Multi-Stage Dry Vacuum Pumps
Botanical Processing, Coating, General Industrial, Laboratory/Scientific, Pharmaceutical, Semiconductor

Multi-stage dry vacuum pumps have been commercially available for over 30-35 years. Early versions were generally water-cooled, and in more recent years some air-cooled versions have been introduced.

Due to the fact that typically 4-6 stages of compression are required to attain pressures close to what oil-sealed pumps are capable of in just two stages, multi-stage dry pumps create a significant amount of heat and require more cooling, specifically in the latter stages. The air-cooled versions of these pumps are also considered PoU (point of use) as they require no water or other facilities besides AC power.

The purpose of identifying these pumps as air-cooled is that there are also water-cooled versions available. As far as oil contamination of product, while they are not completely oil-free, dry pumps are the best option. They have lubricating fluid in the gear chambers and/or the bearing chambers. In most cases the gear chamber has oil and the opposing bearing chamber has greased bearings.

In either case, the lubricating oil is not in the swept gas stream, meaning that the volatiles being pumped through the vacuum pump generally do not directly contact and contaminate the lubricating fluid. This reduces the chances of the operating oil contaminating the product. These pumps have produced some effective results (in some applications) that in some cases are more attractive than rotary vane pumps. However, when they fail (which they will), they can result in higher cost rebuilds than vane or scroll pumps, because the rebuild is typically more specialized.