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Installation
1-6
WARNING
Utility failure can cause damage to the equipment, overheating, and
possible explosions. Designers of the equipment using diffusion pumps
must design their system to protect personnel and property from possi-
ble hazards.
1-6 UTILITY AND SYSTEM CONNECTIONS
1-6-1 Safety Considerations and Interlocks
a. Large pumps are equipped with two thermal switches. Both thermal switches on the HS-20
diffusion pump are mounted on a thermal strap located on the side of the pump. These ther-
mal switches are supplied normally closed. The thermal switches have been designed so
that a cooling water failure, high inlet pressure, or low oil level in the boiler will result in an
increase in temperature, causing the normally closed contacts of the switches to open.
When the problem has been corrected and the temperature lowered, the thermal switch will
automatically reset itself.
b. A small lamp of the same voltage as the diffusion pump heater may be connected across the ter-
minals of the thermal switch.The lamp will normally be shunted by the contacts. However, when
the contacts open, the lamp will receive full line voltage and give a visual trouble indication.
1-6-2 Vacuum Connections
a. The pump must be installed with the body vertical and plumb. Check that the mating flange on
the system (to the pump inlet) is horizontal within plus or minus 1 degree. If this condition is
not met, correct the system before installing the pump. The boiler of the pump (especially for
large pumps) must be horizontal to prevent uneven fluid level and avoid local overheating
where the fluid level would be too shallow.
b. Prepare inlet O-ring seals by wiping them with a clean cloth. Do not use solvents. Use a small
amount of diffusion pump oil to wet the cleaning cloth. Install the O-ring in the groove being
careful not to damage the sealing surface with cuts, nicks, or scratches.
c. Using appropriate lifting apparatus, align the bolt holes of the flanges and assemble the bolts.
Tighten the bolts evenly to compress the O-ring seal until light contact is achieved between
metal flanges.
d. Check fill and drain plugs and the sight glass assembly for tightness. Apply light to medium
torque, enough to compress gaskets. Minute leaks through the gaskets may develop with use
in this location. They may be detectable with very sensitive mass spectrometer leak detectors.
1-6-3 Cooling Water Connections (See Figure 1-3)
The following method of external connections is recommended.
a. Water connections are designed for
1
⁄4 FPT fittings. The cold cap cooling coil and all of the
body and foreline cooling should be connected in series. A cooling water supply of 1.5 gpm at
60°F to 80°F (16°C to 27°C) should be adequate. A higher flow than this will not be harmful.