Pump seals and reasons for failure

Comments 0 by in Pump Repairs
December 16, 2014
Seal failure

Seal failure


Here we have a photograph taken of a mechanical seal fitted to a Calpeda end suction centrifugal pump.

Click on the picture for a high res close up.

The pump was recently supplied by us and our customer returned it after only 3 or 4 weeks use, as the pump had sprung a leak.

We removed the pump volute casing, the impeller and rotary seal spring, and this is what we found.

The seal elastomers had broken down due to excessive heat, and yet the customer had informed us that the pumped liquid was cold water containing a small percentage of glycol (anti-freeze). The seal faces (carbon vs ceramic) were both in reasonable condition so we ruled out dry running. The only possible conclusion we could think of is that the pump had ran against a closed discharge valve, causing the water within the pump to get hotter and hotter (pumped energy has no where to go so starts to heat up the liquid) until the recommended elastomer (rubber) temperature (90 degrees C in this instance) is superseded and the elastomers start to break down.

We put this theory to our customer, and after checking with the operator on the shop floor, it appears that the pump valve on the discharge side had indeed been closed (normally for a short time) whilst carrying out another operation and had forgotten to open it again.

If a pump seal has been fitted incorrectly, then it will leak pretty much straight away. Very rarely do we ever see a mechanical seal fail due to manufacturing or fitting errors, especially on Calpeda pumps, as each pump is individually tested (not batch tested as some do) before it leaves the factory. Also if we are repairing a pump, we always carry out a hydrostatic pressure test before we deliver the pump back to the customer. We are then confident that if a leak has occurred, then it will be down to a system fault and not a faulty seal.

We supply mechanical seals for most makes and types of pump including Lowara, Grundfos, Ebara, DAB, Calpeda, KSB, Caprari and many others, and are happy to advise on correct pump seal selection to suit whichever liquid is being pumped.

Please do not hesitate to call or email us for assistance.