US2245215A - High vacuum - Google Patents

Description

June 10, 1941. s, MORSE 2,245,215

HIGH VACUUM Filed Sept. 2.9, 1:939

I 10 Fig. 2.

AAAAAAA VVvvvvI v Z2 Z6 Z0 WWNW reverse flowing vapors Patented June 10, 1941 men VACUUM Richard S. Morse, Rochester, N. Y., assignor to Distillation Products, Inc., corporation of Delaware Rochester, N. Y., a

Application September 29, 1929; Serial No. 297,146

' Claims. (01.230-101) This invention relates to improvements in high from condensation in a reverse direcmeans for removing vapors pump jets which tend to pass tion to flowing.

A diflioulty with condensation pumps which has never been completely overcome is the tendency of vapors issuing from the jet of the pump to partially pass backwards in a reverse direction. The vapors eventually reach the receptacle being evacuated and consequently prevent the production of the highest vacuajtherein. It has been proposed that these vapors be removed by traps cooled with liquid air or other similar cooling means. However, such traps are expensive to operate because of the cost of the cooling material and also have a rather high impedance to the passage of gases being pumped.

This invention hasfor its object to provide a simple, efflcient and economical method of removing such reverse flowing vapors. Another object is to provide a condensation pump provided with electrical means for removing reverse flowing vapors. A further object is to provide a trap'for which has low. impedance for gases being pumped. Other objects will be apparent from the following description and claims.

These objects are accomplishedin accordance" with my invention which comprises means for applying an electrical charge to reverse flowing vapors and means located atthe high vacuum end of the pump or between the high vacuum jet of the pump and receptacle being evacuated for presenting an oppositely charged surface to that of the vapor molecules so that they are attracted to the surface and condensed thereon.

In the following description I have'described several of the preferred embodiments of my invention, but it will be understood that these are given for the purpose of illustration and not in limitation thereof.

In the accompanying drawing wherein likenumbers refer to like parts:

Fig. 1 illustrates in vertical section a. condensathat in which the gases being pumped are vacuum production and particularly improved thereof. Numeral l2 designates a side conduit integral with the. lower portion of the wall of casing 6 which conduit is L-shaped and the vertical portionof which is provided with reeentrant rings l4. Numeral l6 designates a cylindrical conduit, the lower portion of which is expanded as illustrated at I8 so that its external diameter is only slightly smaller than the internal diameter of casing 6. Numeral designates a truncated cone, the top of which is closed by plate 22 and which is integral with conduit [6 so as to form an expansion ai nular jet 24. Numeral 26 designates a plurality thereof. Flange the condensation pump tion pump provided with electrical means for removing reverse my invention;

Fig. 2 is a top plan view of Fig. 1; and Figs. 3 and 4 illustrate in vertical section modiflowing vapors in accordance with fications oi the apparatus shown in Fig. 1.

Referring to Figs. land 2, numeral 6 designates closed at the base by flange Ill at the top a cylindrical pump casing plate 8 and provided with a integral with the walls of of holes through which working vapors flow into let 24. Numeral 28 designates a plurality of spacers constructed of material which will not conduct electricity and which function to center the base portion l8 so that it is concentric with the lower portion of cylinder 6, but not in actual contact therewith.- Numeral an designates insulating material which forms the base of legs '32 and is attached thereto in such a manner as to electrically insulate cylinder l6 from base plate 8. Numeral 34 designates a baille casing 5 and provided with a central opening as illustrated.- Numeral 36 designates a screen integral with the inside walls of casing 6 to which is connected electrical lead wire 38. Numeral 40 designates an electrical lead wire connected to conduit l6.

Referring to Fig. 3, numeral 58 designates a cylindrical casing of approximately the same diameter as pump casing 6 which is provided with flanges 52 and 54 at the top and bottom ends 54 cooperates with flange Ill of y to securely fasten the two units together in a gas-tight manner. Numeral Sodesignates a cylinder constructed of 'metal gauze which is of somewhat smaller diameter than casing and is mounted therein so that it is substantially concentric with the walls thereof. Numeral 58 designates an electrical lead wire which connects .to gauze 56. Numeral to designates a filament constructed of tungsten or other material adapted to be heated without destruction in a vacuum to which is connected electrical lead wires 62 and 64.

Referring to Fig. 4, numeral 10 designates a cylinder constructed of metal gauze which is of smaller diameter than gauze cylinder 56 and which is located inside and approximately concen- During operation of the apparatusillustrated in Fig. 1, pump fluid is introduced into the base Vapors issuing from jet nozzle 24 do not all havemotion or the same velocity so that many of them pass or burst sideways when they reach the lip of the ,jet and stream backwards in a reversedirection through the opening in baflle 34 and pass into contact with metal screen 36. A positive or negative electrical charge is the same direction of applied to these vapors since the pump is constructed of metal and ischarged to a relatively high potential by lead wire 40 connected to a suitable source of direct current. An opposite charge is applied to metal Therefore, the charged reverse flowing vapors are attracted to the metal screen 36 and become condensed thereon. The pump fluid is thus prevented from continuing backwards into the receptacle to be evacuated where it would otherwise exert a harmful effect upon the vacuum produced therein. a

The potential difference between lead 40 and 38 may be varied considerably. A diirerence of between 500 to 5,000 volts will be satisfactory under ordinary pumping conditions, but it will be understood that lower or higher potential diiferences may be employed with satisfaction.

