US2455460A

US2455460A - Rotary pump for liquefied gases

Info

Publication number: US2455460A
Application number: US725784A
Authority: US
Inventors: George H Zenner
Original assignee: Linde Air Products Co
Current assignee: Linde Air Products Co
Priority date: 1947-02-01
Filing date: 1947-02-01
Publication date: 1948-12-07
Anticipated expiration: 1965-12-07
Also published as: GB633222A

Description

G. H. ZENNER ROTARY PUMP FOR LIQUEFIED GASES Filed Feb. 1, 1947 lNV GEORGE AORNEY Patented en. 7 3948 ROTARY PUMP FDR LIQUEFIED GASES George H. Zenner, Kenmore, N. Y., assignor to The Linde Air Products Company, a corporation oi Ohio Application February 1, 1947, Serial No. 725,784 I 8 Claims. 1

This invention relates-to rotary pumps for liquefied gases and more particularly to pressure balancing means for relieving bearing pressures in rotary pumps for liquefied gases having boiling points below 133 K. such as liquid oxygen and nitrogen. The problem involved is in part similar to that described in U. S. Patent No. 2,340,787, the present invention including an improved solution of the problem with advantages to be described.

In pumps for low temperature liquefied gases it is found advantageous to use bearings made of solid self-lubricating material inert to the liquefied gas to be pumped. Since such materials tend to wear rapidly it is advantageous to reduce the rate of wear by minimizing the bearing pressures. Also since heat generation in the pump tends to adversely affect the pumping efilciency a reduction of bearing pressures has the further advantage of reducing the generation of frictional heat. According to the aforementioned patent the radial load on an inboard pump bearing may be lightened by providing a radial pressure force counteracting the resultant of radial pressure forces acting on the impeller due to the increase of pressure in the pumping channel from the inlet to the outlet thereof and,

there is disclosed one arrangement for obtaining such balancing radial force.

According to the present invention there is provided a different and improved arrangement for obtaining a radial balancing force by applying to .a cylindrical area of the impeller hub a differential pressure on opposite sides thereof,

' one pressure being that of a. lower pressure region of the impeller channel and the other higher pressure being that of the impeller hub region. Also according to theinvention, the axial force acting on the interstage seal of a two-stage pump, which force tends to produce excessive friction and Wear of the bearing surfaces of such a seal, is also relieved by reducing the fluid pressure acting against the inboard end of the impeller hub, such pressure relief being preferably accomplished by the passage means employed for providing the lower of the diflerential pressures acting radially on the impeller hub.

Accordingly, the principal objects of the pres-' ent invention are to providelmproved means and arrangement of parts for reducing radial bearing loads in rotary pumps for liquefied gases; to provide means for reducing excessive axial forcesacting on the lnterstage seal bearing of multistage rotary pumps; and to provide an improved pump construction in which theabove objects Fig. 1 is a view'of a transverse section of a pump for liquefied gases embodying the principles of the invention; and

Fig. 2 is a view'of a section taken along line z 2 of Fig. 1.

The principles of the, invention may be employed in single and multi-stage pumps for liquefled gases, but since the principles are similar in either type of pump and are preferably employed in multi-stage pumps, a two-stage pump is illustrated and described in detail. The pump illustrated is of the turbine type employing bladed impellers revolving in annular pumping channels. In the pump illustrated the casing is shown at Ill having therein two annular pumping channels H and I2, the channel ll being for the low pressure stage and the channel l2 for a second or high pressure stage. Cooperating with the pumping channels H and I2 are the bladed ends l3 of low pressure and high pressure impellers l4 and i5, respectively. The casing is also provided with a partition I6 separating the channels H and i2. The impellers have hub portions l1 and i8, the hub ll of impeller l8 extending to the left and the hub portion l8 of the impeller l5 extending to the right, the latter being relav tlvely long. The impeller hubs are mounted slidingly on a drive shaft i9 that extends axially into the casing ill from one side thereof. For driving the impellers the shaft I9 is provided with a set of splines 2'0 that are set into the shaft and engage corresponding spline ways in the hubs. The low pressure side of the casing I0 is closed by a side cover 2| that has a middle portion 22 extended to form a, housing for the hub H. The middle portion 22 carries internally a thrust bearing 23 positioned to engage the left end of the hub I1 and thus center the impeller id in the casing.

