Somewhere between the dry motor and the wet volute, every pump has to seal a spinning shaft. For a century the answer was gland packing; today it is usually a mechanical seal. Both still exist, and they fail in opposite ways.
Gland packing: the old solution
Braided rings of lubricated fibre compressed around the shaft. It is cheap, tolerant of dirt, and it leaks by design: a slow drip keeps the packing cool and is considered normal. The trade-offs are constant drip, regular tightening, and gradual shaft wear where the packing rubs.
Mechanical seals: the modern standard
Two lapped faces, one stationary, one rotating, pressed together by a spring. The faces are so flat that a film of water a molecule thick separates them. A good seal drips nothing, needs no adjustment, and outlasts packing several times over.
How each fails
- Packing wears gradually and warns you with an increasing drip. The failure is slow and forgiving.
- Mechanical seals work perfectly until they do not. One dry run can score the faces in seconds, and the leak then arrives all at once.
For clean water in homes, agriculture and industry, a mechanical seal is the right choice and is what we fit. Its single weakness, running dry, is exactly what float switches and dry-run protection exist to prevent. Protect it from that one failure and it will usually outlive the bearings behind it.