balanced vs unbalanced mechanical seal brands

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.

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.

Centrifugal pumps are one of the most extensively used pumps in municipal and complex industrial applications. However, a proper sealing arrangement is imperative for these pumps to prevent fluid leakage and protect the pump’s inside from contaminants in the atmosphere. Mechanical seals are preferred for sealing the pump as they require less maintenance and are much more durable than packing seals.

There are a variety of options in the market when it comes to mechanical seal systems. Before illustrating the types of mechanical seals for centrifugal pumps, here are four key considerations when choosing the appropriate seal system.

Consider the type of fluid that will be pumped and how it will affect the seal system design—factors such as lubricity, volatility, corrosive properties, and cleanliness matter the most.

Make a choice depending on the pressure exerted on the seal face. For instance, unbalanced seals are suitable for low-pressure applications, while balanced seals are appropriate in high-pressure conditions.

Temperature considerations will help determine whether you need to choose a pump with heat-sensitive components. For example, balanced seals sustain high temperatures better than their unbalanced counterparts.

These types of mechanical seals are typically low in cost and used for more generalized purposes. However, installing and adjusting standard component seals is time-consuming and requires a fair amount of operational skills. In addition, as they are composed of separate dynamic and stationary components, incorrect installation remains the major cause of errors.

Cartridge type mechanical seals are easy to install and ensure high performance. They are a one-piece unit incorporating all sealing components into a single assembly. Cartridge seals provide substantial maintenance advantages compared to other seal types while reducing installation time and the risk of assembly errors.

Pusher seals rotate along the shaft or sleeve to maintain contact with the faces of the seal to reduce wearing and wobbling caused by any misalignment. They are less expensive and come in different sizes and designs. The only drawback is that the elastomer is subject to wear.Non-pusher type seals maintain contact with the faces without rotating axially. They function under low temperatures and high pressures. However, the bellows used in these seals must be replaced frequently to work in corrosive environments.

Balanced mechanical seals work at high operational pressures while generating lesser heat. They are suitable for handling low lubrication liquids and high vapor pressure. Balanced seals increase seal life by reducing the closing force.Unbalanced mechanical seals are a more economical alternative that works for low/medium pressure applications. They are highly stable and still work in conditions where there are vibrations, shaft misalignments, or fluid cavitations.

All mechanical seals are hydraulically balanced to control the opening and closing forces on the seals rings. The measure of hydraulic balance is called balance ratio. A mechanical seal with a balance ratio of one or more is an unbalanced seal, whereas a seal with a balance ratio of less than one is a balanced seal.

The degree of hydraulic balance is determined by controlling the dimensions of the radially disposed areas of the seal rings. The balance ratio is the area of the seal face compared to the net hydraulic closing area.

An unbalanced seal typically has a balance ratio of around 1.2. In this case, the pressure on the seal face is 1.2 x the sealed pressure, plus the pressure created by the spring force. Therefore, the face pressure on an unbalanced seal is always greater than the pressure being sealed. For this reason, unbalanced seals are limited to a pressure of 10 barg and are used on relatively simple, low pressure applications.

A balanced seal typically has a balance ratio from 0.65 to 0.85, so that the seal face pressure is always less than the sealed pressure. This enables the seal to generate sufficient fluid film between the seal faces and therefore allows operation at high pressure.

Mechanical seals are critical components in centrifugal pump systems. These devices preserve the integrity of the pump systems by preventing fluid leaks and keeping contaminants out. Mechanical seal systems are used on various seal designs to detect leakage, control the seal environment and lubricate secondary seals.

Depending on the pump type and the process variables, there are various mechanical seal types to choose from. Each seal variant has its unique design and characteristics which make it suitable for a specific application. MES has years of experience with industrial mechanical seals and support systems, making us an authority in this area.

Mechanical seal types vary in design, arrangement, and how they disperse the hydraulic forces acting at their faces. The most common seal types include the following:

Balanced mechanical seal arrangements refer to a system where the forces acting at the seal faces are balanced. As a result of the lower face loading, there is more even lubrication of the seal faces and longer seal life. Learn about our mechanical seal lubrication systems today.

