosive substances, It continues to function consistently, reducing the risk in crucial industrial processes.
The main purpose of a seal is to stop leaks, and industrial rubber is a leader in this respect due to its outstanding sealing capabilities. Its natural elasticity permits it to bind tightly to surfaces and close gaps through which gases or liquids could otherwise escape. This makes industrial rubber the ideal material for sealing components for a variety of applications, ranging from valves and pumps to hydraulic systems and more.
Cost is a crucial factor when it comes to industrial processes. While investing in top-quality seal components may initially seem costly, Industrial rubber provides substantial savings over the course of its life.
Its durability, when combined with minimal maintenance requirements and less downtime, translates to significant savings in cost over the course of time.
The benefits of cost: Their long-lasting durability and maintenance-free requirements offer substantial cost savings over time.
Selecting the appropriate material to seal components is not just a decision on the technical level, it’s an essential element in efficient solid industrial operations. Industrial rubber has a myriad of advantages. It is resilient, durable, flexible, and resistant to severe conditions. Additionally, it is cost-effective, which makes it the perfect option for a wide range of sealing needs.
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