The impeller Hi is also positioned by an interstage thrust bearing 24 that engages the right side of the impeller l4 and is mounted within the partition l6 by an externally threaded ring 25 that is threaded into a counterbore 26 in the partition IS. The lnterstage thrust bearing 24 is also provided with a right end surface 21 that frlctionally engages the left side of the impeller IE to form an lnterstage seal bearing and to locate the impeller I6 accurately in its pumping channel.

ing 30 assaeeo s The right end portion of thehub i8 forms a journal that is rotatingly supported within a sleeve bearing 28 mounted within a bearing cap 29 that is mounted on of the side cover Ii which closes the right side of the pump casing ID. The opening 30 of the side cover 3i extends inwardly for a predetermined distance from the inner end of the bearing 28 to a bottom wall 32 that has a central hole 33 therethrouzh that fits the hub IS with a small clearance. The space thus provided around the hub I8 is divided into two chambers by partitions 34 that are seen in transverse section in Fig. 2. The chambers 35 and 88 thus formed are arranged to maintain fluid at higher and lower pressures respectively so as to provide a force acting generally downwardly n the impeller hub IS. A hole 31 through the upper part of the bottom wall 32 provides communication between the high pressure chamber 35 and the hub region of the impeller ii. To obtain a lower pressure in the chamber 36 there is provided a passage 38 connecting the chamber 88 with the pumping channel i2 in a region near its inlet portion. To this end, the passage 08 has a portion 38 extending downwardly to meet an arcuate portion 38" formed in the side cover Ii and extending clockwise as indicated in Fig. 2 to a portion 38" at a point opposite the inlet 41 where the portion 88 enters angularly into the channel i2. The end of the hub I8 is preferably closed by a plug 40 that is arranged to permit relative axial movement between the end of the shaft i9 and the hub l8. In previous pumps of this character the impeller hub pressure would act toward the left on the impeller I! because of the lower pressure at the hub portion of the low pressure impeller ll. Such pressure difference applies considerable force between the impeller "and the seal bearing surface 21. According tothe present invention this is relieved by providing a pressure communication between the chamber 4i. between the end of the hub l8 and the bearing cap 29. and a point of lower pressure, preferably that of the pumping channel i2 in the region ofits inlet. This is conveniently effected by a passage 42 extending in the cap 29 from the chamber ii to the low pressure chamber 38. The diameter of the impeller hub l8 should be adjusted so that all of the axial force tendingto move the impeller it toward the left is not counterbalanced because it is desirable that a relatively small resultant axial force be provided to maintain the sealing and closes a central open- 1 chambers 35 arid 38 about the cylindrical portion of the hub it between the inner end of bearing 28 and the wall 32 and the maintenance of a diflerence of pressure in these chambers will provide a resultant force urging the impeller toward the chamber having the lower fluid pressure. The pressure in the pumping channel l2 increases from an intermediate value in the regionof its inlet 41 to a maximum value in the region of its outlet II, which pressure change creates a generally upwardly acting resultant force on the impeller it. Such force is only partly counteracted' by a similar resultant radial force acting generally downwardly on the first stage impeller it so that additional counterbalancing is preferable. Such additional downward counterbalancing force is herein obtained by having the chamber II in communication through hole 31 with the impeller hub region so that it has a surfaces of the seal bearing surface 21 and the impeller ii in contact.

In Fig. 1 is shown a portion of a tubular housing 43 that encloses the outwardly extending portion of the shaft IS. The housing 43 is welded to the portion 22 of the end cover 2i and is provided at said patent. In Fig. 2, 44 indicates the main inlet to the first stage channel ii, 45 indicates the outlet from the first stage channel which is connected by a pipe 48 (partly broken away) to the inlet 41 of the high pressure stage channel i2, and 48 indicates the final outlet from the high pressure stage channel l2.

It will be seen that the provision of the opposed nicate through passage 38 with the front region of pumping channel l2 which provides a .lower fiuid pressure therein so that a downwardly acting resultant balancing force is provided.

The pressure acting on the left side of impeller II is substantially that of the hub region of the first stage impellenil and such pressure is slightly less than the discharge pressure of the first stage pumping channel. It is also considerably less than the hub pressure acting to urge the impeller I! to the left. The inlet pressure of the second stage pumping channel is only slightly higher than the hub pressure of the first stage and is, according to the invention, applied to the right side of the hub l8. The transverse area of the hub I8 is proportioned to the pressure difference so that the axial forces acting on the imp'eller ii are balanced to the degree desired. It is found preferable, especially in a two-stage pump, that the axial force be not entirely balanced in order that a small resultant force will urge the impeller ll toward the left to maintain contact at the seal surface 21 so that the sealing action is maintained without excessive friction.

