1. VIII. Production of Vacuum

2. Mechanical Pumps
Rotary Vane Pumps
Rotary vane pumps of 10 to
200 m3/h displacement are
used for roughing pumping
and for backing diffusion or
turbomolecular pumps.

3. Two stage rotary pump : lower ultimate pressure
The pumping speed characteristics of single stage and
two-stage rotary vane pumps.

4. Condensation of water or acetone occurs during the
compression stage.
To avoid condensation, gas (air) is admitted through the ballast value.
The added gas causes the discharge value to open before it
reaches the condensation partial pressure of the vapor.

5. Rotary Piston Pumps
- Rotary piston pumps are used as roughing pumps on large
systems alone or in combination with lobe blowers.
- 30 ~ 1500 m3/h
Lobe pumps (Roots pumps)
- Lobe blowers are used in series with rotary pumps to achieve
higher pumping speed and lower ultimate pressure in the medium
vacuum region  The combination costs less than a rotary pumps
of similar capacity
~ 3500 rpm

6. C (blower + rotary piston)
D (rotary piston)
A (blower + rotary vane)
B (rotary vane)

7. Mechanical pump operation
- The exhaust should be vented outside the building
- The vent hose should not run vertically from the exhaust
connection  condensible gas contaminates the pump fluid.
Turbomolecular Pumps
- High pumping speeds, large hydrogen compression ratio,
low ultimate pressures, no backstreaming.

8. TMP is a molecular turbine that compresses gas by momentum
transfer from the high speed rotating blades to the gas molecules
– high speed molecular bat ; 24,000 ~ 60,000 rpm
The blades impart momentum to the gas molecules most efficiently
in the molecular flow region; therefore TMP, like a diffusion pump,
must be backed by a mechanical pump.
Speed-Compression Relationship /
Inlet / outlet
1=flux on the disk at inlet
2=flux on the disk at outlet
a12=fraction of 1 transmitted from
inlet to outlet

9. For no gas flow (ultimate pressure) : W = 0

11. - Maximum speed (pumping) is achieved
when K=1 (pressure drop is zero)
- Ultimate pressure is determined by the K for light gases and
by the amount of outgassing.
 similar to diffusion pump
but diffusion pump has higher K for light gases.
- Hydrogen gas will constitute more than 99% of the residual
gas at the ultimate pressure.

12. Diffusion Pump

13. DP is a vapor jet pump which transports gas by momentum transfer
on collision with the vapor steam. (supersonic)
The maximum “ fore pressure” is less than the boiler pressure
( ~ 200Pa)
25 ~ 75 Pa

14. The DP must be “backed” by another mechanical pump in order
to keep the fore pressure below the critical fore pressure.
Back streaming : pump fluid  chamber
To reduce backstreaming :
use low vapor pressure fluids
water cooled cap (baffle)
LN2 trap

15. Getter and Ion Pumps
- capture gas molecules and bind them to a surface
- clean pump
- certain gases will displace other adsorbed gases and contaminate
“ memory effect ”
Titanium Sublimation Pump (TSP)
- Titanium can be sublimed at lower temperature than other
metals, inexpensive
- Active gases are captured on the fresh titanium surface which
is cooled with water on LN2 to enhance the sticking coefficient.

16. • active gases – large sticking
coefficient at RT.
• hydrogen gases diffuse into
underlying film
• noble gases are not pumped
at all
- TSP operates at pressures below 10-1 Pa
- TSP is used to aid in crossover between a sorption pump
and an ion pump
- TSP is used intermittently at low pressures to provide high speed
pumping of reactive gases.

17. Ion pumps
- It is possible to pump to the ultrahigh vacuum region without
organic contamination.
- Similar to pumping gases by ions in Bayard-Alpert gauges.
- Ions are more reactive with surfaces than neutrals.
Physically embedded in the pump walls if they are energetic.
- “Memory effect” ~ disadvantage
Triode pump
Diode ion pump

18. • Noble gases are not efficiently pumped.
In the triode ion pump the argon pumping speeds are as high as
20% of the N2 speed. This high speed (high implantation rate)
results from the high energy of the neutrals which are scattered
at small angles from the cathode walls with little energy loss.
• Organic gas : easily pumped
• Active gas (O2, CO, N2) : easily pumped  titanium compounds
• H2 : diffuse into the bulk of the titanium hydride