US2875698A - Combination centrifugal-turbine pump - Google Patents

Description

March 3, 1959 L. C. ROTH 2,875,698

COMBINATION CENTRIF'UGAL-TURBINE PUMP Filed March 16, 1955 2 Sheets-Sheet l March 3, 1959 I L. C. ROTH l CQMBINATION CENTRIFUGALJURBINE PUMP Filed Maron 1e, 1955 2 Sheets-Sheet 2 INVENTOR. le@ C. fz,

BY )Luuk lazily/dm United States Patent() 2,875,698 i COMBINATION `CENTRIFUGAL-TURBINE PUMP LeojC. Roth, Moline, Ill., assigner to Roy E. Roth Company, Rock Island, Ill., a corporation of Illinois.` e

Application March 16, 1955, Serial No. 494,632 8 Claims. (Cl. 10S- 108) This invention relates to an improved form of combination centrifugal-turbine pump, and is particularly concerned with improvements which impart to the pump the ability to pump liquids at or near the boiling point.

`Propane is one of the many liquids with low boiling points. It has a boiling point of 40 F. and, atlordinary room or ambient temperatures, produces vapor pressures varying from 25 lbs. per sq. in. to 180 lbs. per sq. in. Anhydrous ammonia also boils at temperatures below normal ambient temperatures and is commonly employed in refrigeration systems where `it is deliberately boiled for refrigeration.

This invention is concerned particularly with pumping the above mentioned liquids into storage and transport tanks and with the filling of cylinders and the like.

The present invention is also concerned with the pumping of various other liquids handled ator nearboiling point in` refineries, gasoline plants, chemical and petrochemical plants. Among these are butadiene, styrene, propane, butane, ethane, ammonia, water and various Water solutions. Such liquids may be at boiling point by virtue of temperature or vacuum conditions.

The invention is also concerned with pumping liquid refrigerants such as Freon, ammonia, methyl chloride, sulphur dioxide, and carbon dioxide in the refrigeration process.

The invention is also concerned `with pumping l-ow temperature liqueed gases such as liquid oxygen, nitrogen, and argon into storage and transporttanks and cylinders. i

A liquid at the boiling point is in a state where slight increases in temperature or slight decreases in pressure create an active boiling which produces vapor. It is obvious that it isimpossible to lift such a liquid from `a lower level `to the pump.` However, it is not so obvious that, even with a static suction head, it is diicult to pump liquids in this state unless the suction heads are so highas to prevent boiling ofthe liquid within the pump. Undermany conditions these suction heads must be so great as to be impractical.

` The turbine pump consisting of a vanedimpeller and annular passage with a peripheral suctionentrance and vertical discharge outlet has` been found widely satisfactory for such applications with liquid suction heads of `2 to 6 feet when operating at 1750 R. P. M., and suction heads of 4 to l2 feet when operating at 3500 R. P. M.

`The range given at each speed is due to the individual characteristics of speciiic models.

Basic turbine pump design is such that the impeller can be located to run free of contact with the side plates and water block. Also due to the repeated impulses provided by the vanes of the impeller there is a gradual pressure build-up which counteracts any increased vapor pressures caused by eiliciency losses. This has resulted in the wide use of this design for high pressure handling of non-lubricating liquids.

However, bel-ow the minimum suction heads indicated above, there is a phenomena encountered peculiar to turbine pumps. Partly due to suction entrance pressure losses and partly due to internal by-pass of high pressure liquid a gradual increase in vapor building up occurs with the progressive lowering of the suction head until at heads of 1 to 3 feet at 1750 R. P. M., and 2 to 6 2,875,698' Patented Mar. 3, 1959 ICC feet at 3500 R.. P. M. a complete vapor lock occurs within the pump.

Many instances are found in industry where it is essential topump liquids at boiling point with suction heads of l foot or less. At present, standard designs, turbine or otherwise, cannot till this need. Previous designs involving use of rotary gear or rotary vane pumps in conjunction with centrifugal stage arenot suitable-for non-lubricating liquids and have a limited life in all liquids because of the metallic contact of the gears or vanes.

It is also desirable to provide pumping equipment to handle boiling liquids with l foot suction head that can operate at conventional speeds for electric motorsnamely 1750 and 3500 R. P. M. permitting direct electric motor drives. e

Accordingly, the present invention provides a special mechanical device introducing preliminary to the `turbine pump and running at the same speed which will provide a mechanical equivalent` to the minimum liquidsuction heads previously indicated.

