Mechanical Seal Troubleshooting: Causes & Fixes

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Problems on this page:

Seal leaking from the first start Seal running dry Seal faces worn or heat-cracked O-rings swelling or hardening Leaking after a restart Vibration and misalignment damaging the seal Seal support system faults Leaking at the sleeve or gland Leaking at standstill but not when running

Seal leaking from the first start

Hits OEE: Quality

Symptoms: A new seal leaks as soon as the pump runs.

Seal set at the wrong working length

Set the seal as the seal maker's drawing shows.

Faces damaged during fitting

Handle the faces with care and keep them clean.

O-rings twisted or cut on fitting

Lubricate and fit O-rings with the right tool.

Wrong seal for the shaft or housing

Check the part number.

Prevention: Seal fitting by trained people with the seal drawing at hand.

Seal running dry

Hits OEE: Availability

Symptoms: Squealing, smoke or heat at the seal, then a leak.

Pump started without liquid

Prime the pump before starting.

Flush line blocked or closed

Check the flush line and valve.

Vapour forming at the seal faces

Check the flush plan and the temperature at the seal.

Prevention: Flush checks on the round.

Seal faces worn or heat-cracked

Hits OEE: Availability

Symptoms: Grooves, chips or heat cracks on the faces at teardown.

Dry running

Find and fix the cause of dry running.

Abrasive particles in the product

Use hard face materials and a clean flush.

Pressure or temperature beyond the seal rating

Check the duty against the seal rating.

Prevention: Faces inspected at every seal change and the findings recorded.

O-rings swelling or hardening

Hits OEE: Availability

Symptoms: O-rings deformed, swollen, cracked or hard at teardown.

Elastomer not compatible with the product

Choose an elastomer for the product.

Temperature above the rating

Use an elastomer rated for the temperature.

Cleaning chemicals

Check cleaning chemicals against the elastomer.

Prevention: Elastomer choice recorded per pump.

Leaking after a restart

Hits OEE: Availability

Symptoms: The seal leaks each time the pump restarts after a stop.

Product crystallising or setting on the faces during stops

Flush the seal at stop and before start.

Thermal shock at start

Warm or cool the seal area gradually as the procedure says.

Missing quench

Check the quench supply.

Prevention: Stop and start procedures include the seal flush.

Vibration and misalignment damaging the seal

Hits OEE: Availability

Symptoms: Short seal life together with high vibration at the pump.

Misalignment between pump and motor

Align after every intervention.

Worn bearings

Replace the bearings.

Bent shaft

Check shaft runout.

Cavitation

Fix the suction conditions.

Prevention: Vibration trended on pumps with seal problems.

Seal support system faults

Hits OEE: Availability

Symptoms: Flush, quench or barrier system alarms, or the barrier pot runs empty.

Flush line blocked

Clean the line and its orifice.

Barrier pot empty or at the wrong pressure

Refill and set the pressure.

Cooler fouled

Clean the seal cooler.

Prevention: Seal support systems on the daily round.

Leaking at the sleeve or gland

Hits OEE: Quality

Symptoms: Leakage comes from the gland or sleeve joint, not the faces.

Gland gasket damaged

Replace the gasket.

Sleeve O-ring damaged

Replace the O-ring.

Gland bolts tightened unevenly

Tighten evenly to torque.

Prevention: Gland bolt torque recorded at each seal change.

Leaking at standstill but not when running

Hits OEE: Quality

Symptoms: The seal drips while the pump is stopped and stops leaking when it runs.

Springs clogged with product

Clean the springs or use a seal with protected springs.

Faces distorted by heat

Lap or replace the faces.

Seal design not suited to the standstill pressure

Check the seal design against the pressure when the pump is stopped.

Prevention: Standstill leakage noted on the round.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: centrifugal pump · progressive cavity pump · mixer / agitator · homogeniser · bearing · gear pump

Stop the same fault coming back

Recurring mechanical seal stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

Book a Fabrico demo

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover