SUBJECT: Pump and seal problems with no apparent cause 4-5

These problems are the ones that drive you crazy. No matter how hard you look, the solution keeps evading you. Over the years I've collected quite a few examples. I offer some of them for your enjoyment and maybe, in the process, they will help you solve the "un-solvable"


The pump cavitated every time it rained.

The pump never cavitated in the summer months, only during the winter when everything was cooler.

The cavitation started suddenly.

The cavitation started after the packing was converted to a mechanical seal. A careful inspection showed that the seal was not leaking air into the suction.

The cavitation kept getting worse with time, nothing obvious had changed in the system.

The cavitation only occurred when there was a higher head at the suction of the pump and stopped cavitating when the level fell in the tank - just the opposite of what should have happened.

Two pumps were installed in parallel, one cavitated the other did not. They had separate suction lines so that wasn't the problem.

The pump had been cavitating for some time, but after a visual check everything appeared normal.

The pump started to cavitate when a flange gasket was replaced on the suction side of the pump.

The pump cavitated about one third of the time it was running.

The pump cavitated, although here was excessive suction head available.


The seal was showing evidence of running dry, but the fluid level was never lost in the pump.

The seal showed evidence of running dry.

There was little to no fluid circulating between the two seals.

The mechanic had marked the seal location on the shaft sleeve before the impeller was installed. When the impeller was tightened against the shaft shoulder, the sleeve moved and over compressed the seal.

Almost all Flowserve pump impellers adjust to the pump back plate. When you make impeller adjustments you over compress the mechanical seal.

A cooling jacket was being used, but the seal continued to get hot. I have seen multiple reasons for this:


The cartridge seal had been hydrostatically tested with water and then put into a hot oil application. It leaked almost immediately.

The seal would start leaking about thirty minutes after the pump started.

The seal was tested in the shop, but leaked when it was installed in a pump that was operating at cryogenic (cold) temperature.

The seal was found to be leaking every Monday morning.

The leakage occurred during the winter months.

The seal would fail only during the winter months. The problem was traced to swelling of the dynamic O-ring but no logical reason could be found for its failure.

The seal area was wet, but no visible leakage could be seen.

The problem was traced to the fact that the mechanic was installing the seal at the wrong dimension. The written instructions were clear and placed in the box and yet the mechanic continued to do the installation incorrectly.

The sealed leaked everytoime the pump ran but stopped when the pump stoppesd

The outside seal in a double seal application failed suddenly. Nothing had changed in the system.

The seal ran great for several days and then started to leak. It tested all right on the test bench after it had been removed from the pump.

The seal was changed several times, but the steady leak persisted.

The seal started to leak after many months of service. A bench vacuum test showed that the seal was all right.

The seal ran approximately six months and then failed.

The seal was installed correctly, but it leaked immediately.


It looked like a seal part had come loose in the stuffing box, but all of the parts were there.

The bellows plates were breaking, but there was no evidence of corrosion, excessive wear, physical contact, or vibration.

The inner seal of a dual, rotating "Back to back" seal was showing excessive face wear in a short period of time.

The carbon seal face showed massive damage in a cryogenic (cold) application.

The metal bellows plates showed massive wear.


The pump had been recently overhauled and at start up the pump was reading high amperage, but low flow.

The pump made a terrific racket during start up. It produced the proper head, but the capacity was less than anticipated.

In an acid application, a stationary seal showed localized corrosion only on the gland.

The dual seal convection tank was running backwards.

The pump was converted from packing to a mechanical seal and then started to break shafts.

The product was solidifying in the stuffing box. Steam was being used to heat a jacket around the pump. The header gauge showed adequate pressure.

The nickel base tungsten carbide face shows evidence of chemical attacked.

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