External Seals

These seals can be used to convert a packed pump to seal operation in the event that the stuffing box has too small a diameter to accommodate a normal seal. The seal operates in reverse mode and it is the seal spring pressure that keeps the seal faces closed. This means that the seal has a limited application because the differential pressure across the seal is limited. Refer to the manufacturer’s instructions for full details but be aware that the seal can “blow” open, if the seal is over pressurized.

491-StatSeal-Cut.JPG (13398 bytes)

However this type of seal came in very handy for a tricky little job on a fuel pump supplying a boiler house. The pump was sited inside the brick bund surrounding the tank. As always the pump was positioned by a plumber instead of a maintenance engineer and the bill for the job was paid by a hard up (?) accountant who thought bricks were too expensive to waste. You get the picture, to do any maintenance other than look over the wall required someone very small and agile! The pump was fitted with gland packing and the fuel oil leaked from the gland at an increasing rate. Not only did this wastage cause the accountant to have a heart attack (only kidding!) but it was messy and environmentally unacceptable. No-one was going to pay for a new pump to replace the existing one with a modern sealed unit and the existing pump had a very small gland housing which meant that a seal could not be fitted inside. The only answer was an external seal. The pressure on the seal housing was calculated to be within the operating limits of the seal. The fuel was cold pumped and not a tar forming substance so I gave the go ahead for an external seal to be fitted. A few hours work to make a new gland plate to carry the seal stationary and a gasket, and to fit the seal, re position the coupling and motor, with the result that there were no more leaks.

Even the most awkward pump application can be approached and solved if you are willing to think the problem through!