Vacuum vapor degreasing degreaser

Vacuum vapor degreasing (WDG) in which the pressure in an enclosed degreaser is reduced by removal of vapor so that emissions may be best contained and the boiling point of the solvent may be reduced. 

Airless enclosed vapor degreasers are just that — vapor degreasers in which the internal volume is not air. The word airless has been used genetically, and as a trademark. Some airless machines are also known as vacuum-to-vacuum vapor degreasers... 

In a second typ>e of airless vapor degteaser, the air is removed to produce a vacuum. This typ>e of airless machine is the most common — a vacuum-to-vacuum machine, a vacuum vapor degreaser. This is done to expose solvent soDed surfaces which are complex and difficult to thoroughly wet, flush, and dry. Examples are multiport injectors, aluminum/alloy honeycomb stmctures used as pands in constmction of aircraft, metal or glass filtration media, long tubing, and completed assemblies of components. 

These devices are found in nearly all airless machines, because most are vacuum vapor degreasers. 

Purchase of a vacuum vapor degreaser is likely to include a rotary vane vacuum pump among the installed components. Commercial rotary vane vacuum pumps also may have more than two rotating vanes as are shown in Figures 2.5a and b. Any even number ofvanes is possible. Figure 2. shows an image of a rotor with six vanes. 

Operate continuously during their useful life, although the pressme-reduction portion of a vacuum vapor degreasing cycle is periodic. Many vacuum pumps are designed for continuous duty. 

An enclosed vacuum vapor degreaser was conceived, designed, and constructed for just this situation. But it wasn t until the latter part of the last decade that such machines became commonly available. Their existence would appear to contradict the NESHAP (Chapter 1.24) finding in 2007 that tube cleaning machines should be exempt from its requirements (Ref. 2, Chapter 4.15). 

But in summary, the power of the airless non-vacuum vapor degreaser is not paramount, because it doesn t enable solvent cleaning in a solvent-only environment — at pressures more or less than ambient, and temperatures more or less than normal boiling points. 

An airtight enclosed t por degreaser which allows that is shown in Figure 2.31, as a vacuum vapor degreaser. 

The addition of a vacuum pump (Chapter 2.2) to an airtight vessel rated to contain fiiU vacuum (Chapter 2.4), produces a parts cleaning system known as a vacuum vapor degreaser. All else is diagrammatically the same between Figures 2.31 and 2.30, including the emission of solvent-rich vapor. 

Using Figure 2.36, one can see that to condua cleaning operations at 50°C with methylene chloride, an airdght (pressure-tight) enclosed vapor degreaser can be used. But it is not a vacuum vapor degreaser because the required pressure is above 760 Torr. 

It may be that use of the "3A" solvents is synergistic with enclosed vacuum vapor degreasers — assuming that the... 

For non-vacuum vapor degreasers, the work chamber contents (air) are displaced by nitrogen prior to addition of solvent. When the cleaning operations are complete, the pressure in the work chamber is 1 atmosphere. So the solvent concentration in the vapor phase is what it would be were the solvent in an open container in open air at the temperature inside the vapor degreaser. 

For vacuum vapor degreasers, the solvent concentration fed to adsorbers is determined by the level of vacuum in the work chamber at the close of the cleaning operations. The assumed value of vacuum used in the calculations of this book is 750TorrV (10 mm Hg), producing the same calculated solvent concentration in the feed to adsorbers - 13,158 ppm ([10/760] x 10 ). 

Instead of a few hundred ppm solvent in the vapor feed from the I ip vents of an open-top vapor degreaser, or instead of several dozen tens of thousands of ppm solvent in the vapor feed from a vacuum vapor degreaser, the solvent concentration can be hundreds of thousands of ppm in the feed from a non-vacuum enclosed vapor degreaser. 

Management of Emissions from Enclosed Vacuum Vapor Degreasers... 

