Vacuum pump, compression mechanical

Positive displacement vacuum pump A mechanical vacuum pump that traps a volume of gas, compresses it, and displaces it through an exhaust port. See also Vacuum pump. 

The Nash vacuum pump or compressor has only one moving part—a balanced rotor that runs without any internal lubrication. Such simplicity is possible because all functions of mechanical pistons or vanes are performed by a rotating band of liquid compressant. 

Two mechanical pumps are commonly used, the Cenco Hyvac and the Welch Duoseal. Each operates by trapping some of the gas in the vacuum system, compressing it, and expelling the compressed gas. The Cenco pump operates with an excentric rotor in an oil bath which sweeps out the- gas as it rotates, and the Welch pump has a rotor with vanes which serve the same purpose (Fig. 3-8). In either case, the oil supplies the seal between inlet and outlet, and the efficiency of the pump is directly related to the condition of the pump oil and the fit of the mechanical parts. 

A rotary vacuum pump is essentially a gas compressor. The mechanism of the pump is designed such that it has an eccentric blade or vane rotating to cause four distinctive actions, namely gas introduction, isolation, compression and gas exhaust. The working principle of the mechanism is therefore divided into four steps during the rotation of the vanes, as illustrated in Figure 2. 6 ... 

The vacuum at the top of the flash column is often produced by a sequence of three elevated steam-jet eductors with intermediate and final surface condensers to remove the steam. A liquid-ring compressor can be substituted for one or more eductors to conserve steam. Mechanical vacuum pumps are seldom used because of the corrosive nature of the off-gas. The noncondensible sour compressed gas and condensate are led away through a water seal for safety in case of steam system failure. The seal pot is equipped to skim off condensed oil continuously. 

Use mechanical vacuum pumps in place of compressed-air venturi vacuum devices. 

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. 

In accordance with DIN 28 426 Part 1, the vapour tolerance of a mechanical vacuum pump which shall pump the taken in vapours without condensing during the compression phase from vacuum to atmospheric pressure, is defined as follows ... 

The vacuum pump is cooled by means of a water jacket. In order to reduce the temperatures inside it is possible to admit cooling gas which can be adapted to the process conditions. For example, the cold gas can be taken downstream from a downstream condenser. But also fresh gas like nitrogen can be used for cooling. This dry compressing pump is not equipped with any valves. Any screw mechanism will be found to be quite insensitive to hquids entrained in the gas... 

Ballast orifice (vacuum technology) An orifice upstream of the mechanical pump that can be used to allow dilution of the pumped gas with dry gas to ensure that vapors in the pumped gas do not condense during compression in the mechanical pump. The ballast orifice also allows the foreline portion of the vacuum pumping manifold to return to ambient pressure in case the mechanical pump stops because of a power failure or a broken belt. This avoids Suck-back. 

Blower (vacuum technology) A low compression mechanical, compression-type vacuum pump. Example Roots blower. 

Mechanical pump (vacuum technology) A compression-type vacuum pump with moving parts. The term is generally applied to pumps used for roughing or backing (Example oil-sealed mechanical pump, piston pump, diaphragm pump, etc.) and not high vacuum pumps (Example turbomolecular pumps). See also Vacuum pump. 

Roots blower (vacuum technology) A compression-type mechanical pump that uses lobeshaped interlocking rotors to capture and compress the gas. The roots pump uses tight mechanical tolerances for sealing (no oil) and so is sometimes classed as a dry pump. See also Vacuum pump. 

Vacuum pump, diaphragm pump A compression-type vacuum pump that operates using a flexible diaphragm that changes the volume of the pumping chamber by mechanical motion. A very clean pump that can be exhausted to atmospheric pressure. Used to back a turbopump with a molecular drag stage. 

Nowadays a shortened McLeod type compression vacuum gauge according to Kammerer is used to measure the partial final pressure of mechanically compressing pumps. Through the high degree of... 

There are many mechanical pump designs, the most common of which is the rotary pump. It is named for its use of rotating internal parts that collect, compress, and expel gas from a system. Despite the simplicity in concept, there are very interesting mechanisms that pump manufacturers have developed to overcome the problem of mechanical pumps, namely, that they are inherently a slow pump. It is their simplicity, however, that has made them the general workhorse for creating a vacuum all over the world. 

To prevent (or limit) condensable vapors that reach a pump from affecting the mechanical pump oil, a gas ballast (also called a vented exhaust) is used. The gas ballast allows a small bit of atmosphere (up to 10%) into the pump during the compression stage so that the gas from the system is only part of the gas in the pump at the time of greatest compression. Thus, at the time of compression, the total percentage of condensable vapor within the pump is much less than there would be otherwise. Because the gas prior to being expelled is at a lower pressure, less of the vapor can be compressed into a liquid. Then, as the veins sweep into the vacuum side of the pump, no condensed vapor can expand back into a vapor. 

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