DETAILED ACTION
Notice of Pre-AIA or AIA Status
This action is in response to the claims set filed 12/10/2024 and Applicant's election of Group I filed 03/06/2026 following the Requirement for Election over Lack of Unity of 12/22/2025. Claims 1-11 are currently pending with claim 11 withdrawn from consideration as being party to a non-elected Group.
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Election/Restrictions
Applicant’s election without traverse of Group I (claims 1-10) in the reply filed on 03/04/2026 is acknowledged. Claims 12-20 are withdrawn from further consideration pursuant to 37 CFR 1.142(b) as being drawn to a nonelected Invention, there being no allowable generic or linking claim.
Specification
The title of the invention is not descriptive. A new title is required that is clearly indicative of the invention to which the claims are directed.
The following title is suggested: “MULTI-STAGE PUMP APPARATUS WITH THRUST BALANCE MECHANISMS”.
Claim Objections
Claims 1 and 3 are objected to because of the following informalities:
Claim 1 (at line 20 on page), “a suction-side impeller located upstream” should likely read “a suction-side impeller of the plurality of impellers located upstream”.
Claim 3 (at line 1 on page), “an upstream impeller located between” should likely read “an upstream impeller of the plurality of impellers located between”.
Appropriate correction is required.
Claim Interpretation
The following is a quotation of 35 U.S.C. 112(f):
(f) Element in Claim for a Combination. – An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.
The following is a quotation of pre-AIA 35 U.S.C. 112, sixth paragraph:
An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.
The claims in this application are given their broadest reasonable interpretation using the plain meaning of the claim language in light of the specification as it would be understood by one of ordinary skill in the art. The broadest reasonable interpretation of a claim element (also commonly referred to as a claim limitation) is limited by the description in the specification when 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, is invoked.
As explained in MPEP § 2181, subsection I, claim limitations that meet the following three-prong test will be interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph:
(A) the claim limitation uses the term “means” or “step” or a term used as a substitute for “means” that is a generic placeholder (also called a nonce term or a non-structural term having no specific structural meaning) for performing the claimed function;
(B) the term “means” or “step” or the generic placeholder is modified by functional language, typically, but not always linked by the transition word “for” (e.g., “means for”) or another linking word or phrase, such as “configured to” or “so that”; and
(C) the term “means” or “step” or the generic placeholder is not modified by sufficient structure, material, or acts for performing the claimed function.
Use of the word “means” (or “step”) in a claim with functional language creates a rebuttable presumption that the claim limitation is to be treated in accordance with 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph. The presumption that the claim limitation is interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, is rebutted when the claim limitation recites sufficient structure, material, or acts to entirely perform the recited function.
Absence of the word “means” (or “step”) in a claim creates a rebuttable presumption that the claim limitation is not to be treated in accordance with 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph. The presumption that the claim limitation is not interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, is rebutted when the claim limitation recites function without reciting sufficient structure, material or acts to entirely perform the recited function.
Claim limitations in this application that use the word “means” (or “step”) are being interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, except as otherwise indicated in an Office action. Conversely, claim limitations in this application that do not use the word “means” (or “step”) are not being interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, except as otherwise indicated in an Office action.
This application includes one or more claim limitations that do not use the word “means,” but are nonetheless being interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, because the claim limitation(s) uses a generic placeholder that is coupled with functional language without reciting sufficient structure to perform the recited function and the generic placeholder is not preceded by a structural modifier. Such claim limitation(s) is/are:
“a first thrust balance mechanism” in claim 1. “mechanism” being the generic placeholder; “thrust balancing” and “a first thrust balance mechanism and a second thrust balance mechanism configured to cancel weight of a rotational structure including the rotation shaft and the plurality of impellers and an axial thrust acting on the plurality of impellers”; insufficient structural language present in the claim for this limitation.
