This article will take an in-depth look at rotary vane vacuum pumps.
The article will bring more detail on topics such as:
This chapter will cover the fundamentals of rotary vane vacuum pumps, including their design features and operational principles.
Rotary vane vacuum pumps create low-pressure areas by rotating internal components against the pump casing. The rotor and housing surfaces are engineered with very tight clearances and are often coated with self-lubricating or low-friction materials such as graphite, PEEK (polyether ether ketone), or PTFE (polytetrafluoroethylene).
The tight clearance between the rotor and the housing in rotary vane vacuum pumps minimizes fluid leakage to the low-pressure side. These pumps provide a more consistent flow with less pulsation compared to reciprocating pumps. However, they are not ideal for handling fluids with abrasive contaminants, as such materials can erode the narrow clearances. Rotary vacuum pumps are classified based on their rotor design.
Among the most common types of positive displacement vacuum pumps is the rotary vane vacuum pump. This pump features vanes that are inserted radially into a circular rotor. The rotor is positioned eccentrically within the stator housing, creating a pump stroke. As the rotor rotates, the chambers separated by the vanes become progressively smaller towards the discharge end. The vanes, which move radially due to centrifugal force, press against the housing. When the rotor is stationary, a spring holds the vanes in their position.
Rotary vane vacuum pumps fall under the category of positive displacement pumps. They create a vacuum by continuously evacuating chambers, without needing infinite expansion. This is achieved by sealing off, exhausting, and then re-expanding one of the pump's sections. Additionally, rotary vane pumps can be designed as either dry pumps or oil-sealed pumps. Dry pumps, specifically, operate without the use of any liquid.
Wet pumps utilize a fluid for sealing and lubrication, whereas dry pumps rely on precise internal dimensions to create a vacuum. Oil-sealed pumps are a specific type of wet pump that uses oil for sealing. Additionally, many rotary vane vacuum pumps feature a direct drive mechanism. Despite variations in design, size, or model, all rotary vane vacuum pumps share a set of fundamental components.
Although specific components may vary depending on the pump's design and model, both oil-lubricated and dry-running pumps generally include the following common components.
Rotor – The rotor is normally wound with copper, while some variants use a cylindrical or "caged" rotor constructed of solid conductors. The rotor is the revolving part of this electrical engine, regardless of design, but it requires energy to turn. The stator is the coiled layout's stationary component. It carries electrical current and wraps around the interior surfaces of the motor's housing. As basic as this arrangement of copper conductors appears to be, the technical concepts underlying the technique are a little more complicated.
Blades and Vanes – These components are broad blades mounted on a rotating wheel or shaft. The vanes ensure a tight seal against the walls of the pumping chamber, effectively preventing fluid from flowing backward through the pump.
Oil Sump – This is the reservoir where the engine oil required for sealing is stored. An oil pump draws oil from the sump and delivers it into the engine block's oil channels through the oil filter. The oil is then returned to the oil sump through the sealing points.
Cylindrical Housing – Typically constructed from die-cast aluminum, this is the outer shell of the pump that encases the compressor.
Suction Flange – Suction flanges are used to attach a suction tube to a hydraulic tank. They create a seal to prevent fluid leaks and block contaminants from entering the tank. Additionally, suction flanges enable access to the suction element without requiring the tank to be drained.
Motor – An electric motor is a machine that converts electrical energy (AC or DC) into mechanical energy. Most electric motors generate force in the form of torque imparted to the motor's shaft by interacting between the magnetic field of the motor and electric current in a wire winding.
Float Valve – This component detects changes in the oil level and automatically opens or closes a valve accordingly to maintain proper fluid levels.
Oil Separator Elements and Filters – These components are placed within the vacuum pump’s exhaust section. They serve to capture oil mist produced during the lubrication process, ensuring that the oil is separated from the exhaust gases.
Oil Separator Housing – This component encloses the oil separator elements and the oil sump, ensuring that the oil and separating elements are properly contained.
Oil – The fluid used for lubrication and sealing within the pump, crucial for its operation and efficiency.
Pressure Regulating Valve – This component is a type of control valve designed to reduce the pressure of a fluid or gas to a specified level at its output. Typically, it is an open valve placed before equipment that is sensitive to pressure changes.
