How does a Roots pump work - Leybold USA

The design principle of the Roots pumps was already invented in by Isaiah Davies, but it was 20 years later before it was implemented in practice by the Americans Francis and Philander Roots. Initially such pumps were used as blowers for combustion motors. Later, by inverting the drive arrangement, the principle was employed in gas meters. Only since has this principle been employed in vacuum engineering. Roots pumps are used in pump combinations together with backing pumps (rotary vane or dry pumps) and extend their operating range well into the medium vacuum range. With two stage Roots pumps this extends into the high vacuum range. The operating principle of Roots pumps permits the assembly of units having very high pumping speeds (over 100,000 m3/h) which often are more economical to operate than steam ejector pumps running in the same operating range.

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A Roots vacuum pump (see Fig. 2.17) is a rotary positive-displacement type of pump where two symmetrically-shaped impellers rotate inside the pump casing past each other in close proximity. The two rotors have a cross section resembling approximately the shape of a figure 8 and are synchronized by a toothed gear. The clearance between the rotors and the casing wall as well as between the rotors themselves amounts only to a few tenths of a millimeter. For this reason, Roots pumps may be operated at high speeds without mechanical wear. In contrast to rotary vane and dry pumps, Roots pumps are not oil sealed, so that the internal leakage of dry compressing pumps by design results in the fact that compression ratios only in the range 10 – 100 can be attained. The internal leakage of Roots pumps, and also other dry compressing pumps for that matter, is mainly based on the fact that owing to the operating principle certain surface areas of the pump chamber are assigned to the intake side and the compression side of the pump in alternating fashion. During the compression phase these surface areas (rotors and casing) are loaded with gas (boundary layer); during the suction phase this gas is released. The thickness of the traveling gas layer depends on the clearance between the two rotors and between the rotors and the casing wall. Due to the relatively complex thermal conditions within the Roots pump it is not possible to base one’s consideration on the cold state. The smallest clearances and thus the lowest back flows are attained at operating pressures in the region of 1 mbar. Subsequently it is possible to attain in this region the highest compression ratios, but this pressure range is also most critical in view of contacts between the rotors and the casing. 

The characteristic quantities to be found in equation 2.17 are only for the combination of the Roots pump and the backing pump, namely maximum compression k0 of the Roots pump and gradation kth between Roots pump and backing pump. 

With the aid of the above equations the pumping speed curve of a given combination of Roots pump and backing pump may be calculated. For this the following must be known: 

a) the theoretical pumping speed of the Roots pump: Sth 
b) the max. compression as a function of the fore vacuum pressure: k0 (pV) 
c) the pumping speed characteristic of the backing pump SV (pV) 

The way in which the calculation is carried out can be seen in Table 2.3 giving the data for the combination of a Roots pump RUVAC WA / E 250 (single-stage rotary plunger pump, operated without gas ballast). 

The method outlined above may also be applied to arrangements which consist of a rotary pump as the backing pump and several Roots pumps connected in series, for example. Initially one determines – in line with an iteration method – the pumping characteristic of the backing pump plus the first Roots pump and then considers this combination as the backing pump for the second Roots pump and so on. Of course, it is required that the theoretical pumping speed of all pumps of the arrangement be known and that the compression at zero throughput k0 as a function of the backing pressure is also known. As already stated, it depends on the vacuum process which grading will be most suitable. It may be an advantage when backing pump and Roots pump both have the same pumping speed in the rough vacuum range. 

The amount of power drawn by the pump determines its temperature. If the temperature increases over a certain level, determined by the maximum permissible pressure difference pV – pa, the danger exists that the rotors may seize in the casing due to their thermal expansion. The maximum permissible pressure difference Δpmax is influenced by the following factors: forevacuum or compression pressure pV, pumping speed of the backing pump SV, speed of the Roots pump n, gradation kth and the adiabatic exponent κ of the pumped gas. Δpmax increases when pV and SV increase and decreases when n and kth increase. Thus the maximum difference between forevacuum pressure and intake pressure, pV-pa must - during continuous operation - not exceed a certain value depending on the type of pump. Such values are in the range between 130 and 50 mbar. However, the maximum permissible pressure difference for continuous operation may be exceed for brief periods. In the case of special designs, which use gas cooling, for example, high pressure differences are also permissible during continuous operation.

Standard flange-mounted motors are used as the drive. The shaft feedthroughs are sealed by two oil sealed radial shaft seals running on a wear resistant bushing in order to protect the drive shaft. Flange motors of any protection class, voltage or frequency may be used. 

