US3443743A

US3443743A - Vacuum pumps

Info

Publication number: US3443743A
Application number: US594563A
Authority: US
Inventors: Pierre Pegon
Original assignee: CLOVER SOC
Current assignee: CLOVER SOC
Priority date: 1966-11-15
Filing date: 1966-11-15
Publication date: 1969-05-13
Anticipated expiration: 1986-05-13

Description

y 13, 1969 P. PEGON 3,443,743

VACUUM PUMPS 4 Filed Nov. 15. 1966 Sheet 0r a FIG.]

Ma 13, 1969 P. PEGON 3,443,743

VACUUM".PUMPS Filed Nov. 15. 1966 Sheet 3 or a P. PEGON VACUUMiPUMPS May 13, 1969 Sheet Filed Nov. 15. 1966 3,443,743 VACUUM PUMPS Pierre Pegon, Paris, France, assignor to Societe Clover, Villejuif, Val-de-Marne, France Filed Nov. 15, 1966, Ser. No. 594,563 Int. Cl. F04f 9/02 US. Cl. 230-101 2 Claims ABSTRACT OF THE DISCLOSURE A vacuum pump which uses the pumping fluid from an outside boiler to drive molecules of gas from a chamber, compressing them by successive stages with the fluid circulating through a piping system having orifices known as ejectors spaced from cooled condensation plates within said chamber with independent heating adjustment in the parts of the piping system.

The present invention relates to vacuum pumps, and more particularly to vacuum pumps of the ejection and diffusion type, with association of ejectors and condensing surfaces.

The invention has mainly for its object to provide a certain flexibility in the mounting and association of the ejectors and condensing surfaces, while at the same time clearly separating the functions of: boiling, ejection, condensation, of the vacuum pump so as to be able to provide a separate control of the parameters which govern the operation of these members.

The design of the form of a pump according to the invention permits:

of its simple adaption to a given particular problem or to a vacuum chamber considered;

of improving the safety of operation of pumping;

of reducing the overall size for a maximum depression;

of facilitating the mounting of the pump in the interior of a vacuum chamber.

These general results are obtained by means of the following special arrangements of the fluid circuits:

The pumping fluid which drives the molecules of gas from the chamber and compresses them by successive stages up to a primary vacuum stage, circulates inside tubes or piping systems provided with orifices known as ejectors. The tubes are provided with independent heating which keeps them at a temperature which can be adjusted at will. Thus, the temperature of the vapour at the level of an ejector is not, as in the prior art, the result of a complex equilibrium which is influenced by all the factors of the data of the apparatus and on which it is not possible to act directly, as is the case with known pumps. In addition, by acting locally on the cross-section of the passage of the distributor tubes, the flow-rate of the vapour is controlled. With the piping systems which bring the ejectors to a predetermined temperature, there are associated cooled condensation plates, over the faces of which flows the pumping fluid, which is subsequently collected and returned to the boiler. The curved lines which indicate the piping of the ejectors are located at a constant distance from the adjacent condensation plates. The piping systems of the ejectors are grouped together in different stages of pumping and the corresponding condensation plates form a pumping unit. This pumping unit which is subsequently multiplied after a number of translations or rotations, constitutes the pump itself.

The boiler is separate from the pump proper; it heats the fluid to a desired temperature which determines the vapour pressure. At the outlet of the boiler, valves are ntted States atent O" 3,443,743 Patented May 13, 1969 provided on the various pipes which permit the boiler and the thermal inertia to be completely isolated.

Other characteristic features and advantages will be brought out in the description which follows below, reference being made to the accompanying drawings which illustrate, purely by way of indication but not in any limitative sense, one form of application of the invention.

In these drawings:

FIG. 1 is a view in cross-section of a cylindrical secondary pump according to the invention.

FIG. 2 is a view in cross-section of an alternative form of the invention, applied to the evacuation of a metallurgical crucible under vacuum.