Motor Fan – Commonly referred to as the impeller, this disk-shaped part with blades creates suction in a vacuum system. It is mounted directly on the shaft of the suction motor, causing it to rotate rapidly. The centrifugal force generated by the spinning air within the fan creates the suction effect.
Exhaust Silencer - Constructed from steel and coated with aluminum to safeguard against high temperatures, exhaust silencers, also known as mufflers, primarily serve to reduce the noise generated by the vacuum pump.
Rotary vane vacuum pumps are a type of Vacuum pump. A vacuum pump is a piece of machinery that may create a partial vacuum or a low-pressure environment by sucking gas molecules out of a sealed chamber. A vacuum is a relative condition in which the chamber pressure is lower than that of the surrounding atmosphere or systems. This is distinct from an absolute vacuum, which has a pressure of 0 Pa absolute and is entirely bereft of gas molecules.
Vacuum levels vary widely, ranging from low vacuums with absolute pressures between 1 and 0.03 bars to extremely high vacuums with pressures as low as one billionth of a Pascal. Applications such as vacuum cleaners, vacuum grippers, incandescent lamps, vacuum furnaces, sandblasting, painting, and negative pressure ventilation commonly utilize low and medium vacuums. High vacuum systems are used in specialized laboratory settings like particle reactors and accelerators.
Partial vacuum generators come in two main types: gas transfer and entrapment. Gas transfer pumps remove gases through mechanical means, utilizing either momentum transfer or positive displacement. Positive displacement pumps use chambers that expand and contract to draw and expel gases, incorporating check valves or non-return valves. Momentum transfer pumps, by contrast, accelerate gases to create a low-pressure area. Entrapment pumps capture gas molecules through methods such as sublimation, condensation, ionization, or adsorption.
Narrow clearances in vacuum pumps help prevent fluid leakage to the low-pressure side. Rotary vacuum pumps provide a more continuous flow compared to reciprocating pumps due to their lower pulsing delivery. However, they are less suitable for fluids contaminated with abrasive materials because the tight clearances between the housing and rotor can suffer erosion. Rotary vacuum pumps are classified based on their rotor design.
The rotary vane vacuum pump is a widely used positive displacement pump. It features radially inserted vanes within a circular rotor, which is offset from the stator housing, a feature known as the pump stroke. As the rotor turns, the chambers divided by the vanes become progressively smaller towards the discharge. The vanes move radially, primarily due to centrifugal force, and press against the housing. When the rotor is stationary, a spring holds or energizes the vanes in position.
Rotary vane vacuum pumps can vary in numerous aspects, but their material compositions tend to be fairly standardized. Typically, these pumps consist of several components made from different materials, including:
Cast Iron - Cast iron is a broad category of ferrous alloys comprising between 1% and 3% silicone and 2% to 4% carbon, with a core of approximately 95% iron by weight. While several casting procedures are used to make cast iron parts, they all follow the same basic process of heating, molding, cooling, and ejecting.
It has good casting attributes and is available in huge quantities, therefore produced in a mass scale. Tools needed for the casting process are comparatively cheap and inexpensive. Hence this results in the low cost of vacuum pumps. It can be made into any complex form and size without using expensive machining operations. Cast iron has 3 to 5 times more compression strength in comparison to steel. Good machinability in gray cast iron is a bonus. Its outstanding damping or anti-vibration properties make it useful in vacuum pumps. Cast iron is outstandingly resistant to wear. It’s also durable and resistant to deformation.
Ductile Iron – Also known as ductile cast iron or nodular cast iron is a type of graphite-rich cast iron. While most variations of cast iron are tensile weak and brittle, ductile iron possesses much more impact and fatigue resistance, because of its nodular graphite additions.
Ductile iron may be cast and machined easily. Its strength to weight ratio is excellent. Ductile iron is much cheaper than steel. Ductile iron gives a designer an exceptional combination of cheap manufacturing, toughness, and reliability.
Steel - Steel is a metal alloy composed of iron, carbon, and other elements. These elements include molybdenum, tungsten, chromium, nickel, silicon manganese, and, among others. Steel is the most important engineering metal by far. It has a high tensile strength at a reasonable cost, making it an excellent choice for vacuum pump construction.
Steel is probably the most popular material among producers because of its durability. Properly processed and plated steel will not decay, distort, split, crack, or catch fire. Wherever and whenever it is utilized, it delivers great structural integrity, resistance to weather, and long-term strength.
