What Is a Mechanical Seal Flushing Plan

A mechanical seal flushing plan is a strategy for maintaining the performance and longevity of mechanical seals in pumps and other rotating equipment.

By implementing the right flushing plan, you can prevent seal failure, extend equipment life, and reduce maintenance costs.

Read on to discover how to choose the optimal flushing plan for your application.

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What is a Mechanical Seal Flushing Plan

A mechanical seal flushing plan is a strategic arrangement of equipment that circulates fluid to or from the seal chamber of a pump in order to maintain optimal pressure, temperature, and solids management for the mechanical seal.

The goal is to create an ideal operating environment for the seal to avoid excessive wear and premature failure, thus prolonging the useful life of the seal and increasing pump reliability.

Why Use Mechanical Seal Flushing Plan

When the mechanical seal is working, a thin layer of liquid between the seal faces acts as lubrication and prevents excessive heat from being generated due to friction.

However, the seal faces are vulnerable to damage from heat, abrasive particles, and dry running. This is where seal flushing plans come in.

How Does Mechanical Seal Flushing Plan Work

How a mechanical seal flushing plan works depends on the specific plan, but the general principle is to introduce a clean, cool fluid into the seal chamber or remove seal chamber fluid for cooling and filtering. The fluid can come from the process itself (internal recirculation) or an external source. The fluid is typically circulated using the pump’s discharge pressure or an external pump.

Some common flush plans include:

  • API Plan 11: A line from the pump discharge recirculates cooled process fluid into the seal chamber through an orifice to control flow.
  • API Plan 13: Similar to Plan 11 but with fluid from an external source.
  • API Plan 21: Fluid from the pump discharge is cooled in a heat exchanger before entering the seal chamber and returning to the process.
  • API Plan 23: A closed loop system where seal chamber fluid is pumped through a heat exchanger and recirculated, without returning to the process.
  • API Plan 32: Clean external fluid is injected into the seal chamber at a higher pressure than the process and allowed to flow into the process.

Benefits of Flushing Plan

  • Prolonging Seal Life: By providing optimal lubricating film between seal faces and controlling temperature.
  • Preventing Dry Running: In upset conditions or process interruptions, ensuring the seal faces do not run dry.
  • Extending MTBR: Avoiding premature seal failures to extend the mean time between repair for the pump.
  • Reducing Product Loss and Emissions: Minimizing seal leakage to decrease product loss and environmental emissions.
  • Avoiding Catastrophic Failures: Preventing unplanned downtime for critical process pumps by mitigating major failures.
  • Lowering Maintenance Costs: Reducing total cost of ownership over the pump lifecycle through decreased maintenance expenses.

Components Used in Flushing Plans

  • Orifices, Flow Control Valves, and Pressure Regulators: Control flow and pressure for consistent flushing.
  • Filters, Cyclone Separators, and Solids Removal Devices: Remove contaminants to protect system components.
  • Heat Exchangers, Seal Coolers, and Temperature Control: Maintain fluid and seal integrity by managing temperature.
  • Seal Pots, Reservoirs, and Buffer/Barrier Fluid Management: Ensure fluid supply and cleanliness, with additional protection as needed.
  • Valves, Piping, and Materials: Essential for efficient fluid flow, with compatible materials to prevent degradation.
  • Instrumentation for Monitoring: Track pressure, temperature, flow, and level to optimize performance and prevent failures.
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How to Select the Optimal Flushing Plan

There are many types of flushing plans that can be selected based on the specific application, process fluid properties, and seal configuration. The key considerations when selecting the optimal flushing plan include:

Process Fluid Properties

  • Cleanliness: Does the process fluid contain any solids or contaminants?
  • Temperature: Is cooling required to maintain an acceptable seal chamber temperature?
  • Vapor pressure: Is the process fluid close to its vapor pressure at seal chamber conditions?
  • Viscosity: Will the process fluid provide sufficient lubrication at the seal faces?

Process Conditions

  • Shaft speed: Higher speeds may require more heat removal
  • Discharge pressure: Determines seal chamber pressure and fluid vaporization margin
  • Suction pressure: Impacts circulation flow in some flush plans

Seal Chamber Design

  • Geometry: Tapered or straight bore can impact flow and venting
  • Mounting: Vertical vs horizontal orientation affects venting and solids accumulation
  • Seal type: Single vs dual seals have different flushing requirements

In general, the simplest flushing plan that meets the application requirements is preferred for reliability and cost effectiveness.

For clean, cool process fluids, a simple recirculation from the pump discharge to the seal chamber (API Plan 11) may be sufficient.

For hot process fluids, a cooler may need to be added to the recirculation loop (API Plan 21) to maintain acceptable seal temperature. Very hot, dirty, or polymerizing fluids may require an external flush with a clean cool barrier fluid (API Plan 32).

Dual seals for hazardous fluids will require a pressurized barrier fluid circulating between the seals (API Plan 53A) to provide backup sealing and leak containment.

Best Tips for Implementing and Maintaining Flushing Plans

  • Provide a throat bushing to isolate the seal chamber from the process
  • Maintain minimum 1 ft/sec velocity through the seal chamber for heat removal and venting
  • Ensure flush fluid is at least 20 psi above seal chamber pressure to avoid vaporization
  • Use seal face materials compatible with the process and flush fluids
  • Provide a means to monitor and control flush flow and pressure
  • Regularly inspect and maintain the seal support system components


By selecting the appropriate flushing plan, you can ensure optimal performance, minimize downtime, and reduce maintenance costs.

Don’t let seal failures disrupt your operations – take action now and consult with our experts to determine the best flushing plan for your specific application.

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