Integral leak tightness of this version is < 10-4 mbar  · l  · s-1.  

In the case of better leak tightness requirements of < 10-5 mbar  · l  · s-1 the Roots pump is equipped with a canned motor. The rotor is seated in the vacuum on the drive shaft of the pump and is separated from the stator by a vacuum- tight non- magnetic tube. The stator coils are cooled by a fan having its own drive motor. Thus shaft seals which might be subject to wear are no longer required. The use of Roots pumps equipped with canned motors is especially recommended when pumping high purity-, toxic- or radioactive gases and vapors. 

 In the case of standard Roots pumps, measures must be introduced to ensure that the maximum permissible pressure difference between intake and exhaust port due to design constraints is not exceeded. This is done either by a pressure switch, which cuts the Roots pump in and out depending on the intake pressure, or by using a pressure difference or overflow valve in the bypass of the Roots pumps (Fig. 2.20 and 2.21). The use of an overflow valve in the bypass of the Roots pump is the better and more reliable solution. The weight and spring loaded valve is set to the maximum permissible pressure difference of the particular pump. This ensures that the Roots pump is not overloaded and that it may be operated in any pressure range. In practice this means that the Roots pump can be switched on, together with the backing pump, at atmospheric pressure. In the process any pressure increases will not adversely affect combined operation, i.e. the Roots pump is not switched off in such circumstances. 

In the case of Roots pumps with pre-admission cooling (Fig. 2.22), the compression process basically is the same as that of a normal Roots pump. Since greater pressure differences are allowed more installed power is needed, which at the given speed and the pressure difference between inlet and discharge port is directly proportional and is composed of the theoretical work done on compression and various power losses. The compression process ends normally after opening of the pumping chamber in the direction of the discharge port. At this moment warmed gas at higher pressure flows into the pumping chamber and compresses the transported volume of gas. This compression process is performed in advance in the case of pre-admission cooling. Before the rotor opens the pumping chamber in the direction of the discharge port, compressed and cooled gas flows into the pumping chamber via the pre-admission channel. Finally, the rotors eject the pumped medium via the discharge port. The cooled gas, which in the case of single- stage compression is taken from the atmosphere and admitted from the pre-admission cooler, and which in the case of multi-stage pump systems is taken from downstream gas coolers, performs a pre-compression and removes by “inner cooling” the heat of compression at the point of time it occurs. 

REBUILT Edwards QMB250F QMB-250F Blower Roots Vacuum Mechanical Booster Pump(These Edwards QMB250F pumps are interchangeable with the (i)QMB 250F Pumps) For sale is the Edwards QMB250F Mechanical Booster Pump. They are compact and have high pumping speeds. Low system pressures can be achieved by using two or more mechanical booster pumps in series. You must use the QMB Mechanical Booster Pump with a suitable backing pump. Preferably the Edwards QDP pumps. The maximum continuous inlet pressure is 20 mbar for the QMB250F and QMB500F Mechanical Booster Pumps and 1 mbar for the QMBF Mechanical Booster Pumps. The QMB250F and QMB500F pumps are air-cooled and the QMBF pump is water-cooled. All the QMB pumps have enclosed, water-cooled motors and are therefore suitable for applications in clean environments where fan cooling is unacceptable. The pump coupling-cover is connected to the pump outlet and forms an integral part of the vacuum system. The connecting pipelines have a filter which removes debris and so prevents contamination of the lubricating oil and bearings. For an even cleaner system, the coupling-cover and bearings can be evacuated by connection to the pump-inlet or to an external vacuum pump.The QMB pumps are positive displacement Roots vacuum pumps. The pump mechanism is driven by a three-phase electric motor through a hydrokinetic fluid-coupling. The motor is enclosed and is cooled by integral cooling-water coils. The pump shafts and rotors are made of high-grade, corrosion-resistant, cast-iron. The internal and external shaft-seals are made of polytetrafluoroethylene (PTFE) or fluoroelastomer. The pump-bearings, gears and seals are lubricated by oil fed from reservoirs in the coupling-cover. A series of seals stops the oil from reaching the vacuum side of the pump. The coupling-cover is evacuated. You can inspect the oil-levels through sight-glasses which are fitted to the coupling-cover. Oil-filler, oil-drain and external evacuation connections are provided on the cover. The QMB250F and QMB500F pumps have rear bearings which are lubricated by perfluoropolyether (PFPE) grease. The QMBF pump gears are lubricated by oil in the gear-cover. The gear-cover of the QMBF has oil-filler and oil-drain plugs and an oil-level sight-glass. The QMB pumps are suitable for use only with PFPE oils and have voltages of 60 Hz, 208 - 230 VAC / 460 VAC 3 phase. The price listed above is for a Edwards QMB250 Blower (Boosters) Vacuum Pump only. We also sell mechanical and blower vacuum pump systems. Please call (505) 872- for more information.