In a turbine pump there are two principal factors which cause the active boiling of the liquid and producey sufficient vapor to make the pump vapor bind or stop pumping. One is a condition in which the pumped liquid, such as a refrigerant, is at a very low temperature and is still at the boiling point. In this case,lthe heat transferred through the pump casing from the ambient temperature outside causes the liquid to boil and produces vapor, even when the pump is at rest. Another fact-or is that the regenerative turbine action of the turbinepump adds heat to the liquid, and some of this superheated liquid is carried over into the pump suction, where it ashes into a vapor, vapor binding the pump.

The cause of vapor binding is thereforethe presence or production of vapor in the liquid in the pump, but this does not completely explain what takes place in a turbine pump when it vapor binds. Because its pumping elements consist of a series of buckets and vanes in the periphery or in the face or faces of the impeller, which elements rotate in an annular channel or raceway interrupted by a liquid block or stop, and because these rotating elements are travelling at relatively high peripheral speeds, the lower inertia of the vapor allows it to fill the bucketsbetween the vanes, displacing the liquid, ,and effectively preventing liquid from entering the buckets unless there is a positive forcel available at the suction of the pump (such as adequate suction head) to compress the vapor sufficiently to initiate the pumping action. Once the pumping action is initiated, the compression of the vapor proceeds rapidly, as the pump builds up pressure in the annular channel, until the vapor is condensed or delivered to the pump discharge.

Attempts have been made to improve turbine pumps in this respect by constructing the suction entrance of the pump in a way to allow` the full weight of staticsuction head to force the liquid'into the suction of the pump under sufficient pressure to prevent the pump from vapo-r binding. In practice, however, improvements of this sort have not been adequate.

The present invention resides essentially in the combination of a centrifugal pump lirst stage andV a turbine pump second stage, and utilizes the following characteristics of both types of pumps: i

A. The centrifugal stage is usedias the iirst stage, because: (l) Its pumping action is not regenerative, and the exterior of the impeller is smooth; therefore it does not add appreciable heat to the pumped liquid. (2) The centrifugal pump does not carry any liquid over from the high pressure discharge tothe low pressure suction in the imp'eller elements themselves (as does a1turbine impeller). (3) The centrifugal pump does not produce high discharge pressures in a single stage,so that whatever leakage takes place between the discharge and suction areas is small in proportion to the capacity of the pump. (4) The centrifugal pump will handle large quantities of vapor providing there is a static suction head available. The centrifugal pump is at least as eiiicient (horsepower consumption vs. horsepower output) as a tur-bine pump under all operating conditions.

B. Because of the above characteristics of the centrifugal pump and because it operates effectively at the same rotative speeds with similar impeller diameters as the turbine pump, the centrifugal pump stage delivers to the turbinepump stage liquid at sufficiently high discharge pressures to effectively prevent, under all reasonable conditions, vapor binding of the turbine stage.

C. The turbine pump is used as the second stage because: (l) Its regenerative pumping action produces high pressures in va single stagel0 to 2O times the pressure of a centrifugal impeller of the same diameter rotating at the same speed. (2) There being no metal-to-metal contact in the rotating parts of a turbine pump, a turbine pump can handle lubricating or non-lubricating liquids without wear. the same rotative speeds as the centrifugal pump.

At least one form of pump with a centrifugal first stage and a turbine second stage, as previously proposed for a different purpose, would not be suitable for the purpose for which the present invention is provided, because it has a leakage patch between a relatively high pressure area ofthe turbine stage and the low pressure area in the suction entrance of the centrifugal stage of the pump. Even with a sealing surface along this leakage path, the normal wear occasioned by the presence of abrasive particles in the pumped liquid would soon open up such a sealing surface to the point where the superheated liquid from the turbine stage, which .leaks across this sealing surface, would produce so much vapor that the centrifugal stage would vapor bind completely and stop the pumping action.

In the aforementionedfprior form of pump the construction is also significantly different in that the centrifugal impeller and turbine impeller are arranged in a manner that would not suice for the purpose of the present invention. The size of the suction entrance of the centrifugal impeller of such pump is limited by the inside diameter of a sealing surface inside the vanes and annular channel. suction entrance of` a pump for the purpose for which the pump of the present invention is provided, should be unusually large to handle satisfactory volumes of liquid and vapor.

