Mechanical Seals

Comments 0 by in Pump Repairs
August 21, 2014

Here we have an example of a mechanical seal removed from a KSB Etabloc cast iron end suction centrifugal pump.

The customer normally carries out their own pump repairs using pump spares sourced elsewhere. However, the pump had always experienced premature seal failures, and couldn’t understand why this should be, after all, they were only pumping oily water with a few metal particles floating around, and were using the original seal pump code reference to order the seal, so what could possibly go wrong?

Well after having searched on Google for a KSB UK area pump distributor, they decided to send the pump to us and see if we could solve the problem. We stripped down the pump and electric motor and examined the mechanical seal. As you can see from the photograph, the rubber parts of the seal had badly swollen causing the seal failure, but why?

Mechanical seal EPDM react with oil

On the pump data plate, after the pump model, KSB place a “G” number which denotes the seal code. Standard seal codes are either G06, G10 or G11 (there are many other bespoke variations to suit the pumped media). The code on this particular pump was G11 and this tells us the seal faces are constructed from Silicon Carbide and Hard Carbon, with EPDM elastomers (rubber parts). EPDM (Ethylene Propylene Diene Monomer) is a good choice if pumping hot water or any Alkaline liquids such as Caustic Soda, but definitely not recommended for use with mineral oils. The customer had been ordering the seal based on the seal code on the data plate, which normally would be the correct thing to do.

KSB Pumps are very thorough when specifying their pumping equipment, and would not spec EPDM for oily water, so we couldn’t understand why this seal had been fitted as standard. So, we quizzed the customer regarding the history of the pump, and it transpired that originally the pump may have been used on another part of the plant pumping something else (probably hot water) and had been surplus to requirements and commandeered to pump the oily water. The customer thought this would be OK, quote : “because after all, oily water is not aggressive because you can put your hand in it and nothing happens” (True, but then hands are not made from EPDM)

So seal problem solved (we specified Code G1 which is Silicon Carbide rotary and stationary with FPM (Viton trademark) elastomers) and this combination is perfect for the job.