The corresponding structure provided in the instant disclosure can be found in paragraphs 31, 36-44, 75-104, 106, 112 and 121 as well as instant figures 1-3, 9-15 and 17.
Based upon the collection of the corresponding structure in the areas referenced above, the general corresponding structure for the various embodiments of the “first thrust balance mechanism” includes: a first wall structure 26, a first low-pressure chamber 23, a first high-pressure chamber 25, and a first partition 30; and equivalents thereof.
Because this/these claim limitation(s) is/are being interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, it/they is/are being interpreted to cover the corresponding structure described in the specification as performing the claimed function, and equivalents thereof.
If applicant does not intend to have this/these limitation(s) interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, applicant may: (1) amend the claim limitation(s) to avoid it/them being interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph (e.g., by reciting sufficient structure to perform the claimed function); or (2) present a sufficient showing that the claim limitation(s) recite(s) sufficient structure to perform the claimed function so as to avoid it/them being interpreted under 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph.
Claim Rejections - 35 USC § 112
The following is a quotation of 35 U.S.C. 112(b):
(b) CONCLUSION.—The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention.
The following is a quotation of 35 U.S.C. 112 (pre-AIA ), second paragraph:
The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.
Claims 9 and 10 are rejected under 35 U.S.C. 112(b) or 35 U.S.C. 112 (pre-AIA ), second paragraph, as being indefinite for failing to particularly point out and distinctly claim the subject matter which the inventor or a joint inventor (or for applications subject to pre-AIA 35 U.S.C. 112, the applicant), regards as the invention.
Claim 9 recites the limitation "the first partition". There is insufficient antecedent basis for this limitation in the claim.
Claim 10 recites the limitation "the first partition". There is insufficient antecedent basis for this limitation in the claim.
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
Claim(s) 1 and 6-10 is/are rejected under 35 U.S.C. 103 as being unpatentable over JP2001248586A, herein referenced as Okubo, in view of JP2007016750A (first cited in the Office Action of 12/22/2025), herein referenced as Matsumura.
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Figure 6 of Okubo
Regarding Claim 1, Okubo discloses a pump apparatus for pressurizing liquid hydrogen, comprising:
a rotation shaft (shaft 30 fig. 6);
a plurality of impellers fixed to the rotation shaft (see plurality of impellers 36 attached to shaft 30 in fig. 6);
a bearing (see bearings 1 and 4 in fig. 6) configured to rotatably support the rotation shaft (30 fig. 6);
a pump casing (casing 31 fig. 6) in which the plurality of impellers (impellers 36 fig. 6) are disposed; and
a second thrust balance mechanism (see fig. 2 or alternatively fig. 8) configured to cancel weight of a rotational structure including the rotation shaft and the plurality of impellers (see shaft and impellers 36 fig. 6) and an axial thrust acting on the plurality of impellers (impellers 36 fig. 6),
wherein the second thrust balance mechanism includes:
a wall structure (see wall structure defined by discharge casing 31b, balancing bushes 8 and 9 and lid-shaped member 5 in fig. 2; alternatively, see discharge casing 31b, first balance bush 45, second balance bush 52, and rear stuffing box 43 fig. 8) having a low-pressure chamber (see low-pressure chamber 17 in fig. 2 or alternatively balance chamber 55 with pressure P3 in fig. 8) and a high-pressure chamber formed therein (see high-pressure chamber 16 in fig. 2 or alternatively volume chamber 46 with pressure P2 in fig. 8; “The pressure in the balance chamber 55 is lower (P3) than the pressure in the volume chamber 46 (P2)” pr. 9); and
a partition (including at least the disc portion 6b, which forms part of the separation of chamber 17 from chamber 16 in fig. 2 or alternatively, see disc portion 44b which separates chamber 55 from chamber 46 in fig. 8) located in the wall structure (shown in both fig. 2 and fig. 8) and located between the low-pressure chamber and the high-pressure chamber (shown in fig. 2 and fig. 8),
