US2971691A

US2971691A - Pumping system

Info

Publication number: US2971691A
Application number: US603722A
Authority: US
Inventors: Lorenz Albert
Original assignee: WC Heraus GmbH and Co KG
Current assignee: WC Heraus GmbH and Co KG
Priority date: 1955-08-16
Filing date: 1956-08-13
Publication date: 1961-02-14
Anticipated expiration: 1978-02-14

Description

A. LORENZ PUMPING SYSTEM Feb. 14, 1961 2 Sheets-Sheet 1 Filed Aug. 15, 1956 INVENTOR. ALBERT LORENZ BY M,M&M

A T TORNE KS A. LORENZ PUMPING SYSTEM Feb. 14, 1961 2 Sheets-Sheet 2 Filed Aug. 13, 1956 INVENTOR. 415547 ZORE/VZ United States Patent PUMPING SYSTEM Albert Lorenz, Hanan am Main, Germany, assignor to W. C. Heraeus, G.m.b.H., Hanan am Main, Germany, a corporation of Germany Filed Aug. 13, 1956, Ser. No. 603,722

Claims priority, application Germany Aug. '16, 1955 '4 Claims. (Cl. 230-45) This invention relates to vacuum pumping systems, and provides an improved pumping system for operation in the range from about .1 mm. Hg to about atmospheric pressure.

Briefly, this invention provides a pumping system which includes a Roots or Connersville blower type pump connected in series with a Nash Hytor or water ring pump. Both of these pumps are well known. The Roots or Connersville blower is described, for example, in Industrial Chemistry by Riegel, fourth edition, printed by International Textbook Press, Scranton, Pennsylvania, on pages 696, 697 and 700. The water ring or Nash Hytor pump is described in the same reference on pages 700 and 701.

Water ring pumps have the advantage of being rugged, insensitive to a wide variety of impurities, and economical to operate clue to their large capacity compared to their relatively small size and small power requirements. However, water ring pumps have the disadvantage that they cannot produce pressures much below 30 mm. Hg due to the vapor pressure of the water used in the pumps. In the operation of water ring pumps, precautions must also be taken to avoid the possibility of water being drawn from the pumps into another part of the system, and precautionary measures must be taken against diffusion of water vapor, when it would be harmful to the systern being evacuated.

As water ring pumps approach their lowest pressure, their pumping capacity falls off sharply, and their energy consumption rises rapidly to a maximum value. This phenomenon is due to the valveless characteristic of the pumps.

It has been found feasible to connect a water ring pump in series with a Roots pump, which is connected to the suction side of the water ring pump. However, the problem is presented of providing an efficient means for driving the two pumps. It has been proposed that an individual drive be provided for each pump so that during the early stages of evacuation of a system, only the water ring pump is operated, and the Roots pump is switched on only when the pressure in the system is reduced to approximately 30 mm. Hg. Such a system will eventually produce a relatively low pressure, say about .1 mm. Hg, which is much lower than can ordinarily be produced by a conventional water ring pump or a conventional Roots pump operating individually. However, the power requirement for this system is large, and the pumping capacity is relatively low.

This invention provides a more eificient type of pump- .ing system for producing relatively low pressures at high speeds by connecting the discharge of a Roots pump to the intake of a water ring type pump and driving the two pumps so that the ratio of the speeds of the two pumps is substantially constant.

Preferably, the pumps are driven by a single motor from a common drive shaft and are turned at the same speed. With this arrangement, both pumps are in operation simultaneously throughout their entire operating ranges. The Roots pump acts as a vacuum stage, and the water ring pump serves as a preliminary or roughing stage. In the preferred system, a constant speed driving motor is used, and a Roots pump is selected with a capacity larger than that of the water ring pump by about thirty percent to about seventy percent.

These and other aspects of the invention will be more clearly understood from the following detailed description in which:

(1) Fig. 1 is a schematic diagram of one form of the invention; and

(2) Fig. 2 is a schematic diagram of an alternate embodiment of the invention.

(3) Fig. 3 is a schematic diagram illustrating one type of coupling between the Roots type pump, the water ring pump and the motor of Fig. 1.

