How to Use Mechanical Seals in Practical Usage

Mechanical seals can operate for many years without issue, as long as they’ve been properly selected for their application. One must identify the application data (or operating conditions) to properly select the type of seal and materials of construction to ensure maximum performance from the seal over its lifetime. Below we define the operating conditions and discuss what material characteristics to consider for preventing improper material selection.

**Please note: There are many things to evaluate when selecting a seal, so be sure to speak with an experienced engineer before your final selection is made.

LIQUID

Identifying the exact liquid being handled is the first step in the seal selection process. Seal material must be able to withstand the fluid being processed. All seal materials must be chemically compatible with the fluid, or there is an increased risk of seal failure.

PRESSURE

Pressure in the seal chamber and seal size determines the type of seal required, balanced or unbalanced.

TEMPERATURE

Seal materials must be selected to appropriately handle the liquid’s temperature. Temperature is important because different seal materials are rated for certain termperatures and you should not exceed the temperature limit of these materials.

LIQUID CHARACTERISTICS

Knowing the viscosity of the liquid is important to ensure appropriate seal life. Abrasive liquids can create excessive wear and will ultimately shorten the seal’s life. Double seals or use of an external flush plan give operator’s the option to use mechanical seals on these difficult fluids.

RELIABILITY & EMISSION CONCERNS

Every company has their own standards and operating procedures when it comes to reliability and emission concerns for an application. The seal type and arrangement selected must meet the desired reliability and emission standards for the pump application. Since environmental safety has become a hot topic among manufacturing companies, double seals are peaking as the solution of choice.

After understanding the seal’s exact operating conditions, you can select the seal’s overall construction material and its face and component materials. When selecting the seal’s material of construction, be sure to consider the following characterstics of the material:

• Temperature constraints
• Chemical resistance properties
• Flexibility
• Wear resistance
• Thermal expansion and conductivity properties

And, when selecting the face and other component materials for the seal, consider these material characteristics:

• Wear resistance
• Low leakage & friction properties
• Good thermal properties
• Corrosion resistant

For more information on elastomer guidelines and compatibility for metals and typical face materials, check out the resources below:

As you work with your local seal supplier, remember that a mechanical seal recommendation is not complete without a seal support plan, such as a seal flush piping plan. And, if you are new to mechanical seals and are considering making the switch from packing to the mechanical seal, read more about it on our blog, Understanding the Basics of Mechanical Seals vs. Packing.

Recently we received a call from a customer. He was attempting to install a mechanical seal and had broken two of them. After a short discussion with one of our service technicians, it became clear that the customer was demonstrating a classic example of how to kill a mechanical seal, not using the correct lubricant.

When I heard about this, I asked the service technician to tell me more. I asked him to share with me the top 5 ways he has seen mechanical seals go down due to installation. He did not disappoint.

1. Not following the installation instructions

Mechanical seals are easily damaged during installation. That’s why it’s imperative to read the installation instructions carefully before attempting to install the seal. See photo here. The installation instructions stated to remove the spacers before starting the unit. The spacer became lodged in the seal, damaging internal components.

2. Install on a misaligned pump

Pump misalignment is caused by pipe strain, deflection during a hard start, shaft run out, or a myriad of other scenarios. Misalignment puts undue stress on mechanical seal components, causing them to not function properly, wear prematurely, and potentially fail.

Be sure to follow proper installation guidelines and use laser alignment tools to ensure the pump (and ultimately the mechanical seal!) is set up for success.

3. Lack of or wrong lubrication on shaft

Lubrication is necessary for proper mechanical seal installation. Lack thereof can damage o-rings or rubber bellows on the seal, causing them to tear, or roll. There are many options available, from petroleum jelly, to silicon grease, to special lubricants. Always check the installation instructions to ensure the lubrication you choose is compatible with seal components and the product pumped.

