US2468170A - Rotary pump for liquefied gases - Google Patents

Description

April 26, 1949- R. v. CARLSON 2,468,170

ROTARY PUMP FOR LIQUEFIED GASES Filed Jan. 9. 1947 55 553g 36 l 40 4/ I /5 /4 54' .l

INVENTORy 76 l L g5 50 5] R'JGER V. CARLSON l wmwunfni- 4 Z5 Z7 ATTORNEY v PatentedApr. 26, 1949 UNITED STATES PATENT 'OFFICE ROTARY PUMP FOR LIQUEFIED GASES t tion of Ohio Application January 9, 1947, Serial No. 721,134

. '8 Claims. l

This invention relates to rotary pumps for liquefied gases, particularly multi-stage rotary pumps for pumping liquefied gases having normal boiling points substantially below 233 K.,

such as liquid nitrogen, and capable of delivering adequate quantities of such low temperature liquid at a considerably elevated pressure.

The pumping of liquefied gases having low boiling points involves unusual problems due to the great volatility of the liquid and its extremely low temperature. The temperature change from room temperature :to that of the liquefied gas causes severe contraction of the pump parts and the construction must allow for such contraction without incurring increased friction or affecting the pumping ediciency. The volatility of the liquid, which is increased by natural heat iiow toward the liquid from the surroundings, makes pumping of such a liquid quite diflcult as generation of heat by the operation of the pump adds to the difficulty and may cause gas binding and failure of operation. The low temperature also makes it impossible to employ ordinary lubricants and therefore bearings of the customary type cannot be used.

To obtain 'higher delivery pressures when pumping a liquefied gas by rotary pumps it is found necessary to employ two or more'stages and when several stages are provided in a single casing with a. single drive shaft the difficulties of accommodating the contraction of the parts have previously resulted in the employment of complicated constructions. Multiple staging introduces the problem of interstage sealing, which is necessary because the increased energyof the liquid inthe higher pressure stage causes vaporization if it leaks toward a lower pressure stage. Such interstage sealing must be accomplished without incurring excessive friction and also be unaffected by expansion and contraction of the parts. It has also been proposed to use bearings made of bonded carbon or graphite in pumps for low temperature liquefied gas. particularly liquid oxygen. Such material is self-lubricating and is not aiected by the low temperature. It does have the disadvantage, however, that it tends to wear rapidly under the nig/h radia1 bearing loads which occur in turbine-type rotary pumps operating at high discharge pressures. Thus solutions that may suggest themselves for many of the diil'iculties are conflicting in that they may enhance others. l

'I'he principal object of the present invention is therefore to provide a pump for liquefied gases such as liquid nitrogen or liquid oxygen embody- (ci. s-96) ing an improved combination of features and associ-ation of parts that successfully overcomes the difiiculties set forth above. The improved pump of the present invention results in part from the 5 discovery that ball bearings are operable successfully in contact with clean liquefied gases of the low boiling point type without requiring fiuid or semi-solid lubricants.

Other objects of the invention are to provide a multi-stage pump in which two adjacent impellers may be fixed toa common drive shaft without incurring diiiiculties caused by expansion and contraction of the parts by employing a shaft bearing that axially positions the shaft with re.- spect to the casing at a point between the impellers; and to greatly simplify the construction of a multi-stage pump for liquefied gas by employing an inboard shaft bearing arrangement between two stages that functions to position the shaft and rotary impellers axially as well as radially with respect to the casing and also functions as an interstage seal.

It is also an object of the present invention to provide a multi-stage pump for liquefied gases with a novelrelationship of the impellers to produce substantially greater discharge capacity and increased discharge pressure.

