Instruction manual

Issue H Oct 04
PAGE
2
GV Dry Vacuum Pumps
INTRODUCTION
2
1.4 Cooling system
Note: The direct cooling system fitted to the pump is
suitable for pump operating temperatures
(measured at the position shown in Figure 1,
item 3) of up to 45
o
C, (113
o
F). If your
application requires pump operating
temperatures of 45 to 90
o
C (113 to 194
o
F),
we recommend that you fit an Indirect Cooling
Kit accessory: refer to Section 7.4.4.
Refer to Figure 1. The pump has a direct cooling
system, in which cooling-water (connected through
the water inlet, 7) circulates around the pump-body
and then passes out of the pump through the outlet
(2). The pump-motor (16) is air-cooled by an
integral cooling-fan (19).
A thermal snap-switch box (4) is fitted to the pump-
body. The snap-switch box has two thermal snap-
switches:
• The output of the warning thermal snap-
switch will go open circuit when the
temperature of the pump-body is higher than
normal. Use this output to provide a warning
of high pump temperature.
• The output of the shut-down thermal snap-
switch will go open circuit when the
temperature of the pump-body is too high.
Use this output to shut-down the pump when
it is too hot.
1.5 Interstage relief valve
The pump has an interstage relief valve (12) fitted in
a pipe between the pump-outlet and the last stage of
the pump. The valve is normally held closed by its
own weight, but opens depending on the pump-inlet
pressure, as follows:
• At pump-inlet pressures of 300 mbar (3 x 10
4
Pa, 225 torr) and above on the GV250, and at
pump-inlet pressures of 200 mbar (2.0 x 10
4
Pa, 150 torr) and above on the GV400, the
interstage pressure forces the valve open.
This allows process gases to pass directly
from the second stage into the pump-outlet,
without compression in the third stage of the
pump.
• At pump-inlet pressures below those
specified above, the interstage pressure is low
and the valve is held closed. Process gases
pass through all stages of the pump; that is,
the process gases are compressed in the third
stage before they pass into the pump-outlet.
The interstage relief valve allows the pump to
provide a constant pumping speed from
atmospheric pressure down to 10 mbar (1 x 10
3
Pa,
7.5 torr) and also prevents excessive electrical
power consumption by the pump-motor when the
pump starts.
Figure 1 - The GV pump: key
1. Gearbox
2. Cooling-water outlet
3. Temperature measurement point
4. Thermal snap-switch box
5. Lifting-bolt
6. Pump-inlet
7. Cooling-water inlet
8. Fixing-holes
9. Frame
10. Gas-ballast flow valve
11. Exhaust-purge port (blanked)
12. Interstage relief valve
13. Pump-outlet
14. Oil-level sight-glass
15. Coupling cover
16. Pump-motor
17. Arrow showing motor rotation direction
18. Correct direction of rotation arrow
19. Motor cooling-fan
20. Oil drain-plug
21. Oil filler-plug
22. Shaft-seals purge inlet