4. Dirty work surface/hands

Dirt on the seal face, even oil from finger prints, can set a mechanical seal up to fail. Tiny particles can create wear and destroy seal faces, causing leakage.

Ensure proper handling during installation by following these tips:

1. Don’t unpack the seal until ready to install
2. Wash hands
3. Avoid touching or handling lapped seal faces
4. Use clean tissue paper on workbench to prevent contamination
5. Don’t set the seal down on its face
6. Clean faces with soft tissue and approved solvent before putting them together on the equipment

5. Uneven or over-tightening of fasteners

This is probably one of the most common mistakes. Over-tightening fasteners can cause seal components to become distorted and leak. Oftentimes when a seal starts to leak, the natural reaction is to tighten even further! Unfortunately this just exacerbates the problem. Instead, try loosening a bit, the problem may correct itself, if the internals haven’t broken already from mechanical shock.

After reviewing this list of 5 ways to kill a mechanical seal, the service technician I worked with on this said he could come up with many more ways. Maybe that will be a follow up post. How have you seen a mechanical seal go down? Let me know in the comments!

Not sure why your mechanical seal is failing? Ask us about it! We gladly provide technical assistance to businesses and municipalities in Wisconsin and upper Michigan.

Thinking of making the switch from conventional packing to mechanical seals? There’s a lot of upside to doing so. Mechanical seals can save maintenance people an immense amount of time and money, but only if they’re installed correctly and properly cared for. Read on for a basic understanding of mechanical seals, and how they differ from packing.

WHY DO PUMPS NEED TO BE SEALED?

In order to understand why pumps need to be sealed, let’s go back to some pumping basics and review how a centrifugal pump operates.

Fluid enters a centrifugal pump through the suction nozzle at the center of a rotating impeller. As the impeller rotates, its vanes fill with fluid, then force it out to the pump casing where it exits the pump through the discharge nozzle.

Unfortunately, the discharge pressure will force fluid back behind the impeller, where it attempts to exit by way of the rotating drive shaft. Attempts have been made by pump manufacturers to minimize this leakage through design, but the leakage won’t be stopped entirely. Some form of sealing method must be put in place to minimize the leakage.

USING PACKING AS A SEAL

Packing materials were originally the sealing method of choice, using soft, flexible materials. Today’s packings come in a wide variety of choices, with something for nearly every application. It’s still a very popular method of sealing pumps because of its low upfront cost, easy installation, and readily available materials. However, it can be a very costly venture over time as they require more maintenance, and also allow more product loss than mechanical seals.

USING MECHANICAL SEALS

The biggest benefit of using mechanical seals is the drastic reduction in leakage. (Here’s an example where a paper mill replaced packing with a mechanical seal to stop leakage.) That reduction in leakage also has an effect on a number of other things as well. Things like a safer work environment without a wet floor, fewer bearing failures caused by leaking fluid, no excessive wear on the shaft sleeve damage from packing (see photo).

The maintenance department also sees a savings in time and budget. No more adjusting or replacing packing.

But before you jump into changing all your packing to mechanical seals, make sure you talk to someone who knows about them. Mechanical seals are complicated pieces of equipment, with a wide variety of materials and configurations to choose from, be sure that what you invest in is exactly what you need for your application.

Thinking of making the switch from packing to mechanical seals? Or have a current problem with a mechanical seal? Ask us about it! We gladly provide technical assistance to businesses in Wisconsin and Upper Michigan.

Learn more about the relationship between mechanical seals and pumps in our eBook!

WHY TO USE MECHANICAL SEALS?

Major advantages of using Mechanical seal are as follows:

• No visible leaks
• No shaft/sleeve wear
• Less maintenance required
• Less power consumption
• Less bearing wear
• Less corrosion of equipment
• Pressure and vacuum
• Shaft speed
• Flushing water etc
• Vertical pumps
• Less wasted product
• Downtime is greatly reduced
• Long life

HOW A SEAL WORKS?