One of the main-objects of the present invention is to -provide an improved combination centrifugal-turbine pump in which there is coactive utilization of the characteristics of both -types of pumps, and in which the arrangement is such that there can be no direct leakage between a relatively high pressure area of the turbine stage and the low pressure area in the suction entrance ofthe centrifugal stageof the pump.

Another object is to provide an arrangement of the centrifugal and turbine stages of the pump in which sealing surface means is provided for restraining leakage of the high pressure liquid from the turbine stage and wherein any liquid that does leak from the turbine stage, passes to an area of the centrifugal stage which is under the pressure of the centrifugal force generated there, which effectively prevents the liquid from flashing into vapor.

Another object is'to` provide an arrangement in which the only leakage that can occur into the suction entrance of the centrifugal first stage is from the discharge of this stage. Because the differential pressures generated in this stage are small relative to the capacity, and since the centrifugal impeller itself adds little heat to the liquid, the possibility of vapor binding this stage is minimal,

This is a serious defect, because the and takes place only under extreme conditions not l usually encountered in actual practice, such as attempt- (3) The turbine pump operates best at ing to operate the pump at terminal or shutoff pressure while handling a boiling liquid.

Another object is to provide an arrangement of the centrifugal and turbine stages of the pump which will not limit the size of the suction entrance of the centrifugal stage, but will permit the suction entrance of the centrifugal stage to be unusually large so as to handle satisfactory volumes of liquid and vapor.

Further objects and advantages of the invention will appear from the following detailed description, taken in connection with the accompanying drawings which show the construction and operation of an illustrative embodiment of the invention.

In the drawings:

Figure l is a longitudinal sectional view taken substantially along the lines 1--1 of Figure 2;

Figure 2 is a transverse sectional view taken along the line 2-2 of Figure l;

Figure 3 is a transverse sectional view through the centrifugal impeller taken along the line 3-3 of Figure 1; and

Figure 4 is a fragmentary detailed section showing another sealing arrangement for sealing olf relativelyhigh pressure liquid at the center of the turbine stage from escaping into the lower pressure centrifugal stage.

Referring to the drawings for a more detailed description, the pump selected for illustration is a combination centrifugal-turbine pump having a pump casing designated in its entirety by the numeral 1. The casing y1 comprises a casing part 2, a pair of casing parts 3 and 4 and a sealing ring or annular casing 5 closely surrounding the cylindrical surfaces 6 and 7 of the casing parts 3 and 4Q The pump shaft S projects through the pump casing part 4, which contains a stutiing box 9 or other suitable sealing means; also through the casing part 3 and into the casing part 2. The pump shaft S is driven by any suitable or preferred prime mover (not shown), and the casing extension 10 may be provided with suitable bearings (not shown) for supporting the shaft 8, and, if desired, with a supporting base. A turbine impeller 11 is fixed, for example, by a key or spline 12 or the like to rotate with the shaft 8. A centrifugal impeller 13 coaxial with and spaced axially from the turbine impeller 11 is also fixed, for example, by a key or spline 14, or the like, to rotate with the shaft 8.

The turbine impeller 11 has at its outer peripherytwo sets of vanes or blades and buckets 15 cut into its opposite sides at the periphery thereof. One set of these vanes 1S opens from one side of the outer marginal portion of the impeller 11, and the other set of vanes 1.5 opens from the other side of the outer marginal por- .tion of the impeller. Both sets of vanes open radially .from the Iouter periphery of the impeller 1 1, and both sets of vanes operate in an annular liquid channel `16 during the rotation of the impeller 11.

The casing parts 3 and 4 have opposed generally annular ribs or anges f7 between which the impeller 11 is accurately and closely spaced, or which abut or cooperate with the opposite sides of the impeller 11 to form sealing surfaces 18 which prevent most of the pressurized liquid from escaping from the discharge of the annular channel 16 radially inwardly between the casing parts 3 and 4 and the opposite lsides of the impeller 11. The liquid channel 16 is interrupted by stop o-rv block members 19 which may be formed integral with the casing parts 3 and i and prevent the pressurized liouid from escaping to the suction of the turbine stage of the pump from the discharge of the annular channel The centrifugal impeller i3 which, as already set forth, rotates with the shaft 8 and the turbine impeller 1l is preferably of the enclosed type as shown more indetail in Figures l and 3. It has an annular hub20 integral with its wall 21 and an annular hub 22 integral with its wall 23. The hub 20 defines the suction inlet Z4 of the centrifugal stage of the Pump and with the arrangement described this suction inlet opening 24 is not limited in size but may be as large as desired. This is an important practical advantage, because the suction entrance of this type of pump should preferably be unusually large to handle satisfactory volumes of liqui and vapor. i