Condition: Rebuilt

Part Number: P

Price: $4,495.00

Currency: US Dollar (USD)

RSV601 Adixen Alcatel Roots Blower Booster Vacuum Pump PN RSV601Adixen Alcatel Part Number NRSV601 The Adixen Alcatel RSV601 RSV 601 Roots Pumps are suited to a wide range of vacuum applications. In combination with primary vane pumps, or dry pumps, they achieve low pressures with high pumping speeds. Adixen Alcatel quality and reliability without any mechanical contact. They are proven in industrial and chemical applications, the Adixen Roots pumps achieve high reliability. The canned motor concept allows the motor armature and drive shaft to be enclosed in a vacuum tight “can“, this design eliminates external shaft seals and potential leaks, resistant to process gases and condensables. The careful choice of quality components makes Adixen Alcatel Roots well adapted to aggressive environments. Aggressive environments require vertical flow Roots, to prevent condensate from accumulating inside the pumping chamber. Simplified maintenance and on site repair and maintenance capability. Low noise Compact design, quiet operation, low vibration level and air cooled. The RSV Series is helium leak tested to < 1.10-7 mbar l/s and is ideally suited for hazardous duty. The lubrication requirements of these RSV 601 booster pumps are limited to the ball bearings and synchronization gear train. The two casings containing the oil are isolated from the pumping chamber by a sealing system (lip seal for dry friction in PTFE + treated friction ring + deflectors) which prevents any possibility of oil contamination of the pumped gases. Roots vacuum boosters operate in conjunction with a roughing pump (RP) which enables the gas flow to be delivered against atmospheric pressure. Consequently, the pumping speed/pressure relation is directly related to the performance characteristics of the associated roughing pump. The power consumption of the Roots machine is according to the pumping speed, the rotation speed and the pressure difference between inlet and outlet sides. The most noteworthy feature of these RSV 601 boosters is the motor coupling which is made only with static parts. The roots RSV units are called ”in vacuum rotor” machines, i.e., the rotor of the electric motor is completely isolated by a stainless steel cylindrical sleeve. This sleeve is centered inside the motor stater and attached to the machine casing, with a static o-ring providing the necessary seal. In this way, any possibility of leaks around the motor/pump coupling is precluded by eliminating the shaft passage with dynamic seal used in conventional set-ups. The oil casings are sealed from the pumping chamber by means of a link tube connecting the casings to the outlet of the machine. This avoids the creation of any pressure difference between the pumping chamber and the casing which would otherwise be conducive to oil migration. An oil mist filter avoids any oil back-streaming into casing tubes. (For Users Manual download .pdf below at AVAILABLE DOWNLOADS.)

Condition: New

Part Number: P

Price: $14,175.00

The company is the world’s best Roots Vacuum Pump For Sale supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