Referring to Fig. 1, an inlet 10 of a Roots pump 12, which may be of conventional type, is adapted to be connected to a system (not shown) to be evacuated. An outlet 14 of the Roots pump is connected to an inlet 16 of a water ring type pump 18. An outlet 20 of the water ring type pump is adapted to discharge to atmospheric pressure.

The water ring pump also includes a water inlet line 22 and a water outlet line 24 so that water may be circulated through the pump for cooling purposes and to remove impurities which collect in the water. A solenoid actuated valve 26 controls the flow of water into the pump. A thermometer 28 is built into the water ring pump, and if desired, the solenoid valve 26 may be made operative in response to water temperature to prevent overheating of the pump. The valve is also actuated by suitable means (not shown) to close when the pumping capacity of the system decreases, say due to power failure.

A shaft 30, which includes two

collinear parts

31 and 32, is driven by a constant speed electric motor 34. Shaft part 31 drives the water ring pump, and shaft part 32 drives the Roots pump.

The operation of the pumping system shown in Fig. 1 is relatively simple, the motor is simply turned on, and the two pumps are driven either at the same speed or at diiferent speeds which are maintained to provide a constant ratio of the two pump speeds. Valve 26 may be either opened or closed to circulate water through the water ring pump if desired.

The pumping system of Fig. 1 represents considerable advancement insofar as providing a system which can evacuate a relatively large volume to a final vacuum of approximately 1 mm. Hg in a surprisingly short time, and with a relatively small power requirement, although neither the water ring pump by itself nor a conventional Roots pump can produce such a low pressure.

The pumping capacity of the system of Fig. l is considerably higher than that of the preliminary vacuum pump systems of the same size and power requirements which were in use prior to this invention. The advantage of the system of this invention is apparently due to the fact that the conventional Roots pump can produce a compression ratio of about 1.5, when handling a relatively large volume. Such a compression ratio is adequate to supply gas to the water ring pump at a high enough pressure to enable the water ring pump to work in the pressure region where its high pumping capacity and low power requirement is an advantage. On the other hand, the efliciency of the Roots pump decreases linearly with increasing pressure at its outlet. There fore, the system of this invention matches the efliciency characteristics of the two pumps so that over the entire pumping range, a large pumping capacity is achieved with minimum power requirements and does not vary with pressure. This provides an important advantage because it facilitates the choice of the motor and permits precise adjustment of the motor to produce the desired pumping capacity, enabling the use of a constant speed motor.

Another advantage of the system is that, since friction losses are very slight in a Roots pump, the pump system can be powered by a motor which is not substantially larger than the motor required by the ring pump alone. Thus, the combination of pumps as provided by this invention provides a pump capacity which is appreciably increased, say from about thirty percent to about sixty percent greater than the water pump alone, with little extra power required. Moreover, the final vacuum of the system is approximately 1 mm. Hg, compared to 30 mm. Hg for the water ring pump alone.

Another advantage of the system is that diffusion of Water vapor from the water ring pump to the low pressure areas of the system is to a large extent suppressed.

Further advantages of this pumping system are that it requires practically no supervision, does not need any oil change, can handle any amount of water vapor, and is virtually insensitive to dust impurities, which are removed by the waste water of the pump.

Anotherimportant advantage of the system of this invention is that the Roots pump need not be of special light weight construction for high vacuum operation. Conventional Roots pumps which are used for pumping gases at near atmospheric pressure can be used, provided that precautions are taken to prevent lubricants or sealing means from giving off gases into the space to be evacuated.

Another advantage of this system is that it is not only possible to dispense with a bypass around the Roots pump from the system evacuated tothe water ring pump, but the bypass is preferably eliminated entirely so that the Roots pump can immediately cooperate over the whole zone of operation of the system. The superiority of the system of this invention is particularly apparent when a comparison is made with pumping systems which have heretofore been used to produce pressures of approximately 1 mm. Hg. The cost of production of the system of this invention is less than one-half and can be as much as two-thirds lower than the cost of systems of the same pumping capacity which have so far been available. Moreover, the space required for the system of this invention is substantially smaller than the space requirements of the previously available systems.