the pump apparatus further comprises:
an intermediate communication line (see holes 7 in fig. 2; alternatively, see first flow path 48 in fig. 8) providing fluid communication between the high-pressure chamber (16 fig. 2; Alternatively, 46 fig. 8) and a discharge side of an intermediate-stage impeller or a final-stage impeller (see discharge port 33 connected to final stage impeller 36 in fig. 2, “high-pressure chamber 16 is connected to the discharge port 33 inside the discharge casing 31b via the multiple through holes 7” pr. 28; Alternatively, see discharge port 33 connected to final stage impeller 36 in fig. 8, “One end of this first flow path 48 is connected to the discharge port 33 in the discharge casing 31b, and the other end is connected to the volume chamber 46” pr. 5) of the plurality of impellers; and
a return line (see 56 in figs. 2, 6 and 8) providing fluid communication between the low-pressure chamber (see 17 in fig. 2; Alternatively, 55 in fig. 8; both shown to communicate with 56 in their respective figures) and a discharge side of a suction-side impeller (see suction-side impeller, i.e. first stage impeller, 36 where the other end of 56 is provided in fig. 6; with reference fig. 6, “Alternatively, instead of providing the orifice 20, the same effect and benefits can be obtained by connecting the balance pipe 56 to the first-stage discharge side (see the dashed line in the figure)” pr. 50) located upstream of the intermediate-stage impeller or the final-stage impeller (first stage impeller 36 shown to be upstream of final stage impeller 36 in fig. 6).
However, Okubo fails to anticipate a first thrust balance mechanism.
Okubo and Matsumura are analogous art since they both relate to the field of endeavor of pump devices.
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Figure 1 of Matsumura
Matsumura teaches a first thrust balance mechanism (see balance piston mechanism 30 in figs. 1, 3 and 6) in addition to a second thrust balance mechanism (see thrust balance mechanism 19 in figs. 1-3). Matsumura further teaches “by installing a balance mechanism (balance piston mechanism 30) below the pump, the load can be easily balanced and the axial thrust at the time of starting the pump can be reduced” in pr. 17; which address the problem that “for a certain period of time immediately after startup, pump discharge pressure does not build up at the rear surface of the final stage impeller, and therefore the thrust balance mechanism 19, which utilizes the static pressure at the rear surface of the final stage impeller, cannot fully demonstrate its function” in pr. 16.
Therefore, it would have been obvious before the effective filing date of invention to one of ordinary skill in the art to have modified Okubo to further include the balance piston mechanism 30 disclosed by Matsumura to obtain the benefit of ‘reducing the axial thrust at the time of starting the pump’ as taught by Matsumura.
Regarding Claim 6, the combination of Okubo and Matsumura comprises the pump apparatus according to claim 1, wherein the wall structure has an inner circumferential surface parallel to an axial direction of the rotation shaft (see inner circumferential surface of second balance bush 52, which is part of discharge casing 31b, at channel 54 that extends axially in fig. 8 of Okubo; “second balance bush 52 is fixed to the discharge casing 31b by bolts 53” pr. 6 of Okubo), the partition (disc portion 44b fig. 8 of Okubo) has an outer circumferential surface parallel to the axial direction of the rotation shaft (outer circumferential surface of disc portion 44b at channel 54 is shown to extend axially in fig. 8 of Okubo), and the entire outer circumferential surface of the partition is surrounded by the inner circumferential surface of the wall structure with a gap formed therebetween (the entire outer circumferential surface of the disc portion 44b is shown to be surrounded by the inner circumferential surface of bush 52, part of discharge casing 31b, with a channel/gap 54 formed therebetween in fig. 8 of Okubo).
