balanced vs unbalanced mechanical seal made in china

The balance of a seal refers to the distribution of load across the seal faces. If there is too much load on the seal faces, it can lead to a leakage of fluids from within the seal which essentially renders the seal useless. Moreover, the liquid film in between the seal rings runs the risk of vaporising.

This can result in higher wear and tear off the seal, shortening its life span. Seal balancing is therefore necessary to avoid disasters and to also elongate the life of a seal.

A balanced seal has a higher pressure limit. This means that they have a larger capacity for pressure and they also produce less heat. They can handle liquids that have a low lubricity better than unbalanced seals.

On the other hand, unbalanced seals are typically much more stable than their balanced counterparts as far as vibration, cavitation and misalignment are concerned.

The only major drawback that an unbalanced seal presents is a low pressure limit. If they are put under even slightly more pressure than they can take, the liquid film will quickly vaporise and will cause the running seal to run dry and thus fail.

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.

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 theflexible mounted face. This secondary seal moves with the springs to keep the seal faces closed and is defined as thedynamic 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.

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.

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.

Marco Hanzon is Vice President of Global Marketing for A.W. Chesterton Company. He has been an active member and past chairman of the Mechanical Seal Committee of the European Sealing Association. Marco"s experience includes working as an In-Field Support Engineer for mechanical seals.

There are various types and arrangement of the mechanical seals being used for the centrifugal pumps. Some of the commonly used ones are described below:

The pusher type of mechanical seals move axially along the rotating shaft or the sleeve to maintain the contact with the faces of the seal. This feature of these seals helps compensate for the wearing that may occur at the seal face, and wobbling due to misalignment. The pusher types of mechanical seals are used commonly, are less expensive and are easily available in the market in wide range of sizes and designs. The only disadvantage of these seals is that they tend to hang up and sometimes there is fretting of the shaft.

The unbalanced types of mechanical seals are used under drastic conditions where there are vibrations, misalignment of the shaft, and the problem of the cavitation of the fluid. These mechanical seals are inexpensive, allow lesser leakage of the fluid and are highly stable. However, these seals can operate only under low pressure range and if the force of the fluid exceeds certain limits the lubricating film between the faces squeezes out and the seal fails.

As the name suggests, the non-pusher or bellow type of mechanical seals don’t have to be moved axially to maintain their contact with the faces. These seals can work under low temperature and high pressure applications. The bellows used in these seals should be upgraded so that they can work under the corrosive environments.

The balanced mechanical seals have the ability to sustain higher pressures across the faces and they generate lesser heat thus they are suitable for handling liquids that have low lubricating capacity and hydrocarbons that have high vapor pressure.

The major advantage of the cartridge seals is that they don’t require complicated setting during the installation as required by the conventional seal. This helps reducing errors associated with seal setting and eventually also reduces the maintenance required.

There are various types and arrangements of the mechanical seals available in the market. It is very important to use appropriate mechanical seal for the required application. If the incorrect mechanical seal is selected there are chances that the fluid would start leaking from the pump and the very purpose of installing the expensive mechanical seal will be destroyed. In addition there would be loss of time, manpower, resources and also some safety hazards.

1) Liquid or fluid to be pumped: The first and the most important factor to consider while selecting the mechanical seal for the centrifugal pump is the liquid or the fluid to be pumped. If ordinary liquid like water is to be pumped, then conventional mechanical seal with ordinary materials can be selected. In fact in many water pumps ordinary glands are used as the sealants since any leakage of water to the external atmosphere is not dangerous. But you can always see the water dripping from the pumps using ordinary glands.

If the pump has to handle corrosive liquids like acids, it is very important to select corrosion resistant materials for the mechanical seals. Some of these materials can be stainless steel, bronze or hastelloy. The mechanical seals also comprise of the mating surfaces and these should also be made up of corrosion and wear resistant materials like ceramic, silicon or tungsten carbide, carbon etc. For the corrosive environments the materials for the stationary parts of the mechanical seal can be Teflon, Buna, EPR or Viton.

2) Pressure of the liquid: The liquid enters the pump at certain pressure and the pump has to increase its pressure to certain level so that it reaches certain height. The total pressure on the seal decides whether one should opt for the balanced seal or the unbalanced type of seal.

3) Temperature of the liquid: Some pumps handle liquids at high temperatures and others handle the liquids at low temperature. The materials and mating surfaces used in mechanical seals should be able to sustain the temperature of the fluid.