In an enclosed vacuum vapor degreaser, operating temperature is an independent variable (Chapter 2.14). Operating pressure is not. It s chosen to adjust the solvent temperature to the desired value. Should it be necessary to adjust the solvent temperature, because of heat losses or the need to heat (or cool) the thermal masses of parts, during the cleaning cycle temperature can be independently adjrrsted with heaters or coolers which are part of the apparatus . 

Open top and vacuum vapor N/A degreasers for circuit assembly cleaning, and flux and ionic residue removal Batch or in-Une vapor N/A... 

EVD-80 Vapor degreaser cylindrical process chamber with vacuum (low emissions) N/A N/A HCFCs, HFCs, HFEs, NPB, and chlorinated solvents... 

The three process steps (Chapter 1.2) incorporated in vapor degreasing are/will be done, not in so-called open-top machines, but in what are known as enclosed machines known as airless and vacuum respectively. They will be covered in Chapter 2. 

Open-top vapor degreasers are not capable of supporting vacuum, nor are exhaust blowers capable of producing it... 

Externally sealed enclosed vapor degreasers are not sealed for pressure or vacuum they can t be, because they are externally sealed. This type of Vapor degreaser is... 

Useful life for mechanical vacuum pumps is considerably shorter than for the vessel which it evacuates. This is simply because it has parts moving at a high frequency and making contact with one another. When evaluating the purchase of an enclosed vapor degreaser with a vacuum pump, one ought to insist on a warranty life of the vacuum pump of at least 2 years, and consider premium value as one which has a 3-year warranty. 

Global suppliers of vacuum enclosed vapor degreasers number as of 2013 number about one-half dozen. The machines (apparatus) of each supplier manage the contact between parts and solvent, and the storage of solvent(s), in ways which are similar and only slighdy different. 

With a vacuum-capable enclosed vapor degreaser, this relationship is easily arranged. Vapor flows easily within whatever torturous paths there are within the arrangement of parts (Chapter 2.15). Reduction of chamber pressure by engaging the vacuum pump, reduces the temperature of the parts (Chapter 2.3). 

In this way, multiple consecutive cycles of rinsing with pristine distilled solvent can be readily achieved. This sequence of rinsing steps is either impossible or very difficult to implement in a conventional open-top degreaser (Figure 1.9), or any enclosed vapor degreaser other than one capable of producing a vacuum. And, hot solvent vapor added after formerly cold parts are heated will dry liquid rinse material from the parts as it contacts them. 

To emphasize, vacuum capability to produce a chamber pressure of 1 Torr absolute is provided with some enclosed vapor degreasers for the purpose of controlling the vapor environment or accelerating the rate of drying. It s not provided to clean parts at -70°C ... 

Using Figures 2.37 and 2.38, one can see that to conduct cleaning operations at 50°C with perchloroethylene and n-propyl bromide, the absolute operating pressures in a vacuum enclosed vapor degreaser (nearly inert free) should be about 100 and 500 TorrV respectively. 

An airtight enclosed cleaning vapor degreaser may be used to dry the parts under vacuum, even if the parts aren t being cleaned under vacuum conditions. It may be that the only processing step which is completed under reduced pressure is the final one (Table 2.10, page 41). 

Often the first step in drying of parts under vacuum is to flush the contents of the work chamber with hot nitrogen at atmospheric pressure — as is done in an airless enclosed vapor degreaser. This can remove most water, avoiding the need to supply its high heat of evaporation. 

One may operate an airless enclosed cleaning vapor degreaser under vacuum conditions to achieve the highest possible rates of drying. In that case, the work chamber must be rated to contain full vacuum conditions, and the apparatus noted as being of the airtight type. 

Commonly used in atmospheric open-top vapor degreasers, and enclosed vapor degreaser which operate at atmospheric pressure, ultrasonic transducers are seldom found in machines which create a vacuum environ-ment " ". The reason is perceived cost — of the needed... 

Process Equipment Open Tank Enclosed Vacuum Machine Modified Vapor Degreaser... 

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