Cryo-Torr High-Vacuum Pump Installation, Operation and Maintenance Instructions
P/N 8040613
2-7
C
HELIX TECHNOLOGY CORPORATION
-
TI
CRYOGENICS
Optimizing Crossover Pressure
The calculated crossover pressure may not be optimized for your system.
To help prevent any backstreaming during the roughing of the vacuum
chamber, you should stop roughing at as high a pressure as possible. The
optimum crossover pressure for a vacuum chamber should cause a very
slight rise in temperature with a rapid recovery. Increase the roughing
pressure in small increments (15-20%) until the rise in temperature is
noted; then drop the value by a small amount (10%). This will be the
optimum pressure for that vacuum chamber.
Cryo-Torr Cryopump Capacity Calculations
Cryopump capacity is defined as the total standard liters of gas that can be
accommodated within a cryopump prior to regeneration. The number of
hours between regeneration cycles can be easily calculated in the case of a
continuous gas flow of a known gas species:
Where:
A = Duration of operation with a continuous gas flow (hours)
B = Gas flow (scc/min.)
C = Cryo-Torr capacity for the particular gas species being flowed (std.
liters) as shown in Table 2-2.
Table 2-2: Condensable Gases Capacity (Argon, Nitrogen, Oxygen, etc.)
Parameter
Value
Cryopump
Cryo-Torr 10F
Standard Liters
2000
Torr-Liters
1,500,000
A =
16.6 x C
B
