Gland pack for reciprocating machines operating at high pressure

A gland pack for reciprocating machines operating at high pressure, constituted by a number of cylindrical gland boxes disposed adjoining each other concentric to the machine plunger and extending axially along said plunger from the head end to the crank mechanism end of said machine, said gland boxes each comprising a flat sided cavity concentric to the plunger and open towards it, in the first cavity or cavities at the head end there being housed a pressure breaking ring or rings, whereas in each of the subsequent cavities there is housed a seal assembly arranged to press a seal element against the plunger by the effect of the pressure difference between its exterior and interior, wherein said seal assembly is constituted by three flat sided rings adjoining each other along their adjacent flat sides, of which the central ring, enclosed coaxially between a first and a second metal anti-extrusion ring and constituting the seal element, is constructed of self-lubricating plastics material and is composed of a number of pseudotangentially cut segments held together by a circumferential spring, and said first metal anti-extrusion ring situated at the head end of the cavity comprises radial grooves in its flat surface on the head side, the said two first and second metal anti-extrusion rings being sized such that there is a small radial gap between them and the plunger traversing their bore, and such as to deform elastically by reducing their diameter when subjected to a differential pressure between their exterior and interior, and thus approach the surface of the plunger but without ever pressing against it.