The hub 20 rotates within a bushing 25 which lines the inner end of the opening inthe hub 26 of the casing part 2. The bushing 25 provides a sealing surface around the suction opening 24 to prevent the escape of liquid from the discharge of the volute channel 27 to the suction inlet 24 of the centrifugal stage of the pump. The hub 22 of the centrifugal impeller 13, along with the hub 28 of the turbine impeller 11, rotates within a bushing 30 which seals off relatively high pressure liquid at the center of the turbine stage from escaping into the lower pressure discharge of the centrifugal stage.

The construction for sealing the relatively high pressure liquid at the center of the turbine stage from escaping into the lower pressure discharge of the centrifugal stage may be altered in various ways within the scope of the present invention. For example, as shown in Figure 4, the shaft 8 itself, which corresponds with the impeller shaft previously described, may project through a hole or bushing `30 between the two stages to prevent the high pressure liquid from escaping to a lower pressure portion of the pump. Other parts of Figure 4, which are similar to parts shown in Figures l-3, are designated by primed reference characters corresponding to those used in Figures l-3.

The suction inlet 24 of the centrifugal ,stage opens into the spaces between the walls 21 and 23 and the enclosed blades 32 of the impeller 13 and these spaces open radially outwardly to the volute channel 27. The volute channel 27 opens into the suction entrance 34 of the turbine stage of the pump. The discharge of the annular channel 16 of `the turbine stage delivers the pressurized liquid to the pump outlet 35 which thus opens from the discharge of the annular channel 16.

The casing part which, as already set forth, surrounds or encircles the casing parts 3 and 4 fits between" a flange 38 on the casing part 2 and a flange 40 on the casing part 4 and the casing parts are secured together, for example, by screws or bolts 42. The impeller 13 is secured in place on the adjacent reduced diameter end of the shaft 8 by a nut 45 between which and the adjacent wall of the impeller 13 a washer 46 is interposed.

In the operation of the pump, the liquid enters the suction entrance 24 of the centrifugal impeller 13 and is discharged from the periphery of this impeller into thel volute channel 27 at increased pressure and higher velocity. Under the pressure of the centrifugal force of the rst stage the liquid passes through the suction entrance 34 into the annular liquid channel 16 of the turbine stage. The regenerative pumping action of the turbine impellerll builds `up sufficient pressure to deliver the liquid to the outlet 35 of the turbine stage, by constant recirculation of the liquid through the` impeller vanes and annular channel 16.

Since the liquid in the suction entrance of the turbine second stage is always under the pressure of the centrifugal force from the centrifugal first stage, vaporization cannotoccur, and this stage will not vapor bind. Further, it has been found that the centrifugal type pump, when properlydesigned for handling liquids at or near the boiling pointand operating with a static suction head, will itself not vapor bind except at terminal or shutoff pressure, because, since there is no recirculation ofthe liquid and because of the smooth exterior of the impeller, very little heat is added to the pumped liquid. Since the second stage will not vapor bind if the rst envases stage does not fvapor bind, and sinceunder all pumping conditions the first stage will not, it isv evident `the complete device as described will not vapor bind.

It `will be apparent from the foregoing descriptionthat the combination centrifugal-turbine pump of the present invention coactively utilizes the characteristics of both types of pumps and that the arrangementis such that there can be no direct leakage between areas of suiicient differential pressure to vapor bind or stop `the pump. The high pressure liquid from the turbine sec ond stage is first restrained along radial paths by the sealing surfaces 18 and the opposite sides of the turbine impeller 11 inwardly of the vanes 15. Whatever liquid may leak by the sealing surfaces 18 is restrained from leaking to the centrifugal stage by the sealing surface ,around the hubs 22 and 28 of the centrifugal and turbine impellers 13 and 11, and between these hubs and the bushing 30 in Figure l, or between the shaft 8' and the bushing 30' in Figure 4. Even then such liquid as may leak to the centrifugal stage is still under the discharge pressure of the centrifugal stage or the centrifugal force generated there, which effectively prevents the liquid from flashing into vapor.