4) Nature of fluid: The liquids to be handled by the pump may be having ordinary flow, but there can also be chemical solutions that have high viscosity and slow flow, there can be precipitates, there can be abrasive liquids and so on. These types of fluids usually cause more wear and tear of the parts of the mechanical seals and in such cases it is advisable to use double seals.

5) Safety and Environmental concerns: The safety of human being handling the pump is of prime importance so are the permissible emission standards. To be on the safer side it is always better to used double seals that work as the better sealants and are more reliable.

Structural Features: single end, multi springs, unbalanced, independent rotary direction, screw pin and lug combined transmission. The transmission method is simple and reliable. All compensation components are pre-assembled so the seal component itself is easy to be installed with great compensation performance. The loads on seal faces are well balanced and the whole seal is easy to adjust with stable sealing performance.

Mechanical seals have classified several types. In this article, we will see the basic classification of mechanical seal that is the “Mechanical Seal – Balanced and Unbalanced Type”.

The pressure in any stuffing box acts equally in all directions and forces the primary ring against the mating ring. The force (F) acts only on the diameter (Do) across the seal face, it acts as a closing force on the seal faces.

To relieve the force at the seal faces, the diameter of the shoulder on a sleeve or the seal hardware is decreased. Thereby the seal face pressure can be lowered. This is called seal balancing.

A seal without a shoulder in the design is an unbalanced seal. A balanced seal is designed to operate with a shoulder. Only metal bellows seal is a balanced seal that does not require a shoulder.

Virtually all mechanical seals are available in either unbalanced ( Ref. Figure) or balanced versions. The term “unbalanced” is used when the stuffing box pressure times the area exposed to the pumped fluid (closing force), acting to close the seal faces, is greater than the average pressure between the seal faces (pressure gradient)times the area of contact between the faces. In other words, unbalanced mechanical seal exhibit net hydraulic closing forces which are generated by the actual pressures to be sealed.

For example, if there were a stuffing box pressure of  50 psig (3.4barg), the spring load would have to be added. Hence, the “face load” or closing force on the faces would be even higher than 50 psig times the face area. This, of course, limits the pressure sealing capacity of an unbalanced seal.

Unbalanced seals are often more stable than balanced seals when subjected to vibration, misalignment and cavitation. The disadvantage is their relatively low-pressure limit. If the closing force exerted on the seal faces exceeds the pressure limit, the lubricating film between the faces is squeezed out and the highly loaded dry running seal fails.

The balanced seal has the same opening (face) area as the unbalanced seal, but the closing area has been reduced about the face area. Because force equals pressure times area, reducing the closing area reduces the closing force. Consequently, less heat is generated and the seal generally has a longer life.

To simplify the explanation, balancing mechanical seal involves a small design change which reduces the hydraulic forces acting to close the seal faces. Balanced seals have higher pressure limits, lower seal face loading, and generate less heat. They are better able to handle liquids with low lubricity and high vapour pressures. This would include light hydrocarbons. Because seal designs vary from manufacturer to manufacturer and from application to application, it is not possible to standardize on either configurations or materials that cover all conceivable services. Available basic designs have variations that were often developed to meet specific applications. Each seal design has its own strengths and weaknesses.

Nowadays most of the seal manufactures are used only balanced mechanical seal. In some special mechanical seals (ie., engineered seals) are designed with unbalanced mechanical seal.

Balanced mechanical seals are more preferred than unbalanced mechanical seals. Seal balance can range from 0.65 to 1.35, depending on operating conditions.

Mechanical seals with area ratio B≥1 are called unbalanced mechanical seals; mechanical seals with area ratio B<1 are called balanced mechanical seals.

The area ratio is equal to the ratio of the effective area of the sealing fluid A2 (internal type) or A1 (external type) to the sealing surface area Af, namely

For non-balanced mechanical seals with a sealing fluid area larger than the sealing surface area, the force on the sealing end surface increases as the pressure of the sealing fluid increases, so it is only suitable for low pressure.

In the balanced mechanical seal, the force on the sealing end changes little with the pressure of the sealing fluid, so it is suitable for high pressure.

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The mechanical seals markers are defined as a leak control device, which is found in circulating materials such as pumps and mixtures to prevent leakage of liquids and gases. Mechanical signals help to mark the rotating part of the shaft against the vertical part of the pump housing. Mechanical markers are widely used by various industries such as oil and gas, the chemical industry, and others.