Fig. 1: Working of Mechanical Seals

Refer Fig. 1. The lapped face of a mechanically loaded rotating component (sealed to the shaft) rubs against the lapped face of a fixed component (sealed in a housing). Sealing is achieved across the seal faces because of their incredible degree of flatness. The faces are initially held together by a mechanical load applied to those faces.

Evaporation & Solids Formation (Fig. 2):

Fig. 2: Evaporation & Solids Formation

THE KEY TO SUCCESS IS “Maintaining A Stable Fluid Film”

Fluid Film & Seal Faces (Fig. 3):

Fig. 3: Fluid Film & Seal Faces

Mechanical Seal Technology:

Face Flatness / Lapping-The primary seal is the basis of all mechanical seal design. This seal consists of two flat faces, one fixed, one rotating, and running against each other, with a liquid film between them providing lubrication.

The width or thickness of the lubricating film is dependent upon a number of variables but the distance between the two faces is constant in that this has the greatest influence, the closer these are together, the thinner the fluid film and the least likelihood of leakage across the faces.

It therefore follows that the flatter these surfaces are within practical manufacturing constraints, the better.

The process of achieving face flatness adopted by the mechanical seal industry is called lapping.

In this process a lapping machine is used, which provides one or a number of rotating ‘plates’ on to which the face or seat of a mechanical seal is placed. The surface to be finished is in contact with the lapping plate.

Following lapping the workpiece surface is then polished to a reflective finish. Final surface finish must be polished to a degree of light reflection, sufficient for its flatness to be checked.

Final surface finish must be polished to a degree of light reflection, sufficient for its flatness to be checked.

The degree of face flatness is checked by what is known as the optical interference fringe method.

Here an optical flat (a quartz or Pyrex disc, with surfaces finished to within 0.000001/0.000005-0.025/0.125 microns) is placed over the lapped and polished face and placed under a helium light source, from this a pattern of fringe interference is produced.

This pattern is then translated into a measurement of flatness by comparison of the pattern obtained with various patterns (usually in chart form) which indicate the flatness accuracy.

Fig. 4 & Fig. 5

Figure 4 shows a helium light source (wave length approximately 0.0006mm/0.00002) hitting the optical flat (A) it then passes through the optical flat. When it reaches the other side, some is reflected (Point B) and the rest reflects from the specimen (Point C). When the light hits the optical flat again (Point D) it passes back through the optical flat. The two reflections (E and F) can then be observed from above the optical flat.

Flatness is measured in light bands, one light band = 0.000011 or 0.0003mm. There are 85 light bands to one thousand (0.001) of an inch.

Small diameter seal faces ( 4” Diameter) faces less than five light bands.

The additional sheet shows how face patterns are interpreted, the process is similar to reading the contours on a map.

Figure 5 shows a typically flat surface, a series of straight, parallel equi-shaped lines shows that a face is flat to within one light band.

Seal Faces under a Microscope (Fig. 6):

Fig. 6: Seal Faces under a Microscope

Fluid Film Condition Relates To:

• Fluid Viscosity
• Face Closing force
• Surface Finish
• Surface Speed
• Contract Face Parallelism

WHAT HAPPENS WHEN A SEAL RUNS (Fig. 7)?

Fig. 7: What Happens when a Seal Runs

FLUID FILM:

Think about Bearings!

Seals & bearings are both lubricated by a hydrodynamic fluid film

FLUID FILM PROVIDES LUBRICATION

• Prevents Dry Face Contact
• Frictional Heat Build Up
• Solids Contamination

WHAT CAN HAPPEN?

• Dry Face Contact / Dry Running
• Excessive Wear
• Frictional Heat Build Up
• Solids Contamination

Fig. 8: What can Happen?

