High vacuum processing system having improved recycle draw-down capability under high humidity ambient atmospheric conditions

摘要

Water contamination of the oil in vacuum pumps of high vacuum systems is a major problem in maintaining efficient operation of those pumps. The problem is especially acute where a system includes an evacuated work chamber that must be repeatedly opened for loading products into and unloading them from that chamber where the ambient atmosphere has high humidity. The invention involves utilizing first stage mechanical vacuum pump means in conjunction with final stage high vacuum diffusion pump means, and a cryocoil with fast defrost capability located in the vacuum duct leading from the work chamber to the pumps, in combination with an auxiliary low capacity vacuum pump and a flip/flop valving arrangement which connects the discharge side of the diffusion pump selectively to the first stage mechanical pump or to the auxiliary pump. The flip/flop valving arrangement allows the auxiliary pump to maintain moderate vacuum condition in the diffusion pump during idling periods and also serves as a continuous scavenger of water vapor present in the system, particularly during cycles of defrosting the cryocoil. The invention insures that any water vapor in the system not exhausted by the main pumps to ambient atmosphere or trapped as frost by the cryocoil, is prevented from accumulating in and emulsifying with the oil of the main vacuum pumps. By means of the invention system, any residual water is collected in the sump of the auxiliary pump and is prevented through the provision of the flip/flop valving arrangement from revaporizing and backstreaming through the main pumps during their pump-down cycle. Periodic replacement of the low cost auxiliary pump oil removes the residual water trapped in that pump.