FIG. 3 is a view in cross-section of another alternative form, in which the modular vacuum pump is contained in the chamber of which it ensures the pumping.

FIG. 4 is a partial section taken along the line IV--IV of FIG. 3.

There is shown in FIG. 1 a pump in which, by carrying away molecules of gas from the opening 3 of the pump, a fluid 4 produces a high vacuum in the chamber 2. The boiler 5 sends vapour 4 into the pipes 6 heated to a predetermined temperature.

These pipes 6 are connected to ejection pipes 7 through the intermediary of couplings 8. These pipes are also heated to a pre-determined temperature and they are provided in places or continuously with orifices which constitute the ejectors proper 9.

Although other fluids may equally well be employed in a pumping system according to the invention, in the example chosen here, oil vapour has been adopted. In this case, it is advantageous to use glass pipes carrying the ejectors. A conducting deposit having the function of a heating resistance 10 is deposited on this glass by conventional means.

The outgoing conduits 6 are heat-insulated, the vacuum-tight passage 11 is insulated electrically from the casing 13 of the pump, and the heating means for the pipes 6 and the pipes 7 are connected together electrically in known manner.

It is known that in conventional diffusion pumps, the vapour reaching the ejection orifices is frequently humid, that is to say it contains small droplets of fluid; these droplets have a low speed which slows down the speed of the vapour and they serve as condensation nuclei for the vapour which is cooled by depressurisation. The phenomena contributes to reduce the performances of conventional pumps, and in addition droplets are frequently deposited on the lips of the ejectors and are then re-evaporated, thus forming a substantial back-flow. Finally, in conventional diffusion or ejection pumps, the temperature of the ejectors is the result of a complex thermal equilibrium of the whole unit, the only pro-adjusted parameters being, in this case, the heating of the boiler and the flow-rate of water into the cooling conduits which surround the pump body.

The vapour passing out of the ejectors converts its pressure energy to kinetic energy, and it carries away the molecules of gas in the direction of its movement, which results in a pressure gradient. After having played its part of mechanical impulsion, it is important that the vapour should be condensed as rapidly as possible. When the molecules of vapour have played their part of carrying away, that is to say when they have lost the coherence of their movement, they become harmful to the effectiveness of the pump. The efiiciency of the pump is in fact diminished by the oil vapour pressure in the compressed zone, since it is in fact necessary to impart to it a momentum so as to maintain it in this zone. The efficiency is also reduced by the back-flow which is formed by the rebounding of the oil molecules from the mechanical parts of the pump.

Thus, all these parts of the pump will be very strongly cooled and the molecules will be condensed by associating with the cooled pipes 7 carrying the ejectors 9, large cooled surfaces forming the casing 13 of the pump and plates 12 inside the pump. These surfaces are cooled by conduits 14. The oil is condensed on these surfaces, trickles down and is collected in a tank 15. It is taken-up by a pump 16 and returned to the boiler 5.

It will be recalled that in conventional ditfusion pumps or ejection (booster) pumps, the body of the pump is cooled; on the other hand, due to the very design of these pumps, the intake chimneys of the vapour cannot be cooled; these chimneys constitute the internal structures and are directly connected to the boiler. According to the invention, on the contrary, the condensation surfaces are multiplied, and the association of the ejection pipes and the cooled plates permits remarkable compactness of the pumps to be obtained.

This is particularly illustrated in FIG. 1, in which, in a pump having an external shape which is generally that of conventional pumps, two additional pumping stages, of which one is a booster stage, are located in the space usually reserved for the vapour-intake chimneys. Following this arrangement in accordance with the invention, the pumping rate is increased and the critical starting pressure is raised.

The possibility of distributing vapour in the independently-heated conduits 7 which carry the ejectors 9, and the association of these conduits with the cooled surfaces 12 are two factors which make it possible to modify the usual structure of the pumps with great freedom.

This can be seen from FIG. 1 when looking at the interior of the pump body 1 below its secondary valve 22, and it is seen in particular in FIGS. 2 and 3 which will be described later.