Balanced mechanical seals are particularly suited to higher operating pressures, typically above 200 PSIG. They are also a good choice when handling liquids with low lubricity and higher volatility.

Unbalanced mechanical seal types are commonly employed as a more economical option to the more complex balance seal. Unbalanced seals may also exhibit less product leakage due to tighter control of the face film, but as a result can exhibit much lower mean time between failure. Unbalanced seals are not recommended for high pressure or most hydrocarbon applications.

Pusher seals utilize one or multiple springs to maintain seal closing forces. The springs can be in the rotating or stationary element of the mechanical seal. Pusher type seals can provide sealing at very high pressures but have a drawback due to the elastomer under the primary seal face that can be subjected to wear as the face moves along the shaft/sleeve during operation.

Non-pusher seals utilize a metal or elastomeric bellows to maintain seal closing forces. These seals are ideally suited to dirty and high temperature applications. Bellows seals are limited to medium/lower pressure applications.

Conventional seals are typically lower cost and often installed on general service equipment. These seals require higher operator skill to service as they installed as individual components.

Cartridge type mechanical seals incorporate all of the seal elements into a single assembly. This dramatically reduces the potential for assembly error and the time require for seal replacements. Learn more about the difference between cartridge and non-cartridge mechanical seals today.

When deciding on the type of seal system for a centrifugal pump, operators must choose according to their unique application. Failure to select the proper seal type can lead to loss of pump integrity, breakdowns and costly repairs. To avoid these undesirable results, all operators must consider the following factors before deciding.

The amount of pressure exerted at a mechanical seal’s faces has a significant effect on its performance. If a pump is to be operated at low pressures, an unbalanced mechanical seal will be suitable. However, in conditions where higher pressures are anticipated, balanced seals will prove a more reliable solution.

Balanced mechanical seals perform better than their unbalanced counterparts in conditions where the operating temperatures are higher than normal. Heat sensitive components are better preserved in balanced mechanical seals compared to other seal types.

As it goes for all types of machinery, operator safety is the top priority. The use of double mechanical seals in centrifugal pumps provides additional protection as they have increased sealing capacity and are generally more reliable.

A. A balanced seal is a mechanical seal configuration in which the fluid closing forces on the seal faces have been modified through seal design. Seal balance, or balance ratio of a mechanical seal, is simply the ratio of two geometric areas. These areas are called the closing area (Ac) and the opening area (Ao). The closing area is different when pressure is on the outer diameter of the seal than when the pressure is on the inner diameter. When the pressure is on the outer diameter, the closing area is from the seal face outer diameter down to the lowest point, where the secondary seal rests against the shaft or sleeve. When the pressure is on the inner diameter, the closing area is from the highest point, where the secondary seal rests against the primary ring counter bore, down to the sleeve diameter.

The opening force is always the area of the sealing faces. The balance ratio is then Ac/Ao. A seal with a balance ratio less than 100 percent is called a balanced seal. A seal with a balance ratio greater than 100 percent is called an unbalanced seal. Most balanced seals have a balance ratio between 60 and 90 percent. Most unbalanced seals have a balance ratio between 110 and 160 percent.

Pusher seals normally require a step in the shaft/sleeve or internal hardware to achieve a balanced design. Metal bellows seals do not require this step. The balance diameter, or mean effective diameter (MED), of metal bellows seals is located near the middle of the convolution. When pressure is applied to the outer diameter of the seal, the MED shifts downward, lowering seal balance. The opposite is true when the seal is subject to internal pressure. The rate of change in the balance depends on the face width and the bellows leaflet design.

Pusher seals can be designed to withstand pressure from either direction. This is accomplished by trapping the O-ring between two diameters as shown in Figure 4.1. The cavity must be long enough to allow the O-ring to move, allowing pressure to act on the primary ring. These designs allow the seal to withstand system upsets.