The only leakage into the suction entrance 24 of the centrifugal first stage which can occur is from the discharge of the centrifugal stage across the sealing surface around the hub 20 of the centrifugal impeller 13 as provided by the bushing `25. Because the differential pressures generated in the centrifugal stage are small relative to the capacity, and since the centrifugal impeller 13 itself adds little heat to the liquid, the possibility of vapor binding this stage is minimal, and, as previously set forth, takes place only under extreme conditions not usually encountered in actual practice, such as attempting to operate the pump at terminal or shutoff pressure while handling a boiling liquid.

The structural arrangement described does not limit the sizeof the suction entrance 24 of the centrifugal stage of the pump, but enables making this suction entrance 24 unusually large or, at least, as large as desired to handle satisfactory volumes of liquid and vapor for the purposes contemplated.

The use ofthe pump of the present invention is not limited to handling a particular liquid or particular class of liquids; but the pump may be employed for pumping any liquids at or near the boiling point.

The centrifugal impeller provided in the` pump of the present invention is of special type of low volumetric efciency and very low pressure creating characteristic. Since maximum discharge head of l0 feet at 1750 R. P. M., and 20 feet at 3500 R. P. M. is required all other considerations have been sacrificed to the need of pumping boiling liquid with 1 foot or less suction head.`

To this end the special features of the centrifugal impeller are as follows:

(l) Disproportionately large suction entrance about `50% of the full impeller diameter.

(2) Shrouded impeller eye machined inside and outside to a very thin wall.

(3) Deep blades at the impeller eye parabolic with reference to the radius and helical with reference to the aXIS.

(4) A rapid but even volumetric closure of the impeller cavity at the periphery.

(5) Streamlining of all surfaces in contact with the liquid stream.

By the foregoing means I provide a. centrifugal impeller of special design for developing heads up to l0 feet at V1750 R. P. M. and up to 20 feet at 3500 R. P. M. in capacities up to 200 G. P. M specifically for use in conjunction with the turbine impeller at the above speeds to take boiling liquids, volatile liquids or liquied gaseswith suction heads ofl foot or less and produce discharge heads up to 800 feet per turbine stage. t

` yThe claims of the present application are not` limited autres to a combination centrifugal-.turbine pump with a centrifugal stage and a single turbine stage butare of a scope to lcover a centrifugal-turbine combination with two or more lturbinestages arranged in series (or tandem).

The embodiments of the invention shown inthe drawings are for illustrative purposes only, and it is to be expressly understood that the drawings and the accompanying specification are not to be construed as a definition ofthe limits or scope of the invention, reference being had to the appended claims for that purpose.

I claim:

1. A centrifugal-turbine pump capable of pumping liquids and liquified gases at or near the boiling point thereof with suction heads not greater than about 1 foot, comprising a pump casing having a first pumping chan# nel and a second pumping channel disposed laterally of said first pumping channel, a driving Shaft disposed axially o f said pumping channels, a high pressureregenerative turbine impeller fixed for rotation at all times and in the `same direction with said driving shaft and having peripheral varies forming liquid-propelling buckets in opposite sides of the periphery of said turbine impeller and opening peripherally therefrom, said second pumping channel extending generally annularly about and spaced outwardly from the periphery of said turbine impeller so that the liquid Will enter the buckets at both sides of said turbine impeller and be circulated peripherally into and out of said buckets for almost a full revolution of said turbine impeller, said second pumping channel having a discharge outlet opening generally radially from one end L thereof, said casing having block means separating the discharge outlet end of said secondpumping channel annularly from said first pumping channel, said casing having a suction entrance for the turbine stage opening laterally from said first pumping channel to said other end of said second pumping channel, and a centrifugal impeller of low volumetric eliiciency and low pressure creating characteristics fixed .for rotation within said first pumping channel and at all times and in the same direction with said driving shaft and said high pressure regenerative turbine impeller, said centrifugal impeller having a large diameter axial suction inlet eye of substantially the same diameter as a suction inlet for the centrifugal stage defined by said casing and closed blades spaced inwardly from the periphery of said first pumping channel. so that liquid entering said suction inlet eye will be thrown out by centrifugal. force into said first pumping channel and pass 'through the ysuction entrance for the turbine stage into said other end of said second pumping channel to prevent vaporfformation within the pump and provide a mechanical equivalentto the minimum suction head at which thc rcgenerative turbine impeller yis operable without vapor binding.

