US3116872A - Gas ballast pumps - Google Patents

Description

Jan. 7, 1964 B. BUECHEL ETAL 3,116,872

GAS BALLAST PUMPS Filed May 18, 1959 www@ CMT, A*

ATTORNEY y 3,116,872 GAS BALLAST PUMPS Baptist Buechel, Balzers, and Rene Haefer and Gilbert Zinsrneister, Vaduz, Liechtenstein, assignors, by mesne assignments, to Bendix-Balzers Vacuum, Inc., Wilmington, Del., a corporation of Delaware Filed May 18, 1959, Ser. No. 814,115 1 Claim. (Cl. 230-158) For the sucking-olf of vapors or gas-vapor mixtures single-stage or multi-stage gas ballast pumps. are known, Which are characterized in that the introduction of the ballast gas, particularly of air, takes place at a point of the pump chamber capable of being isolated from the recipient, that is, the chamber to be evacuated. The proportion of ballast gas admixed to the vapor sucked oli is dimensioned so large that the formation of the liquid phase in the pump by condensation of the vapors suckedot is just prevented or reduced to an innocuous extent.

Moreover devices for the sucking-oit of gas containing vapors have become known in which for the prevention or the condensation of Ithe vapors in the compression operation in the -pump a jet ejector is connected to the suction duct of an ordinary rotary oil airpump, which ejector is operated with gases non-condensible at room temperature. The jet ejector accordingly lies between the recipient or chamber to be evacuated and the pump operating against atmospheric pressure. This jet ejector may also be operated in a manner known in itself with two or more stages in order to attain as high as possible a pressure difference. In .this last mentioned device, in which the ballast gas required is not introduced directly into a chamber of the oil airpump but into the jet ejector arranged upstream serving at the same time for the operation thereof, the prevention of condensation is based likewise on the same principle as that of an ordinary gas ballast pump.

All these known devices are limited in their capability of pumping-oit vapors in continuous operation. The accurate value of the suction pressure (partial pressure), which .the vapors to be pumped oli must not exceed, depends-apart from the type of pumpessentially also on the kind of vapors, the vapor pressure curve which is decisive.

Lt is a disadvantage of the known gas ballast pumps, that they are capable of taking in ballast gas to an insullicient extent only at comparatively high intake pressures of the vapors to be pumped oit.

lt is an object of the invention to improve the existing pumps in this respect in orde-r to be able to suck off vapors at higher pressures than hitherto possible.

The use of a gas ballast valve, which with an increased passage area and disposition at a suitable point of the pump could effect the entry of a quantity of ballast gas exceeding the usual maximum, would appear obvious, but fails in practical realization in that at the high rotational speeds at which rotary oil air pumps are to be operated in order to attain high volumetric suction etiects, the time interval available for the introduction of the ballast gas, during which the ballast gas vsupply pipe is in communication with a certain pump chamber, is too short. This supply pipe has inevitably a certain resistance to flow.

When the ballast gas is for example introduced into the compression space of the pump it is possible to attain- 3,116,872 Patented Jan. 7, 1964 ICC depending on the point of the pump casing, where the supply pipe is located-that this supply pipe is in communication with the said space for a more or less extended period. However, this period is by no means suicient when the vapors to be pumped off are to be sucked in at high pressures, and when the ballast gas is at atmospheric pressure as in the case with the usual use of dry atmospheric air as the ballast gas.

One could conceivably intend fto press a suiiicient quantity -or ballast gas into the pump by the application of excess pressure, but this solution would require a considerable technical expense. The use of a compressor for introducing a suiiicient quantity of ballast gases would also have the disadvantage that under the influence of the increased pressure of the ballast gas more gasl would be dissolved in the pumping liquid and would accordingly be carried along to the vacuum side.

The present invention has the main object of overcoming the aforesaid diilculties and of providing a gas ballast pump which attains higher outputs at even higher intake pressures.

With these and other objects in view which will become apparent later from this speci-cation yand the accompanying drawing, we provide a gas ballast pump installation -for the sucking-oli of vapors or vapor-mixtures from a recipient or chamber to be evacuated, comprising in combination: at least two pump stages connected to s-aid recipient in series, each ot said stages having rotational slidable pump vanes, and at least two inlets lfor gas ballast, at least one oi which is arranged at a place of said installation isolated `from said recipient and yfrom any other gas ballast inlet by said slidable pump vanes of a pump stage.