The mechanical seal market is segmented on the basis of type, product type, industry, and region. As types of mechanical seal market arecartridge seals, unbalanced and balanced seals, non-pusher and pusher, conventional seals and others. Based on industry, it is categorized into metals & mining, oil & gas, aerospace, energy and power, food & beverage, marine, manufacturing & construction and others. The oil and gas industry became the largest market share in the mechanical seals industry and is expected to see significant growth during the coming years. In addition, the segment of the wastewater and water sector is believed to be growing rapidly by the coming years. On the basis of Product type, it is divided as Cartridge Seals, Split seals, Dry Gas Seal, Cassette Seals, Slurry Seals, Bellows Seals, Component Seals, Mixer Seals, Others. Based on segment region it is divided as North America, Asia-Pacific, LAMEA, Europe. The Asia-Pacific region is expected to continue its dominance over the forecast period. The region is a lucrative market worldwide due to emerging economies such as India and China.

COVID-19 Impact analysisCOVID-19 virus has closed the manufacturing of many products in the Mechanical Seals market accolade to the lockdown in worldwide. This has hampered the growth of Mechanical Seals market from the last few months and is likely to continue during 2021.

COVID-19 has so far impacted the sales of Mechanical Seals Market in the first 4 month of 2021 and is expected to create a negative effect on the growth of market all over the year.

By 2020, COVID-19 impact negatively on the Mechanical Seals Market, leading to a decline in shipping of Mechanical Seals products as well as revenue received from them. Due to which, the decline in market growth showed in the first half of 2020.

Industrial Seals companies rely heavily on the supply of raw materials, components and materials from different countries around the world. With so many governments limiting exports, manufacturers had to stop production due to a shortage of raw materials.

The CORONA epidemic has had a devastating effect on Mechanical Seals Market prices. India, US, China, and Japan have been hit hard by the epidemic, are playing a key role in the production of the Mechanical Seals Products that are being promoted worldwide. The agricultural, industrial, printing presses, conveyors, automobiles, motorcycles, telephone and bicycles which is expected to continue for a brief period due to land recession.

The dominant factors in the steady development of the mechanical seal market is the growing need for heat-resistant, strong, and thermal signals that allow for rapid power development between the two circular moving elements. Temperature is a key factor in this process which will cause heat-resistant seals during the weather. Factors such as increased productivity and providing full performance are reason of increasing demand in the production sector will also boost industrial seal market growth in the off-season. In addition, the growing trend in custom-made industrial brands going to open new opportunities for earning money during the monsoon season.

The mechanical seal market has shown significant growth over the time and is hoped to develop over time. The growth of development in industries in the emerging economy are hoped to trigger additional development and investment policies. The several types of seals available on the market offer cartoon markers, balanced and non-proportional markers, non-pusher and pusher markers, and common symbols that contribute to the growth of the marking market in developing countries.

The growth of the machinery industry is draining the entire market share, due to the use of power tools in compressors for sealing, centrifugal pumps and separating liquids in rotating barrels. Therefore, the increase in market need for mechanical seals in various industries are expected to drive market development soon. In addition, high market development is expected to be confirmed in Asia-Pacific, and after that North America.

Market TrendsIn May 2021, AESSEAL plc., They goes beyond Absolute Zero. AESSEAL seeks independent confirmation of its indirect release of Scope 3, as well as the measuring effect of the unauthorized release of the use of company products in the major industry. A separate test was performed on the Scope 3 release, which included indirect deductions from the company’s value chain such as business trips, as well as avoidances that were included in one of the company’s leading environmental programs.

A five-year partnership with Shell done by Flowserve Corporation, with the aim of providing standard services for their FLNG facility. A business partnership with Al-Ahed Trading and Contracting Co by John Crane with the aim of aiding service providers to achieve the first set of dry gas seals.

Key Benefits of the ReportThis study presents the analytical depiction of the Mechanical Seals Market along with the current trends and future estimations to determine the imminent investment pockets.

The report presents information related to key drivers, restraints, and opportunities along with detailed analysis of the Mechanical Seals Market share.

The report provides a detailed Mechanical Seals Market analysis based on competitive intensity and how the competition will take shape in coming years.

Key Market Players A.W. Chesterton Company, EagleBurgmann, AESSEAL plc., Flowserve Corporation, Flex-A-Seal, Inc., John Crane, Avon Seals Private Limited, TREM Engineering SC, PPC Mechanical Seals, Meccanotecnica Umbra S.p.A.

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