As distinct from conventional pumps, in which the boiler is intimately associated, if not incorporated in the pump body, the boiler according to the invention is in this case separated from the pump proper 1. It can be isolated from the oil recovery tank and from the distribution conduits 6 by closing the

valves

18 and 19. This boiler is coupled to a primary pumping unit by the pipe carrying the valve 17.

As the boiler is treated as a separate unit, its temperature does not affect the thermal equilibrium of the pump, which permits a considerable freedom of action in the choice of the method of heating. This fact, associated with the presence of

long distribution conduits

6 and 7 permits achieving elimination of the disastrous repercussions of eruptive boiling on the pumping speed.

In addition, in order to stop the secondary pump, it is only necessary to close'the

valves

18 and 19, and after a few seconds, air can be admitted to the interior of the pump which does not contain any hot oil. This constitutes an appreciable advantage as compared with conventional pumps.

The pump shown by way of example in FIG. 1 comprises four pumping

stages

24, 25, 26 and 27. The

stages

24, and 27 are supported on the internal edge 28 of the cylindrical part of the pump; this is also the case for the cooling plate 121) and the ejection trumpet 31. The stage 26 together with the cooling plate 12a and the ring 33 which acts as an ejection trumpet, are supported on the removable lower portion 34 of the pump. These various parts are centered with respect to each other. The condensation oil flows into the tank 15 either through the interior of the ejection booster or through. a pipe 35 and the flexible coupling 29.

FIG. 2 illustrates a special application of the principles previously described to the constructions of a vacuum furnace located in the interior of the secondary pump which is itself incorporated in the interior of the chamber.

The pumping fluid 4 which effects the vacuum by carrying away the molecules of gas from the chamber 30, from the opening 31 of the pump 4', is conveyed from the boiler 5 by means of conduits 6 heated to a given temperature. These pipes are connected to the ejection pipes.

7 through the intermediary of couplings 8; these pipes 7 are also heated to a given temperature and are provided locally or continuously with orifices 9 forming ejectors. On the pipes 7, there has been shown a heating resistance 10. The pipes 6 are thermally insulated. The electrical heating connections between the

conduits

6 and 7 have not been shown in detail, and this also applies to the vacuum seal 23.

The pumping fluid condenses on the cooled surfaces 12 which have a water circulation system 63. The oil trickles down over the surfaces and is collected in a cooled tank 15 through the intermediary of a conduit 35 having a flexible coupling 29 to facilitate assembly. It is taken-up by the pump 16 which sends it into the boiler 5. The boiler, the tank, the secondary pump and the chamber are connected to a primary pump (not shown) through the

piping systems

20 and 21. The

valves

17, 18 and 19 enable the boiler to be isolated; the valve 36 isolates the chamber from the primary pumping circuit, and finally the valve 37 on the primary circuit and the annular valve 32 permit the secondary pump 4 to be isolated.

The secondary pump shown in FIG. 2 comprises three

stages

24, 25 and 25'. It is also provided with a cooled baflie 38, moved by the piston 39 passing through the cover 40 of the vacuum chamber. The cover 40 of the vacuum chamber shown in FIG. 2 pivots about the shaft 41 and is clamped on the body of the chamber, before pumping, by means of the nut 42. It contains a crucible 43, a heating device 44, the electrical connection of which is shown at 47, radiation screens 45 and supports 46. All this equipment is known and does not require any more detailed explanation.

In order to pump the chamber to the primary vacuum, the

valves

36, 37 and 17 are opened to communicate respectively on the chamber, the secondary pump and the conduit 6, and on the boiler. The starting-up of the secondary pump can then begin. The valve 17 is closed and then the heating element 68 of the boiler is switched on together with the heating resistances of the

pipes

6 and 7; finally the

valves

19 and 18 are opened. The fluid circulates in the pipe 6 and reaches the ejectors 9. In order to pump in secondary in the chamber, the secondary valve 32 is then opened. The pump 16 for returning the oil from the tank to the boiler is controlled by a level reference located in the boiler. In order to cut off all secondary pumping, it is only necessary to isolate the boiler by closing the

valves

19 and 18. FIGS. 3 and 4 are illustrations of an alternative form in which the portion which carries out the pumping is located inside the chamber, the boiler and the return tank being mounted outside the chamber.

