Vacuum pumps are used to remove gases from sealed volumes in order to leave behind a partial vacuum. In order to achieve a relative vacuum, vacuum pumps generate a vacuum within their capacity.
Table of Content
- Vacuum pump overview
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- How does the Vacuum pump work?
- Vacuum stages
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- Types of vacuum pumps and their operating principles
- Oil-Less vs. Oil-Lubricated Vacuum Pumps
- Evaluating Vacuum Pump Performance
- Vacuum Level
* Vacuum Pump Overview
Vacuum pumps work by pushing air or gas molecules out of a sealed chamber in order to generate a partial or low-pressure vacuum. The vacuum state occurs when the chamber pressure is lower than the ambient atmosphere or adjacent systems. A vacuum devoid of gas molecules is different from an absolute vacuum, in which the pressure is 0 Pa.
The equipment used to generate vacuum is similar to that used to generate air. Depending on how it is installed, the same machine can generate compressed air or vacuum. Vacuum pumps generally can be considered compressors in which the discharge, rather than the intake, is at atmospheric pressure.
We all know that the essence of air compression is the increased number of molecular impacts per second. In contrast, vacuum generation relies on reducing these impacts. Creating a vacuum in a chamber involves physically removing air molecules and exhausting them.
Removing air from the enclosed system progressively decreases the air density within the confined area, causing the absolute pressure of the remaining gas to drop. A vacuum is created.
As the maximum pressure difference at the work site is equal to atmospheric pressure (nominally 29.92 in. Hg at sea level), it is critical to know this value at the work site.
As an example, consider a pump that can achieve a maximum vacuum of 24 inches. Hg cannot generate 24-in. When the atmospheric pressure is 22 inches, there is a vacuum. However, the amount of air evacuated will remain the same. As a result, this pump will pull a distance of 22 x 24/29.92 or 22 x 24/30 = 17.6 inches Hg vacuum.
* How does the Vacuum pump work?
By evacuating the air inside a system, a vacuum pump converts mechanical input energy into pneumatic energy. As a result, the internal pressure becomes lower than the outside pressure. Depending on the volume evacuated and the pressure difference created, energy is produced.
The pumping mechanism of mechanical vacuum pumps is similar to that of air compressors. However, the unit is installed so that air is drawn from a closed volume and exhausted to the atmosphere.
A vacuum pump differs from other types of pumps in that the air entering it is under atmospheric pressure. This pressure becomes vanishingly small at higher vacuum levels. Among the other differences between an air compressor and a vacuum pump are:
Pump action cannot produce a pressure difference greater than 29.92 inches. Hg (14.7 psi), since this represents a complete vacuum.
• As the vacuum level increases, the mass of air drawn into the pump on each suction stroke decreases, resulting in a decrease in absolute pressure. Section IV 70
• The pump passes significantly less air at high vacuum levels. Since pump operation generates so much heat, the pump structure itself will need to absorb and dissipate it.
* Vacuum Stage
As in compression, the vacuum-generating process can be accomplished in just one pass through a pumping chamber. Or several stages may be required to obtain the desired vacuum.
The mechanical arrangements are also similar to those for air compression. The discharge port of the first stage feeds the intake port of the second stage. This reduces the pressure, and hence the density, of air trapped in the clearance volume of the first stage. The net effect is, using a Gast diaphragm pump as an example, that the second stage boosts the vacuum capability from 24 to 29 in. Hg.
* Types Of Vacuum Pumps?
There are many types of vacuum pumps available on the market. Vacuum is used in a variety of industrial processes, such as packaging, bottling, drying, degassing, picking, and placing, among others. A vacuum pump is used to create, improve, and maintain a vacuum during these processes.
- Rotary vane vacuum pumps
- Screw vacuum pumps
- Diaphragm vacuum pumps
- Roots booster vacuum pumps
- Liquid ring vacuum pumps
- Radial vacuum pumps
- claw vacuum pumps
Rotary vane vacuum pumps
Kalbro’s has two types of Rotary vane vacuum pumps.
- Oil-Lubricated Rotary Vane Vacuum Pumps
- Oil-Less (Dry) Rotary Vane Vacuum Pumps
Oil-Lubricated Rotary Vane Vacuum Pumps
For high vacuum applications, oil-lubricated rotary vane vacuum pumps are an excellent choice.
