Rotary Vane Vacuum Pumps

Rotary vane vacuum pumps are vacuum pumps that generate low-pressure zones by rotating the moving parts against the pump casing. The mating surfaces of the rotor and the housing have very...
Please fill out the following form to submit a Request for Quote to any of the following companies listed on
This article gives industry insights into vacuum systems and vacuum pumps. Read further to learn more.
A vacuum pump is a piece of equipment capable of generating a partial or low-pressure vacuum by pushing gas or air molecules out of a sealed chamber. A vacuum is a relative state at which the chamber pressure has a lower pressure than the ambient atmosphere or adjacent systems. This is different from absolute vacuum, where the pressure is at 0 Pa and devoid of gas molecules.
One of the key elements of a vacuum pump is atmospheric pressure, which is the weight of the air pressing down on the earth. This pressure is created by the weight of air molecules that decrease at higher altitudes. Air pressure or atmospheric pressure has a significant effect on the operation of machines, especially vacuum pumps. Pressure always attempts to equalize as molecules move from high to low areas to fill a space, a process that is based on the idea of pushing molecules.
The purpose of all pumps is to convert energy into pressure. The amount of energy necessary to run a pump changes in accordance with atmospheric pressure. The higher the atmospheric pressure, the more efficiently the operation of a vacuum pump. Since atmospheric pressure plays such a vital role in vacuum pump efficiency, it is an important factor in the cost of operating a vacuum pump and will vary depending on temperature, humidity, and altitude.
There are different degrees of vacuums that can be created. They can range from a low vacuum with an absolute pressure range of 1 to 0.03 bars to a high vacuum with a pressure of a billionth of a Pascal. Low and medium vacuums are commonly seen in industrial systems such as vacuum grippers, vacuum cleaners, incandescent bulbs, painting, sandblasting, vacuum furnaces, and negative pressure ventilation. Higher vacuum systems are used for laboratory applications such as particle reactors and accelerators.
There are two main categories of generating partial vacuum. One is by gas transfer or gas feeding and the other is through entrapment. Gas transfer types of vacuum pumps work by mechanically removing gasses through positive displacement or momentum transfer. Positive displacement vacuum pumps have chambers that alternately expand and contract with check or non-return valves to draw and eject flow. Momentum transfer pumps work by accelerating gasses creating a low-pressure region in its wake. Entrapment vacuum pumps, on the other hand, capture gas molecules by various principles such as condensation, sublimation, adsorption, ionization, and so on.
Vacuum ranges are characterized by the measurement of the absolute pressure of the system. Which represents the number of remaining molecules left in the system. The remaining gas molecules are normally nitrogen, oxygen, and water vapor, with traces of neon, helium, and hydrogen. As more and more molecules are removed, it becomes increasingly difficult to remove any additional ones. The fewer molecules there are to be removed, the more a vacuum is required to work harder and use more energy, since fewer molecules lowers the pressure reading.
Different vacuum ranges require different pumping techniques. Low and medium vacuum ranges can be achieved by positive displacement vacuum pumps. These are suited for most industrial systems. Achieving high and ultra-high vacuum ranges for special applications such as surface analytic techniques, microscopy, and nanolithography are achieved by both momentum transfer and entrapment pumps.
Vacuum Range |
Absolute Pressure (Pa) |
---|---|
Atmospheric |
101,325 |
Low Vacuum (Rough, Coarse) |
1.01 x 10⁵ to 3.33 x 10³ |
Medium Vacuum |
3.33 x 10³ to 1 x 10⁻¹ |
High Vacuum |
1 x 10⁻¹ to 1x10⁻⁷ |
Ultra-high Vacuum |
1 x 10⁻⁷ to 1 x 10⁻¹⁰ |
The two main classifications of vacuum pumping principles are gas transfer and entrapment. Gas transfer is further divided into positive displacement and momentum transfer. To further grasp the concepts of vacuum pumps, it is best to understand the three types of flow: viscous, transitional, and molecular. Viscous or continuous flow occurs at high pressures to medium vacuum. In this type of flow, the gas is dense enough for gas molecules to collide with each other. The mean free path or the average distance traveled by a gas molecule is less than the dimensions of the chamber. When a higher vacuum is reached, the gas molecules tend to collide on the walls of the chamber more than other gas molecules. Transitional flow occurs when the viscous flow starts to change into molecular flow. Molecular flow is characterized by the random movement of gasses where their mean free path is much longer than the dimensions of the chamber.
Fluids flowing under viscous flow can be pumped mechanically by positive displacement pumps. However, molecular flow will be reached when the gas cannot be evacuated by pressure difference. At this point, another pumping system, either momentum transfer or entrapment, is used. Most high vacuum systems have two pumps in tandem. Positive displacement pumps alone are not sufficient at higher vacuum. Momentum transfer pumps will stall if the system is operated at viscous flow. Entrapment pumps will be frequently regenerated or exhausted when there is too much gas to be captured particularly at viscous flow.
Positive displacement vacuum pumps operate by expanding and contracting a sealed chamber where the flow of fluid is controlled by one-way valves. The vacuum generation process starts by expanding a sealed chamber generating a vacuum. This vacuum draws the fluid into the chamber through an intake valve. Upon reaching the maximum expansion, the intake valve closes while the exhaust opens. The fluid is ejected out of the chamber as it compresses or contracts. The cycle repeats several times per second itself creating a pulsating flow.