CONCERNS WITH HEAT:

• Product Vaporisation
• Corrosion Rate Increase
• Damage to Components
• Product Vaporization / Corrosion Rate Increase
• Change in State of Fluid Film / Solids Deposition
• Reduction / Loss of Fluid Film …………..SEAL FACES RUB AGAINST EACH OTHER…HEAT GENERATED! THIS HEAT MUST BE REMOVED…

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I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

One thought on “ Mechanical Seals for Rotary Pumps ”

This a very good illustration of mechanical seals.
It’s like a crash course for anybody who is starting to know about mechanical seals.
A valuable effort was put in this article.

Technology is always moving forward, but some things stand the test of time.

One of those things is the O-Ring, which was first patented in 1896. What is an O-Ring? It’s a doughnut-shaped loop designed to prevent the passage of liquids or gases. It’s one of the simplest precision mechanical pieces ever produced, and continue to be one of the most widely-utilized sealing products.

O-Rings can be made from plastic or metal, but for the purposes of our blog, we’ll focus solely on rubber – or elastomeric — O-Ring design.

An O-Ring, also known as a “torus,” works in tandem with the glands in which they are installed. The gland is normally cut from the metallic hardware, and works with the O-Ring to seal. The gland and the O-Ring must be designed together to insure top performance.

How does an O-Ring seal?

Seals prevent fluids from escaping through the gaps in mating pieces of hardware. The O-Ring sits in the middle of a gland when it’s at rest, but as pressure begins to rise in the sealing system, the O-Ring shifts to the opposite side of the pressure.

Because the material is soft, the O-Ring is mechanically squeezed to plug the hole between the two mating hardware pieces.

Limitations of O-Ring use

“Although it has been stated that O-Rings offer a reasonable approach to the ideal hydraulic seal, they should not be considered an immediate solution to all sealing problems.”

That was D.R. Pearl of the United Aircraft Corp. in 1947, in a paper presented at the S.A.E. annual meeting.

Pearl wrote those words almost 70 years ago, but distinct limitations remain for using O-Rings as a primary seal. These limitations include:

• Rotary speeds above 1,500 feet per minute
• Improper mating hardware design
• Incompatible temperature, pressure and fluid chemical compatibility

To learn more about applications where O-Rings will perform, download our detailed guide to O-Rings. This 36-page document deals with O-Rings’ technical performance characteristics, materials, chemical and temperature compatibility, hardware considerations and failure modes.

What is a pump shaft seal?

Shaft seals prevent liquid escaping from a rotating or reciprocating shaft. This is important for all pumps and in the case of centrifugal pumps several sealing options will be available: packings, lip seals, and all types of mechanical seals – single, double and tandem including cartridge seals. Rotary positive displacement pumps like gear pumps and vane pumps are available with packing, lip and mechanical seal arrangements. Reciprocating pumps pose different sealing problems and usually rely on lip seals or packings. Some designs, such as magnetic drive pumps, diaphragm pumps or peristaltic pumps, do not require shaft seals. These so-called ‘sealless’ pumps include stationary seals to prevent liquid leakage.

What are the main types of pump shaft seals?

Packing

Packing (also known as shaft packing or gland packing) consists of a soft material, which is often braided or formed into rings. This is pressed into a chamber around the drive shaft called the stuffing box to create a seal (Figure 1). Normally, compression is applied axially to the packing but it can also be applied radially by a hydraulic medium.

Traditionally, packing was made from leather, rope or flax but now usually consists of inert materials such as expanded PTFE, compressed graphite, and granulated elastomers. Packing is economical and commonly used for thick, difficult-to-seal liquids such as resins, tar or adhesives. However, it is a poor sealing method for thin liquids, especially at higher pressures. Packing seldom fails catastrophically, and it can be replaced quickly during scheduled shutdowns.

Packing seals require lubrication to avoid the build-up of frictional heat. This is usually provided by the pumped liquid itself which tends to leak slightly through the packing material. This can be messy and in the case of corrosive, flammable, or toxic liquids is often unacceptable. In these cases a safe, external lubricant may be applied. Packing is unsuitable for sealing pumps used for liquids containing abrasive particulates. Solids can become embedded in the packing material and this may then damage the pump shaft or stuffing box wall.

