Uniweld's® Vacuum Pump Oil is specially refined with excellent thermal stability for maximum efficiency and use in any vacuum pump. For maximum pump performance, it is recommended that the oil be changed after every evacuation. To properly test the oil, use Uniweld's DVG1 Digital Micron Gauge. If after directly attaching the micron gauge to the pump, a deep vacuum reading is not achieved, the oil is contaminated and needs to be changed.