Chemtech Services, Inc.

Contact Us

Telephone: 815-744-4696

Fax: 815-744-3938

Email Us Directions To Our Facility

Ruvac®

WA/WAUAir-Cooled Flange-Mounted Motors
WS/WSUAir-Cooled Canned Motors
WS/WSU(W) PFPEWater-Cooled Canned Motors
WSLFFor Laser Gas Systems
RAFlange-Mounted Motors

Principle of Operation

Roots vacuum pumps, which are also called Roots blowers, are rotary plunger type pumps where two symmetrically shaped impellers rotate in opposite directions inside the pump housing. The figure-of-eight rotors are synchronized by a gear which ensures that the impellers are counter-rotating in such a way, that they are near to one another and to the housing without actual contacting. In rotor positions I and II the volume of the intake is increased. As the rotors turn further to position III a part of the volume is cut off from the intake side. In position IV this volume is opened to the exhaust side and gas under forevacuum pressure (higher than the intake pressure) flows in. This gas compresses the gas coming from the intake. As the rotors turn further the compressed gas is ejected through the exhaust flange. This process repeats itself twice for each rotor per full turn. As the rotors do not come into contact with the pump’s housing Roots vacuum pumps may be operated at high speeds. Thus a high pumping speed is obtained from comparably small pumps. The pressure difference and the compression ratio between intake and exhaust is limited in Roots vacuum pumps. In practice the maximum attainable pressure difference is of significance only in the rough vacuum range (p > 10 mbar (p > 7.5 Torr)) where-as in the medium vacuum range (p < 1 mbar (p < 0.75 Torr)) the attainable compression ratio is of importance. Roots vacuum pumps from Oerlikon Leybold Vacuum have been designed to specially meet the requirements of the fine vacuum range. They are normally used in connection with backing pumps (exception RAV) or in closed gas cycles (WSLF series).

Applications

For many years now Roots vacuum pumps have been well established in the area of vacuum technology. In combination with backing pumps, which compress against the atmosphere, these pumps offer the following advantages:
Shifting the Operating Pressure into the High Vacuum Range
As a rule of the thumb one may say that Roots vacuum pumps are capable of improving the attainable ultimate pressure of a pump system by a factor of 10. With two Roots vacuum pump stages and a corresponding backing pump it is possible to attain pressures in the range down to 10-5 mbar (0.75 x 10-5 Torr). Under certain circumstances this will make the use of additional high vacuum pumps (turbomolecular pumps or diffusion pumps) unnecessary.
Multiplied Pumping Speed
Due to the non-contact rotation of the impellers, Roots vacuum pumps are able to run at higher speeds. Thus a high pumping speed is obtained with a relatively small size pump. Pumping speeds in excess of 1000 m3/h (589 cfm) can only be attained with Roots vacuum pumps. When selecting the right kind of backing pump (sizing) it will be possible to pump large quantities of gas in connection with smaller backing pumps. Energy consumption of such a pump system is much less compared to a single backing pump offering the same pumping speed. The use of Roots vacuum pumps in the area of vacuum technology has resulted in further specializations and improvements:
- Through an integrated bypass (pressure equalization line) it is also possible to utilize the pumping speed of the Roots vacuum pump at high pressures and large quantities of gas at an early stage. This reduces the pumpdown time especially for cyclic operation.
- High-purity gases or hazardous gases impose strict requirements on the leak-tightness of the system. Canned motors are hermetically sealed. There are no seals in contact with the atmosphere which might be subject to wear. This prevents leaks and failures due to oil leaks. A service life of over 20000 hours without maintenance is quite common.
- Tolerances and the quality of the balancing combined with force fed lubricated bearings and toothed gears permit high speeds and the use of frequency converters. Thus it is possible to attain a high pumping speed while the process is in progress and to reduce the speed when the process has been stopped or while changing the batch. This results in a lower consumption of energy and a longer service life with uncompromising reliability.
- Conversion from vertical to horizontal flow is easily implemented and can be performed at the place where the pump has been installed. Thus the pump can be adapted more closely to the operating conditions of your system.
Lately, a further characteristic is gaining prominence: Roots vacuum pumps are capable of compressing the media in the pump chamber without the presence of any further media. This mostly avoids interaction between different media in the pump itself and also in the connected vacuum chamber. Therefore
- the medium which is pumped is not contaminated with lubricants or sealants; complex accessories (exhaust filters, separators, etc.) are not needed;
- the lubricant in the side chambers is hardly affected, so that service life is not reduced;
- backstreaming of oil from the backing pump into the connected vacuum chamber is prevented.
The effective air cooling arrangement reduces operating costs to a minimum. Cooling water is not required. These characteristics make the Roots vacuum pump attractive for almost all rough and medium vacuum applications.Semiconductor Technology In the area of semiconductor technology, Roots vacuum pumps are found in etching processes among others, and in use with dry compressing vacuum pumps. The pumping speed of the combination of backing pumps amounts to 200 to 500 m3/h (118 to 295 cfm) and it ensures a cut-in pressure of 10-1 mbar (0.75 x 10-1 Torr) for the turbomolecular pump. In the case of dry compression, corrosive gases which also have a high particulate content must be pumped. Canned motors and PFPE fluids provide a good seal against the outside and allow long periods between servicing, high reliability and thus very low operating costs (WS PFPE types). Specific suitable for this processes and use in clean rooms are Roots vacuum pumps filled with PFPE and water cooled motors. These kind of motors have only a little heat dissipation.
Central Vacuum Supply Systems
Large Roots vacuum pumps, usually in connection with single-stage rotary vane vacuum pumps serve several consumers of vacuum (packaging machines, for example) at the same time. Due to the uncontrolled influx of gas, a high of pumping speed must be attained quickly, in order to keep the vacuum (1 to 30 mbar (0.75 to 22.5 Torr)) permanently available to all consumers. This in particular, is implemented by Roots vacuum pumps having a pressure equalization line (WAU types).
Chemistry
Replacement of vapor jet or gas jet pumps on liquid ring pumps in drying and distillation plants is necessary for attaining the required operating pressure of about 1 mbar (0.75 Torr). Reduction of operating costs by entirely eliminating vapor or gas quantities includes separation of these on the pressure side (WA and RA types).
Laser Systems
Continuous circulation of the gas in order to remove heat from a closed cycle in which pressure differentials of up to 100 mbar (75 Torr) must be maintained. The tough requirements regarding purity necessitate a total absence of contamination by oil and dust. This is ensured by reducing the pressure level in the oil chambers as well as by coating the pump chamber. The pumps are assembled and tested under clean room conditions. The canned motor ensures a high degree of leak-tightness to the outside and permits operation in connection with a frequency converter (WSLF types).