More particularly a gas ballast pump installation accordinig to the invention comprises in combination: an upstream and a .downstream pump stage connected to said recipient in series, each of said stages having rotational slidable pump vanes, a pump chamber of said downstream pump stage wherein condensation is to be counteracted in operation, a first gas ballast inlet into said pump chamber, and a second gas ballast inlet into a place of said installation isolated from said recipient and from said rst gas ballast inlet by said slidable pump Vanes of said downstream pump stage.

More particularly still a gas ballast pump installation according to the invention comprises in combination: an upstream and a downstream pump stage connected to said recipient in series, each of said stages having rotational slidable pump vanes, said downstream pump stage having a compression chamber and a non-return valve discharging from said compression chamber into the atmosphere and a suction duct connected t-o said upstream pump stage, a iirst gas ballast inlet into said compression chamber and a second :gas ballast inlet into said suction duct.

These and other features of the present invention will be clearly understood from the following description of an embodiment thereof given by way of example with reference to the accompanying drawing, in which:

FIG. 1 diagrammatically shows a two-stage gas ballast pump according to the invention,

FIG. 2 diagrammatically shows a three-stage gas ballast pump according to the invention.

1 denotes the rst or downstream stage on the side of the atmosphere of a rotary foi-l air pump, which is in Communication through a connecting pipe 2 with a second pump or upstream stage 3 on the high-vacuum side. The pump stage 3 is connected Iat 4 to the recipient or chamber to be evacuated. The lirst stage is provided, as a `gas ballast pump in a manner known in itself with a gas ballast valved inlet AS. Through this valve dry air is supplied to the compression chamber of the -rst pump stage as a ballast gas which, together with the vapours to be pumped off, is to be compressed to atmospheric pressure and then to be discharged into the open through the exhaust valve 6. Moreover a second gas ballast valved inlet 7 is provided, which allows to introduce ballast gas, preferably likewise air, into the connecting pipe 2.

This second gas ballast valved inlet 7 may be of the simplest kind, and may for example consist of a simple bore or of an aperture which can be obt-urated by a cock acting as a throttling point for the air lowing in.

The introduction `of the ballast gas through the second gas ballast valved inlet need not, as illustrated in the ligure, be effected into the connecting pipe between the two pump stages, but may be effected at any point desired of the pump rwall which is capable o being sealed at least temporarily from the recipient as well as from the point of intake through the rst gas ballast valve.

Even with single-stage rotating oil air pumps or lat an individual stage of a multi-stage pump, the application of the invention is possible, when a pump stage comprises at least two pump chambers sealed from one another and from the recipient. According to the invention ports and/or gas supply pipes are then provided for introducing gas ballast into at least two of these pump chambers.

The surprising progress attainable by the invention will become clear from the following example:

It has been found that a usual known two-stage gas ballast pump which had been capable of conveying 350 grams lof Water vapor per hour at a suction pressure of 20 mm. Hg when introducing the ballast 'gas into the compression space of the pump, after having been rebuilt as a pump according to the invention (by providing a bore, capable of being 4obturated by means of a cock, in the connecting pipe between the rst and the second pump stage) was then capable of conveying about 900 grams of water vapor at a suction pressure of about 50 mm. Hg in continuous operation. Similar large increases in output have been attained also with other types of pumps by tit-ting a second gas ballast valved inlet.

The quantity of the ballast gas to be introduced through the second (or any further) gas ballast valved inlet when operating the device according to the present invention depends on lthe pressure of the vapors to be sucked ott. By a simple preliminary test it can easily be ascertained how far the second gas valved inlet is to be opened in order to prevent any condensation in the pump at a given suction pressure of the vapors. Conversely, for a pump the second gas ballast inlet of which consists merely of a simple bore, it can be easily ascertained by a preliminary test, up to what vapor pressures this pump can suck orf vapors without danger of condensation.

Of course one will not make the quantity of gas ballast controllably introduced through the second gas ballast inlet unnecessarily large. The convenient quantity of the ballast gas to be introduced through the second gas ballast inlet is sometimes larger than required for preventing the condensation in the second intake chamber, the quan- 'tity of the ballast gas in excess relative to this second intake chamber is, ho-wever, needed for securing also in the rst intake chamber, into which the lfirst gas ballast inlet cannot introduce suicient ballast gas, the required quantity thereof.