Steel’s flexibility is just as important whether the vacuum pump requires machining, welding, or painting. The wide variations of steel products available show that its design flexibility is boundless. Vacuum pumps are a testament to its flexibility.
Carbon Graphite - Carbon graphite is a material used for replacement and specialty components because it offers high-temperature capabilities, wear resistance, self-lubricating qualities, and the ability to be utilized with corrosive materials when properly prepared.
Carbon graphite devices are usually composed of two materials: powders and binders. Natural or synthetic graphite, carbon black, petroleum coke, or other types of carbon are used to make powders. Coal tar pitch is a popular binder in carbon graphite compounds.
Carbon graphite and graphite parts are self-lubricating and will not seize or gall while in use. Furthermore, because carbon graphite is dimensionally solid, temperature variations will not distort the portion. Pushrods and vanes are frequently made of carbon graphite and graphite parts.
Polyetheretherketone (PEEK) - is a semi-crystalline engineering thermoplastic with good performance. This stiff opaque (gray) material has a one-of-a-kind combination of mechanical characteristics, chemical resistance, wear, fatigue, and creep resistance, as well as extraordinarily high temperature resistance, reaching 260°C (480°F). The polymer belongs to the polyketone family of polymers, of which PEEK is the most frequently utilized and mass-produced.
PEEK has excellent tensile characteristics. Tensile strength of 29000 psi may be attained when strengthened with carbon fibers, with outstanding characteristics retained at 299°C. The polymer also has a high creep resistance. When paired with flexural and tensile qualities, it provides a great balance of qualities where the material must sustain strong loadings for extended periods of time at high temperatures without permanent deformations.
Its flexibility modulus at extremely high temperatures can be enhanced further using glass or carbon reinforcing. (Reinforcement also improves creep and fatigue resistance, polymer thermal conductivity, and heat distortion temperature). It has crystallinity which provides great resistance to a wide range of liquids as well as superior fatigue performance.
Here’s how rotary vane vacuum pumps operate:
The rotary vane pump operates on the principle of increasing pressure through volume reduction. As the blades rotate inside the cylinder, a thin layer of oil helps minimize wear. This lubrication is maintained by the differential pressure within the housing, aided by connected pipes. The rotor is positioned eccentrically within the housing, and centrifugal force presses the blades against the housing wall, creating three chambers to capture air. When the initial chamber opens, air is drawn into the compressor chamber through the suction flange.
As the rotor continues to turn, the next vane closes off the first chamber and opens the second. At this stage, the blades are positioned to maximize the air volume. The oil and gas mixture is then compressed by reducing the volume and directed into the oil separator housing. Some pump designs include exit valves to prevent air from flowing back once maximum pressure is reached or when the pump is turned off. In the oil separator housing, gas and oil are separated through a specific process.
The oil is then redirected to the oil sump. This process effectively removes 95-98 percent of the oil from the air. To eliminate any remaining oil particles, the residual gas and oil mixture is passed through fine filters. The filtered oil particles are then returned to the pump's oil circuit via a float valve. With the gas now nearly free of oil, it can be expelled through the air exit or via pipes or hoses.
Dry running pumps, similar to lubricated pumps, operate on the principle of increasing pressure through volume reduction. In these pumps, dry graphite vanes come into contact with the housing cylinder, creating a graphite layer that helps protect the pump from wear. Like lubricated pumps, dry running pumps also need to filter the compressed air to remove any particulates. Additionally, the air is often routed through a cooler to reduce the temperature of the exhaust.
Rotary vane vacuum pumps and systems are defined by several key specifications. The most important of these are the ultimate operating vacuum and the pumping speed.
Ultimate (Maximum) Operating Vacuum – This specification indicates the lowest pressure the vacuum pump can achieve, typically within a certain timeframe. It’s important for buyers to understand the conditions under which this pressure is calculated, as manufacturers might base this figure on ideal conditions that may not reflect typical operational scenarios, such as neglecting the presence of condensable gases like water vapor.
Pumping Speed – This refers to the rate at which gas is evacuated from the vacuum chamber, measured in m3/s, ft3/min (cfm), L/min, or gal/min (gpm). The rated pumping speed represents the highest speed achievable across the pump's entire pressure range, and is often specified at standard temperature and pressure (STP). The required pumping speed should align with the application's needs, which are influenced by the system's desorption rate, chamber volume, and process gas loads. Rotary vane pumps typically offer pumping rates ranging from 1 to 650 cfm (cubic feet per minute).
