Page 224 - Boiler_Operators_Handbook,_Second_Edition

Maintenance 209

gree with the water that’s in it to create another chemi- that the glass will break when you tighten the packing.
cal that helps bond it together. When using heat drying Packing of pumps usually includes a lantern ring
material it’s important to avoid letting it air dry. You (Figure 6-8) that has to be properly positioned in the
should fire up the boiler to apply the heat in accordance packing gland. Always count the number of pieces of
with manufacturer’s instructions as soon as possible. packing you take out from under one. The lantern ring
The best option is to use a combination material and it’s provides a space for distribution of leakage into or out of
always important to treat all of them gently so the repair the packing gland. When the packing is sealing the high
isn’t destroyed in its first few hours of operation. Bring pressure side of a pump the leakage into the space con-
the boiler up to operating temperature as slowly as pos- taining the lantern ring bleeds off to the pump suction,
sible. which is at a lower pressure. That recovers some of the
fluid. The remaining packing, between the lantern ring
and atmosphere is only exposed to suction pressure. For
PACKING cooling and lubricating some flows between the packing
and the shaft to the outside of the packing gland.
A lot of modern designs and new materials are When the packing is on the suction side of a pump
eliminating packing as I know it but it will be a long operating at pressures equal to or below atmospheric
time before you won’t encounter a pump, a valve, or the lantern ring space is piped to the pump discharge
other device with packing. Packing is material pressed or an intermediate pump stage. The purpose here is to
into a space between a metal housing and a metal shaft provide lubrication of the packing and shaft plus seal-
to provide a seal to prevent or control leakage of water, ing the pump to prevent air leaking into the fluid. That’s
steam, or another fluid. important for condensate pumps to keep oxygen out of
I trust you noted that I used the words (or control the condensate. Flow in that case is into the lantern ring
leakage) because in many pumps that’s very important. space. It then splits with some flowing into the pump
I’ve run into many a new operator or maintenance tech- suction and the rest leaking out of the packing gland in
nician that was thoroughly convinced that the packing the other direction.
on a pump shouldn’t leak and destroyed the pump by Whenever you’re re-packing a pump you should
tightening the packing to stop the leak. Unless a small be aware that the gland could contain a lantern ring. I re-
amount of fluid leaks along a constantly moving shaft member seeing one feed pump where the operators were
to lubricate the shaft, and protect it from rubbing, the not aware of the packing
packing will cut into the shaft. If you ever see a pump gland and had repeatedly
shaft or sleeve reduced in diameter with gouges from pressed the packing down
the packing that’s what happens. until the lantern ring was
Whether it’s a pump, a valve, a control float, it re-
ally doesn’t matter, there’s a standard arrangement for
installing packing. Many leaky valves I’ve seen consist
of a repair where the installer simply wrapped packing
around the shaft in a spiral, cut it off, jammed it in, and
expected it to seal. That doesn’t work. Packing should be
arranged in cut segments that barely fit around the shaft
stacked as shown in Figure 6-7. The stacking doesn’t
have to be precisely as shown, just alternate placing
the open seams first 180 degrees out of phase then 90
degrees to produce a complex path for any leakage to
follow.
It’s actually better to have the packing rings cut a
little short than a little long. If you have to jam the ends
together to get the packing into the opening it will create
a hard bump that can bear all the pressure placed on the
packing gland so the rest of the packing ring isn’t com-
Figure 6-7. Figure 6-8.
pressed and doesn’t seal. If you jam ends when packing
Packing segment stack Lantern ring
the gland on a gauge glass you’ve increased the odds