The pump laccording to the invention can also be operated-as known also for the usual gas ballast pumpswith a minimum lof ballast gas in such a manner that just a very small condensation takes place in the pump chamber in continuous operation which, however, does .not vyet exert any detrimental etlect on the pump.

When operating the device according to the invention, gas ballast is introduced through the said second (or any further) gas ballast inlet at a point nearer yto the recipient but capable of being isolated `from it, even if there is no danger of condensation of vapors at all in this space. Against tting a gas ballast inlet at such a point of the suction duct there existed the prejudice that-in order to prevent an undesirable increase ofthe motor power required for driving the pump and an unnecessary deterioration cf the end vacuum-gas ballast may be introduced into a certain pump chamber only, when the danger of formation of the liquid phase by condensation in this chamber existed, and then only as much as absolutely 'necessary for preventing condensation in Ithis chamber.

The idea of the present invention accordingly does not simply consist in preventing the condensation of vapors in the space into which ballast gas is introduced through the second gas ballast valve. Prevention of condensation in any pump chamber desired by the introduction of gas ballast has been known per se for a long time. The discovery of the present invention is, on the contrary, to be seen to consist in that it is now made possible to introduce at an inlet point nearer to the recipient, but capable of being isolated from the same, sutlicient gas ballast into the pump, without any special auxiliary means such as compressors, additional jet ejectors or like devices, and without noticable deterioration of the end vacuum (as compared with the end vacuum tof usual gas ballast pumps), when the suction pressures exceed cer-tain limits (which can jus-t be coped with by the known gas ballast pumps). At the same time the invention means that a gas ballast inlet is to be provided not only at one point of the suction pipe, but at least at two different points.

When in a given pump arrangement more than two pump chambers and/or pipe sections sealed against one another and against the recipient are available, it is obviously possible in the sense of the invention to provide addi-tional gas ballast inlets at further points of the suction duct.

Referring now to FIG. 2, a third pump stage 8 has been connected to the intake 4 of pump 3. The intake 9 of pump 8 is then connected to the recipient or chamber to be evacuated (not shown). A third inlet means, controlled by a gas ballast valved inlet 10, is provided in the duct between the pump stages 8 and 3, so that gas ballast can now be introduced at the three points 10, and 5. Thereby the capability ofthe combined pump arrangement for pumping oit vapors is further improved considerably, and at the same time a better end vacuum still is attained owing to the three stage arrangement.

While we have described herein and illustrated in the accompanying drawing what may be considered typical and particularly advantageous embodiments of our said invention, we wish it to be understood that we do not limit ourselves to the particular details and dimensions described and illustrated; for obvious modications will occur to a person skilled in the art.

What we claim as our invention and desire to secure by Letters patent, is:

A gas ballast pump installation for the sucking off of vapors or vapor-gas mixtures and adapted for connection to a chamber to be evacuated, comprising an upstream pump stage and a downstream pump stage, each of said pump stages including a pump having a stator structure, rotor and movable vanes therein, each said pump stage having an inlet passage and outlet passage with the inlet of the upstream pump stage being adapted for connection to the chamber to be evacuated, a transfer duct connecting the outlet of said upstream pump stage to the inlet of said downstream pump, the outlet passage of said downstream pump stage having a non-return valve discharging into the atmosphere, a rst gas ballast inlet opening into the outlet passage of said downstream pump stage, adjustable valve means for controlling said first gas ballast inlet, a second gas ballast inlet opening into said transfer 5 duct, adjustable valve means for controlling said second gas ballast inlet, said first gas ballast inlet being at all times isolated from said second gas ballast inlet by the rotor, vane and stator structure of said downstream pump stage, said second gas ballast inlet being isolated at all times from said upstream pump inlet passage by the rotor, vane and stator structure of said upstream pump stage.

References Clted in the file of this patent UNITED STATES PATENTS 6 Gaede Feb. 20, 1940 Karasick July 16, 1940 Dubrovin Dee. 28, 1943 Van Atta Dec. 20, 1949 Dubrovin May 5, 1959 Sadler Mar. 22, 1960 FOREIGN PATENTS Germany May 31, 1943 Great Britain Dec. 22, 1932 OTHER REFERENCES German application, 1,023,854, Feb. 6, 1958.

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