WHAT IS A VACUUM VAPOR DEGREASER ?
Many of us remember how simple it was to place a part to be cleaned in the vapor zone of the open top style vapor degreaser and returning in a few minutes to find a cleaned part. Cleaning in these old-style degreasers was so effective because the vapor zone contained pure clean solvent vapor. Of course, these old style open topped Vapor Degreasers (OTVD) came with some drawbacks, like safety, and cost to name a couple. Today, the same type of vapor cleaning can be attained in a Vacuum Vapor Degreaser (VVD), while at the same time improving performance and safety over the OTVD of the past. The key to VVD’s success is the removal of air from the process, allowing pure vapor to rapidly flush the part surface as the vapor condenses. When viewed the rapid condensation often appears as a spray, since there is no air to impede a large amount of vapor reaching the parts. As the part to be cleaned approaches the vapor temperature the condensing process slows both in OTVD and in VVD systems. However, in the VVD design, the cleaning process is not disrupted by air slowing down the process or being trapped in blind holes, tight areas, or complex structures. These areas often get little to no cleaning. This is not true in a VVD. Solvent reaches all surfaces previously occupied by air to produce a thoroughly cleaned part.
A critical factor for effective vapor cleaning in an OTVD is the operating temperature. In an OTVD the operating temperature is controlled by the Normal Boiling Point (NBP) of the solvent. Solvents with high boiling points require more energy, long drying times. These high operating temperatures can also damage some parts. Too low an NBP and not enough vapor condenses on the surface of the parts. A true VVD can overcome the operating temperature limitations of the OVTD since operating temperature are variable in a VVD (See Vacuum Vapor Degreasing Efficiency).
There are a number of cleaning machines on the market that claim to be Vacuum Vapor Degreasers (VVD). The Key word here is VAPOR! Just because a unit uses vacuum, that does not mean it is a VVD. The most common imposters are the “modified alcohol” units. These are soak units. The normal boiling point (NBP) of “modified alcohol” is above 160 C (320 F). At 100C these units do not produce the vapor required of effective vapor degreasing (see vapor Pressure Curve). These units submerge parts in the “alcohol” and often require some form of agitation to enhance the cleaning process. Ultrasonic energy is often employed. Solvents with high NBP’s do not cavitate well, essentially limiting the effectiveness of the cost involved in the ultrasonic technology. Since this is an immersion (soak) process, multiple soaks may be required to ensure complete film free cleaning. As previously point out solvent vapors are always pure and clean.
High NBP also leads to problems with drying and solvent distillation. The vacuum pump is the key to drying and distillation in both VVD’s and the “modified alcohol” systems. In a system with high NBP’s the vacuum levels achieved result in slow distillation and slow often incomplete drying. Slow drying can lead to spotting. Often to speed up drying heated external air is used. As a result, expensive activated carbon filters are required to meet air quality regulations such as found in Europe, California’s South Coast Air Quality Management District (SCAQMD) and many states in the US. Carbon filters add a waste stream. Slow distillation reduces the availability of clean solvent which can affect process time and cleaning quality. A true VVD does not come with these drawbacks.