Note: The actual speed of the pump may differ from the rated pumping speed within the device’s chamber. Performance parameters should be compared to application requirements based on conditions similar to those used for determining the ultimate pressure.
Rotary vane vacuum pumps are generally powered by either alternating current (AC) or direct current (DC).
AC power is the most common power source for rotary vane vacuum pumps and systems. Single-phase AC motors are widely used and tend to be less expensive than three-phase AC motors. However, single-phase motors are also less efficient (for the same horsepower) and larger in size.
DC power supplies use DC current from a battery or power supply.
The pumping speed and vacuum level are crucial factors that affect other aspects of the system. Here are some common classifications and their typical ranges:
When determining the appropriate pumping speed, there are two key factors to consider:
To achieve the desired pump down time and vacuum level, it may be necessary to use a combination of different vacuum pump technologies.
Fore vacuum pumps operate within the medium and rough vacuum ranges. They function by compressing gases and then releasing them into the atmosphere. Typical applications for these pumps include food packaging, heat treatment, and freeze drying.
High and ultra-high vacuum pumps, such as diffusion and turbomolecular pumps, are used in conjunction with fore vacuum pumps and rely on the molecular transfer principle. These pumps are commonly used in fields such as metallurgy, coating, and analytical work.
Various types of rotary vane vacuum pumps include:
A standard lubricated rotary vane pump is typically a single-stage unit with a closed-loop oil-circulation system. It features a durable and compact design, with an average lifespan of around 50,000 hours. The rotor is eccentrically placed within the pump's cylinder. As the rotor turns, the space between the rotor and vane segments captures the inlet gas. This results in an increase in the cell volume on the inlet side, creating a vacuum effect.
Due to the rotor's eccentric position relative to the pump chamber, the volume between the vanes, rotor, and housing decreases, which causes the rotor to spin faster. As the rotor continues to turn, the air is compressed and then expelled into the exhaust box.
These vacuum pumps utilize reliable rotary vane technology. They operate without the need for external lubricants, as the rotor vanes are self-lubricating. Compression occurs during a completely dry operation.
Optimal material selection, specialized graphite vanes or blades in the compression chamber, effective heat dissipation, and advanced, precise manufacturing all contribute to maintaining a consistently high vacuum level during continuous operation.
When the vacuum pump is turned off, an optional non-return valve prohibits air from entering the vacuum chamber. The unit is powered by an integrated motor with a high efficiency rating.
This compressor model operates with minimal pulsation and requires no oil. A robust cooling fan effectively dissipates heat from both the motor and the pump.
A liquid-ring pump operates using positive-displacement rotation. While often used as a vacuum pump, it can also function as a gas compressor. It works in a manner similar to a rotary vane pump, but instead of separate vanes, the rotor itself includes vanes that create a rotating liquid ring, which forms the compression chamber seal. Since the rotor is the only moving part, these pumps experience minimal friction, with sliding friction occurring only at the shaft seals. Liquid-ring pumps are typically driven by induction motors.
The liquid-ring pump compresses gas by rotating a vaned impeller eccentrically within a cylindrical housing. Liquid, typically water, is introduced into the pump, creating a rotating cylindrical ring along the inner surface of the casing due to centrifugal force. This liquid ring forms a series of seals between the impeller's vanes, establishing compression chambers. The eccentric alignment of the casing’s geometric axis and the impeller’s axis of rotation results in cyclical variations in the volume within the vanes and liquid ring.
Gas, usually air, is drawn into the pump through an inlet port at the end of the casing. The gas is trapped within the compression chambers formed by the impeller's vanes and the liquid ring. As the impeller rotates, it compresses the gas, which is then expelled through the discharge port at the end of the casing.
Upon discharge, the compressed gas contains a small amount of the working liquid, which is typically separated out using a vapor–liquid separator.
This chapter will explore the applications and advantages of rotary vane vacuum pumps.
Although rotary vane vacuum pumps have a straightforward design, they are often not ideal for achieving very high vacuums. However, they are widely used in various applications where creating a vacuum or evacuated environment is essential. These applications include electron microscopy, the production and development of electronics such as superconductors, and certain analytical instruments. Such environments require vacuum pumps to eliminate trace airborne contaminants. Additionally, rotary vane vacuum pumps are commonly used in healthcare settings to provide suction during surgical procedures.
