8 Pumps
308
is a braided rope, mostly manufactured from teflon and graphite. It is appropriate
for circumferential speeds under 20 m/s and pressures under 15 bar. A small leakage
flow should be allowed for lubrication and for removing friction heat. If the pumped
liquid contains solid particles, it may be advantageous to rinse the packing rings
with pure liquid from an external source. This rinsing prevents the solid particles
from penetrating into the packing. The rinse water is pressed into the seal through a
ring with radial perforations, placed halfway the stuffing box. Liquid injection may
be useful as well if the pump is operated with a suction pressure lower than atmospheric pressure, to prevent air intake. The injection liquid may then be tapped from
Fig. 8.20 Multistage vertical
pump. (courtesy ANDRITZ)
Fig. 8.19 Axially split casing
double-suction pump. (courtesy Sulzer)