Lip seals

Lip Seals, also known as radial shaft seals, are simply circular elastomeric elements which are held in place against the drive shaft by a rigid outer housing (Figure 2). The seal arises from the frictional contact between the ‘lip’ and shaft and this is often reinforced by a spring. Lip seals are common throughout the hydraulic industry and can be found on pumps, hydraulic motors, and actuators. They often provide a secondary, backup seal for other sealing systems such as mechanical seals. Lip seals are generally limited to low pressures and are also poor for thin, non-lubricating liquids. Multiple lip seal systems have been applied successfully against a variety of viscous, non-abrasive liquids. Lip seals are not suitable for use with any abrasive liquids or fluids containing solids as they are susceptible to wear and any slight damage can lead to failure.

Mechanical seals

Mechanical seals essentially consist of one or more pairs of optically flat, highly polished faces, one stationary in the housing and one rotating, connected to the drive shaft (Figure 3). The faces require lubrication, either by the pumped liquid itself or by a barrier fluid. In effect, the seal faces are only in contact when the pump is at rest. During use, the lubricating liquid provides a thin, hydrodynamic film between the opposing seal faces, reducing wear and aiding heat dissipation.

Mechanical seals can handle a wide range of liquids, viscosities, pressures, and temperatures. However, a mechanical seal should not be run dry. A key advantage of mechanical seal systems is that the drive shaft and casing are not part of the sealing mechanism (as is the case with packing and lip seals) and are not therefore subject to wear.

Double seals

Double seals utilise two mechanical seals positioned back to back (Figure 4). The space internal to the two sets of seal faces can be hydraulically pressurised with a barrier liquid so that the film on the seal faces necessary for lubrication will be the barrier liquid and not the medium being pumped. The barrier liquid must also be compatible with the pumped medium. Double seals are more complex to operate because of the need for pressurisation and are typically used only when it is necessary to protect personnel, external components and the surrounding environment from hazardous, toxic or flammable liquids.

Tandem seals

Tandem seals are similar to double seals but the two sets of mechanical seals face in the same direction rather than back-to-back. Only the product-side seal rotates in the pumped fluid but seepage across the seal faces eventually contaminates the barrier lubricant. This has consequences for the atmospheric side seal and surrounding environment.

Cartridge seals

A cartridge seal is a pre-assembled package of mechanical seal components. Cartridge construction eliminates installation issues such as the need to measure and set spring compression. Seal faces are also protected from damage during installation. In design, a cartridge seal can be a single, double or tandem configuration contained within a gland and built onto a sleeve.

Gas barrier seals

These are cartridge-style dual seats with faces designed to be pressurised using an inert gas as a barrier, replacing the traditional lubricating liquid. Seal faces may be separated or held in loose contact during operation by adjusting the gas pressure. A small amount of gas may escape into the product and atmosphere.

Summary

Shaft seals prevent liquid escaping from a pump’s rotating or reciprocating shaft. Often several sealing options will be available: packings, lip seals, and various types of mechanical seals – single, double and tandem including cartridge seals.

Book • Sixth Edition • 2014

Book • Sixth Edition • 2014

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About the book

Description

Seals and Sealing Handbook, 6th Edition provides comprehensive coverage of sealing technology, bringing together information on all aspects of this area to enable you to make the right sealing choice. This includes detailed coverage on the seals applicable to static, rotary and reciprocating applications, the best materials to use in your sealing systems, and the legislature and regulations that may impact your sealing choices.

Updated in line with current trends this updated reference provides the theory necessary for you to select the most appropriate seals for the job and with its ‘Failure Guide’, the factors to consider should anything go wrong. Building on the practical, stepped approach of its predecessor, Seals and Sealing Handbook, 6th Edition remains an essential reference for any engineer or designer who uses seals in their work.

