5 Operation
5.1 Stuffing box
1.
Stuffing boxes with packing rings - less quenching liquid or grease lubricator:
Periodically inspect stuffing box to see that there is sufficient leakage to lubricate the packing and
maintain a cool box. Never draw up packing so that the stuffing box heats, as this will cause
damage to both packing and sleeve. Draw up gland nuts slowly and evenly and only when pump
is running.
After pump has been in operation for some time and the packing has been completely run in, at
least 40 to 60 drops per minute of the liquid should be allowed to trickle from the stuffing box at
all times for cooling and lubricating the packing and shaft sleeve.
2.
Stuffing boxes with packing rings - with quenching liquid:
The same precautions as described above apply. However, the amount of leakage through the
packing cannot be easily determined, due to the quenching liquid. In most cases, the valve on
the quenching liquid supply line can be shut off for a short period and the amount of leakage de-
termined as in step1 above. In no instance should the gland be drawn up tight. Never throttle the
clean liquid supply into the stuffing box as a substitute for proper adjustment of packing, a steady
flow from the seal cage into the pump is required to prevent entrance of pumpage into the pack-
ing.
3.
Stuffing boxes with packing rings - with grease lubricator:
Operation is the same as directed in step 1 above, with the addition that the handle on the lubri-
cator should be given a tum or two about every 100 hours of operation.
4.
Stuffing boxes with mechanical seal:
This type of box requires no attention other than to make sure that the circulating lines do not
become clogged.
5.2 Operating at reduced capacities
Do not operate a centrifugal pump at greatly reduced capacities or with discharge gate valve closed, be-
cause the energy required to drive the pump is converted into heat. The temperature of the liquid in the
pump may increase until the boiling point is reached. If this occurs, the rotating parts are exposed to va-
por with no lubrication and they may score or even seize to the stationary parts.
NOTICE:
If running clearances have enlarged due to wear, seizure may not take place and continued
operation under these conditions may create an explosive
Hazard due to the confined vapor under high pressure and temperature.
To guard against possible damage, protective devices are available, such as:
1.
Liquid temperature relay or thermostat which will shut off the unit if the liquid temperature in the
pump exceeds a predetermined maximum. This device guards against possible damage due to
running the pump against a closed valve.
2.
Constant open by-pass orifice between the pump discharge and any check or regulating valve in
the discharge line. The liquid through the orifice is returned to the suction source. The amount of
liquid bypassed is a function of input horsepower and the allowable temperature rise. This device
5 Operation
34
3107 Installation, Operation and Maintenance Instructions
