About Mechanical Compression Packing:

The problem of containing fluids in pumps has existed since the invention of the lift pump many centuries ago. Initially the rods on these early reciprocating pumps were sealed with lubricated fibers. Since that time, many types of fluid handling equipment have been developed which required increasingly sophisticated sealing devices.

The oldest of these devices is still the most common – mechanical compression packing – so named because of the way it functions. Mechanical compression packing is also called braided packing, gland packing or rope packing. It is found in almost every industry but is primarily used in processing industries. These can include pulp & paper, hydroelectric & power generation, petrochemical & refineries, mining, pharmaceuticals, wastewater treatment and among many other industries and applications. It is used to seal fluids and gases such as water, steam, acids, solvents, petroleum and other chemicals under a wide range of operating conditions.

Mechanical packings are made from various compliant fibers and appropriate lubricants that are selected for their suitability in specific applications. These materials are usually braided on specialized machines designed to generate a square cross section. This “square rope” is then cut into a number of rings that are fitted to the equipment shaft and inserted into the stuffing box (an annular space about the shaft in the equipment housing) which retains the packing.

The installed packing is compressed by tightening a gland against the packing, which is then forced to expand radially between the shaft and housing, creating a seal. Mechanical packings are the easiest sealing device to install, require little maintenance after installation, and when properly selected and installed, provide reliable service.

Mechanical compression packings used in both reciprocating and rotating equipment, depend upon the existence of a thin fluid film between the packing surface adjacent to the moving shaft for lubrication and cooling. Upon start-up, this film is initially provided by lubricants melted out of the packing itself (break-in lubricant). Shortly after start-up, the fluid being sealed (or a lubricating barrier fluid) provide this cooling lubrication on a continuing basis. If a clean barrier fluid (often called seal water) is used, there is usually a lantern ring (seal cage) inserted in the packing set at the axial location of the barrier fluid inlet.

During the break-in period, the gland is adjusted to gain control of leakage to reduce it to a minimum while maintaining the cooling and lubricating film on the shaft. If this process is too rapid or if the lubricating film is eliminated by over-tightening the packing set on the shaft, the packing can “burn out”. When this occurs, the inner surface of the ring set glazes (becomes hard and non-compliant) and the equipment must be repacked.


Mechanical packings are made in a variety of constructions. Each type of construction has a particular set of advantages and some disadvantages when compared to another construction. The principal types of braid which have been introduced over the past few centuries along with a radical improvement to the fourth type are described below:

Twist Braid

Twist Braid Twist is made from multiple yarns, or metallic ribbons by turning the individual strands around each other at a constant number of turns per foot (or per meter). Usually it is round in cross section but in the case of metallic ribbons, it is normally formed into a square section during the twisting operation. Single yarns of non-metallic twist may be removed from the twisted bundle to obtain optimum sizing in a stuffing box. This means that one size may be stocked to seal several stuffing box cross sections. Twisted metallic packings are frequently used as shaft bearing support in gear pumps in addition to performing their packing function.

Round braid

Round braid is made on maypole type braiding machines usually having between 8 and 32 yarn carriers on the braider deck. These machines generate a braided tube which may be used as a gasket tape. The finished packings are usually calendared into a square or rectangular cross section. If center strands or a plastic core are used, braid-over-braid and braid-over-core are generated.


Braid Over Braid Braid-over-braid packings are manufactured by braiding multiple jackets around a round braid, the size of the packing is determined by how many jackets have been braided one over the other. These packings can be quite dense and, when wire reinforced, are normally used in slow speed (below 500 FPM, 2,8 M/sec) high pressure applications like valve stems, blade type gate valves, expansion joints, older design plunger pumps, and in gear pumps. Braid-over-braid, when not reinforced with wire, is quite conformable and thus is useful in medium speed (to 1500 FPM, 7,6 M/sec) low pressure situations when equipment is worn as well as many of the applications above.


Braid-over-Core Braid-over-core packings are produced by round braiding one or more jackets over a central core. The core can be made of a variety of materials such as plastics however the most common core used is different grades of rubber compounds. Refer to our Vibradamp® Rubber Core Packings page for more information on why cores are used in certain applications.

Plait (Square) Braid

Square Braid Plait braid, commonly known as square braid, is manufactured on 8 to 24 carrier braiders having two tracks. This classic braid form, generated in a square cross section, is quite soft and normally contains a high percentage of lubricant. It is useful in high speed – low pressure applications (rotary and reciprocating pumps and valves). Since it is “softer” than interlocking braid, it is also useful where equipment is worn.

Interlocking Braid

Interlocking Braid Interlocking braid is generated on 3 and 4 track braiding machines usually with 12, 18, 20, 32 or 36 yarn carriers which weave the yarns from the surface diagonally through the body of the packing. Because each strand is locked into position by the other strands, an integral structure is formed that cannot easily work apart or unravel in use. It is relatively dense yet is flexible and conformable. These characteristics make it the most universal braid for use in rotating and reciprocating pumps, valves and other equipment even at the highest speeds and pressures. In typically constructed interlocking braid, there is an even density throughout the braid when straight.

The uniform density of the packing when straight creates the problem of non-uniformity when wrapped around a shaft or valve stem. It is the problem of the “Keystone Effect” which is applicable to all materials of square or rectangular cross section that are brought into a circle. This causes the tops of the packing ring to pinch inward while the bottom of the ring (along the shaft) is spread out laterally. This requires the packing to be forced back into a square shape to work. Refer to our ANTI-KEYSTONE® Design History page for more information on the “Keystone Effect”.

Other mechanical compression packing constructions include roll-up, extruded, laminated, die cut, molded, and machined. Each construction is used to form packings which answer the needs of a particular application.



The following steps are important to achieve the greatest value in service with mechanical packings:

  1. Proper selection of the packing material. The packing style must be carefully selected for a given application (equipment) and service (the fluid being sealed).
  2. Proper environment for the packing material. The controls to maintain the lubricating film must be provided.
  3. Proper equipment maintenance. The equipment must be in good operating condition – a true running, balanced shaft with a smooth polished sleeve ensures the longest service.
  4. Proper installation. Attention to fit and cleanliness during installation is essential.
  5. Proper break-in procedure. A little extra care at start-up can extend the service life of a packing set many times.



There are a few considerations one must make when selecting the proper packing to use in an application. Use this acronym to remember what you need to know.


S. Size: What are the stuffing box dimensions?
T. Temperature: What is the temperature of the fluid?
A. Application: What kind of equipment is it?
M. Media: What is the fluid being sealed? (pH)
P. Pressure: What is the pressure of the fluid?
S. Shaft Speed: What is the surface speed of the shaft?

Properly selected and installed, mechanical packing can provide the lowest cost and the highest value in service of any sealing device.


*Certain styles & sizes are special order only and may be subject to minimum quantities and/or additional terms & conditions.

**For informational purposes only. New England Braiding Co., Inc. (NEBCO™) believes this information to be the best available. Any specific application you have should not be undertaken without independent study and evaluation for suitability, safety and material compatibility. No warranty is expressed or implied as each application is unique. While we have used the utmost care in the preparation of this information, we assume no liability for errors or responsibility for consequential damages resulting from the use of these products.