In operating the apparatus of Fig. 3, flange 52 'is connected to the system to be evacuated and the condensation pump is put intooperation as described in connection with Fig. 1. However, it should be pointed out that the jet assembly of the pump is not charged by a lead wire such as 40 as described in connection with Fig. 1. Filament 60 is heated to a temperature at which electrons are emitted by passage ofcurrent through lead wires 82 and 64. A potential of high voltage either negative or positive is also applied to filament 60 by means of lead wire 62. An opposite charge to that appl'edto filament 60 is applied, to, gauze cylinder 56 by lead wire 58. In the preferred-embodiment the filament is negatively charged and themetal gauze is positively charged. Electrons emitted from filament 60 collide with vapors passing in reverse direction through the system. These pump fluid vapors, therefore, become charged and are attracted to oppositely charged screen 56 where they are condensed and thus The potential difference between filament 60 and metal gauze 56 can likewise vary considerably, but potential differences of between 200 and aout 5,000 volts are preferred. A voltage of 500 applied to filament 60 and +500 applied to gauze cylinder 56 has been found to operate satisfactorily. V v

During operation of the apparatus illustrated in Fig. 4, an electrical charge is applied to screen and an opposite charge is applied to screen 56.

Filament 60 is heated and is maintained at' a zero potential with respect to screens 56 and 10. Electrons given off by the heated filament charge and/or ionize the pump fluid molecules which are then attracted to the screens 56 or 10, depending upon whether they become positively or negatively charged. They thus become condensed thereon and are prevented from exerting screen 36 by lead wire 38.

removed from the system;

harmful action. The voltage difl'erences in the apparatus of'Fig. 4 may be the same as that described in connection with Figs. 1 and 3.

In some cases it is recommended that voltages be employed which are sufllciently high to produce visible ionization. However, even with low voltages, the pump fluid will acquire a slight charge suflicient for it to be attracted to or repelled'by suitably charged screens or electrodes as described.

- If desired, the surfaces upon which the vapors are condensed may be cooled by providing suitable means for circulating cooling fluid into contact therewith. This precaution is usually unnecessary, however, since the reverse flowing vapors are of relatively low volume as compared with the volume of the vapors issuing from the pump jet. Provision may also be made for collecting' condensate from the charged surfaces and returning it to the boiler. Since the volume is small, it is usually satisfactory to merely allow the condensate to accumulate and if accumulated in sufliciently large amounts to form drops, it will drop or flow through the opening in bailie 34 down the inside walls of easing 6 and be returned to the boiler of the pump.

Although I have illustrated my invention in connection with a simple condensation pump of conventional construction, it can be applied to the removal of reverse flowing vapors derived from any type of condensation pump. It is 01' value in connection with pumping by means of fractionating condensation pumps which are described in Hickman Patent 2,080,421, May 18, 1937.

Baflle 34 serves to condense and remove a substantial proportion of back-streaming vapors. Therefore, its use is desirable. Baille systems have been devised for removing to a substantial extent such back-streaming vapors without too greatly hindering flow of gases All such baflle systemstmay be used. If desired. the baffle may be eliminated entirely, although I do not recommend such construction. It should be understood that the bailie does not remove all of the back streaming or reverse flowing vapors and that a battle system which would effectively do so would present such impedance to the pump gases that it would be unsatisfactory.

The invention can be operated in connection with any type of condensation pump and will effectively remove vapors whether of the organic type such as diamyl or di-octyl phthalate or sebacate or inorganic such as mercury.

What I claim is:

l.In a high vacuum vapor jet or condensation pump the improvement which comprises means for applying an electrical charge to pump fluid vapors which pass in a direction opposite to that in which gases are pumped, and means positioned in the high vacuum or intake end of the pump adapted to receive an electrical charge opposite to that of the pump fluid vapors whereby during operation, reverse flowing, charged vapors are attracted to said last named oppositely charged means and condensed.

2. In a high vacuum vapor jet or condensation pump the improvement which comprises means for applying an electrical charge to the pump fluid vapors which pass in a direction opposite to that in which gases are being pumped, and means positioned in low impedance to the flow being pumped.

the high vacuum or intake.

of vapors therethrough, whereby during operation, reverse flowing, charged vapors are attracted to said last named oppositely charged means and condensed while gases beingpumped flow substantially unhindered into the condensation pump. 1 I

3. The apparatus described in claim 2 in which the low impedance means is a metal screen.

4. In a high vacuum vapor jet or condensation pump the improvement which comprises a filament located intermediate the highest vacuum jet and the high vacuum or intake end of the pump, means for heating the filament, means for applying an electrical charge to the filament,- an electrode positioned near the filament and intermediate the highest tacuum jet and the intake end or the pump which electrode has low impedance to the flow or gases therethrough and means for applying to the electrode a charge opposite to that applied to the filament whereby during operation vapors which pass in a reverse direction from the high vacuum jet are electrically charged and then are attracted to the opposite'ly charge electrode and condensed thereon.

5. The combination which comprises a high vacuum vapor jet 'or condensation pump, means for applying an electrical charge to pump fluid vapors which during operation pass in areverse direction from the high vacuum jet and into the intake end of the pump and means positioned between the high vacuum jet and the intake end oi! the pump adopted to receive an electrical charge opposite to that applied to the pump fluid vapors whereby during operation, reverse flowing, charged vapors are attracted to said oppositely charged. means and condensed.

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