Oil-Less Rotary Vane Vacuum Pumps
A rotary vane vacuum pump is similar to other vane pumps in that it does not use oil. These pumps offer unique advantages over standard vacuum pumps. Rotary vane pumps have straightforward construction with a single shaft direct drive for long-lasting, low-maintenance operation.
Screw vacuum pumps
- A screw vacuum pump is a dry positive displacement pump used for rough vacuums. Rotors spin counterclockwise, and the rotors are enclosed in a housing. Drive gears are not needed with direct drive via an integrated frequency inverter.
Diaphragm vacuum pumps
- Diaphragm pumps operate completely oil-free since the gas path has no sliding components. The regular operation leaves them completely abrasion-free. Due to particle generation, often encountered with scroll pumps, vacuum procedures are largely protected from contamination.
Roots booster vacuum pumps
- Positive displacement pumps with roots are known as root booster vacuum pumps, or root blowers. Their operation is similar to that of rotary vane pumps. Pumps such as these are ideal for applications that require high pumping speeds.
Liquid ring vacuum pumps
- Process vacuum is provided by liquid ring vacuum pumps in many industries. This includes chemical, electric power, environmental, food and beverage processing and packaging, marine, mining, oil & gas, pharmaceuticals, pulp & paper, and textiles.
Radial vacuum pumps
- There is a high volume of air delivered by radial blowers. An integrated frequency inverter in the motor allows precise adjustment of the volume flow.
claw vacuum pumps
- Vacuum pumps that use hooks and claws have the same working principle as rotary vane pumps, which use positive displacement. There is no oil or liquid in contact with claw pumps during operation. During this process, two claw-like rotors rotate in opposing directions, so neither one touches the other nor the chamber.
* Oil-Less vs. Oil-Lubricated Vacuum Pumps
Vacuum pumps are normally either oilless or oil-lubricated, depending on the application. It is possible to use either type in a wide range of applications.
Oil-Less
In production processes where oil vapor can’t be allowed to enter the exhaust air, oil-less pumps are almost essential. As well as saving time and money, they also avoid the hassle of having to regularly refill the oil reservoirs. It is especially important when the pumps are located in an inaccessible area.
Based on ambient temperature and air cleanliness, modern piston pumps have Teflon rings that last for hundreds of hours. Pumps with rocking pistons and diaphragms are designed to operate without oil.
Oil-Lubricated
Maintaining oil-lubricated systems correctly has distinct advantages. Lubricants serve primarily as a seal between moving parts, allowing them to produce vacuum levels as high as 20 percent higher. Due to their cooler operation, they typically last about half as long as oil-less units. Additionally, they are less likely to be corroded by condensed water vapor.
Evaluating Vacuum Pump Performance
There are some important performance characteristics of vacuum pumps that should be considered when evaluating certain types and sizes. In a separate section, we will discuss how these characteristics relate to the pump selection.
Three characteristics are the main performance criteria:
- Power required.
- Rate of air removal.
- Vacuum level that can be produced.
Somewhat less critical are temperature effects and certain other characteristics. When choosing a pump for a specific job, it’s generally best to choose one that has the largest pumping capacity at the required vacuum level. In addition, it should operate within an acceptable horsepower range.
Vacuum Level
A pump’s vacuum rating is the maximum vacuum level for which it is recommended. Depending on the duty cycle, the rating can be expressed in inches/Hg.
The theoretical maximum vacuum of 29.92 in. Hg at sea level is not achievable by most vacuum pumps due to internal leaks. In the case of a reciprocating piston pump, the upper vacuum limit may be 28 or 28.5 in/hg. This is roughly 93 to 95 percent of the maximum theoretical value.
There is a limit to the amount of vacuum that can be produced by a pump based on internal leakage and clearance volume. This can also be the vacuum rating for some pumps.
Some types, however, have problems with heat dissipation. There is a possibility that the maximum vacuum rating of these devices will be determined by the allowable temperature rise. For example, good wear life for some rotary vane pumps requires a maximum 1800 F (820C) rise in casing temperature at the exhaust port. Based on this temperature rise, vacuum ratings will be determined. For intermittent duty, they will probably be higher than for continuous duty
The vacuum rating listed for a pump is based on operation at 29.92 in. Hg. Operating where the atmospheric pressure is lower will reduce the vacuum the pump can produce. By multiplying actual atmospheric pressure by the nominal vacuum rating to standard atmospheric pressure, an adjusted vacuum rating can be calculated:
Adjusted Vacuum Rating = Actual Atmospheric Pressure * nominal Vacuum Rating/Standard Atmospheric Pressure
