Mechanical seal support systems

Reliable pump operation depends on more than the mechanical seal itself. Mechanical seal support systems exist to control that environment and give the seal the best possible chance to perform as intended. Understanding their role is fundamental to mechanical seal reliability. 

How process upsets affect mechanical seals 
Mechanical seals operate at the interface between a rotating shaft and stationary equipment. This makes them particularly vulnerable to changes in operating conditions. Temperature, pressure, vibration and fluid cleanliness all directly influence seal performance. 

If any part of a pump skid or the broader process falls outside operational ideals, the impact is often first seen at the seal. A common example is bearing condition. Poorly maintained bearings can lead to increased vibration and shaft runout. That movement is transmitted directly to the seal faces, disrupting the lubricating film and accelerating wear. In many cases, reduced seal life becomes the earliest indication that something elsewhere in the system is not performing as it should. 

Conditions that mechanical seals are designed to handle 
Mechanical seals rely on a stable operating environment to function correctly. While liquid-lubricated and gas-lubricated seals differ in design and operation, their fundamental requirements are closely aligned. 

Both types of seals require a stable fluid film to form between the seal faces. That fluid must: 

Temperature control is a critical factor for most seal designs. All mechanical seals generate heat during operation, either through direct contact at the seal faces or through viscous shear in gas-lubricated seals. Without effective heat removal, this heat can cause thermal damage and shorten seal life. 

In most applications, maintaining temperature requires some degree of flow. That flow serves two purposes: delivering lubrication to the seal faces and removing heat generated during operation. 

Across all mechanical seal types, a single requirement applies.  

When the process is not enough 
In some applications, the natural conditions inside the pump seal chamber already meet the needs of the mechanical seal. When the pump is filled with clean, stable process fluid within acceptable temperature and pressure limits, no additional equipment may be required. In these cases, seal life depends entirely on the proper operation and maintenance of the pump and associated equipment. 

Many services, however, expose mechanical seals to conditions that are not suitable for reliable operation. The process fluid may be too hot, too cold, contaminated or otherwise incompatible with the seal design. In such situations, relying solely on the natural seal chamber environment is insufficient. 

Equipment and features added to a pump to create the right conditions for the seal are collectively referred to as seal support systems. These systems are designed to supplement or modify the seal environment, allowing the seal to operate within its intended design parameters. 

Seal support systems may be designed to: 

Almost all wet mechanical seals require some form of seal support system. A continuous flow of cool liquid across the seal faces removes heat, helping to prevent thermal damage. Without this controlled flow, seal temperatures can rise rapidly, leading to accelerated wear or failure. 

Dual mechanical seals introduce additional requirements. These seals operate with a separate fluid, either a liquid or a gas, between the two seal faces. A seal support system is required to contain that barrier or buffer fluid and to condition it so that both seals can function correctly and predictably. 

In all cases, the mechanical seal support system is tailored to the specific needs of the seal and the service in which it operates. 

Seal support systems as a platform for monitoring and control 
Seal support systems also provide a practical location for instrumentation. Depending on the configuration, monitoring may include: 

These measurements support alarm functions and enable timely operator intervention when conditions begin to deviate from acceptable limits. 

By providing early visibility of changing conditions, seal support systems help prevent minor deviations from developing into seal damage or unplanned downtime. While the specific instrumentation used varies by application, the objective remains the same: to support informed, proactive operation and maintenance. 

Why does no single seal support system suit every application? 
The wide variety of seal support system designs reflects the diverse services in which mechanical seals operate. The aspects of the seal environment that need to be controlled vary by application. 

For example, pumps handling liquids containing abrasive solids present a different challenge than those handling clean fluids. In services involving solids, a support system may be required to remove these solids from the seal environment or to protect the seal faces from them. Where solids are not present, those features are unnecessary. 

As a result, seal support systems range from very simple arrangements integrated directly into the pump to complex assemblies of equipment mounted on dedicated skids. There is no single unifying appearance or configuration. 

What defines a seal support system is not how it looks, but the function it performs: delivering the specific conditions required for reliable mechanical seal operation in a service. 

API 682 piping plans and standardised support systems 
To bring consistency and structure to seal support system design, API 682 defines a series of recognised configurations known as API piping plans. Each piping plan describes a specific collection of equipment, its intended use and the design constraints required to ensure sound engineering practice. 

API 682, 4th edition, currently lists 32 piping plans. Each revision of the standard has introduced additional plans to address emerging mechanical seal requirements and new application challenges. 

These piping plans cover a broad range of functions, including: 

In practice, multiple piping plans are often combined on a single mechanical seal. This significantly increases the number of possible seal support system configurations, allowing systems to be tailored closely to specific application needs. 

Even with this extensive range, not every application can be fully addressed by the standard plans alone. API piping plan 99 exists to define engineered solutions that fall outside the scope of the standardised plans. This recognises that some services require bespoke approaches to seal support. 

Mechanical seal requirements beyond the seal itself 
Seal support systems are a critical part of mechanical seal reliability. They provide the controlled environment that seals need to operate as designed, particularly in demanding or non-ideal services. From simple features integrated into a pump to complex engineered systems, their purpose is always the same: to supply clean lubricating fluid at the right conditions. 

A clear understanding of how seal support systems function, why they are used and how they vary across applications is essential for anyone responsible for pump reliability. By focusing on the fundamentals of seal environment control, seal support systems help turn mechanical seals from a point of vulnerability into a contributor to long-term operational stability. 

Supporting seal reliability with system expertise 
John Crane supports operators across the full range of mechanical seal support system requirements, with expertise covering simple arrangements, standard API piping plans and engineered solutions. Details on seal support systems, API piping plans and available configurations can be found here [API 682 Overview | John Crane].