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Mechanical Seals Basics & Design Principles

Swagelok Mechanical Seal Support System
API Plan 74 with Optional Components

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.


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. 


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.


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.  Inclusion 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.

Plan 53B
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.

Continue reading about seal support systems
Download the Application Guide