Pumping to a very low pressure does not necessarily speed up the outgassing of the absorbed water vapor. Most systems are too big and complex to be easily heated and baked, and there is usually insufficient time available without making the process uneconomic. Several other things can be done to add energy to speed up the process of water vapor removal. One method is to bleed gas in during the roughing pump stage of the pumpdown sequence. This gas introduction has the effect of the gas bouncing off the surfaces that assists in ejecting the water vapor molecules from the surfaces. Normally, the pumpdown will take the pressure down and so there will be fewer gas molecules hitting the surfaces to help eject the water vapor and so adding a dry gas, possibly with a heavier molecular weight, such as argon, will increase the bombardment. It will slow or stop the pumpdown at a high pressure, but once the gas supply is switched off, the resumed pumpdown will be quicker, as the contribution from the surface water vapor will have been reduced. This method of removing the water vapor also means that the system does not have to sit at a low base pressure where it could suffer from oil backstreaming. A second option is to use ultraviolet lamps that can also impart energy into the water vapor and thus speed up the desorption process.