Packing seals, also known as gland packing, are traditional sealing systems used in pumps and valves to prevent leakage along shafts. They provide a simple and cost-effective sealing solution across a wide range of operating conditions, although they require regular adjustment and controlled leakage for lubrication. This page explains packing seal design, materials, operating limits and typical engineering applications.
Packing seals work by compressing soft or metallic packing rings around a shaft to restrict fluid leakage. The sealing effectiveness depends on the applied gland force, packing material properties and operating conditions. A small amount of leakage is necessary to provide lubrication and prevent overheating.
The packed gland is used primarily for sealing process valve shafts (axial movement) and for process pump shafts(rotary movement). The packed gland has provided a low tech. convenient solution throughout the history of engineering. In modern times the packed gland is being replaced by more exotic solutions.
A packed gland seal consists of rings of compressible packing material installed within a stuffing box and compressed around the shaft using a gland follower. The compression creates a sealing effect while allowing slight controlled leakage for lubrication and cooling.
The packed gland seal for pump applications is now rarely fitted to new pumps. This is due to it's high maintenance requirements. When fitted it is mostly used in conjunction with long coupled bed plate mounted pumps. Specific operating conditions require distinctly different types of packed gland seals. They require regular checks and maintenance adjustments.. Proper lubrication of the gland packing requires a certain leakage rate. Special manufacturers recommendation's are to be observed individually. Service life expectancy is between 1 and 2 years, this can sometimes extend to several years on favourable conditions. Extremely bad fluid conditions (sediments, additives, overheating) can however drastically cut short their service life. Packed glands should preferably be used in conjunction with shaft sleeves in order to avoid damage to the shaft by aggressive fluids or due to improper treatment of the packed gland.
The packed gland is still widely used for stem sealing of various types of
valves including gate valves, globe valves, and ball valves. The packed gland provides a low cost
option with the capabilities of sealing under a wide range of operating conditions with a wide range of
fluids by selecting appropriate packing materials. A packed gland is often used in conjunction
with another type of seal or fluid containment e.g an o-ring seals, bellows containment etc.
The gland packing generally creeps over time and therefore needs to be regularly tightened to maintain
the seal. The packing can be continuously spring loaded using disc springs or similar to extend
the maintenance period.
The properties of a packing system required for good sealing and trouble free operation include
Yarn packings can be based on vegetable , animal or synthetic fibres and are based on various types of fibre.
In plaited and braided packings reinforcing wires are used for operation at higher
temperatures and pressures. For high temperatures, woven types of copper and
aluminium packing can be produces. Metal foils of lead, aluminium, and copper can be
used to form packings.
Combinations of packings having hard metal end rings with softer inner rings are
used for higher performance duties including gases and abrasive fluids.
Annular rings are sometimes included between two sets of packings to allow introduction of lubricant, cooling or flushing fluid.
The shaft/ sleeve surface in contact with the seal should have a surface finsh of 0.4 micrometres or better. The clearances above and below the packings should be such to prevent extrusion of the packing material along the shaft. The clearance should not be too small that contact between the static and rotating metal is possible
Table provided for guidance only, final design values must be obtained from suppliers
| Material | Temperature Range Deg C |
| Jute, Flax, hemp | 0 to 60 |
| Cotton | 0 to 70 |
| Rubberised Cotton | 0 to 80 |
| PTFE | -250 to 220 |
| Aramid | -200 to 280 |
| Aluminium Mesh | 0 to 420 |
| Wrapped Metal foils-Varios types | 0 to 450 |
| Graphite Fibre | -200 to 600 |
| Asbestos Reinforced St.Steel or Inconel | 0 to 800 |
| Copper Mesh | 0 to 800 |
| Aluminia Silica filiment/ Inconel reinforced | 0 to 1200 |
Table provided for guidance only, final design values must be obtained from suppliers
| Material | Surface Speed Range m/s |
| Aluminia- silica | 0 to 0.2 |
| Copper Mesh | 0 to 0.5 |
| Jute | 0 to 4 |
| Hemp and Cotton | 0 to 6 |
| Flax | 0 to 10 |
| PTFE | 0 to 12 |
| Wrapped Metal foils-Various types | 0 to 20 |
| Aramid | 0 to 22 |
| Aluminium Mesh | 0 to 25 |
| Asbestos (Not acceptable -UK) | 0 to 25 |
| Grahite Fibre /Foil | 0 to 50 |