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the shaft, is supplied through one opening by the pump helix. Product leaking through the
seal is removed through the other opening.
Pacific has developed a radial seal (see Fig. 4b) for bottom-entry agitator shafts. This
can be used at process fluid pressures p ~ 10-15 atm, temperature T ~ 200~ and shaft rota-
tion speed v ~ 4 m/sec. Springs, which rotate with the shaft, provide contact between the
sealing rings. Operating fluid leakage through the seal is removed through an opening with
the sealing fluid. Accumulation of solids or crystallized product in the seal zone is pre-
vented by constant circulation of the sealing fluid. Operating fluid leakage is removed
through one of the openings.
Pacific has developed a special radial seal for 240 mm diameter shafts used in a 200
m 3 volume polymerization reactor and 20 atm process fluid pressure with a bottom-entering
agitator (Fig. 5). The reliability of this seal is increased by using a special safety sys-
tem which prevents entry of the process fluid into the seal housing during emergency or ex-
cess leakage. This seal and drive can be repaired without removing product from the vessel
by the design of this system. The safety system consists of rings which are pressed to the
ridge of the shaft by oil pressure in case of an emergency. This prevents ingress of the
operating fluid into the seal. The seal can then be removed from the shaft and disassembled.
Examination of the exhibits showed that foreign firms have developed special designs of
mechanical seals for bottom-entry drive and small radial seals as well as improving existing
designs of mechanical seals for agitators. High seal efficiency under severe conditions is
achieved by using special cooling systems and the selection of high-quality anti-friction
materials for the sealing rings. Process temperature limit is 2000C for seals without special
cooling. Seals with cooling systems can operate up to 350~ Unbalanced seals are used in
vessels with 14 atm maximum pressure, 15 atm the sealing fluid pressure, and 4 m/sec sliding
speed.
Mechanical seals for agitators assembled with special cooling systems are supplied by
Pacific and Burgmann. The operation of these systems is based on natural circulation in sys-