Welch Premium DirecTorr Hydrocarbon Vacuum Pump Oil, 1 Quart 8995P-11. Welch Premium DirecTorr Vacuum Pump Oil is fractionated especially for use in Welch Direct Drive vacuum pumps. Premium DirecTorr Oil is checked to insure it meets rigid requirements for proper vapor pressure, chemical stability, viscosity and other essential characteristics. Long experience has proven the wisdom of using it. We recommend that you change your vacuum pump oil at least every 3 months to prolong the life of your vacuum pump.