Seals and Sealing Handbook, 6th Edition provides comprehensive coverage of sealing technology, bringing together information on all aspects of this area to enable you to make the right sealing choice. This includes detailed coverage on the seals applicable to static, rotary and reciprocating applications, the best materials to use in your sealing systems, and the legislature and regulations that may impact your sealing choices.

Updated in line with current trends this updated reference provides the theory necessary for you to select the most appropriate seals for the job and with its ‘Failure Guide’, the factors to consider should anything go wrong. Building on the practical, stepped approach of its predecessor, Seals and Sealing Handbook, 6th Edition remains an essential reference for any engineer or designer who uses seals in their work.

Designs, Application, Selection, Installation, Troubleshooting and Maintenance

Introduction

This Mechanical Seals is an intensive, highly practical, and useful five-day online training course. The participant will gain up-to-date information and practical understanding of the basics, applications, troubleshooting and failure diagnosis, installation, and maintenance of mechanical seal. Mechanical seal for pump and compressor applications will be addressed. Recent design like dry mechanical seal will also be addressed.

The highlights of this online training course are as follows:

• Lubrication and sealing concepts
• Mechanical Seal and Dry Gas Seal design
• Different arrangements of mechanical seals
• Optimal selection of seals and flush plans
• Failure diagnosis and troubleshooting

Objectives

At the end of this GLOMACS online training course, participants will:

• Understand the different types of seals
• Have learned about selection, operation, and maintenance strategies
• Be able to troubleshoot seal problems
• Understand how seals are fitted
• Understand how seals are tested
• Understand API flush plans

Training Methodology

This online training course will utilize a variety of proven online learning techniques to ensure maximum understanding, comprehension, retention of the information presented. The training course is conducted Online via an Advanced Virtual Learning Platform in the comfort of any location of your choice.

Organisational Impact

On completion of this GLOMACS online training course, the delegate will be able to critically analyse the methodologies employed within the organisation and instigate improvements where required.

The knowledge gained in this Mechanical Seals online course will:

• Enable the delegate to optimize the operation and maintenance of various types of pumps & compressors
• Give the delegate confidence to carry out failure analyses on seals thereby avoiding repetitive failures
• Improve seal operating and maintenance techniques
• Enable measures to quantify equipment condition
• Give better control of mechanical seal providers
• Enable better identification and specification of new and replacement seals
• Allow tighter control of maintenance budgets by the avoidance of unplanned equipment failures in service

Personal Impact

• Improved confidence when dealing with suppliers and contractors
• Better understanding of how manufacturers design and develop mechanical seals for environments
• Better control of the management of pumps and compressor maintenance and operation
• Improved personal knowledge of sealing systems
• Better ability to troubleshoot seal problems and avoid recurrence
• Confidence and ability to select the appropriate flush plan thereby improving reliability and personal profile to senior management

Who Should Attend?

This GLOMACS online training course is directed towards:

• Supervisors
• Team Leaders in Maintenance, Engineering and Production

This online course on Mechanical Seals will also benefit anyone who wishes to update themselves on Maintenance Engineering Technologies, judge the suitability of these technologies for their needs, and learn how to implement them for the benefit of their organisations.

DAY 1

Basic Concepts of Fluid Sealing

• Role of tribology, leak rates, heat transfer, design considerations, materials, application to mechanical seal
• Lubrication fundamentals
• Basic fluid mechanics, Reynolds equation, lubrication solutions, application to mechanical seal

DAY 2

Mechanical Seal Design

• Theoretical aspects and design
• Factors affecting design
• Materials of construction
• Mechanical seal selection
• Data requirements for seal selection
• Seal type selection
• Selection of the primary seal
• Selection of the seal arrangement

DAY 3

Mechanical Seals Configurations

• Mechanical seal applications
• Seals Classification
• Wet mechanical seal
• Dry mechanical seal
• Balanced and unbalanced mechanical seals
• Mechanical seals pump considerations
• Mechanical seals compressor considerations
• Mechanical seals troubleshooting