A high vacuum pumping system, say mm. Hg and lower, is readily provided by combining the pumping system of this invention with a diffusion pump or with a Roots pump which is particularly constructed for operation in the high vacuum range. The latter is characterized by a double-walled housing which is completely sealed from the exterior in a vacuum tight manner, and in particular, has no shaft openings. A reduced pressure is maintained in the space between the doublewalled housing, so that the pressure in that space is between the pressure in the pump and atmospheric pressure. The driving motor for the high vacuum Roots pump is situated as far as possible inside the vacuum sealed outer housing, and advantageously placed on the rotor of the pump.

Fig. 2 shows a high vacuum pumping system which includes a water ring pump 40 having an outlet 42 and an inlet 44 connected to an outlet 46 of a conventional Roots pump 47. The water ring pump and the conventional Roots pump are driven by, a common shaft (not shown) as described for the apparatus of Fig. 1.

An inlet 48 of the conventional Roots pump is connected to an outlet 50 of a flow control chamber 52, which has an inlet 54 connected to an outlet 56 of a high vacuum Roots pump 58. An inlet 60 of the high vacuum Roots pump is connected to a discharge 62 of a coarse separator chamber 64. A solenoid actuated valve 66 is in the connection between the coarse separator and the high vacuum Roots pump so that these twouuits may be isolated if desired. An inlet 68 of the coarse separator is connected to an outlet 70 of a cyclone separator 72, which has an inlet 74 adapted to be connected to a system (not shown) to be evacuated. A valve- 76 in the connection between the coarse separator and the cyclone separator permits these two elements to be isolated from each other if desired.

The apparatus of Fig. 2 is particularly suitable for evacuating large volumes such as vacuum steel furnaces in which dust-like products accumulate. The cyclone and coarse separators remove most of the dust-like products.

A return valve 78, which is operated by a solenoid 80, is adapted to open and. close the inlet of the flow control chamber. A flow valve 82, operated by a solenoid 84, is adapted to open and close a relief line 86 which opens from atmospheric pressure into the flow control chamber. In the event of failure of the pumping system, for example due to a power failure, the return valve is automatically closed to isolate the high vacuum end of the system from the conventional Roots pump and water ring pump, and the flow valve is automatically opened to admit air into the control chamber, the conventional Roots pump, and the water ring pump to prevent water being pulled from the water ring pump into the conventional Roots pump. Thus, the high vacuum end of the system is protected from sudden pressurizing, and the conventional Roots pump is protected from damage or contamination by water from the water ring pump.

I claim:

1. In a vacuum pumping system: the combination which comprises a Roots type vacuum pump having an inlet for coupling the pump to an area being evacuated and an outlet for discharging pumped gases, a water ring type pump having an inlet connected to the Roots pump outlet for pumping the gases discharged from the Roots pump, and a constant speed motor including a shaft, the Roots type pump and the water ring type pump being directly coupled to the shaft whereby the pumps will be driven over their entire operating ranges at a constant speed.

2. In a vacuum pumping system: the combination which comprises a Roots type pump having an inlet for coupling the pump to an area being evacuated and an outlet for discharging pumped gases, a water ring type pump having an inlet connected to the Roots pump outlet for pumping the gases discharged from the Roots type pump, a motor, and means for coupling the motor to each of said pumps to drive the pumps over their entire operating range at a constant speed ratio. 7

3. The combination as defined in claim 2 including a solenoid actuated valve disposed in the Roots pump inlet and responsive to failure of the power to the motor for closing the Roots pump inlet to isolate the area being evacuated from the Roots type pump and the water ring type pump to thereby protect the area being evacuated from sudden pressurizing.

4. The combination as defined in claim 2 including a relief conduit connected to the water ring type pump and means including a solenoid actuated valve disposed in the relief conduit and responsive to a failure of the power to the motor for admitting air into the water ring type pump to thereby prevent water from being pulled from the water ring type pump into the Roots type pump when the power to the motor fails.

References Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) 5 UNITED STATES PATENTS Peterson Mar. 19, 1940 Jennings Feb. 4, 1941 Grunert et a1. Apr. 13, 1943 5 Paget Aug. 5, 1947 Shaw May 17, 1949 Van Atta Dec. 20, 1949 6 Schneider Apr. 26, 1955 Hardy Sept. 6, 1955 Van Atta Oct. 25, 1955 FOREIGN PATENTS Germany Ian. 23, 1914 Germany June 18, 1928 France Sept. 10, 1956