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REBUILT Edwards iQMBF iQMB-F Blower Roots Vacuum Mechanical Booster Pump (These Edwards iQMBF pumps are interchangeable with the QMB F Pumps) For sale is the Edwards iQMBF Mechanical Booster Pump. They are compact and have high pumping speeds. Low system pressures can be achieved by using two or more mechanical booster pumps in series. You must use the QMB Mechanical Booster Pump with a suitable backing pump. Preferably the Edwards QDP pumps. The maximum continuous inlet pressure is 20 mbar for the QMB250F and QMB500F Mechanical Booster Pumps and 1 mbar for the QMBF Mechanical Booster Pumps. The QMB250F and QMB500F pumps are air-cooled and the QMBF pump is water-cooled. All the QMB pumps have enclosed, water-cooled motors and are therefore suitable for applications in clean environments where fan cooling is unacceptable. The pump coupling-cover is connected to the pump outlet and forms an integral part of the vacuum system. The connecting pipelines have a filter which removes debris and so prevents contamination of the lubricating oil and bearings. For an even cleaner system, the coupling-cover and bearings can be evacuated by connection to the pump-inlet or to an external vacuum pump. The QMB pumps are positive displacement Roots vacuum pumps. The pump mechanism is driven by a three-phase electric motor through a hydrokinetic fluid-coupling. The motor is enclosed and is cooled by integral cooling-water coils. The pump shafts and rotors are made of high-grade, corrosion-resistant, cast-iron. The internal and external shaft-seals are made of polytetrafluoroethylene (PTFE) or fluoroelastomer. The pump-bearings, gears and seals are lubricated by oil fed from reservoirs in the coupling-cover. A series of seals stops the oil from reaching the vacuum side of the pump. The coupling-cover is evacuated. You can inspect the oil-levels through sight-glasses which are fitted to the coupling-cover. Oil-filler, oil-drain and external evacuation connections are provided on the cover. The QMB250F and QMB500F pumps have rear bearings which are lubricated by perfluoropolyether (PFPE) grease. The QMBF pump gears are lubricated by oil in the gear-cover. The gear-cover of the QMBF has oil-filler and oil-drain plugs and an oil-level sight-glass. The QMB pumps are suitable for use only with PFPE oils and have voltages of 60 Hz, 208 - 230 VAC / 460 VAC 3 phase. The price listed above is for a Edwards QMB Blower (Boosters) Vacuum Pump only. We also sell mechanical and blower vacuum pump systems. Please call (505) 872- for more information.

Condition: Rebuilt

Part Number: P

Price: $10,995.00

Currency: US Dollar (USD)

Leybold RUVAC WS WS Blower Booster Vacuum Pump, Differential Pressure Bi-Pass Valve, Rebuilt Refurbished Rebuilt for Oxygen Safe and Chemical Resistant PFPE Oil (208/460 VAC 3 ph) The Leybold RUVAC WS Root's blower vacuum pump is a Single Stage Roots Pump and driven by an air-cooled canned motor, the term canned means that the blower's electric motor operates inside the pump's vacuum region. In the canned motor design, the motor's rotor operates on the drive shaft of the pump inside a vacuum-tight can made of a nonmagnetic material. The motor's stator slides over the outside of the vacuum tight can and operates in air. This canned electric motor design allows the WS blowers to be particularly leak tight and operate without the need for shaft seal which would be subject to wear. For these reasons the Leybold WS blower vacuum pumps are often used in vacuum processes which require evacuation of chemical process gases. The WS pumps are easy to operate! For Start up Procedures See Section 2-9 in the Operation Manual.pdf manual at Downloads to the side of this ad. These Oerlikon WS Root's blower booster vacuum pumps have ASA 4 in. inlet and exhaust flanges, have a pumping speed of 660 CFM, and have been rebuilt for oxygen save and chemical resistant PFPE vacuum pump oils, such as, Fomblin and Kyrtox. This price is for a rebuilt Leybold WS Root's blower (Booster) vacuum pump only, backing pumps and blower vacuum pump systems are sold separately. Please call (505) 872- for more information.

Condition: Rebuilt

Part Number: P

Price: $10,092.60

Currency: US Dollar (USD)

Leybold RuVac WS WS Blower Booster Vacuum Pump, Rebuilt Refurbished Rebuilt for Oxygen Safe and Chemical Resistant PFPE Oil The Leybold WS WS- Root's blower vacuum pumps are driven by an air-cooled canned motor, the term canned means that the blower's electric motor operates inside the pump's vacuum region. In the canned motor design, the motor's rotor operates on the drive shaft of the pump inside a vacuum-tight can made of a nonmagnetic material. The motor's stator slides over the outside of the vacuum tight can and operates in air. This canned electric motor design allows the WSU blowers to be particularly leak tight and operate without the need for shaft seal which would be subject to wear. For these reasons the Leybold WSU blower vacuum pumps are often used in vacuum processes which require evacuation of chemical process gases. Do not switch on the Leybold RUVAC WS WS until the backing pump has evacuated the vacuum vessel to the cut-in pressure. For processes in which condensable vapors are pumped, it is advisable to evacuate the vacuum vessel via a roughing line to the cut-in pressure. Electrically switch on the Roots pump together with the backing pump and cut it in upon reaching the cut-in pressure. The initial bypassing of the Roots pump serves to prevent condensation of vapours in the cold pump. The permissible cut-in pressure can be calculated based on the ratio between the Roots pump and the backing pump. A typical cut-in pressure for the Leybold WS around 33.5 Torr. With small vacuum vessels, the maximum permissible pressure differential can be briefly exceeded (max. 3 min) upon start-up. If a pressure switch has been installed, do not set it to this higher pressure because it will fail to protect the pump against overload in the event of a greater gas quantity. It is advisable to switch the Leybold RUVAC WS WS on and off via a pressure switch to ensure that it runs only in the permissible pressure range. The price for the pump listed is for a Leybold WS blower booster vacuum pump only, backing pumps are extra. We also sell mechanical and blower vacuum pump systems. Please call (505) 872- for more information. Nominal Pumping Speed m3h-1, 707ft3min-1 (CFM) Maximum Pumping Speed with Backing Pump - Example Leybold SV300 - m3h-1, 588 ft3min-1 (CFM) Ultimate Total Pressure <3 X 10-2 Torr Rotational speed 60 Hz supply (0 - rpm) Max. permissible pressure difference during continuous operation 0 - 80 mBar, 0 – 60 Torr Connection Flange 100 ISO-K Electrical supply voltage 3-phase, 60 Hz, 208 - 230 VAC / 460 VAC