Regarding Claim 7, the combination of Okubo and Matsumura comprises the pump apparatus according to claim 1, wherein the second thrust balance mechanism further includes a balance chamber (see second liquid chamber 13 fig. 2 of Okubo) located between the low-pressure chamber and the high-pressure chamber (13 shown to be between low pressure chamber 17 and high pressure chamber 16 in fig. 2 of Okubo), a variable gap is formed between the partition and the wall structure (see axial gap a2 between disc portion 6b of balance disc 6 and second balance bush 9 in fig. 2 of Okubo; “ first and second balance bushes 8 and 9 are fixed to the discharge casing 31b” pr. 27 of Okubo), and a magnitude of the variable gap changes according to an axial position of the rotation shaft (“when the impeller thrust increases, the entire main shaft 30, including the balance disc 6, is displaced toward the suction side (left direction in Figure 2), causing the axial gap a1 to decrease and the axial gap a2 to increase” pr. 32 of Okubo).
Regarding Claim 8, the combination of Okubo and Matsumura comprises the pump apparatus according to claim 1, wherein [the second thrust balance mechanism is] disposed at a discharge side of the plurality of impellers (shown to be provided at the discharge side of the impellers 36 in figs 2, 6 and 8 of Okubo). Matsumura, as used to modify Okubo, presents the first thrust balance mechanism on the suction side instead (see figs. 1 and 3 of Matsumura).
However, the combination of Okubo and Matsumura fails to explicitly disclose that the first thrust balance mechanism [is also] disposed at a discharge side of the plurality of impellers.
The prior art combination reads onto the claim except with regard to the position of the first thrust balance mechanism, the instant invention having the first thrust balance mechanism disposed at a discharge side of the plurality of impellers (as opposed to a suction side of the plurality of impellers); the instant disclosure does not provide an unexpected result nor assign any particular benefit/criticality for this arrangement. Further, it has been held that shifting the position of a component which would not have modified the operation of the device would not be patentably distinct. Therefore, it would have been an obvious matter of rearrangement of parts to one of ordinary skill in the art in the modification of Okubo in view of Matsumura, to had provided the balance piston mechanism of Matsumura on the discharge side of the pump when modifying Okubo such that the both the first and second thrust balance mechanisms are provided at a discharge side of the plurality of impellers. This would not have modified the operation of the pump device since the first thrust balance mechanism in the combination would similarly provide a thrust balancing means but just on an opposite end of the shaft. See MPEP 2144.04 VI. C. “Rearrangement of Parts” for more details.
Regarding Claim 9, the combination of Okubo and Matsumura comprises the pump apparatus according to claim 1, wherein the first thrust balance mechanism includes:
a first wall structure (see casing 31 in fig. 6 of Matsumura, as used to modify Okubo above) having a first low-pressure chamber (low pressure chamber 36b fig. 6 of Matsumura), a first balance chamber (low pressure chamber 36a fig. 6 of Matsumura), and a first high-pressure chamber (high pressure chamber 35a fig. 6 of Matsumura) formed therein; and
the first partition (see bushing 34a which is attached to and inside casing 31 in fig. 6 of Matsumura, as used to modify Okubo) located in the first wall structure and between the first low-pressure chamber (low pressure chamber 36b fig. 6 of Matsumura) and the first balance chamber (low pressure chamber 36a fig. 6 of Matsumura),
wherein a variable gap is formed between the first partition and the rotational structure (an axial gap between the bushing 34a (which is fixed to the casing 31) and the balance piston 33b (which is fixed to the shaft 12 and greater rotational structure) in fig. 6 of Matsumura, as used to modify Okubo, this axial gap would change with movement of shaft 12 relative to casing 31) including the rotation shaft and the plurality of impellers, and a magnitude of the variable gap changes according to an axial position of the rotation shaft (the magnitude of the axial gap between bushing 34a, fixed to casing 31, and the balance piston 33b, fixed to shaft 12, would change with the movement of shaft 12 relative to casing 31 in fig. 6 of Matsumura, as used to modify Okubo).
