Varian DS31 General Purpose Mechanical Pump Oil (sold here by the 0.5 liter bottles 9499305) is quality mechanical vacuum pump oil for the ultimate performance of your Varian DS42 Rotary Vane pumps. Varian DS31 Oil is specially prepared by Varian to meet the Rotary Vane exclusive specifications. We recommend that you change your vacuum pump oil at least every 3 months to prolong the life of your vacuum pump.