balanced vs unbalanced mechanical seal for sale

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.

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.

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.

 Here we describe the difference between a balanced and unbalanced mechanical seal. The mechanical seal is the most important and most used part. If you check its specification and type, then it can be classified into balanced and unbalanced mechanical seals.

 Before we check their difference, let’s understand what mechanical seal balance is first. It is the load that acts across the seal faces. This load between the seal faces should be optimum.

 If the load is exceptionally high, then the liquid film gets oozed out. When it vaporizes, it causes unstable conditions. Because of the thermos-electrical instability, there is high wear and tear on the sealing surface.

When the seal is balanced, it avoids this situation and leads to reduce energy consumption. It extends the life of the seal. The pressure in a stuffing box is applied equally in all directions. This pressure keeps the primary ring stable against the mating or rotating ring.

The face area or opening area of a balanced seal is the same as an unbalanced seal. But the closing area is maintained in proportion to the face area. When the closing area reduces, the closing force also reduces proportionately. Thus, less heat is generated, and the seal has an extended life.

A crucial step in preventative maintenance in pumps is finding and using the correct seal for the job. Mechanical seals are used to seal the rotating shaft in pumps and other equipment. With so many mechanical seal designs on the market, it can be difficult to identify which kinds to use. A.W. Chesterton Company’s mechanical seal design utilizes 5 design principles to maximize its sealing capabilities. These principles have been refined by Chesterton since the company brought its first mechanical seal to market in 1970. After all the lessons learned from successes and failures, they have determined the Five Key Features that a mechanical seal should have to reduce unplanned maintenance and downtime. To provide the greatest mean time between failures (MTBF) and avoid downtime, they utilize these five design principles in their sealing devices.

Typically, within early mechanical seal designs, the springs were submerged within the fluid. However, this can lead to trouble when fluids with dirt or other contaminates interact with the springs. When the contaminates collect within the spring, it cannot correctly maintain the alignment necessary for a complete seal. Chesterton’s mechanical seal design protects the springs within the mechanical seal from the fluids being pumped.

The second design feature and open secret of Chesterton’s mechanical seal design is balance. On the mechanical seal, there are two main sides, the fluid side, and the atmospheric side. To prevent moisture from leaking out of the seal, both sides put equal pressure on each other to trap the fluid. Many seals will often see that the fluid side exerts greater pressure than the atmospheric side. Not only does this reduce the quality of the seal, but it can also ruin the pump with time. Balanced seals reduce the seal ring area on which the hydraulic pressure of the liquid in the pump acts. This allows for better lubrication that results in lower heat generation, face wear, and power consumption. Balanced seals will generally have higher pressure ratings than unbalanced seals.

Fretting on a pump shaft refers to the way that a material is worn away on a shaft by an elastomeric material. An example may be a 316 stainless steel shaft sleeve that is damaged by a Viton O-ring. Stainless steel protects a shaft from corrosion by forming a chrome oxide layer on the surface.  The dynamic O-ring wears that protective surface away and it then reforms.  Over time the chrome oxide gets imbedded into the O-ring and works like sandpaper removing even more material.  The result is a groove worn into your expensive sleeve and a leaking mechanical seal. Chesterton seals utilize designs that have any dynamic O-rings operating against a non-metallic surface, usually the sacrificial face.

Additionally, some manufacturers offer seals that are self-fretting, rather than shaft-fretting. What this means is that these seals do not fret or damage the shaft, they harm seal itself. While this protects the pumps, the O-rings still work against metal, reducing the lifespan of the seal itself.

Some mechanical seal designs utilize an inserted seal face, typically made of carbon or graphite inserted into a metal holder. However, the disadvantage to this technique is these non-metallic materials often react to heat differently than the metal of the seal. The result is the face of the seal is easily deformed- leading to leaks and early replacement of the seal. Proper mechanical seal design uses monolithic seal faces without using a holder and inserted face. By using Finite Element Analysis (computer modeling), Chesterton’s monolithic seal face designs are made more efficiently than ever.

Mechanical seals can either use rotating or stationary springs. 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 so this alignment cannot be assured. To compensate for the misalignment, the springs must adjust each time the shaft rotates to keep the seal faces closed. At motor speeds this adjustment happens thousands of times per minute (for 1800 rpm, 3600 adjustments occur) which is not only difficult to accomplish, the springs will fatigue and fail causing seal failure.  Rotary seals are simple in design which makes them inexpensive

In contrast, a stationary seal is 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 the rotation of the shaft or how fast the shaft rotates. The springs do not need to correct or adjust with each rotation; they adjust for misalignment only once when installed. Chesterton uses this as the fifth design requirement, and this provides greater life to their mechanical seals.

Using these five design principles, Chesterton has updated its 150 seals to the new 1510 seal. The new design uses a monolithic seal face and changes where the dynamic O-rings are placed to be a non-fretting seal. Chesterton unveiled this updated seal in the US in September of 2022. However, Chesterton also has one additional add-on for this new seal. Starting at the end of October 2022, Chesterton will be releasing the 1510L. The 1510L has all the same design capabilities of the 1510, the difference between the two is the installation process. The 1510L utilizes a lock ring mechanism to simplify installation requiring the installer to tighten only one screw to connect the seal to the shaft.

To request a demonstration for the 1510L mechanical seal, click here. Learn more about Northwest Pump’s mechanical seals by contacting us here, emailing us at sales@nwpump.com, or by calling 1-800-452-PUMP.

For service on your mechanical seals by our Chesterton certified pump technicians, contact us here, email us at service@nwpump.com, or call 1-866-577-2755.

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.

This seal has been designed in compliance with DIN 24960/EN12756 standards and can be used in a wide range of applications, in particular in cases in which the fluids are not particularly viscous or have a tendency to solidify. In the HS version is a balanced seal can withstand pressures of up to 40 bar. For extreme applications it may be possible to modify the stated specifications.

The seal has been subject to continuous development over time, enhancing its robustness and reliability which have significantly improved the positive drive on the rotary seal, which is in most cases solid.

The difference from the single spring seal is that the multi-spring feature has a greater response to stress and a more uniform distribution of the load.

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 mechanical 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.

It is important to think about the mechanical seal in terms of its total lifetime costs – not so much by its initial cost. Start a reliability program that defines the cost of failure and justify it by increasing the mechanical seal’s mean time between failures.

These series are internal mounted single spring unbalanced/balanced Mechanical Seals suitable for wide service applications. It is independent of direction of rotation, these seals driven by drive ring or drive collar, rotary is driven by the motion transmitted by shaft to spring, seals are having easy fitment & pushed with drive ring or drive collar support. As all parts are Interchangeable,