A boiler 5 sends vapour 4 into conduits 6 heated to a controlled temperature. This boiler is connected to a primary pumping set (not shown) through the intermediary of the conduit 20, and to a return pump 16 coupled to the tank 15.

Various valves

19, 17 and 18 enable this boiler to be isolated. After having passed through the chamber 2', the piping system 6 extends to the

pipes

38 and 37, then by means of connections such as 8, pass the ejection piping 7' which carry the ejectors. These latter are arranged vertically. There have been shown the ejectors 9 and also a heating resistance 10. As in the previous case, all these piping systems are brought up to a definite temperature.

With the vertical ejectors are associated cooled vertical plates 12, the shape of which is shown in FIG. 4. The cooling circuit 63 passes through the chamber 2' and then supplies two

horizontal racks

45 and 46, to which the cooling circuit of the plates is connected at points such as 47 and 48.

The plates have been designed in such manner that by symmetry and repetition a pump is obtained which has a very large suction surface. The pump is constituted by a modular assembly of ejection piping and plates; it opens into the chamber at two opposite faces.

The oil streaming over the cooled faces is collected by gravity on the flow surfaces 52 and thence passes into two collectors 49 which are joined together at 53. The flow continues through the pipe 55 down to the tank 15 after having passed through the chamber by the passage 54.

There has thus been shown a four-stage pump, the last stage of which compresses the gas to a primary vacuum pressure. The gas is then pumped by means of the collector pipes 49 and then the pipe 55 carrying the valve 56 and then the tubular coupling 21, by a primary pumping set (not shown). The pump is provided with a cooled cover 57 and a bottom 58, and rests on feet 59. It is advantageous to group all the vacuum passages (water, oil heating resistances) together on a single flange 60. No secondary valve has been provided on this secondary pump.

It will of course be understood that the present invention has been described above purely by way of explanation, and that any modification of detail may be made thereto in conformity with its general outline without thereby departing from its scope.

I claim:

1. A vacuum pump comprising a chamber to be evacuated,

ejection pipes within said chamber having electrical heating resistances thereon,

a boiler located outside said chamber for producing a vapor and connected to said ejection pipes by tubes having heating means for said tubes,

condensation plates within said chamber and located on opposite sides of said ejection pipes having a shape of converging walls in two opposite directions with a section view through said walls substantially in a sinusoidal wave 'form, said plates having a cooling means for cooling said plates,

said ejector pipes parallel to said condensation plates and constituting stages from the point of wider separation of said converging walls to the point of lesser separation forming a throttled portion,

and exhaust means connected to said chamber,

whereby vapor from said boiler passes with controlled temperature through said tubes and through said ejection pipes and carries away molecules of gas from said chamber to be evacuated.

2. The pump of claim 1, further characterized by said ejector pipes each having a rectilinear shape opening toward said throttled portion of said converging walls.

References Cited UNITED STATES PATENTS 2,150,685 3/1939 Hickman 23010*1 2,608,343 8/1952 Colaiaco et al. 230-101 2,899,127 8/1959 Power 230 l01 2,975,957 3/1961 Geller et al 230 101 X 3,144,756 8/1964 Arnold et a1 23010'1 X 3,203,624 8/1965 Smith 230 101 3,245,609 4/1966 Rangabe 230-101 X 3,326,451 6/1967 Gaydou 230-101 X 3,332,608 7/1967 Landfors 230-401 3,344,979 10/ 1967 Chester 230101 DO-NLEY I. STOCKING, Primary Examiner.

WARREN I. KRAUSS, Assistant Examiner.