DAY 4

Failure Diagnosis

• External symptoms of seal failure
• Visual seal examination
• Common seal failure modes-seal faces
• Common seal failure modes-secondary seals
• Common seal failure modes-seal hardware
• Seal installation tolerances
• Vibration effect on a mechanical seal
• High temperature effect
• Running speed effect
• Rotor balance effect

Mechanical Seal Operation

• Operating limits
• Operating conditions

DAY 5

Mechanical Seal Performance

• Acceptable performance
• Mechanical seal related standards
• Pre-installation machine checks
• Mechanical seal installation
• Mechanical seal maintenance
• Seal handling and inspection

Testing and Verification of Mechanical Seals

• Degree of testing
• Type of test

• On successful completion of this online training course, GLOMACS E-Certificate with eligible Continuing Professional Education credits (CPE) from National Registry of CPE Sponsor, will be awarded to the delegates
• Continuing Professional Education (CPE) credits : In accordance with the standards of the National Registry of CPE Sponsor, one CPE credit is granted per 50 minutes of attendance

Endorsed Education Provider

In Association With

PetroKnowledge

Our collaboration with Petroknowledge aims to provide the best training services and benefits for our valued clients

Oil seals or shaft seals are an integral part in any rotating and moving part assembly. Oil seals find great deal of usage in gearboxes, hydraulic cylinders, etc. The usage of the seals in areas concerned with motion also earns them a name of “Dynamic Oil Seals.” The purpose of the oil seals is

· To act as a physical barrier retaining the lubricating oil where it is bound to be.

· To prevent thelubricating oil from leaking outside even under high pressure of the oil.

· To act as a barrier and prevent dirt, contamination and other external entities from entering the system containing the lubricating oil.

Constructional Aspects of an Oil Seal:

1. The oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal.

The outer skin is made of nitrile rubber and various other materials which are used based on the requirement.

The spring on the lip of the oil seal tends to provide support to the lip and prevents the lubricant from leaking outside and also prevents the entry of contaminants from outside.

Based on the application of the oil seal, the outer skin layer tends to differ. Here are some types of the materials used for the outer skin of the oil seal.

1. Nitrile rubber – The commonly used material for oil seals

Silicone – Used in specific applications where only light loads are applied.

Fluroelastomer also popularly known as Viton. – The high temperature resistant material used in places where temperature is more than 120 Degree Celcius.

The oils seals require certain prerequisites to be maintained for their proper working. They are as follows:

a) The shaft on which the oil seal is to be mounted should be ground with the surface finish or surface roughness between 0.2 to 0.8 Microns. It is best for the shaft to be hardened atleast to 40 – 45 HRc in order to prevent groove formation on the shaft due to the pressure exerted by the spring.

b) The area where the oil seal is seated is to be plunge ground in order to prevent wear grooves that normally tend to wear out the lip of the oil seal at a faster rate.

c) The lip of the oil seal needs to be lubricated in order to prevent the direct contact of the oil seal lip to the shaft.

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Better by Design

Rotating equipment engineers are responsible for avoiding unplanned downtime and making sure pumps are online and operational. As fluid system experts, Swagelok supports those responsibilities by designing and building seal support systems that are reliable, easy to maintain, and safe to operate. Our easy-to-configure, locally built, and reliable solutions help you reduce costs, save time, and improve safety.

Configurable

Swagelok’s API 682 standard designs incorporate all the recommended components and adhere to best practices. For better operation and service of the seal and pump, we go beyond the standards to design systems specific to your application. This includes optional isolation valves, bypass loops, and instrumentation to assist the pump operator in both maintaining the system and monitoring the health of the seal.

Local

Swagelok mechanical seal support systems are designed and built by your local authorized sales and service center how you want them and when you need them.