Other objects and features of novelty will be apparent from the following description and the 80 accompanying drawings in which:

Fig. 1 is a view of a longitudinal cross-section,l

through a pump embodyingthe principles of the present invention. the extended drive shaft portion of the pump being broken away; and

Fig. 2 is an enlarged fragmentary sectional view showing lthe mounting of the ball bearing in the pump. -1

Referring now to the drawing, the pump illustrated is of the two-stage type and has a main l4i) frame or casing Ill containing iirst and second stage annular pumping channels il and l2 with a partition; I3 between them. Operating inthe pumping channels Il and i2 are rotary impellers M-and I5 respectively provided with suitable blades I6 at their peripheral portions for propelling the uid through the pumpingchannels. Each pumping channel is provided vwith a suitable inlet and outlet passage, which passages do not appelaI in the section 'as shown. The outlet of the ir stage channel Il is connected to the inlet of th second stage channel l2. The arrangement the pumping channels and their inlet and outlet passages is similar to that shown and described in United States Patent No. 2,340,- 787. Such arrangement is not illustrated since it are made substantially wider than the first stage channel II and its impeller. One side of the casing -Ill is closed by a. cover internally to form part of the pumping channel I2 and to provide close clearance between it and one side of the impeller I5 and is also formed with a cup-like central depression I8 for enclosing the hub I9 of the impeller I5. The other side of the casing I9 is provided with a closure 20 similar to the cover I1'but having an annular I1 which is shapedA terstage fluid seal to prevent iiow of liquid from the high pressure stage through the ball bearing and into the low pressure stage.

The shaft 24 passes through a stuillng box at the outer end of the housing 23, which stuillng box may be of the customary type or for example as shown in United States Patent No. 2,296,640. A supporting bearing is also provided at the outer end of the shaft 24 which may be of any cuscentral member 2I secured thereto.' The central member 2l provides a closure for the hub portion 22 of the impeller I4 and also has secured gas-tightly thereto a tubular extension 23. for enclosing an extended drive shaft 24. The member 2l also has a portion extending inward toward the shaft 24 on the left side of the hub 22 to form a fluid barrier 2|' to impede circulation of liquid into extension 23.

The drive shaft 24 extends axially into the casing I0 and the impellers I4 and I5 are rigidly secured thereon. To this end the drive shaft 24 has an integral collar 25 adjacentthe inner side of the impeller I4, the hub portion 22 of which extends outwardly and is internally threaded to engage threads 26 formed on the shaft 24. The impeller I4 is thus threaded on the shaft 24 to abut tightly against the collar 25. To the right of the collar 25 the shaft has a cylindrical portion 21 adapted to carry the inner race 28 of a bearing assembly indicated generally at 29. 'I'he bearing 29 is of the type having rolling elements between annular races, preferably a ball bearing. The inner side of the impeller I5 is provided with an annular portion 30 that clamps the race 28 against the collar 25. The rightwardly extending hub portion I9 of the impeller I5 is internally threaded to engage threads 3| formed on the inner end of the shaft 24. If desired, the end of the shaft may be formed with fiat areas as at 3I' to provide a means for gripping it with a Wrench so that the impeller I5 may be secured tightly.

The ball bearing 29 is preferably of the 'type which is self-centering so as to position the shaft axially as well as radially. 'Ihe bearing' may have one or morey rows of balls or it may fem-v ploy rollers. It is also preferable that the balls or rollers be held out of contact with each other. As shown in the drawing, the bearing is provided with a single row of balls 32 between the inner race 28 and an outer race 33 and spaced from each other by a suitable retainer 34. The outer race 33 is rigidly secured with respect to the partition I3 by retaining rings. 35 and 36. To this end the partition I3 has an' opening therethrough with a shoulder 31 and anenlarged threaded portion 38.-.The rim` of the ring 35 has threads engaging the threads of opening 38 and abuts tightly against the shoulder 31. The ring 35 has a bore 39 into. which the outer race 33 is fitted so as toabut'against the bottom of the bore 39 which is formed by an annular iiange or shroud portion 40 of the ring 35. The shroud portion 40 extends radially inwardly for a distance sufcient to 'completely cover the space between the inner and outer races. The outer race is clamped in place by the ring 36 which has external threads engaging those of the bore 38 and has at its inner rim a shroud 4I which covers the space between races 28 and 33. The shrouds 40 and 4I form a labyrinthtype of intomary type but constructed so that it allows for axial expansion and contraction movement of the outer end of the shaft.

