We will introduce the rotary vane vacuum pump. We will discuss their working principle, their application, when to use the rotary vane vacuum pump, their advantages and disadvantages.
What is a rotary vane vacuum pump?
Rotary vane vacuum pump is a kind of oil sealed vacuum pump, which means that the suction chamber is full of specially prepared mineral oil, which plays the role of sealant and lubricant between the blade and the vacuum pump chamber shell. The rotary vane vacuum pump has one or two stages. A typical volumetric flow rate is between 2 and 20 cubic feet per minute (CFM). Rotary vane vacuum pumps can produce a vacuum of about 1 millitore, which is why they are more suitable for rough pumping in excess vacuum applications.
How does the rotary vane vacuum pump work?
The gas enters the suction chamber and is immediately compressed by the blades of the rotor. When the rotor rotates, it pushes the gas molecules around the pump chamber and toward the exhaust port to discharge into the atmosphere.
The blades are spring loaded, which is how to form a gas tight seal between the rotor and the pump housing. Instead, the blades and rotor housings are sealed with a specially formulated low vapor pressure oil that is used as a sealant, lubricant, and coolant for vacuum pumps.
There are several types of actuators that power the vacuum pump rotor. The first is direct drive, which is connected to a rotating power source through a crankshaft and coupling, in most cases an electric motor. The second type of drive is a belt drive pump, which is connected to a rotating power source through a pulley and belt.
The direct drive vane pump normally operates at approximately 1750 rpm and 70 ° C. The pump using the reduction pulley (belt drive) operates at a lower rpm. The operating temperature of the belt drive pump is 10 to 20 degrees lower than that of the direct drive vacuum pump. However, the operating temperature of each type of pump depends on several factors to a great extent, such as speed, viscosity of vacuum pump oil, quality of oil, service life of vacuum pump, quality of gas pumped, and quality and type of vacuum pump.
There are usually two types of rotary vane vacuum pump: single stage or two stage, sometimes called double stage. The second stage is generated by connecting the air inlet of the second rotor to the exhaust port of the first rotor. The advantage of two-stage rotary vane pump is that it can achieve lower vacuum degree and higher volume flow through this way.
As with any other vacuum pump, the volume flow rate decreases as the vacuum in the vacuum system or chamber increases. This is because the less air there is in the vacuum chamber, the more difficult it is to remove additional gas molecules from the vacuum chamber or system. However, with the decrease of absolute pressure, the performance of two-stage vacuum pump becomes more obvious. In the range of coarse vacuum, the pumping speed is basically the same, but when the absolute pressure is more than 1 Torr, the two-stage vacuum pump keeps its pumping speed, while the single-stage vacuum pump starts to decline.
According to the chart, you can see clearly why the single-stage vacuum pump is more effective than the two-stage vacuum pump, and vice versa. In severe vacuum environment, there is no difference between single-stage and two-stage vacuum pumps, which means that single-stage vacuum pumps will provide the same performance and reduce the cost by about 30% to 50%. On the other hand, the performance of single-stage vacuum pump began to decline after 1 Torr, and two-stage vacuum pump became an obvious choice.
What uses a rotary vane vacuum pump?
Rotary vane vacuum pump is used to discharge air (or gas) from the vacuum chamber or vacuum system in the whole rough vacuum range. “Coarse vacuum” is called a system of absolute air pressure between 760 Torr (ambient) and about 1 Torr. There are many high vacuum pumps, such as turbo molecular vacuum pumps, which cannot be operated and will be damaged in the coarse vacuum series. Therefore, rotary vane pump is called rough machining pump for many times. The roughing pump is a pump used to extract the absolute pressure of a vacuum chamber or system from atmospheric pressure to 0.001 torr or 1 micron. At this point, the secondary vacuum pump (e.g. turbine pump) will open and take over to evacuate to bring the vacuum chamber or system to a higher vacuum, e.g. 10-5 Torr.
Performance of rotary vane vacuum pump
The performance index of any vacuum pump is its final pressure level, usually Torr (μ m), mbar or Pascal (PA), and its pumping speed is CFM, L / min or m3 / h.
Rotary vane vacuum pump is a very popular vacuum pump for the following reasons:
Advantages of using rotary vane vacuum pump
Practical and general
Rotary vane pump is one of the few options used as a crude or main vacuum pump, which can reduce the absolute pressure to the level where other vacuum pumps can be started (e.g. turbo pump).
In addition, the rotary vane vacuum pump can also be connected to the exhaust port of Roots vacuum pump to quadruple the pumping speed and volume flow. Please remember that roots vacuum pump cannot operate by itself, and the rotary vane vacuum pump must be connected to its exhaust device.
Good vacuum rating
A decent rotary vane vacuum pump can reach a maximum vacuum level of 1 μ m, equivalent to one thousand Torr.
The vacuum rating is 99.999% vacuum, as you can see, covering most of the vacuum range. This means that the rotary vane vacuum pump can be used in many vacuum applications, except in the field of ultra-high vacuum.
Rotary vane vacuum pumps are used in small and medium-sized vacuum systems because they produce an average air flow range of 4 to 35 cubic meters (2 to 20 CFM) per hour. Although, some pumps can produce higher airflow, up to 120 CFM, depending on the setting. This makes them good candidates for backup pumps of turbomolecular pumps or diffusion pumps.
Cost effectiveness in
Under the same conditions, rotary vane pump is a kind of relatively cheap vacuum pump. A very good heavy vacuum pump can be purchased for about $2000. At the same time, if you need to be cheap, you can be cheap and buy one of the low quality, low load vacuum pumps, as low as $80. Therefore, as you can see, you can save a lot of trouble, because you have a variety of choices and diversity in the rotary vane vacuum pump.
With proper care, the rotary vane vacuum pump can be used for several years. Proper maintenance means that you should change the oil frequently, and do not install the vacuum pump into the corrosive or damaged vacuum system of the pump, instead of using appropriate protection components, such as humidity filter or drain valve.
Disadvantages of rotary vane pump
Risk of contamination of vacuum pump oil
The first disadvantage is the presence of low vapor pressure oil. The vane vacuum pump cannot operate without oil, which means that it must be constantly observed, refilled and replaced with oil. This also puts the vacuum pump at risk of being contaminated by high vapor pressure gas, which in turn reduces the performance of the vacuum pump and damages its components.
One way to reduce pollutants entering the vacuum pump chamber is to install the filter and drain valve before the vacuum pump inlet. This minimizes the contamination of the vacuum pump oil.
In addition, the rotary vane vacuum pump sprays the discharged oil mist and water mist into the surrounding environment. After a period of time, a single rotary vane vacuum pump can smoke in a closed room to the extent that it may cause harm to health. This makes the rotary vane vacuum pump can not be used in clean room or close environment or indoor environment.
By installing oil mist eliminator or exhaust filter on the exhaust device of vacuum pump, the oil mist emission can be minimized. This simple step can reduce emissions by 99.95%.