As everyone familiar with pump maintenance would know, one of the most common reason for pumps to need repairing is seal failure. The reasons why seals fail were covered on a previous post, and this post discusses the different types of seal to choose from.
This is when material (usually braided or in formed rings) is packed into the stuffing box of the pump, which compresses it against the shaft to form a seal. While it’s economic and reliable, it’s best to only use packing for thicker liquids (especially at higher pressures) as they will tend to leak too much otherwise. They are designed to weep slightly so that they stay lubricated in any case. Watch out for over-packing these as well, as they can damage the pump shaft.
Simply a circular seal in a rigid outer housing. Also economical, but again best avoided where higher pressure and/or thinner liquids are being pumped. There are options such as cartridge triple lip seals for pumping higher viscosity liquids.
A mechanical seal uses two highly-polished faces running against each other to form a seal. There are a myriad of different designs and seals for different applications, so this is the most adaptable and therefore most common type of seal. They can quickly and catastrophically fail however, so make sure it’s properly specified and regularly checked.
Technically a mag drive pump is seal-less, so shouldn’t be included here, but it’s an alternative to seals that is worth knowing about. Mag drive pumps use magnetic force to turn the shaft without there being any physical contact between the drive of the motor and the shaft of the pump. This makes them ideal for pumping liquids where zero leakage is required, but the price is much higher. A good option for high-value, high-risk pumping applications.