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Can the Mechanical Seal Flushing Water Be Shut Off Immediately After Pump Stoppage?

Luojiang industrial zone,hemudu town,yuyao city,ningbo,china
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Can the Mechanical Seal Flushing Water Be Shut Off Immediately After Pump Stoppage?

Time of issue:2026-06-10

(Summary description)For a rotor pump transporting low-temperature easily crystallizable solutions, the mechanical seal was scratched by hard crystals and the spring was stuck, resulting in leakage after the pump was put on standby. The root cause of the accident was that the flushing water was shut down immediately after the pump stopped, causing the residual liquid to cool down and crystallize. The on-off of flushing water should not be determined by the rule of "pump stops, water stops", but should be based on the crystallization tendency of the medium in the stationary cavity.

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Can the Mechanical Seal Flushing Water Be Shut Off Immediately After Pump Stoppage?

(Summary description)For a rotor pump transporting low-temperature easily crystallizable solutions, the mechanical seal was scratched by hard crystals and the spring was stuck, resulting in leakage after the pump was put on standby. The root cause of the accident was that the flushing water was shut down immediately after the pump stopped, causing the residual liquid to cool down and crystallize. The on-off of flushing water should not be determined by the rule of "pump stops, water stops", but should be based on the crystallization tendency of the medium in the stationary cavity.

Categories:Development path
Author:Bonve Pump Industry Marketing Department
Origin:Bonve Pump Industry Marketing Department
Time of issue:2026-06-10 08:50
Views:

Information

First of all, we need to understand that mechanical seal flushing has two core functions: heat dissipation and displacement. When the pump is running, the heat generated by end face friction must be continuously carried away by the flushing fluid to maintain a stable lubricating liquid film. At the moment the pump stops, the frictional heat generation disappears, and the demand for heat dissipation seems to no longer exist, but the real risk has just begun.

- Bonve Pumps Cam-type Twin Rotor Pump -

After the pump stops, the stationary and rotating rings are still tightly pressed together by the spring force, and the residual heat in the seal cavity cannot be carried out through the main medium circulation. Shutting off the water immediately at this time will trap the seal assembly in a high-temperature stationary evaporation environment: after the liquid film evaporates slowly, the end faces turn into dry contact, and uneven shrinkage during cooling is prone to microcracks. For easily crystallizable media, what is more fatal is the destruction of the dissolution equilibrium: the solution remaining in the seal end faces and spring gaps loses temperature maintenance and flow displacement, and crystallizes in situ after cooling to the precipitation point. The hardness of these hard crystals far exceeds that of soft sealing materials such as graphite. When the pump is started next time, they will plow grooves on the end faces like abrasives; the spring is swollen to death by crystals and loses its compensation ability, and leakage often occurs within a few seconds of startup.

This hazard is extremely insidious. Operators often believe that standby pumps have no operating losses and neglect turning inspection. Once started, it will cause unplanned shutdowns, and the loss is far greater than the consumption of flushing water for several hours.

Whether the flushing water can be turned off after the pump stops needs to be treated differently according to the medium characteristics: for easily crystallizable, easily polymerizable, easily curable or high-viscosity media, it is strictly prohibited to shut off the water immediately. External flushing should be continued until the original medium in the seal cavity is completely displaced and the temperature drops below the crystallization point. If the pump must be shut down and emptied for a long time, the seal cavity should be filled with non-crystallizable protective liquid, or the pump should be manually turned at specified intervals to interrupt whisker growth and prevent end face adhesion.

In addition, the selection of flushing schemes must be linked with the shutdown strategy. Pumps using self-flushing lose flow immediately when stopped, completely relying on the properties of the medium. Easily crystallizable media should be changed to continuous flushing or isolation fluid systems with external clean water sources. The flushing schemes recommended by manufacturers usually only consider operating conditions. On-site personnel must incorporate the chemical stability of the medium during shutdown and standby periods as an independent safety dimension into the review.

In the final analysis, the core criterion for whether the flushing water can be cut off after the pump stops is not whether the pump is rotating, but whether the stationary residual medium in the seal cavity will undergo destructive phase changes. Curing "post-shutdown medium behavior assessment" as a necessary step in operating procedures can fundamentally avoid such mechanical seal accidents.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.