Why Seal Flushing Is Required and How To Minimize Its Frequency

Selecting the correct mechanical seal for a pump requires a thorough understanding of the pumping process—the fluid, temperature, pressure, and expected operating cycles.  

The reliability and performance of centrifugal pumps that process fluids such as irrigation water and high-pressure, high-temperature toxic hydrocarbons depend on the proper functioning of mechanical seals. These carefully engineered components with tight tolerances are designed to prevent leakage.

Why seal flushing is required during maintenance

There’s one more critical task in keeping pumps operational—scheduled maintenance procedures for pumps and their seal support systems. Throughout the life of a pump, you can expect to conduct maintenance flushes to prevent or remedy problems with mechanical seal performance. The purpose of the maintenance procedure is to flush any debris from between the seal faces. That debris may have come from particulates in the process fluid, corrosion from aging piping, or metal from an abraded pump volute or impeller. 

Requirements and tips for a seal flushing procedure

The fluid used for the seal flush must be compatible with the process fluid. Plant water, a water/glycol mix, or steam delivered at a pressure higher than the process fluid pressure works for process fluids that tolerate water. The alternative is flushing oil, natural or synthetic, pumped at pressure and compatible with the process fluid. In most cases, there’s no need to stop the pumping process. The maintenance flush is delivered via a dedicated flush port in the mechanical seal body and runs long enough to flush any debris that may have accumulated between the seal faces. 

Seal flushing frequency

The frequency of mechanical seal flushing depends on process conditions. For properly-maintained centrifugal pumps, the schedule for maintenance flushes should be based on performance data obtained from your EAM system. Considering that some plants have hundreds to thousands of pumps, the time and cost allotted for maintenance flushes could be considerable. Overall, you want to find the right balance between a proactive and reactive seal flushing maintenance schedule.

When is seal flushing required too often?

If you’re conducting seal flush maintenance with increasing frequency to prolong the life of the mechanical seal, it may be time to check for causes of seal degradation. Factors that contribute to seal degradation are usually tied to the inability of the seal support system to maintain the proper seal chamber environment. Let’s consider the most likely reasons, and discuss methods to reduce the frequency of these flushes:

1. Problems cause by particulate and slurries

Process fluids with high particulate concentrations or slurries can impact centrifugal pump and mechanical seal integrity. You’d expect these pumps to require seal flushing more frequently to clear particulates from the seal chamber, mechanical seal components, and seal faces. 

Nonetheless, if your EAM system shows that the MTBF for a particular pump is lower than the average for pumps of that class and process conditions, look into these factors that can be affecting pump performance: 

• Consider replacing the filter/strainer on the seal support system (API Plans 12 and 22) with a cyclone separator (API Plan 31 or 41) to more effectively remove particulates from the process fluid delivered to the seal chamber. Building in a bypass makes filter swaps simple and environmentally safe.
• Upgrade a single, process-side mechanical seal and seal support system to a dual-seal with a barrier fluid seal support system (API Plans 52, 53A/B/C, 54, or 74) delivered to more effectively prevent particulates from infiltrating seal faces.

2. Inadequate pressure = poor lubrication

If clean, filtered process fluid from the discharge side of the pump is not delivered at the correct pressure (higher than pump chamber), process fluid won’t adequately lubricate the seal faces and prevent particulates from degrading the seal faces—leading to eventual seal failure.

Blockage in a clogged orifice (pump discharge), clogged filter, or accidentally crimped tubing leading from discharge to seal chamber are the likely causes of inadequate pressure. The addition of a pressure gauge and pressure transmitter can alert to pressure drops that need to be addressed immediately. 

API Plan 21 - Cooled Flush with gauges to monitor process fluid pressure and alert to problems.

Tips to minimize seal flushing frequency

Seal flushing maintenance procedures should be part of your planned maintenance program, with seal flushing frequency based on maintenance records for that class of pumps with similar pumping conditions. By proactively flushing debris that can damage seal faces, you extend the life of the seal and boost pump reliability. However, if you’re doing more seal flushing than indicated on your scheduled maintenance plan, it’s likely that the problem is an underperforming seal support system. 

Getting help with seal flushing

How we can help

Swagelok has assisted process engineers and maintenance personnel in the chemical, petroleum, energy, utility, and semiconductor industries in Northern California by designing and assembling seal support systems tailored to the specific needs of each pumping process. With access to a worldwide team of fluid engineering specialists, our experience is unparalleled in helping industries reduce maintenance costs by enhancing pump reliability. 

About Malik Durojaiye | Field Engineer, Assembly Services

Malik Durojaiye began his Swagelok career in 2019 as a Custom Solutions Engineer in our Assembly Services group. Prior to Swagelok, Malik developed as a design engineer as well as a manufacturing engineer for 6 years serving Kentucky and California with Altec Industries; a leading provider of products and services to the electric utility, telecommunications, tree care, lights and signs, and contractor markets.