Material guides, tolerances and the questions we get asked most

Gland packing is a braided sealing material compressed into the stuffing box around a rotating or reciprocating shaft, on pumps, valves and agitators. Tightening the gland follower squeezes the rings against the shaft, leaving a small controlled leak that lubricates and cools the contact face. It is a maintainable seal: rings can be adjusted or replaced in place rather than dismantling the equipment.

Packing is classified by the fibre it is braided from. Graphite for high temperature and steam; PTFE for chemical resistance and high-purity duty; aramid for abrasive media and higher pressures; carbonised fibre as a general-purpose high-temperature option; and natural fibres such as flax or cotton for water and lighter duty. Most are supplied with a PTFE or graphite impregnation to lower friction on the shaft.

Broadly, graphite for heat and PTFE for chemicals. Graphite conducts heat away from the shaft and stays stable at high temperature, which suits steam and hot process duty. PTFE is chemically inert to almost everything and has very low friction, which suits aggressive media and high-purity applications. Where both matter, a PTFE-impregnated graphite or a combination braid is the usual answer.

Flexible graphite tape is wound as the filler inside spiral wound gaskets, and used as a sealing strip on valve stems, flange faces and irregular joints. It conforms to imperfect surfaces and tolerates high temperature. It is supplied plain or with a self-adhesive backing to hold it in place during assembly.

Most stuffing boxes take four to six rings, depending on the depth of the box. Cut each ring square to length rather than coiling one continuous piece, stagger the joints by 90 degrees or more as you fit them, and seat each ring individually before adding the next. Leave room for the gland follower to enter the box, because if it bottoms out the packing cannot be tightened later.

Seawater is mildly abrasive and corrosive rather than chemically aggressive, so the usual choice is an aramid or aramid/PTFE braid, which resists abrasion without scoring the shaft. Pure PTFE is chemically capable but softer and wears faster under abrasive duty. A lantern ring with a clean flush is normally used to keep grit out of the packing.

Thickness follows the condition of the flange, not the pipe size. A machined, flat, clean face needs only a thin sheet; worn or pitted faces need more material to bridge the damage. Thicker is not safer: a thick gasket relaxes more after installation, needs more bolt load to seat, and is easier to blow out.