From the above description it will be seen that a great simplification of construction has been effected in a rotary multi-stage pump for low temperature liquefied gases. Previously it had been necessary to provide axially adjustable connections between the drive shaft and the impellers, to provide thrust bearing-means for centering each impeller in its pumping channel, to provide means such .as balance cylinders for counteracting the resultant radial force of the liquid pressure acting on the high pressure stage impeller, and to provide means for reducing the axial pressures acting on the impeller hub. According to the invention such complications are avoided by utilizing a rolling element type of bearing positioned in the partition between the impellers,.the bearing being constructed to withstand substantial radial loads and also to resist substantial axial forces. A two-point contact bail bearing 29 is found to give good results in resisting the combined radial and axial forces because the rotating speeds of the pumps are 5 in excess, of 1,500 R. P. M. For heavier duty a double-row ball bearing may be substituted for the single-row type.

The location of the 'bearing 29 in the partition I3 between the impellers I4 and I5 allows the 40 impellers to be rigidly fixed to the shaft 24 so -tered in their pumping channels.

j Y Ill is of cast metal and the shaft is made of wrought metal, their coeflicients of expansion are that the bearing maintains both impellers cen- The axial movements of the parts due to expansion and contraction are thus symmetrical and the same in amount for each impeller. Since the casing different, but the distance between the center -of'the bearing and the furthest side of each impeller 'is so short that the effect of differential expansion and contraction is now small enough to be negligible and the clearances between the covers 20 and I1 and the sides of impellers I4 and I5 remain at the desired close values for eillcient'operation.

As previously mentioned the invention relies in part upon the discovery that metal bearings of the rolling element type are successfully operable without customary lubricants when subject to low temperature liquefied gases. It has been universal practice to run ball bearings in an oily or grease lubricant even though there is very little if any sliding friction. The lubricant preserves the fine finished surfaces of the balls and races and removes heat due to the metal resil-v lments.A Thus' itis preferable to employ a suitable ring-shaped retainer provided with spaced pockets for the balls. The retainer travels with the balls andzlany friction that may occurbetween` the retainery and theballs is relatively small.

The metal :of which the bearing is. made; should i;

be chosen-according to the character of the lique-l fied gas ybeing pumped; With non-oxidizing For emcient operation, excessive leakage from the` high pressure stage toward the low pressure stage should be prevented. To this end the bearing is constructed to prevent or limit such leakage. With a ball bearing, adequate sealing is accomplished by the shroud flanges 40 and 4I that cover the space between the races 28 and 33 that are arranged to have a very close running clearance with the sides of the inner race 28. The clearance between the side of the impeller I5 and the ring 36 is also kept small so that in effect a labyrinth type of seal is provided. Such sealing arrangement is found to be adequate as a small amount of leakage can be tolerated without a measurable effect on the pumping. Such small amount of leakage is advantageous to bring liquefied gas into contact with the rolling elements which are thereby adequately cooled by a clean liquid.

In rotary liquid pumps of the type disclosed` herein it has been customary to make the second stage impeller of the same width or narrower 4 than the first stage impeller on the theory that the liquid is slightly compressed due to the increased pressure. It has been discovered, however, that with liquefied gases of the character of liquid nitrogen, both increased discharge capacity and higher discharge pressure are attainable if the bladed portion of the second stage impeller is made wider than the first stage; with of course a corresponding greater width of the pumping channel in which the bladed portion runs. For example, when the second stage impeller of a two-stage pump was made almost twice the width of the first stage, the discharge capacity increased from 175,000 cubic feet. per hour with the narrow second stage impeller to 240,000 cubic feet per hour with the wider impeller when discharging against a pressure of 225 p. s. i. gauge. For a given discharge rate, the pump with the wider second stage impeller easily attained a considerably higher discharge pressure. It is not essential that the second stage be exactly twice as wide as the first stage because any substantial increased width provides improved discharge capacity and/or pressure, although increased widths beyond two times are not expected to provide suflicient further improvement worth the increased weight of the parts.

