Packing Rings

High safety and economic efficiency

Pre-pressed graphite rings are used either in endless or split design. The split design allows rings to be replaced without complete disassembly of the gland. As variants for stuffing box packings there are cords type MMD-GP-C as yard goods, but also compression molded rings type MMD-GP-C-MR, mostly with oblique slits. The package is cut to the appropriate length and pre-pressed in a mold. The most common variants are compression molded rings type MMD-GP-MR made of graphite or PTFE-graphite compounds. To reduce friction and diffusion, the graphite packing ring can be provided with a PTFE sleeve (PTFE jacket) type MMD-GP-MR-TFJ. To reliably prevent blowing out, compression molded graphite rings with burst protection rings (blow-out preventers) type MMD-GP-BOP are chambered from laminated graphite flat gaskets with metallic smooth foil inserts.

The packing and burst protection rings can also be used alternately to reduce friction. The optimum quantity is three rings, more than five rings should not be used if possible.

Materials

Different materials are used for packings and cords. They determine the application limits with their material properties. The most common type is a packing made of one material, with or without additional impregnation or lubricant.

Positive properties can be achieved by combining different packing yarns. Packings with cross braiding, supporting edges made of a stronger yarn, often aramid, chamber the PTFE or PTFE-graphite fibres and improve the oscillating properties. This makes them particularly suitable for piston pumps. Material combinations of aramid and PTFE-graphite, PTFE and PTFE-graphite fibres or PTFE and aramid fibres as hybrid braiding improve the properties in the rotating direction and are therefore particularly suitable for pumps with a high number of revolutions.

Spindle sealing systems

The Chevron-Sealings of the MMD-GSS-CHS type are made of PTFE, PTFE-graphite compounds or other materials. The pressure rings and support rings can also be made of metallic materials such as stainless steel or bronze. In addition to the frequently used ones, systems made of laminated packing rings MMD-GP-MR or MMD-GP-MR-TFJ with burst protection rings MMD-GP-BOP are also used. The versions with only burst protection rings MMD-GSS-PC generate higher friction forces than the types with mixed rings MMD-GSS-PCM. Relatively slim packing systems can be realized by laminating the burst protection rings onto a packing ring at only half the height. It is recommended that these systems are not used in a split design.

Gland packings are increasingly being replaced by systems such as MMD-GSS. Their advantage is the low leak rate, their disadvantage is the reduced maximum operating temperature due to the O-ring materials. The carriers can be made of elastomers (PEAK, PP, etc.) or metallic materials.