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A mechanical shaft seal is supplied in place of a
packed stuffing box when specifically requested. The
change from packing to an alternate arrangement may
be made in the field by competent service personnel.
Conversion kits may be ordered from your
Goulds Water Technology Sales Representative.
Single mechanical seal
Pumps containing single mechanical seals normally
utilize the pumped liquid to lubricate the seal faces.
This method is preferred when the pumped liquid
is neither abrasive nor corrosive. If the liquid being
pumped is not suitable, an external flush should be
provided. (See "External Liquid Lubricant" page 22.)
Double mechanical seal
A double mechanical seal consists of two single seals
mounted back-to-back and a suitable sealing liquid
which is introduced into the seal chamber. The sealing
liquid (preferably clear water) is injected into the
box at a higher pressure than that which exists at the
entrance to the seal cavity on the pump side. The
pressure differential isolates the sealing faces from the
pumped liquid. Double mechanical seals are normally
preferred in pumps handling sewage, slurries, or any
other solids suspended in the pumped liquid.
Lubrication for the double seal is provided by the
sealing liquid which is introduced through the tap
in the seal cavity. The sealing liquid pressure must
always be higher than the pressure on the seal closer
to the suction side. If sufficient sealing pressure is not
maintained, the pressure within the pump can force
open the lower seal and allow the pumped liquid to
enter the box which can damage the seals.
Two methods are used to provide sealing liquid to the
stuffing box:
1. A common method utilizes a pressure line which is
installed from a tap on the discharge nozzle to the
tap in the stuffing box cartridge. A filter is installed in
the line to trap the solid particles. The filter must
be capable of screening out all particles above
25 microns in size.
Since the liquid is bypassed from the high pressure
(discharge) side of the pump, and dead-ended in the
stuffing box cartridge, there are no problems in
maintaining a sufficient pressure differential provided
the filter is not clogged.
2. Clear, clean water can be supplied from an external
source in some installations. City water can be used
if there is an air break between the water supply
and the water being provided to the pump. Various
municipal ordinances require this break to prevent
contamination of the city water supply.
Operation
Pre-start checks
Before initial start of the pump, make the following
inspections:
1. Check alignment between pump and motor
2. Check all connections to motor and starting device
with wiring diagram. Check voltage, phase, and
frequency on motor nameplate with line circuit.
3. Check suction and discharge piping and pressure
gauges for proper operation.
4. Check impeller adjustment, see specific section
for proper adjustment.
5. Turn rotating element by hand to assure that it
rotates freely.
6. Check stuffing box adjustment, lubrication,
and piping.
7. Check driver lubrication.
8. Assure that pump bearings are properly lubricated.
9. Assure that coupling is properly lubricated, if
required.
10. Assure that pump is full of liquid, (See "Priming"
below) and all valves are properly set and
operational, with the discharge valve closed,
and the suction valve open.
11. Check rotation. Be sure that the driver operates in
the direction indicated by the arrow on the pump
casing as serious damage can result if the pump
is operated with incorrect rotation. Check rotation
each time the motor leads have been disconnected.
CAUTION: ROTATION SHOULD BE CHECKED WITH
COUPLING DISCONNECTED ON COUPLED UNITS.
Priming
If the pump is installed with a positive head on the
suction, it can be primed by opening the suction and
vent valve and allowing the liquid to enter the casing.
If the pump is installed with a suction lift, priming must
be done by other methods such as foot valves,
ejectors, or by manually filling the casing and
suction line.
CAUTION: UNDER EITHER CONDITION, THE PUMP
MUST BE COMPLETELY FILLED WITH LIQUID
BEFORE STARTING. THE PUMP MUST NOT BE RUN
DRY IN THE HOPE IT WILL PRIME ITSELF. SERIOUS
DAMAGE TO THE PUMP MAY RESULT IF IT IS
STARTED DRY.
Starting
1. Close drain valves and valve in discharge line.
2. Open fully all valves in the suction line.
3. Turn on seal water to the stuffing box. (If pumped
fluid is dirty or if leakage of air is to be prevented,
these lines should be always left open.)
4. Prime the pump.
