Valve stem seals for LIP-TYPE Packings
| Lip-type packing expand laterally because of the flexibility of their lips, which are forced against the restraining side walls by the fluid pressure. This mode of expansion of the packing permits the use of relatively rigid construction materials, which would not perform as well in compression packing. On the debit side, the sealing action of lip-type packing is in one direction only. |
| Most lip-type packing for valve stems are made of virgin or filled PTFE. However, fabric-reinforced rubber and leather are also used, mainly for hydraulic applications. Most lip-type packing for valve stems are V shaped, because they accommodate themselves conveniently in narrow packing spaces. |
| The rings of V-packing made of PTFE and reinforced rubber are designed to touch each other on small areas near the tips of thier lips, and large areas are separated by a gap that permits the fluid pressure to act freely on the lips. Leather V-packing ring lack the rigidity of those made of PTFE and reinforced rubber, and are therefore designed to fully support each other. |
V-packing made of PTFE and reinforced rubber are commonly provided with flared lips that
automatically preload the restraining lateral faces. In this case, only slight initial tightening of
the packing is necessary to achieve a fluid seal. V-packing rings made of leather have straight
walls and require a slightly higher axial preload. If a low packing friction is important, as in
automatic control valves, the packing is frequently loaded from the bottom by a spring of
predetermined strength to prevent manual overloading of the packing.
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