Dry Compressing Vacuum Pump

In accordance with DIN 28 400 (Part 2) a dry compressing vacuum pump is a positive displacement vacuum pump which operates without an oil seal (as the liquid seal). A diaphragm vacuum pump is a dry compressing pump, a type of pump which chiefly has its role in connection with laboratory apphcations. Here the diaphragm vacuum pump replaces the universal laboratory water jet pumps, the water consumption of which and thus the high operating costs due to the generation of contaminated waste water are factors which are not desired. 

For the same reasons on which the move in the chemistry laboratory to dry compressing vacuum pumps is based, dry compressing pumps have also been developed for chemical production facilities. The different pumps operate according to... 

Chemical process engineering demands of vacuum pumps a high level of operational reliability. Also no waste, like waste oil or waste water shall be produced as far as possible. The requirement as to the avoidance of additional waste quantities is optimally fulfilled by dry compressing vacuum pumps. However, the question as to their operational and process reliability arises. Here the benchmark for the intended level of process reliability should always be the liquid ring vacuum pump. 

In order to dissipate the compression heat, which is a fundamental problem for all dry compressing vacuum pumps, a cooled water jacket is provided. This dry compressing chemistry vacuum pump attains through its three stages pressures down to under 1 mbar. The shaft seals for the oil-covered gear chamber consist of shaft sealing rings made of a material which is chemically resistant as far as possible. 

Owing to the ongoing dynamic further development as in the past which also needs to be assumed in the future for the area of dry compressing vacuum pumps for industrial process engineering, this chapter will have to be updated frequently also over the next years and decades. 

Fig. 2.29.1. Working schema of a dry vacuum pump operating on the so-called claw principle. 1 rotors 2, compression chamber 3, suction chamber 4, exhaust slit 5, suction slit 6, purge between stages (Figure from [2.241).

Like Roots pumps, claw pumps belong to the group of dry compressing rotary piston vacuum pumps (or rotary vacuum pumps). These pumps may have several stages their rotors have the shape of claws. 

The pumps of the DRYVAC family are the classic dry compressing claw vacuum pumps that are preferably used in the semiconductor industry, whereby the pumps need to meet a variety of special requirements. In semiconductor processes, as in many other vacuum applications, the formation of particles and dusts during the process and/or in the course of compressing the pumped substances to atmospheric pressure within the pump, is unavoidable. In the case of vacuum pumps operating on the claw principle it is possible to convey particles through the pump by means of so called pneumatic conveying". This prevents the deposition of particles and... 

One option involves the condensation of (or part of) the permeate under atmospheric instead of vacuum conditions. This requires the use of dry-vacuum pumps , able to compress the permeate vapour from vacuum to atmospheric pressure, after which condensation is performed at a higher temperature [23]. In this case, the operating conditions have to be carefully monitored since these pumps may lead to unsuitable heating of the vapour and eventually aroma deterioration, despite the low residence time. Alternatively, the use of liquid ring vacuum pumps where the service liquid can take some of the aromas from the permeate stream has been proposed [24]. 

In the past, environmental problems associated with the commonly used pump fluids, namely water and oil, have led to the development of dry vacuum pumps that compress without contact. Rotary lobe and screw-type vacuum pumps (Fig. 5 and 6) are the types most commonly used for industrial applications. 

Dry Vacuum Pumps (DVPs) These use the operating principles of rotary-lobe roots blowers, claw compressors or screw compressors, and hence require electrical power. They run dry and hence at very high temperature due to the heat of compression. Usually,... 

Figure 4.8 Set up for sampling volatile organic compounds from the coffee flow. Volatiles were introduced into the dilution lance by a flow created with a vacuum pump and were then diluted 7.5 fold using dried compressed air containing a standard for mass calibration [187]. Reprinted with permission from Sinchez-Lopez, J.A., Zimmermann, R., Yeretzian, C. (2014) Insight into the Time-resolved Extraction of Aroma Compounds during Espresso Coffee Preparation Online Monitoring by PTR-ToE-MS. Anal. Chem. 86 11696 11704. Copyright (2014) American Chemical Society...

Positive displacement pumps diaphragm vacuum pumps, liquid ring vacuum pumps, rotary vane and rotary piston vacuum pumps as well as Roots vacuum pumps (dry compressing claw and screw pumps are not yet mentioned here but also belong to this group of pumps). 

Old and new requirements from the area of chemical process engineering regarding the process vacuum pumps described, resulted beginning at the end of the 80s of the twentieth century in considerable development efforts of all leading manufacturers of mechanical vacuum pumps so as to be able to offer process-capable dry compressing pumps for the area of chemical and pharmaceutical process engineering. 

Dry compressing rotary vane vacuum pumps based on multi-vane designs with self-lubricating vane materials are hardly used. This dry compressing type of vacuum pump has been found to be too prone to wear if used in chemistry applications. 

Dry Compressing, Three-Stage Roots Vacuum Pump with Exhaust, Respectively Non-Return Valves between the Stages... 

It is quite obvious to utilise the known principle of the Roots vacuum pump also for dry compressing machines. 

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