Ask the Expert: How Does a Diffusion Pump Work?

Ipsen vacuum furnace diffusion pump

The Basics of Vacuum Furnace Pumping Systems

Vacuum furnace systems use various types of pumps to evacuate atmospheric pressure from the chamber to achieve required vacuum levels. There are typically two subsystems included in each vacuum furnace pumping system⁠—the roughing pump and vacuum booster pump. The addition of a diffusion pump will result in a lower system pressure than what can be achieved with the two-stage system alone. The diffusion pump cannot operate independently; it requires a holding pump to operate simultaneously during idle modes to reduce the diffusion pump’s inner pressure. During the operation of the diffusion pump, the valve to the holding pump is isolated, and the roughing and booster pumps act as the backing system for the diffusion pump. A diffusion pump will reduce the vacuum level from atmospheric pressure to a level of 8.0 x 10-6 Torr, as opposed to 4.5 x 10-2 Torr with the two-stage system (in a clean, dry and empty furnace).

How do diffusion pumps work?

Agilent Diffusion Pump

For the diffusion pump to function properly, the main and foreline valves must be open, allowing the furnace to operate in high vacuum. Fluid at the bottom of the pump is heated to boiling and forced up through the center of the jet assembly. Supersonic oil mist molecules shoot in a downward direction from the jet nozzles, forcing the lighter gas molecules toward the bottom of the pump. The gas molecules are collected at the ejector nozzle and pulled out of the pump by the pumping system. The oil, upon contacting the cold side walls, returns to liquid form and gathers at the bottom of the pump to be reheated. To think about it another way, a diffusion pump works in a similar fashion as a coffee percolator.

Agilent Diffusion Pump

Do I need a diffusion pump?

Whether or not you need a diffusion pump is dependent on your process requirements. Many industries, including aerospace and nuclear power, mandate high vacuum operation in their standard operating procedures. Certain processes, like brazing, also require a lower system pressure to produce cleaner parts. Likewise, if you are processing high-end alloys, a diffusion pump will help parts come out clean and bright. On the other hand, most hardening applications do not require a diffusion pump.

For more information on diffusion pumps, check out these helpful resources:

Ipsen, your one source for all vacuum furnace components, offers OEM pricing on pumps and parts and has inventory in stock. For new vacuum pumps, parts, related services or any other questions, call Ipsen Customer Service at 1-844-GO-IPSEN.

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