Rootes blower

Bulletin S-5627, LAL Spiraxial Compressors, Roots-Dresser Industries, Roots Blower Operation, Conner ille, Ind. 

QMS) and an ellipsometer complete the setup. The typical pressure is in the range of 0.15-0.5 mbar. The deposition chamber has a volume of 180 1. During processing it is pumped by a stack of two Roots blowers and one forepump (total pumping capacity is about 1500 m /h) otherwise it is pumped by a turbo pump (4501/s), with which a base pressure of 10 mbar is reached. 

As shown in Figure 2.25, it is more efficient to use a backing pump combined with one or two roots blowers (Fig. 2.27). The backing pump requires only 40 m3/h capacity, combined with a roots pump of 200 m3/h. This system evacuates the 1000 L also in 8 min down to 0.01 mbar, but below 0.1 mbar the system has a capacity of 200 m3/h or 2.2 10 3 g/s at 0.05 mbar. Such a pumping system is preferable for freeze drying compared with a large two-stage pump alone. 

The system operates at about 400 mTorr and with flow rates of about 1 slm, so a roots blower is used to pump the system to base pressure ( 1 mTorr) and then handle the gas flow at these low pressures. 

The ultimate pressure of a Roots blower/backing pump combination is approximately that of the backing pump divided by the compression ratio (k0) for the Roots pump at this pressure. In practice, however, the calculated value should be multiplied by a factor of 4 to 5 to take into account performance deficiencies of the backing pump. 

Schematic representation of the operating principle of a Roots blower.

Pumping system of the BAK 1200 consisting of rotary vane pump. Roots blower and refrigerator cryopump. 

Three-phase AC induction motors were used in the power equipment (pump. Roots blower. 

Dry Vacuum Pumps (DVPs) These use the operating principles of rotary-lobe roots blowers, claw compressors or screw compressors, and hence require electrical power. They run dry and hence at very high temperature due to the heat of compression. Usually,... 

Positive displacement (roots) blower can deliver steady constant volumes even if there is high pressure drop in the system. However, the drive motor will draw heavy current in such a simation but there is less chances of process upsets or production loss. 

However, the motor for roots blower will draw heavy current if there is a high backpressure due to some choke in the system and will continue to deliver air. It will not matter whether the air/gas flowmeter is working accurately or not. 

Provide a revolution counter metre, i.e. RPM metre, for the rotational speed. The roots blower delivers an almost steady volume (the desired value can be set as per speed)... 

Vacuum pump set, one roots blower, two oil-free pumps in series, end pressure < 1 x 10 mbar, evacuation time of loaded plant down to 0.08 mbar 12 min. Pressure control during MD either by injection of dry N2 or by closing and opening the valve between condenser and pump set ... 

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