Regarding Claim 10, the combination of Okubo and Matsumura comprises the pump apparatus according to claim 1, wherein the first thrust balance mechanism (thrust balance mechanism 30 fig. 3 of Matsumura, as used to modify Okubo above) includes:
a first wall structure having a first low-pressure chamber and a first high-pressure chamber formed therein (see casing 31 and lid 32, which together form a wall structure, low pressure chamber 36 and high pressure chamber 35 in fig. 1 of Matsumura, as used to modify Okubo); and
the first partition located in the first wall structure and between the first low-pressure chamber and the first high-pressure chamber (see balance piston 33 which forms a partition between the low pressure chamber 36 and high pressure chamber 35 in fig. 1 of Matsumura, used to modify Okubo),
wherein a radial gap is formed between an outer circumferential surface of the first partition and an inner circumferential surface of the first wall structure, and a magnitude of the radial gap does not change regardless of an axial position of the rotation shaft (see radial gap between the axially aligned balance piston 33 fixed to the shaft and the axially aligned balance bush 34 fixed to the casing side in fig. 1 of Matsumura, used to modify Okubo, this gap would not change from movement of the shaft due to the vertical/axial alignment of 33 and 34 shown in the figure).
Claim(s) 2 is/are rejected under 35 U.S.C. 103 as being unpatentable over the combination of Okubo and Matsumura, as applied to claim 1 above, and further in view of WO2018173769A1, herein referenced as Hosoda.
Regarding Claim 2, the combination of Okubo and Matsumura comprises the pump apparatus according to claim 1, but fails to teach it further comprising a check valve attached to the return line to allow the liquid hydrogen to flow only from the low-pressure chamber to the suction-side impeller.
Hosoda is analogous art since it relates to the field of endeavor of pump assemblies.
Hosoda teaches of a check valve attached to the return line (see check valve 60 attached to balance piping 18 in fig. 11) to allow the liquid hydrogen to flow only from the low-pressure chamber to the suction-side impeller (piping 18 shown to only allow one-way flow, such as for a liquid, to the discharge of the first stage impeller in fig. 11). Hosoda further teaches that “focusing on the flow of liquid through the balance pipe 18, the check valve 60 prevents the liquid from flowing from the suction side of the multi-stage pump through the balance pipe 18 to the balance chamber 16. As a result, only a thrust force in the opposite direction to the suction side is applied to the balance disc 15, thus preventing contact between the balance disc 15 and the balance sheet 12” in pr. 42.
Therefore, it would have been obvious before the effective filing date of invention to one of ordinary skill in the art to have modified the return line in the combination of Okubo and Matsumura (see 56 in fig. 6 of Okubo) with a check valve as disclosed by Hosoda to obtain the benefit of ‘preventing liquid from flowing from the suction side of the pump through the pipe and to the chamber, thus only applying a thrust force opposite to the suction side which prevents contact between components’ as taught by Hosoda.
Allowable Subject Matter
Claims 3-5 would be allowable if rewritten to overcome the claim objections set forth in this Office action and to include all of the limitations of the base claim and any intervening claims.
The following is a statement of reasons for the indication of allowable subject matter:
Regarding Claim 3, no prior art was found which anticipated or rendered obvious the claimed invention. Specifically, “an upstream communication line that provides fluid communication between the high-pressure chamber and a discharge side of an upstream impeller located between the intermediate-stage impeller or the final-stage impeller and the suction-side impeller; and a check valve attached to the upstream communication line to allow the liquid hydrogen to flow only from the upstream impeller to the high-pressure chamber” in context of all preceding limitations; including the interpretations under 35 USC § 112(f). While references were found which disclosed of a communication line that connects a chamber with a discharge of a first stage impeller or intermediate stage impeller (e.g. WO2016152892A1), they failed to present of two communication lines connected to a single high pressure chamber which are then connected at outlets of different impeller stages. Matsumura (JP2007016750A) cited above discloses of a thrust balance means where the high pressure chamber is separated into two different high pressure chambers, each with their own communication line which would be coupled the respective chamber to the pump casing. However, it still fails to present two communication lines connected to a high pressure chamber which are then connected at outlets of different impeller stages. As such, claim 3 is deemed to contain allowable subject matter.
