High Vacuum Pump Stacks, Cryopumps, Turbomolecular Pumps, and Clean High Vacuum Pumps from Bemco Inc.

Recommended High Vacuum Pumping Systems

Pump Type	Primary Advantages	Primary Disadvantages	Pressure
Description	As a High Vacuum pump	As a High Vacuum pump	Ultimate
Helium Cryopump	Clean pumping and high speed	Regeneration, Noble Gasses (2)	5 x 10-8 Torr (1)
Turbomolecular	Clean pumping, no regen.	Potential vibration, low speed	5 x 10-8 Torr (1)
Ion Pump	Clean pumping, no regen.	Low speed, magnetic field	5 x 10-8 Torr (1)
Oil Diffusion Pump	Pumps all gasses, inexpensive	Oil back streaming in workspace	5 x 10-8 Torr (1)
Ti Sublimation	Pumps all gasses	Sputtering of Titanium, service (3)	5 x 10-8 Torr (1)

Pump Table Notes:

Refer to the "System Performance Chart" below for standard system ultimate and working pressure ranges.
Cryopumps require periodic regeneration and have limited capacity for pumping noble gasses
Ti Sublimation pumps require periodic replacement of the Titanium source.

Cryopumps

Cryopumps work by cryocondensation and freezing. Cryopumps selected by Bemco are multistage systems that first trap condensable gases such as water on an external shield maintained at approximately -185 C, then condense or freeze gasses that are susceptible at about -263 C, and finally trap (cryoadsorb) the remaining gasses like helium, hydrogen, and neon within an expanded matrix maintained at about -265 C.

Because gasses are condensed, frozen, and trapped, the pump requires regeneration when its internal surfaces become saturated. Cryopumps are the cleanest type of high vacuum pump. They utilize no exposed lubricants or fluids.

Turbopumps

Bemco Drawing of Turbomolecular Pump Stack

Resembling a jet engine, turbo molecular pumps recommended by Bemco are usually of the modern Turbo-Drag type. These pumps work by progressively mechanically accelerating molecules with multiple angled blades and by momentum transfer. Molecules that enter the throat of the pump are forced downward towards higher pressure. A drawing of a turbopump with roughing valve, slide valve, right angle elbow, and elbow cold trap is shown at the left. An optional elbow heat exchanger is shown to limit thermal face loading on the pump at high temperature.

Bemco selected pumps utilize magnetic levitation and a dedicated motor speed control to eliminate the need for bearing lubrication, maintain alignment, and reduce wear. For proper operation these pumps require a backing pump.

They are generally more expensive than a Cryopump but offer the ability to reliably pump particle laden and corrosive gasses.

Other High Vacuum Pumps

Bemco Integral Ion Pump End Bell, 10 Feet Diameter

A large (10-feet in diameter) Bemco designed, triode type, integral Ion pump is shown to the left. Sputter ion pumps operate by ionizing gas within a magnetically confined cold cathode discharge. This type of pump requires a high voltage power supply and is more expensive than a Cryopump. They do a good job of pumping noble gasses.

Oil diffusion pumps are chosen for their ability to pump almost all gasses. They are currently seldom selected due to their potential for hydrocarbon back streaming. Many diffusion pumps are still in use in older facilities. Bemco offers large scale cryopumps with liquid nitrogen cooled outer shrouds and cryoengine cooled inner structures to replace pumps from 36-inches to 72-inches in diameter. These replacement units utilize commercial cryoengines combined with Bemco thermal shroud and vacuum vessel technology. We also provide replacement cryopump and turbomolecular pump stacks for smaller systems. Please request an analysis of your replacement needs.

Recommended Roughing Pump Systems

Pump Type	Primary Advantages	Primary Disadvantages	Pressure
Description	As a High Vacuum pump	As a High Vacuum pump	Ultimate
Rotary Piston Pump	Oil sealed pumping, lower cost	Oil back streaming, requires trap	5 x 10-2 Torr
Scroll Pump	Oil free roughing and pumping	Expensive, limited maximum size	5 x 10-2 Torr
Rootes Booster	Pumping speed at low pressures	Expensive, use with large system	5 x 10-4 Torr
Rotary Vane Pump	Oil sealed, lower vibration	Oil back streaming, requires trap	5 x 10-3 Torr

Oil Sealed Pumps

Example of Oil Sealed Vacuum Pump with Filter

Bemco recommends rotary vane and for much larger systems, rotary piston pumps with gas ballast for roughing standard thermal vacuum and space simulation systems down to the switch over pressure required by the selected high vacuum pump.

All Bemco oil sealed pump systems include a dive valve to immediately reduce pressure in the foreline when power is removed, an isolation valve for leak checking, and a heated molecular sieve trap to limit the potential for oil back streaming in the event of power failure. Also furnished is a digital vacuum gauge and control to monitor foreline pressure.

Clean Pumps

Scroll pumps and for much larger systems, Rootes booster package pumps, and Screw pumps are selected for “Oil Free” roughing of thermal vacuum and space simulation systems where the proposed test load is sensitive to even the lowest level of hydrocarbon back streaming.

Scroll pumps are the most common selection. They are completely oil-free and make an ideal complement to a turbomolecular pump or a cryopump in a system intended for optical testing. They require no filters, no foreline trap, little routine maintenance, and no oil changes.

Typical Performance with Various Pumping Systems

Operating	Recommended	Special Accessories
Pressure	Pumping System	Disadvantages or Notes
5 x 10-3 Torr	Roots Booster Package	HV breakdown may occur
5 x 10-5 Torr	Cryopump, Turbopump or Ion Pump	Reliable range with high outgassing
5 x 10-6 Torr	Cryopump, Turbopump or Ion Pump	Normal Bemco operating range
5 x 10-7 Torr	Cryopump, Turbopump or Ion Pump	Normal Bemco ultimate, no bakeout
5 x 10-8 Torr	Cryopump, Turbopump or Ion Pump	Requires bakeout, dual seals, and clean system

Available Literature Includes:

Bemco AH Series Space Simulation, Ultra High Vacuum, and Thermal Vacuum Systems. Coverage includes PCL-III Portable Liquid Chillers for cooling vacuum thermal shrouds, Bemcoil DE (double embossed stainless steel) Shrouds, Bemcoil FOS (flat one side) stainless steel shrouds and Bemco PV and MCT Poppet Valves and Traps. Document is 12 pages, 1,003 KB download.

The systems described above are our Standard Models. We make custom equipment to your specifications. If you have any questions, need assistance in preparing a specification, or have a technical problem you want help with, we are ready. Our quotations and advice are free.

Environmental Chambers and Space Simulation Systems