Condition: Rebuilt

Part Number: P

Price: $8,900.00

Currency: US Dollar (USD)

Leybold RuVac WSU WSU Blower Booster Vacuum Pump, Rebuilt RefurbishedRebuilt for Oxygen Safe and Chemical Resistant PFPE Oil The Leybold WSU WSU- Root''s blower vacuum pumps are driven by an air-cooled canned motor, the term canned means that the blower''s electric motor operates inside the pump''s vacuum region. In the canned motor design, the motor''s rotor operates on the drive shaft of the pump inside a vacuum-tight can made of a nonmagnetic material. The motor''s stator slides over the outside of the vacuum tight can and operates in air. This canned electric motor design allows the WSU blowers to be particularly leak tight and operate without the need for shaft seal which would be subject to wear. For these reasons the Leybold WSU blower vacuum pumps are often used in vacuum processes which require evacuation of chemical process gases. The price for the pump listed is for a Leybold WSU blower booster vacuum pump only, backing pumps are extra. We also sell mechanical and blower vacuum pump systems. Please call (505) 872- for more information. Nominal Pumping Speed m3h-1, 707ft3min-1 (CFM)Maximum Pumping Speed with Backing Pump - ExampleLeybold SV300 - m3h-1, 588 ft3min-1 (CFM)Ultimate Total Pressure<3 X 10-2 Torr Rotational speed60 Hz supply (0 - rpm)Max. permissible pressure difference during continuous operation0 - 80 mBar, 0 – 60 TorrConnection Flange100 ISO-KElectrical supply voltage3-phase, 60 Hz, 208 - 230 VAC / 460 VAC

Condition: Rebuilt

Part Number: P

Price: $11,226.60

Currency: US Dollar (USD)

Leybold RuVac WAU WAU Blower Booster Vacuum Pump, Differential Pressure Bi-Pass Valve, Rebuilt RefurbishedRebuilt For Standard Hydrocarbon Vacuum Pump Oil The Leybold WAU WAU- Roots blower vacuum pumps are driven by an air-cooled electric motor. The Roots blower’s pump shaft feeds out of the vacuum region through a shaft seal to couple to the electric drive motor’s shaft. For this reason, the WAU pumps are often used in standard industrial applications that do not contain harsh chemical process gases. The WAU pumps are easy to operate! They include a pressure differential valve that allows them to be started at the same time as the roughing pump. When pumping at high pressures near atmosphere excessive pressure will build across the blower, this will cause the differential pressure valve to open, and part of the pumped gas will cycle back to the intake flange. This allows for improved pumping speed even at high intake pressures now that the blower and backing pump can operate together over the full pumping range. These Leybold RuVac WAU WAU Roots blower booster vacuum pumps have ISO-100 inlet and exhaust flanges, have a pumping speed of 627 cfm, and have been rebuilt for standard vacuum pump oil (Ideal Vacuum Product’s IVP-200 vacuum pump oil). The WAU-, this blower was factory oriented to operate with vertical flow. These WAU- pumps can be rotated to operate in either directions. This price is for a rebuilt Leybold WAU- Roots blower (Booster) vacuum pump only, backing pumps and blower vacuum pump systems are sold separately. Please call (505) 872- for more information.

Condition: Rebuilt

Part Number: P

Price: $9,600.00

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