Although a preferred embodiment of the invention has been described in detail it will be understood that modifications in details of construction may be made and certain features used without others without departing from the spirit and scope of the invention as defined in the claims.

What is claimed is: "il: 1A multi-stage rotary pump having a casing, at least-two rotary impellers therein, an annular Pummnghphel, for the *peripheral portion of each of saidimpellers, andan" axiallyextending*y drive shaft for saidimpellers, said casing having a partitionbetween' the pumping'channels, said sides of said partition, and' a bearing for lsaidf shaft disposed betweenvthe impellers, said bear-jA ing being ofthe type having rolling' elements be` tween annularsinnerandlouter races and includl lng interstage fluidsealingmeans, theinnerrace` being secured toy the shaft and,thejhouterrace being supported in said partition, said bearing,l and seal being Aconstructed and arranged to'position -said shaft` and. rotors yradially Aand axially y with respectto saidpartitionl .m l,

2. A- multi-stage rotary pump having a casing,

at least -two rotary impellerstherein, an annular ,E pumping channel'lfor the peripheral portion of each of said impellers, and anaxially extending drive shaft for said impellers, said casing "having a partition between the pumping channels, said impellers being secured to the shaft on opposite sides of said partition, and a bearing for said shaft disposed between the impellers, said bearing being of the type having balls engaged between annular inner and outer races and including interstage fluid sealing means, the inner race being secured to the shaft and the outer race being suported in said partition, said bearing and seal being constructed and arranged to position said shaft and rotors radially and axially with respect to said partition.

3. A multi-stage rotary pump having a casing, at leasttwo rotary impellers therein, an annular pumping channel for the peripheral portion of each of sai'd impellers, and an axially extending 0 drive shaft for said impellers, said casing having said shaft disposed between the impellers, said bearing having its inner race secured to the shaft and its outer race mounted in means securing it to said partition, said securing means including` shrouding flanges providing a fluid seal, said bearing and seal being constructed and arranged to position said shaft and rotors radially and axially with respect to said partition.

4. A multi-stage rotary pump having a casing with at least two pumping channels each having inlet and outlet channels, rotary impellers having bladed peripheral portions operating in each ofV said pumping channels and an axial drive shaft for said impellers, one of said impellers and its pumping channel constituting a later stage being substanitally wider than the prior stage.

5. A multi-stage rotary pump having a casing with at least two pumping channels each having inlet and outlet channels, rotary impellers having bladed peripheral portions operating in each of said pumping channels and an axial drive shaft for said impellers, one of said impellers and its pumping channel constituting a later stage being substantially wider than the prior stage, said casing having 4a, partition between the pumping channels, said impellers being secured to said shaft on opposite sides of said partition, and a bearing for said shaft between the impellers and mounted in said partition, said bearing including interstage fluid sealing means and being constructed and arranged to position said shaft and i 1 rotors radially'and axially with respect to raid partition.

6; A multi-stage rotary pump according to claim 5in which said bearing is of the type hav ing rolling elements between inner and outer annular races.

'1. A multi-stage rotary pump comprising a casing with first and second nels. ilrst and second stage rotary impellell. having bladed peripheral portions operating in said respective channels andan axial drive shaft for said impeliers. the second stage channel and at least the peripheral portion ot its impeller-being substantially wider but no more than twice as wide as the ilrst stage channel and impeller.

8. A multi-stage rotary pump comprising a casing with iirst and second stage pumping channels, ilrst and second stage rotary impellers having bladed peripheral portions operating in said restage Pllmlllnl chan- 8 spective channels and an axial drive shaft for said impcliers. the second stage channel and at least the peripheral portion of its impeller being substantially wider than the first stage channel and impelier thereby providing improved capacity and/or pressure characteristics when pumping queued Els;

ROGER. V. CARLSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS

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