Liquid ring vacuum pumps feature a rotating assembly with vanes that spin within a cylindrical enclosure. Unlike rotary vane pumps, they are termed "liquid vane pumps" because they use a ring of water for sealing. This liquid ring aids in compressing air and preventing it from re-entering the evacuated space. Additionally, both oil-sealed or lubricated pumps and dry vacuum pumps employ rotating blades in their operation.
Rotary vane vacuum pumps are among the most common types of vacuum pumps. In fact, many vacuum pumps utilize spinning vanes, blades, paddles, or impellers to move gas in and out of an enclosure. Any vacuum pump featuring these components is classified as a rotary vacuum pump.
One drawback of rotary vane vacuum pumps is their reliance on low vapor pressure oil. Since the pump requires oil to operate, it needs regular monitoring, refilling, and replacement. This dependency can lead to contamination from high vapor pressure gases, which may impair performance and damage components.
To mitigate this, installing traps and filters before the pump's intake can prevent contaminants from entering the vacuum chamber, thereby reducing the risk of oil contamination.
Additionally, rotary vane pumps emit oil and water mist into the environment through their exhaust. Over time, this can create a smoky environment that poses health risks, making these pumps unsuitable for clean rooms, sensitive environments, or indoor applications.
Attaching an exhaust filter or oil mist eliminator to the pump's exhaust can significantly reduce oil mist emissions, achieving up to a 99.95 percent reduction.
Maintenance for rotary vane vacuum pumps involves:
Because rotary vane pumps use a significant amount of oil, regular oil changes are essential for maintaining pump performance. It is generally recommended to change the oil every six months; however, this interval may need adjustment based on the pump's usage and the type of process gases it handles. The oil’s color is a good indicator for when an oil change is due. Fresh oil is clear, but it darkens with use. Once the oil turns amber, it should be replaced. If the oil reaches black or dark red hues, it may indicate potential pump failure and the need for a complete overhaul.
High-performance oil is refined to the highest purity, ensuring it is free from contamination and dilution. Using low viscosity oils is not recommended, as they can decrease pump speed, ultimate vacuum performance, and overall pump lifespan.
Wearable elements such as gaskets, O-rings, and seals must be replaced on a regular basis in every rotary vane pump. Without this, the pump's sealing capability deteriorates and its performance begins to deteriorate. The frequency of clean and overhaul is determined by the size of the pump. Larger vacuum pumps having pumping speeds of 40 m3/h-1 and higher necessitate annual clean and overhaul maintenance. Smaller pumps having pumping speeds of up to 28 m3/h-1 can run for two years before requiring a clean and overhaul.
Rotary vane pumps operate using revolving vanes, also known as blades. Since these vanes are subject to wear from exposure to process gases, they need regular replacement. It is advisable to replace the vanes during routine cleaning and overhauls. For larger vacuum pumps (40 m3/h and above), vane replacement is typically required every three years. For smaller pumps (up to 28 m3/h), replacement is generally needed every four years.
Another crucial aspect of maintaining a rotary vane vacuum pump is ensuring it stays cool. Excessive heat can significantly shorten the motor's lifespan. If the pump operates in a confined space, using a fan can help dissipate heat. Overheating causes the oil's viscosity to decrease, which impairs the pump's ability to generate an effective vacuum.
Solids and liquids entering a rotary vane vacuum pump can lead to pump failure if the filter does not perform adequately. Therefore, it is important to replace the filter as specified by the manufacturer's instructions, similar to how you would change the oil.
Vacuum pumps generate low-pressure zones by rotating the moving parts against the pump casing. The most popular form of positive displacement vacuum pump is the rotary vane vacuum pump. Rotary vane pumps, aside from being positive displacement pumps, can be constructed as dry pumps or oil-sealed pumps. In a nutshell, dry pumps operate without the usage of any liquid.
Wet pumps use a fluid seal/lubrication to work, while dry pumps depend on internal dimensional tolerance to make a vacuum. Rotary vane vacuum pumps may differ in a variety of ways. Their material compositions, on the other hand, are usually relatively standardized.
They are widely used in a variety of situations that necessitate the generation of an artificially evacuated environment or vacuum. Some of these include the use of electron microscopy, the manufacture and design of electronics such as superconductors, and the use of certain types of analytical apparatus.
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