Single Spring Balanced & Unbalanced SealOwing to our industrial expertise, we are able to manufacture, export and wholesale premium quality Single Spring Balanced & Unbalanced Seal. With an aim to ensure that offered unbalance seals are able to stand tall on the expectations of patrons, we manufacture these using best grade material. Along with this, we keep in mind industry set quality standards while manufacturing these unbalance seals. Prior to dispatch, we make these unbalance seals pass a quality check so as to ensure their flawlessness.

We are a prominent Industrial Balanced and Unbalanced Single Spring Seal. Clogging type applications. Torque Transmission from Retainer Shell to Dynamic Ring is done through Drive Lugs. GLOBE STAR Make Balance and Unbalance Single Spring Seals are Single Helical Coil Spring Seals Developed for clogging type applications.

Secondary Seal: U71 & B71 : Viton, EPDM, Silicon, Aflas, EPR, Kalrez, TCV, U76 & B76 : GFT, PTFE, FEP, Grafoil, Hardware : SS 316, SS 304, Hast - C, Monel, Alloy -20

Our organization is one of the prominent names in the market engaged in providing Inside Mounted Balanced and Unbalanced Single Spring Seal. These seals are of U71 &U76, B71 & B76 series and are Single Helical Coil Spring Seals. Provided seals are suitable for dirty media & clogging type applications. Drive lugs help torque transmission from retainer shell to dynamic ring. In these seals all the parts are fasten together through a snap ring that aid convenient installation & removal. All the parts can be changed from U71 to U76 & B71 to B76 by interchanging only the dynamic ring and the secondary seal.

We manufacturer U71 &U76 and B71 & B76 series of Slurry Seal. Contact with us to get the best deal of Slurry Seal. We also provide Slurry Seal on customized base.

We manufacture, supply and export the finest quality of single spring unbalance seals, for various industrial applications. The single spring unbalance seals are used mainly in dirty and congealing application. The seals are highly demanded for the anti abrasive applications. These seals are easy to install and operate for different application being used in various industries. These seals are compact in design for handling liquids of varying contamination including Slurries Sludge, sewage, Viscous and crystallizing Solution. These Seals are designed in both balanced and unbalanced version based on pressure parameters. Spring clogging does not occur in single spring seals. We are the manufacturer of pusher seal.

We are a highly esteemed General Purpose Multi Spring Unbalanced Seal. Their Compact Design permits their use in all types of Centrifugal Pumps. All Components are held together by a Snap Ring that helps in easier installation & removal. this kind is widely used in various industries for different applications such as rotating equipment, pumps, mixers, agitators and compressors.

Since failure of the mechanical seal on the shaft is the number one cause of pump shutting down, it is important to know the standard terms of the world of mechanical seals.

Mechanical seals are comparable to precision instruments. These seals use margins with many decimal places. The mechanical seal life depends on many factors, and it can vary from a few intense minutes to many trouble-free years. In general it can be stated that: the more attention paid to the mechanical seal and related equipment, the longer they will last.

Years ago, packing materials such as stuffing box packing were used for most shaft seals. These types of shaft seals required a fair amount of leakage to keep the packing properly lubricated and cooled. Until 1915 the mechanical seal was invented. This shaft seal managed to keep the fluid in by using two incredibly flat surfaces (one that rotates with the shaft, and one stationary in the housing). Despite the fact that these treads also need a little bit of ‘leakage’ to create a hydrodynamic layer, this is often not noticeable as this liquid evaporates. Most pumps today have mechanical seals. However, because the parts and surfaces are so delicate, it is also the number one cause of pump failure. This requires a better understanding of this type of seal and its application.

A set of (very flat lapped) treads as primary seal: the minimum distance between these treads, which are perpendicular to the shaft, minimizes the leakage. Often two different materials are used as the tread, a harder and a softer material, to prevent the materials from sticking together. One of the treads is often anti-friction corrosion material such as carbon graphite. A relatively hard material such as silicon carbide (SiC) or ceramic alumina is often used for the other tread. However, when processing abrasive substances, two hard surfaces are normally used.A tread is mounted stationary in a house.

