What are the two categories of seals available?

Double (or dual) mechanical seals are designed to ensure maximum sealing safety. These seals virtually eliminate leakage of the fluid or gas being handled in pumps or mixers.

• Double seals provide a level of safety/zero emissions compliance not possible with single seals. This is essential when pumping or mixing a dangerous or toxic substance.
• Double seals are a must-have for certain applications in many countries
• These seals are increasingly used by companies to meet specific environmental goals or emissions requirements.
• A properly installed double seal also allows for near complete control over the seal operating environment and fluid film over the seal faces. This factor alone can greatly maximize seal life.

How It Works

A double mechanical seal has two primary seals with a barrier or buffer fluid area in between. Each primary seal typically consists of a softer, narrower stationary face accompanied by a harder, wider rotating face. This arrangement enables the softer seal to wear while maintaining the integrity of the harder faced seal during service.

When to Use Double Seals

Pump and seal manufacturers recommend double seals for a variety of reasons:

• Prevent a hazardous product from reaching the atmosphere/polluting the environment
• Avoid leakage of an expensive process fluid product
• Maximize seal life by controlling the type of fluid film on the seal faces
• Isolate the mechanical seal from atmospheric conditions
• Provide an alternative when the process fluid will not provide stable and reliable lubrication of the seal faces (such as gaseous media, viscous fluids, non-settling slurries, or fluids liable to harden)
• Establish a backup seal in the event of an inboard seal failure or planned equipment repair (or to identify seal failure during operation)
• Avoid contamination of the process media should one seal fail

Full Control Over the Seal Environment

To extend the life of any seal, you want to control the fluid film that comes into contact with the seal face. This establishes the ideal lubrication, temperature, and pressure. A dual seal allows you to control of all these factors.

Double seals require fluid exchange between the inboard and outboard seal faces. Each double seal must be installed with an environmental control/support system that introduces a barrier or buffer fluid in between the primary seals. This fluid is typically delivered from a tank to cool and lubricate the seal faces using a piping plan. The use of level and pressure meters on support tanks are crucial for both containment and safety.

Depending on the pressure and seal arrangement, such a system can be used to:

• Control the operating temperature (up/down) of the seal
• Provide lubrication and/or clean fluid to the seal faces (other than the process fluid)
• Isolate the seal from the atmospheric conditions
• Control the pressure drop occurring across the seal faces

The fluid can also be used to remove process and frictional heat. It can combats issues with cavitation and dry running. The correct fluid set-up can also effectively direct the hydraulic load to the inboard or outboard seal to meet operational needs and to increase the life of the seal.

Barrier vs Buffer Fluids

There are two modes of operation to choose from:

1. Barrier Fluid: Fluid pressure is 15-30 Psig/1-2 Bar higher than the pumped fluid pressure
   • Used when the process fluid is highly dangerous and a failure of one primary seal could put employees or the environment in danger
   • Displaces the sealed fluid across the inboard seal and lubricates the seal faces
2. Buffer Fluid: Fluid pressure is lower than sealed pressure
   Used if contamination of the process fluid is unacceptable and if the sealed fluid provides adequate primary seal lubrication.

Use a Barrier Fluid to:

• Keep process fluid from crossing the seal faces (especially in slurry operations)
• Prevent process fluid that is sticky or has a tendency to settle from generating high face torques  during startup
• Prevent the process fluid from vaporizing across the seal faces
• Prevent process fluid from causing damage to the inboard mechanical seal faces
• Lubricate inboard and outboard seal

Turn to a Buffer Fluid to:

• Prevent leakage into the atmosphere or environment
• Prevent the process fluid from becoming contaminated
• Reduce the operating stress of the inboard seal
• Identify possible seal failure while operating
• Lubricate the inboard face of the seal (while process fluid will lubricate outboard seal faces)

Fluid Options
A variety of possibilities exist for the Barrier or Buffer Fluid, but the key factor is compatibility with the sealed media. Liquids used fall into several categories:

• Water and water glycol solutions
• Mineral-based hydraulic and lubricating oils
• Synthetic-based hydraulic and lubricating oils
• Heat transfer fluids
• A dilution of the process fluid, or the process fluid itself
  

We will address how to select the best fluid for your application in an upcoming post.

Dual Seal Configurations

Double mechanical seals come in rotary and stationary versions. There are three typical configurations:

• Back-to-Back: Typically used for general applications
• Tandem (sometimes referred to as ‘Face-to-Back): Provides absolute backup should one seal fail
• Face-to-Face: Stationary – Becoming less popular

There are no hard-and-fast rules for the right configuration. This is where your operation’s reliability/environmental goals come into play and where the experience of a seal manufacturer’s specialist can be invaluable.