Design

The pump chamber of Roots vacuum pumps is free of any sealing agents or lubricants. Only the toothed wheels of the synchronous gear are lubricated with oil. Toothed gear wheels and bearings of the RUVAC are placed in two side chambers which also contain the oil reservoir. These two side chambers are separated from the pump chamber by piston ring seals. Suitably designed oil supply systems in both chambers ensure that a sufficient quantity of oil is supplied to the gear wheels and bearings at all permissible speeds. Almost all RUVAC Roots vacuum pumps are designed for a horizontal and vertical pumping action.

Types

Various types of Roots vacuum pumps have been developed to ensure optimum adaptation to the widely varying applications for this type of pump.
- Flange mounted motor: The drive shaft of the pump is directly connected to an electric motor via a flexible coupling. The required seal of the drive shaft against atmospheric pressure is obtained by oiled shaft seals.
- Canned motor: In the canned motor, rotor and stator pack are separated by a vacuum-tight can made of a nonmagnetic material. The rotor operates on the drive shaft of the pump in the vacuum, so that a shaft seal which would be subject to wear is not required.
- Pressure equalization line: The integrated pressure equalization line connects the exhaust flange to the intake flange through a differential pressure valve.
This valve opens at a high pressure differential between the flanges. Part of the gas then flows through this line back to the intake flange. This is why the Roots vacuum pump may be switched on at atmospheric pressure together with the backing pump. This also increases the pumping speed of the pump combination at high intake pressures.
- Special ACE vibration absorber: These pumps are best used in applications involving frequent pumpdown cycles. The vibration absorber is of an oil sealed or filled design where minute amounts of oil may enter the vacuum system via the piston of the vibration attenuator.
RUVAC WA/WAU, WS/WSU
The series WA/WAU Roots vacuum pumps are provided with directly flange- mounted air-cooled standard three phase motors. The oiled radial sealing rings of the RUVAC WA/WAU for sealing the shaft against the atmosphere are made of FPM (fluor caoutchouc). The WS/WSU series pumps are driven by air or water-cooled canned motors. Roots vacuum pumps of the series WAU/WSU are provided with an additional integrated pressure equalization line and a differential pressure valve. Pumps from these series are supplied with a vertical pumping action as standard. RUVAC WS with FC This type of pump is equipped with an integrated frequency converter fitted directly to the canned motor. The frequency converter has been specially matched to the pump.
The main characteristics of the RUVAC WS are:
Simulation of a pressure equalization line: The frequency converter has been matched to the pump so that the possibility of mechanically overloading it is excluded. In the case of a pressure difference which is too high, the rotational speed of the pump is automatically reduced until its load drops in to the permissible range.
Operation at any rotational speeds: The frequency converter is equipped with a 0 to 10 V signal input and is thus in a position to control the rotational speed of the pump. Increasing the pumping speed The pump is prepared to handle a maximum rotational speed of 6000 rpm so that the frequency converter permits an increase in the nominal pumping speed of up to 100 %.
RUVAC WSLF
The pumps of these series are especially adapted Roots vacuum pumps from the RUVAC WS series which are intended for operation with gas lasers. They are driven by a canned motor so that a shaft seal for sealing against atmospheric pressure is not required. Air-cooled series with nominal pumping speeds of 1000 m3 x h-1 (589 cfm) are available. The RUVAC WSLF series with increased motor ratings is intended for operation in connection with frequency converters. These pumps are available with nickel plated or plasma-nitrated surface as standard. All pumps of these series are supplied with a horizontal pumping action. Vertical pumping action is available upon request.
RUVAC RA
RA series Roots vacuum pumps are equipped with a directly flange-mounted three-phase motor (RA 13000 via V-belt drive).

Backing Pumps

The backing pumps from Oerlikon Leybold Vacuum listed in the following are recommended for connection to the RUVAC Roots vacuum pumps:
- Rotary vane vacuum pumps
- TRIVAC B with pumping speeds between 16 and 65 m3 x h-1 (9.4 and 38.3 cfm)
- SOGEVAC with pumping speeds between 16 and 1200 m3 x h-1 (9.4 and 707 cfm)
- Dry compressing piston vacuum pumps
- ECODRY M with pumping speeds between 38 and 48 m3 x h-1 (22 and 28 cfm)
- Dry compressing screw vacuum pumps
- SCREWLINE SP250 and SP630 with pumping speed of 250 and 630 m3 x h-1 (147 and 371 cfm)
- Rotary piston vacuum pumps
- E and DK with pumping speeds between 200 and 250 m3 x h-1 (117.8 and 147.3 cfm)
- Roots vacuum pumps with pre-inlet cooling
- RUVAC RAV G with pumping speeds between 250 and 8100 m3 x h-1 (147.3 and 4770.9 cfm)
- Liquid ring vacuum pumps upon request.