Mechanical seals require a fluid to maintain lubrication. The running surfaces are usually lubricated by a very thin layer of liquid (or gas) between the two running surfaces. Lubrication can also come from another fluid other than the product, depending on the seal requirements.

Pusher seals use a secondary seal that moves axially along the shaft or shaft sleeve to maintain pressure on the running surfaces. This allows the seal to compensate for wear and any less accurate shaft alignment. The advantage is that this seal type is the cheapest. The main disadvantage of this configuration is that the secondary seal can gall on the shaft or shaft sleeve, especially when processing abrasive product.

This is the category in which the bellow seals fall. These seals do not use a secondary seal that must be able to move along the shaft or shaft sleeve to maintain contact. The secondary seals do not move with this type of seal under any circumstances, not even during use. The tread wear is compensated for by an elastomer or metal bellows. A disadvantage of this type of seal is the higher cost price of the seal and that a larger seal must be used in a corrosive environment because the material of the bellows is otherwise too thin.

We speak of a balanced seal if the pressure on the running surfaces caused by the pressure in the system is taken into account. It may sound crazy if the goal is to achieve shaft seal, but a mechanical seal must leak! After all, the running surfaces of the primary seal must be lubricated with the pumped product. When the pressure on the product side exceeds approximately 250 psid, the pressure on the treads can increase to such an extent that no liquid film can form between the surfaces. The lack of lubricating film will cause the seals to wear out very quickly.

To overcome this problem, the balanced seal was introduced in 1938. With a balanced mechanical seal, high pressure is taken into account by adjusting the surface of the tread, which distributes the stuffing box pressure over a larger surface. Balanced seals are easy to recognize, there is a step in the shaft sleeve and/or the running surface. Incidentally, this works a bit more complicated with a metal bellow, but the principle remains the same. Mechanical seals can also be designed to balance for overpressure on both sides of the tread assembly.

Cartridge seals consist of a pre-mounted mechanical seal on a shaft sleeve that can be installed as a whole over the shaft or shaft sleeve. Cartridge seals are very easy to install and the chance of short service life due to suboptimal installation is less probable. It should come as no surprise that cartridge seals are a lot more expensive than the previously discussed seals. On the other hand, there are lower maintenance costs. Incidentally, it is not always possible to apply a cartridge seal if, for example, there is no space in the house.

Historically, centrifugal pumps have usually been designed with packing seals. Packing seals are packed with a lubricated fibrous material that came into direct contact with the shaft, so flush water is necessary to cool and lubricate the shaft. Flush water has to be directed away from the process to prevent contamination, and care has to be taken to protect the bearing box from flush water that contaminates the oil, as well as to prevent the safety problem of water pooling on the floor.

Mechanical seals may have a higher initial cost, but they often save a great deal of operational cost depending on how much flush water a packing seal pump consumes.

Balanced Seals have a system where forces acting on both faces are balanced, so there is more even lubrication of seal faces. Balanced seals have a higher cost than unbalanced seals, and they tend to last longer. Unbalanced seals show less leakage and are more inexpensive, but they have a lower mean time between failures and are not recommended for high pressure applications.

Pusher seals use one or more springs to maintain sealing forces, while non-pusher seals use elastomeric or metal bellows. Pusher seals can be used at very high pressure applications, but they have an elastomeric seal that can wear. Non-pusher seals are ideal for medium/low pressure and high temperature or dirty applications.

Conventional mechanical seals are installed as components. Cartridge seals have all the seal elements contained within a single assembly, so they are quick to install and reduce the chance of installation errors.

Many industrial processes still use a packing seal for positive displacement pump applications. Packing seals, which are designed to allow some controlled leakage, can be a reliable method of preventing excessive leaks. However, stricter standards in industries like food processing are reducing the amount of acceptable leakage.

Here you know more about manufacturer balanced and unbalanced mechanical seals. Read the Many types of Mechanical Seals for the Unbalanced Seals and Balanced Seals.