The bottomline is that the double seal option is unmatched in terms of safety, leak/emission-free operation, and Life-Cycle Cost (LLC). Learn more about double seal set-up and operation in our upcoming posts.

Next in This Series:

Part 2: Double/Dual Mechanical Seal Arrangement Options
Part 3: Support Plans for Double/Dual Mechanical Seals
Part 4: How to Select the Best Barrier/Buffer Fluid for Your Application
Part 5: Saving Water with Double Seals

From holding pressure to preventing leakages to keeping out contaminates, industrial seals play a crucial role in the performance of your equipment. A seal’s service life and reliability can make all the difference in reducing friction, extending maintenance, and increasing sustainability. That’s why it’s important to understand the different types of seals and the industrial applications they’re most suited for when it comes to selecting the right sealing solution for your operation. In this article, we’ll walk you through seven different types of seals for power transmission, hydraulic, fluid handling, and custom-engineered applications. 

Power transmission seals are most often used for rotary applications that are intended to either seal the openings between a rotating and stationary component or two components in relative motion. The two different types of seals that are most commonly used in power transmission applications are radial shaft seals and axial shaft seals.

Radial Shaft Seals

Designed to protect bearings, keep lubricants in, and improve system reliability, radial shaft seals feature a sealing lip, metal case, and tensioning spring, as well as a dust lip. This seal type can be used for a range of applications from small, high-speed machine tools to large wind turbines. 

Axial Shaft Seals

Axial shaft seals are designed to seal axially against a counterface perpendicular to the shaft or pin and serve as a reliable secondary seal, while tolerating small misalignments. This seal type is best used in highly contaminated environments that are exposed to sand, soil, mud, and water.

Hydraulic seals are intended to separate or block liquid in reciprocating applications and can be molded or machined for different factors, such as working temperature, cylinder speed and operating pressure, medium, and more. They are used in machinery equipment and two different types of seals that are primarily used in these applications are piston seals and rod seals.

Piston Seals

 

Piston seals are typically single-acting seals, but are also available as double-acting seals. They ensure liquid doesn’t pass around the piston by pushing the piston down the cylinder, while allowing an oil film to minimize friction and wear. This seal type is often used in hydraulic presses and agricultural machinery.

Rod Seals

Rod seals serve to guard against outer contaminants by providing a thin lubrication film on the piston rod. Through a sliding motion between the cylinder head and piston rod, rod seals are able to maintain sealing contact. This seal type can be customized for use across a wide array of applications. 

Fluid handling seals come into direct contact with aggressive fluids and often have to meet some of the most stringent regulatory requirements. They are primarily used in the oil and gas industry and the food and beverage industry, with o-rings and back-ups rings and wiper seals acting as two different types of seals that are most commonly used.

O-Rings and Back-Up Rings

O-rings and back-up rings are frequently used as a static sealing element, as they seal through their own deformation between surfaces. Back-up rings help keep o-ring extrusions from getting into the clearance gap. This seal type is best used in applications that need to withstand temperature extremes and pressure differentials.

Wiper Seals

Wiper seals often pair with other sealing components for a tight fit to prevent contaminants from being transported into the hydraulic system with the reciprocating piston rod. This seal type is commonly used in applications for construction, mining, and agriculture.

For more customized solutions, manufacturers like SKF offer machined seals that can meet the unique needs of virtually any application. With the ability to produce solutions for any dimension or design, SKF’s innovative production system, SKF SEAL JET, provides a fast, flexible alternative to moulded seal production. Through extensive application engineering support and a wide selection of seal profiles and materials, SKF is able to provide on-demand manufacturing that ranges anywhere from a single seal to a low-volume series for fluid power, fluid handling, and power transmission applications. 

Look to SKF for These Different Types of Seals

With over 100 years of industrial application experience, SKF offers an unmatched understanding of the interaction between bearings, seals, and lubrication, as well as the dynamics of reciprocating systems. That’s why SKF has an industry-leading reputation for providing different types of seals made at the highest quality for virtually any application. SKF seals will help you improve the capability, durability, and performance of your equipment. 

Find Solutions for Different Types of Seals at IBT

IBT Industrial Solutions takes pride in our long history of providing exceptional bearing and sealing solutions for applications spanning all industries. With our deep knowledge and decades of expertise, we’re here to help you find the best parts for your application and environment.

For further guidance on selecting the right seals for your equipment, contact IBT’s Bearing and Power Transmission team today. Or if you know which products you’re looking for visit ShopIBT to purchase seals directly.