Regarding Claim 4 (and its dependent claim 5), no prior art was found which anticipated or rendered obvious the claimed invention. Specifically, “wherein the first thrust balance mechanism is disposed at a discharge side of the plurality of impellers, and the second thrust balance mechanism is disposed at a suction side of the plurality of impellers” in context of all preceding limitations; including interpretations under 35 USC § 112(f). The closest prior art found was Matsumura (JP2007016750A), with particular reference to fig. 3, which discloses of a pump apparatus with a first thrust balance mechanism provided at a discharge side of the plurality of impellers and a second thrust balance mechanism provided at a suction side of the plurality of impellers and the second thrust balance mechanism being coupled with a first pipe and a second pipe. However, Matsumura fails to disclose of the “an intermediate communication line providing fluid communication between the high-pressure chamber and a discharge side of an intermediate-stage impeller or a final-stage impeller of the plurality of impellers; and a return line providing fluid communication between the low-pressure chamber and a discharge side of a suction-side impeller located upstream of the intermediate-stage impeller or the final-stage impeller” and instead presents an arrangement where the piping 40 connected to the low pressure chamber is coupled with a higher pressure and downstream location (“piping 40 connects the low-pressure chamber 36 of the balance piston mechanism 30 to the middle or near the outlet of the final stage outlet-side deceleration structure of the pump” in pr. 25) than the piping 37 that is connected to the high pressure chamber 35 which is coupled to a more upstream section of the pump apparatus. This being opposite from what the invention of claim 4 requires for the thrust balance mechanism provided at the suction side of the impellers. Regard the combination of Okubo and Matsumura utilized above, it would have been non-obvious to have modified this combination to comprise the structure required by claim 4 since the thrust balance mechanism of Okubo which discloses the structure required by claim 1, is incompatible with being merely rearranged to be at the suction side of the impellers given that its structure is constructed specific to its location at the discharge side of the impellers as the outlet of the final stage impeller is fluidly coupled to thrust balance mechanism adjacent there. As such, claim 4 is deemed to contain allowable subject matter.
Conclusion
The prior art made of record and not relied upon is considered pertinent to applicant's disclosure.
US 10704559 and US 11542947 – discloses a liquid pressurizing apparatus including a submerged multistage pump with a thrust balancing means provided at a discharge side of the pump, the means comprising two fluidly connected chambers which are each connected to a communication line which connects with the outer casing of the pump or a discharge of an impeller.
GB884115A – discloses of a centrifugal pump with a thrust balancing means provided at a discharge side of the pump, the means having a high pressure chamber that is connected to a discharge of an intermediate stage impeller by a first pipe and a lower pressure chamber that is connected to the pump inlet by a balance pipe, the first pipe having a value which is controlled based upon reading provided by a flow meter on the balance pipe.
US 4725196 – discloses a centrifugal compressor for gas with a thrust balancing piston device and includes at least a pair of chambers on each side of the rotor shaft.
EP3808984A1 – discloses a multi-stage pump which has two thrust balancing means provided at opposite sides of the impeller assembly, providing a balance drum at both ends of the pump shaft improves the rotor dynamics.
US 9938983 discloses a multi-stage compressor with a thrust balancing apparatus, the compressor also including an abutment system at a suction side of the compressor to restrict axial movement of the shaft.
US 5676528 – discusses differences between a single impeller pump and a dual impeller pump
US 2009/0004032 – discloses a structure with similarities to the first thrust balance mechanism of the instant invention.
US 7530781 – discloses a multistage pump with a plurality of communication lines, the lines being provided to communication the outlets of the impellers with hydrostatic bearings.
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/W.L.F./Examiner, Art Unit 3745
/COURTNEY D HEINLE/Supervisory Patent Examiner, Art Unit 3745
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