Like ordinary pumps, positive displacement vacuum pumps are classified according to the motion and the design of the chamber. There are two main categories: reciprocating and rotary.
Reciprocating vacuum pumps can also be classified according to the number of the chambers mainly to address the problem of pulsating flow. A pulsating flow is an undesirable characteristic of reciprocating pumps where the flow is delivered in short bursts. Adding more pistons and cylinders will create a more constant flow. This brought the development of reciprocating pumps with multiple piston-cylinder assemblies known as multiplex pumps.
In terms of the achieved cycle phase per stroke, reciprocating pumps are categorized as either single- or double-acting. Single-acting pumps create only either vacuum or compression in a single stroke. In this configuration, the piston or diaphragm is coupled to only one chamber where only one side engages the fluid. A double-acting pump, by contrast, creates both vacuum and compression in a single stroke. A common configuration is a twin piston-cylinder or twin diaphragm assembly which is actuated by a single drive rod. Other designs can feature a single piston or diaphragm serving two chambers. Double-acting pumps are more commonly used due to better efficiency, higher flow rate, and less pulsating flow.
Momentum transfer pumps operate by inducing the movement of gas or liquid molecules through kinetic energy transfer. This happens at the molecular flow, in contrast to the viscous or continuous flow occurring in positive displacement pumps. The uniform velocity distribution of the molecules is altered continuously to a preferred direction by the fast-moving surfaces hitting them. These surfaces are not only limited to impeller surfaces, but to other liquids as well. An example is a diffusion pump where high-speed jets of motive fluid impart momentum to the gasses to be drawn from the inlet. Momentum transfer pumps are suited for creating a high vacuum. However, to create a molecular flow, low pressure must exist throughout the system. The exhaust cannot be directly released to the atmosphere or at pressures where backstreaming can occur. To solve this problem, a backing pump is installed in tandem with the vacuum pump. The backing pump can be a positive displacement pump that operates at a lower vacuum level which can directly discharge to the atmosphere.
Entrapment vacuum pumps employ multiple physical and chemical phenomena to capture gas molecules. The working principle is different from each type. Common to almost all entrapment pumps is their ability to operate at high vacuum regimes without any oil contamination. Entrapment vacuum pumps do not rely on rotors or other moving parts. The downside, however, is that it cannot operate continuously since it needs to be regenerated once the surface or material capturing the gasses is full. Moreover, they cannot remove lighter gasses such as hydrogen, helium, and neon. Below are some of the common entrapment vacuum pumps.
The main part of a centrifugal pump is its impeller that accelerates the movement of a liquid and is attached to the shaft that transmits torque inside the shaft sleeve.
Aside from the pumping principles, vacuum pumps can be categorized according to the type of lubrication and sealing system. Vacuum pumps can be wet or dry lubricated. Choosing between the two mainly affects other performance factors such as wear resistance, pumping speed, fluid contamination, and so on.
A vacuum ejector is a type of vacuum pump that operates using the Venturi effect. Inside the vacuum ejector is a venturi, which is referred to as a jet nozzle or orifice. The venturi has a cross-section that narrows into a smaller area and then gradually expands to the cross-section of the discharge pipe. Connected immediately after the venturi is another stream of fluid that is the vacuum connection.
The Venturi effect is based on Bernoulli's principle. This physical concept is basically the law of conservation of energy applied to fluids. It states the inverse relationship of kinetic energy and pressure. When a fluid‘s velocity increases, its pressure decreases, and vice versa.
A motive fluid is used to create the Venturi effect. The motive fluid initially has a higher pressure which is converted into velocity as it passes the venturi. The high-speed jet of the motive fluid has a lower pressure which creates a vacuum in the surrounding regions. Vacuum is produced to any connection made on the low-pressure regions.
A vacuum ejector has two main advantages.
On the other hand, the disadvantage of using a vacuum ejector is the inevitable mixing of the motive fluid and the fluid from the vacuum connection. If the intention is to recover the fluid drawn from the evacuated chamber, special separation techniques must be performed.
Vacuum ejectors are usually used in applications for drawing liquids such as water and steam where mixing the motive and vacuum streams poses no negative issues. They are commonly seen in power plants, petroleum and petrochemical plants, and water treatment facilities.
Rotary vane vacuum pumps are vacuum pumps that generate low-pressure zones by rotating the moving parts against the pump casing. The mating surfaces of the rotor and the housing have very...
A ball valve is a shut-off valve that allows or obstructs the flow of liquids and gasses in a piping system by rotating the ball having a bore inside the valve for 90°. The ball is mounted against two seats and has a stem that connects it to the operating and control mechanism that rotates the ball...
A butterfly valve is a quarter-turn rotational motion device that utilizes a rotary disc to allow, obstruct, or control the flow of fluids in a piping system. It features a rotating disc that is situated on the passageway of the flowing media...
A check valve is a safety device designed to allow fluids and gasses to flow in one direction. Under pressure, fluids enter the valve at the inlet and exit through the outlet. Uninterrupted flow continues until the pressure drops, or the pump is shut down...
A PVC or polyvinyl chloride ball valve is a plastic on and off valve that has a rotary ball with a bore where turning the ball a quarter turn can stop the flow of a fluid. They are highly durable, cost effective and can be...
A spring check valve is a valve that ensures unidirectional flow and prevents reverse flow. They have a single inlet and outlet and must be placed in proper orientation to function correctly. On the side of a spring check valve, and all...