In a single stage pump the arrangement for the single pumping channel and impeller may be similar to that of the second stage illustrated herein. In such case the interstage seal would be replaced by a thrust hearing but the means for balancing radial and axial forces would be similar to that herein described, although preferably the totalar'ea and/or the ratio of the areas of the impeller hub exposed in the balancing '

chambers

35 and 36 would be adjusted and corpurpose of illustration, that the pressure in chamber 35 is 20 pounds per square inch and that in chamber 36 is 10 pounds per square inch, the net downward force will be 10 pounds; If now the length of hub exposed in the chambers is increased so that 2 square inches is exposed in each chamber, the ratio of areas is still 1 but the net downward force is increased to 20 pounds. The ratio of the exposed areas can be charmed a limited amount by shiftingthe partition 34 away from the diametral position. A downward shift of the partition 34 will increase the area exposed in chamber 35 and decrease the area exposed in chamber 36 so that the ratio could be 1.25 to 1 for example to increase the net downward force accordingly. The pressure ratio can also be selected within limits by choosing the point where the passage portion 38" connects into the pumping channel l2. However the location of the passage portion 38" close to the inlet as shown provides the largest differential of pressure, thus permitting the use of the least total exposed area in the

chambers

35 and 36 to provide the desired net balancing force.

Although a preferred embodiment of the invention in a two stage pump has been described in detail, it is contemplated that modifications of the construction may be made and that some features may be employed without others without departing from the spirit and scope of the invention. For example, in certain instances either the radial balancing means or the axial force compensating means may be employed alone without the other.

What is claimed is:

1. In a rotary pump having a casing with an annular pumping channel, a rotary impeller operating in said pumping channel, and a drive shaft for said impeller, the pumping action causing an increasing fluid pressure in said channel from the inlet to the outlet thereof, which pressure increase produces a net radial force acting on said impeller in a certain direction; a radial bearing in said casing for the inboard end of said chambers being substantially on opposite sides and extending peripherally about said cylindrical surface for a portion only of the circumference, a fluid passage connecting one of said chambers to a lower pressure region of said pumping chan-' nel, and a passage connecting the other of said chambers to a region of higher fluid pressure in .the casing adjacent said impeller, the areas of said surface exposed in the chambers and the relation of such areas being correlated with the pressures in the chambers to provide a resultant radial force substantially balancing said net radial force acting on the impeller.

4. In a rotary pump having a casing with an laterally extending hub portion, and a passage shaft; and means for balancing said radial force comprising a cylindrical surface rotatable with said shaft, chambers in said casing about said cylindrical surface, said chambers being substantially on opposite sides and extending peripherally about said cylindrical surface for a portion only of the circumference, a fluid passage connecting one of said chambers to a lower pressure region of said pumping channel, and a passage connecting the other of said chambers to a region of higher fluid pressure in the casing adjacent said impeller, the areas of said surface exposed in the chambers and the relation of such areas being correlated with the pressures in the chambers to provide a resultant radial force substantially balancing said net radial force acting on the impeller.

2. A rotary pump according to claim 1 in which said fluid passage connecting one of said chambers to said pumping channel enters said pumping channel at its inlet portion.

3. In a rotary pump having a casing with an annular pumping channel, a rotary impeller operating in said pumping channel, said impeller having a laterally extending hub portion, the pumping action causing an increasing fluid pressure in said channel from the inlet to the outlet thereof, which pressure increase produces I. net

radial force acting on said impeller in a certain direction; a radial bearing in said casing in which said hub portion is Journalled; and means for balancing said radial force comprising a cylindrical surface on said hub portion, chambers in v said casing about said cylindrical surface, saidconnecting said-chamber with a lower pressure region of said pumping channel.

5. A rotary pump accordingv to claim 4 in which said pump is a multi-stage .pump and said thrust bearing seal is mounted in a partition portion of the casing between said impeller and a lower pressure stage.

6. In a rotary pump having a casing with an annular pumping channel, 'a rotary impeller operating in said pumping channel, said impeller having a laterallyextending hub portion, the pumping action causing an increasing fluid pressure in said channel from the inlet to the outlet thereof, which pressure increase produces a net radial force acting on said impeller in a certain direction; a radial bearing in said casing in which said hub portion is journalled; means for balancing said radial force comprising a cylindrical surface an said hub portion, chambers in said casing about said cylindrical surface, said chambers being substantially on opposite sides and extending peripherally about said cylindrical surface for a portion only of the circumference, a fluid passage connecting one of said chambers to a lower pressure region of said pumping channel, and a passage connecting the other of said chambers to a region of higher fluid pressure in the casing ad- Jacent said impeller, the areas of said surface exposed in the chambers and the relation of such areas being correlated with the pressures in the chambers to provide a resultant radial force substantially balancing said net radial force acting on the impeller; a combined thrust bearing and seal mounted in said casing cooperating with the impeller side opposite said sleeve'bearing; a chamber enclosing the end of said laterally extending hub portion; and a. passage between said last-mentioned chamber and said passage connecting to. the lower pressure region of said pumping channel.

GEORGE H. ZENNER.

No references cited.-