or formed rings that are compressed in the stuffing box of the pump.
As the packing is tightened, it compresses against the shaft and
stuffing box bore to create the seal.
- Excellent for sealing thick,
difficult to seal liquids such as chocolate, molasses, asphalt,
resins, tar, and some adhesives
- Seldom catastrophically fails
- Poor seal for thin liquids,
especially at higher pressures
- Requires lubrication either
externally or by the liquid being pumped; this means packing must be
allowed to leak slightly (weep)
- Can damage the pump shaft if
adjusted too tightly
circular elastomeric seal element in a rigid outer housing
- Come in a wide variety
including cartridge triple lip seals for higher viscosity liquids
- Typically limited to lower
- Poor for thin, non-lubricating
liquids or for abrasives
- Can catastrophically fail
Simplified, mechanical seals use highly polished faces (one stationary
and one rotating) running against each other* to form a seal.
*actually, seal faces only
touch when at rest. While turning, they are separated by a thin
film of the liquid being pumped, barrier fluid, or gas
- Mechanical seals come in a
wide variety of designs and materials for nearly every application.
- Offer designs which can be
easily replaced or repaired
- Like lip seals, can
- Higher end double cartridge
seals and gas barrier seals are quite expensive and require external
Drive pump is a sealless pump that utilizes a magnetic coupling to
create a static shaft seal. Drive magnets (outer) align with
driven magnets (inner) and use magnetic force to turn the shaft through
a static containment shell (canister).
- Mag Drive pumps are a truly
sealless design which ensures zero leakage of liquid or emissions,
making them ideal for hazardous, toxic, corrosive, flammable, or
- Extremely reliable for maximum
insurance against seal leakage and maximum seal life
- More expensive than most shaft
seal options, but this must also be weighed against the added costs
of seal replacement, including labor and cleanup.
- Typically limited to about
500�F / 260�C maximum (heat can permanently damage the magnets)
- Based on the cost and risk of
damage due to heat, monitoring devices are typically recommended to
protect these pumps from damage.