Teikoku USA | Chempump
Instruction Manual G-Series
15
2.4.2 Reverse Circulation (Plan 13-SE)
For normal clean fluid applications, G-Series pumps are cooled
and lubricated by the fluid being pumped; which flows through
the circulating tube; into the rear of the rotor chamber; across
the rear bearing, rotor, and front bearing; and then back into the
main pumped stream through small holes provided in the rear of
the impeller in the suction area. However, when the fluid being
pumped is at or near its boiling point, plus the additional heat
picked up from the motor, combined with the low pressure at the
impeller suction, the recirculated fluid may vaporize. The reverse
circulation method of lubricating the bearings and cooling the
motor should be used. Flow rates should duplicate those shown
in
Table 2-8
.
With reverse circulation, the rotor chamber will be under dis-
charge pressure, with cooling fluid circulating from the pump
end, through the rotor chamber, out the rear bearing housing,
and back to the vapor space of the suction vessel. Flow through
stator-rotor cavity must be controlled to allow for a good balance
of pressure and temperature without excessive flow, typically
through the use of an orifice. See
Figure 2-4
, for a typical reverse
circulation installation. When provided, the reverse circulation
modification is noted on the order.
Procedure:
1. Connect tubing or flanged piping (preferably 1/2" tubing at
least) to the circulating tube port in the rear bearing housing.
2. Run the tubing from the connection port fitting in the rear
bearing housing back to the vapor space of the suction re-
ceiver, preferably above the liquid level.
3. Use large size suction line and gate valve for a low pressure
drop and thus improve available NPSH.
2.4.3 Pressurized Circulation (Plan 1-SD)
As an option to reverse circulation when pumping fluids close to
their vapor pressure, pressurized circulation may be used. Fluid
to cool the motor flows from the pump discharge to an auxiliary
impeller (See
Figure 2-5
) in the back of the pump that adds pres-
sure to the flow through the motor and returns the flow to the
main stream at discharge pressure. With this recirculation system,
the fluid heated by the motor is at sufficient pressure so the heat
added by the motor will not cause the fluid to vaporize.
2.4.4 Electrical Isolation
To eliminate electrolytic corrosion when handling solutions during
an electrolysis or plating operation, the G-Series pump should be
electrically isolated. Insulated couplings or nonconductive plastic
piping must be used in the primary suction and discharge lines.
The pump must be isolated electrically from the tank, and sepa-
rately grounded as shown in
Figure 2-6
.
Figure 2-4. Reverse Circulation
LOWEST LIQUID LEVEL
HIGHEST LIQUID LEVEL
REVERSE PIPE
BYPASS PIPE
SUCTION
DISCHARGE
Q
S
Q
D
Q
R
Q
M
HRS
Q
S
Q
D
Q
M
Q
R
RESTRICTION
ORIFICE
Figure 2-5. Pressurized Circulation
LOWEST LIQUID LEVEL
HIGHEST LIQUID LEVEL
VENT PIPE
SUCTION
DISCHARGE
Q
S
Q
D
Q
V
HRS
Q
S
Q
D
Q
V
Figure 2-6. Back-Flush Installation with Electrical Isolation