Reliable

Swagelok’s fluid system expertise leverages design practices that maximize your seal support system’s operation and safe maintenance. And Swagelok products are backed by our Limited Lifetime Warranty.

Designed for Reliability and Maintenance

Proper system start-up and commissioning are critical for the reliable operation of mechanical seals and their associated support systems. I nclusion of air within the system at start-up can lead to issues with the seal support system. Flow can be disrupted or stopped in systems with chillers or seal pots. Air inclusions can also prevent the support system from providing the desired rate of cooling. Swagelok design options include high-point vents in the seal support system, allowing the system to be vented and cleared of entrapped air.

System maintenance during turnarounds and projects requires seal support systems to be drained for servicing. When taking a pump out of service, including low point drains allows the system to be purged of buffer, barrier, or flush fluids, quickly and safely.

Pressure and temperature measurement devices help plant personnel understand what is happening in the seal chamber and seal support system. Many Swagelok seal support systems offer additional instrumentation options at points where measuring either pressure or temperature would assist in troubleshooting an issue or provide other operational benefit.

Designed for Appropriate Flow

Whether the system delivers a flush fluid to the inboard seal or buffer and barrier fluids are circulated between seals in a dual seal arrangement, maintaining proper flow and circulation through the support system and seal chamber is a requirement for effective seal operation. A common flow issue is clogged orifices, which can cause a loss of flush fluid to the seal chamber, resulting in seal failure. Additionally, improper circulation of buffer and barrier fluids can also cause operational issues due to lack of appropriate system cooling.

When designing seal support systems, it is important to have pressure drop and flow control happen at appropriately engineered locations, such as orifices and flow control valves. Components such as filters and strainers can become clogged and create unwanted flow restrictions in seal support systems. These serviceable items should be located in areas that are easy to access and maintain. Additional options such as bypass loops can be added to the system to ensure a continued supply of flush fluid when a filter or strainer element is being replaced or cleaned.

In addition to individual system components that will need to be serviced, the design of tubing runs should be considered critical to the effectiveness of seal support systems. All tubing runs should be sloped, especially those running to and from the seal. A half inch per foot (40 mm per meter) of slope is recommended. One-half inch (12 mm) OD tubing is acceptable for differential pressure or pumped flow systems, while 3/4 inch (18 mm) tubing is recommended for systems utilizing a pumping ring or a thermosyphon effect. It is best practice to eliminate the use of elbow fittings and to use large-radius bends in the tubing to further assist flow.

API Plan 53B Designed for System Safety

API 682 recommends specific wall thicknesses for 1/2 inch (12 mm) to 1 inch (25 mm) OD tubing. While thinner-walled tubing, such as that used in general instrumentation installations, is often sufficient to handle the pressure and temperature of seal support systems, heavier-wall tubing provides extra rigidity in high-vibration service. Tubing with a heavier wall also creates systems that are more robust in areas where large pieces of equipment are being maintained and personnel may inadvertently come into contact with the tubing.

In contrast to larger liquid systems which mainly use 1/2 inch (12 mm) and 3/4 inch (18 mm) tubing, API 682 offers no guidance regarding tubing wall thickness for systems under 1/2 inch (12 mm). Tubing wall thickness for 1/4 inch (6 mm) and 3/8 inch (8 mm/10 mm) systems can be selected from Swagelok’s Tubing Data Sheet, MS-01-107, based on the pressure and temperature of the service. These systems are typically nitrogen filtering and regulating systems for gas seal plans. Swagelok recommends these API gas plans are mounted on a panel with commonly serviced items such as filters and regulators placed with ease of maintenance in mind.

One final safety consideration when choosing the appropriate design for an API 682 plan is the incorporation of block-and-bleed valves on all instruments, including gauges. This recommendation by API adds an additional level of safety for items that need to be calibrated or removed for servicing. Wherever practical, Swagelok seal support systems offer options including 2-valve manifolds or other appropriate isolation on instruments.