Diffusion pumps are the most economical high vacuum pumps available. They offer the highest pumping speed of any high vacuum pump. For that reason, they are common pumps for large chambers and coating processes that do not require an ultra clean environment.
Diffusion pumps are passive (no moving parts) throughput high vacuum pumps. They work by heating oil in the boiler section and sending this stream of heated oil vapor through jets aimed down toward the foreline exhaust. The pressure at the exhaust is typically 10 to 200 microns. A mechanical pump, commonly referred to as a backing pump, maintains the low pressure and pumps the molecules out of its exhaust.