2. In a rotary pump for pumping liquids and `liquified gases at or near the boiling pointA thereof, a high pressure regenerative turbine impeller having peripheral varies forming liquid-propelling buckets in opposite sides of the periphery thereof and opening peripherally from said tur- -turbine impelle'r'to produce a regenerative pumping action and high pressures, said turbine impeller having an annular wall separating said liquid-'propelling buckets on one side of said impeller from said liquid-propelling buckets on the opposite side of said impeller, a centrifugal impeller of low volumetric efiiciency and low pressure creating characteristics positioned ahead of said turbine impeller with respect to the direction of movement of the liquid through the pump and fixed to turn at all times in the same direction Vandat the same rotative speeds. as said turbine impeller, acasing havingl a first pumping channel for said centrifugal limpeller and provided with a large diameter axial suction inlet for the centrifugal impeller and a single peripheral outlet, said casing having a second pumpchannel extending generally annularly about and spaced outwardly from the periphery of said turbine impeller .SQ that the liquid will cater the buckets 'at both i sides of said turbine impeller and be circulated periph? erally into and out of said buckets for almost a full revolution of said turbine impeller, said second pumping channel having a peripheral suction entrance in communication with the single peripheral outlet of said first pumping channel and a single vertical dischargey outlet, and block means separatingsaid discharge outlet of said second pumping channel annularly from said peripheral suction entrance of said second pumping channel. Y

3. A rotary pump according to claim 2 wherein the block means separating the discharge outlet of said second pumping channel from `the suction entrance of said second pumping channel is integral with the interior of said casing and extends generally radially inwardly therefrom between the discharge outlet and the peripheral suction entrance of said second pumping channel.

4. A rotary pump according to claim 2 wherein the centrifugal impeller has closed blades constructed parabolically with reference to the radius and spirally with reference to the axis thereof.

5. A rotary pump according to claim 2 wherein the turbine impeller and the centrifugal impeller have oppositely extending tubular hubs which abut one another and through which a driving shaft connected to turn said turbine and centrifugal impellers therewith extends with one end of said shaft terminating at about the inner surface of a radial wall forming a part of a closure for the blades of the centrifugal impeller, and a nut coacting with said radial wall of said centrifugal impeller and screwed axially into the adjacent end of said shaft for securing the centrifugal impeller in place on said shaft.

6. A rotary pump according to claim 2 wherein the axial suction inlet for the first pumping channel is about half the size of the rotor diameter of the centrifugal im peller.

7. A rotary pump according to claim 2 wherein there are annular ribs integral with the interior of the casing and cooperating with opposite sides of the turbine impeller radially inwardly of the liquid-propelling buckets in the periphery thereof for preventing liquid from moving radially inwardly of the turbine impeller.

8. A rotary pump according to claim 2 wherein the turbine impeller and the centrifugal impeller have oppositely extending tubular hubs which abut one another and through which a driving shaft connected to turn said turbine and centrifugal impellers therewith extends with one end of said shaft terminating at about the inner surface of a radial wally forming part of a closure for the blades of the centrifugal impeller, a nut coacting with said radial wall of said centrifugal impeller and screwed axially into the adjacent end of said shaft for securing the centrifugal impeller in place on said shaft, and an annular bushing surrounding the oppositely extending tubular hubs of the turbine and centrifugal impellers and cooperating with said casing to seal, the first and second pumping .Channels from 01.1@ another.

References Cited in the 'rile of this patent UNITED STATES PATENTS 1,875,419 Claypool Sept. 6, 19.32 1,879,803 Johnson Sept. 27, `1932 1,912,452 Hollander' June 6, 1933 2,055,587 Pigott Sept. 29, 1936 2,190,245 `Sartell Feb. 13, 1940 2,272,469 Lannert Feb. 10, 1942 2,374,122 Nelson Apr. 17, 1945 2,468,246 Thayer Apr. 26, 1949 2,601,828 Lobanolf July 1, 1952 2,765,748 Buchi Oct. 9, 19,56

FOREIGN PATENTS 513,423 Belgium Aug. 30, 1952 641,391 GreatBritain Augf9,A 195.0 654,854 Great Britain A July 4, 1951 711,791 germany ..J-s-l.. Qt- 7. 1.9.4.1

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