FORMULA & FACTORS
1
standard atmosphere = 760 torr (mm Hg) - 29.9"
1 inch Hg = 25.3 torr (mm Hg)
1 mm Hg = 1000 millitorr (microns) = 1 torr
.1 mm Hg = 100 millitorr (microns) = 10-¹ torr
.01 mm Hg = 10 millitorr (microns) = 10-² torr
.001 mm Hg = 1 millitorr (micron) = 10-³ torr
.0001 mm Hg = .1 millitorr (micron) = 10-4 torr
1 ft.³ = 28.3 liters
1 CFM = 28.3 1/min = 0.47 1/sec
1 1/sec = 2.12 CFM
Pump
down time and pump speed
T
= time in minutes
S = average pumping speed between atmosphere and desired
pressure
V = Volume in liters or CFM (cubic feet per minute)
F = Factor determined by desired pressure
=8 at 1 torr
=10 at 100 millitorr
= 12 at 10 millitorr
EXAMPLES
1.
Your customer has a volume (V) of 3 CFM that he has to evacute
to 100 millitorr (F=10) in 4 minutes (T)
answer
= T
divided by VF = S, (4 divided by 3.10 = 7.5
CFM)
2. John Smith has a volume
of 5 CFF he wants to evacute to 10 millitorr with a 1397 pump (17.7
CFM). How long will it take?
answer
= S
divided by VF = T, (16.3 divided by 5.12 = 60 over 16.3
= 3.7 minutes)
|
