Models 947, 948 and 960 Leak Detectors Operations and Service Manual
1-25
1.16.2 Liquid Nitrogen (Models 948/960 only)
The amount of liquid nitrogen needed to keep the cold trap operational is approximately
three liters per day (slightly more on initial startup).
NOTE
Add liquid nitrogen to the trap only when the leak detector is
on and under vacuum.
1.16.3 Oil-Sealed Vacuum Pumps
The 947/948/960 is available with either dry or wet (oil-sealed) mechanical pumps. Units
built with oil-sealed pumps are shipped with the proper initial charge of oil, however, the
oil level should be checked after the pumps have been running for at least ten minutes. On
the front of each of the roughing and forepumps is an oil level sight glass. See “Rough Pump
and Forepump Oil Level Check (Oil-sealed Mechanical Pumps)” on page 4-32 for
instructions on how to check the oil level. The location of the mechanical pumps is shown
in Figure B-10 on page B-15. If you require more information, the pump manual you
received with the leak detector includes detailed instructions.
1.16.4 Special Installation Requirements
Additional services recommended for clean room use include:
Roughing/foreline
pump exhaust hose
Vent to the outside of the room using the KF-25 (ISO NW 25)
connection on the back of the leak detector. This reduces
particulate count and the helium background signal.
Cooling fan air
exhaust hose
Connect to the optional 4" air duct that can be installed on the back
of the unit. This reduces the air flow turbulence around the
machine and particle emanation from the inside of the leak
detector cabinet into the clean room.
Dry vent gas
Vent using the gas fitting on the back of the leak detector for the
nitrogen, or other gas. By using a dry vent gas instead of room air,
moisture contact with vacuum-exposed surfaces is decreased,
resulting in better pump down performance.
1.16.5 Installation Services
Installation, operational checkout, and operating instructions for your 947/948/960 can be
provided by a qualified Varian Vacuum Technologies representative.
When your leak detector is unpacked and the required services are available, contact your
local Varian Vacuum Technologies office to arrange for field installation.
