Rotary Vacuum Pump G-100D
This rotary pump is located in the Ulvac DLMS-531 Helium leak detector (Blue leak detector). It gets to around 4 mTorr in 2 minutes with a blank and not hoses attached. Tested on Jan 10/2017, by keeping 4 mTorr in 30minutes.
Precaution: A sudden stop of the pump may contaminate the vacuum space. Due to, the inlet side of the pump is at negative pressure (-14.7 PSI) and the exhaust is at atmospheric pressure. The atmospheric pressure on the exhaust side of the pump will try and get into where the negative pressure. The oil in the pump is between the inlet and the exhaust. Then, oil molecules will go in to the vacuum space. Therefore, in order to avoid the contamination, bring the system to atmospheric pressure before turning off pump, you may use a valve in the system to vent the pump inlet to atmospheric pressure before stopping pump.
The manual of operation is here.