Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
DIAPHRAGM CONSTRUCTION FOR A MULTI-STAGE COMPRESSOR
Technical Field
The field of art to which the invention pertains
comprises the art of turbo machinery and component con-
struction therefor.Background of the Invention
In any manufactured product sold in competitive
markets, the cost of producing the produc-t es-tablishes
the base from which the manufacturer can profitably compete.
In complex structures such as in a multi-stage centrifugal
compressor, the cost of each individual component becomes
a significant factor contributing ultimately toward that
base. At the same time, details of construc-tion as well as
closely held tolerances on the various component confi~ura-
tions need to be adhered to in order to assure performancestandards of the equipment.
A component problem in a multi-s-tage centrifugal
compressor has been the construction of the stationary
diaphragm which serves between impellers to provide support
for the stationary elements such as the diffuser faces,
guide vanes, return bend, labyrinths, etc. Typically, each
semi~annular section of the diaphragm has been cast as a
single piece split at its horizontal center line which is
located with rabbet fits and secured via tie bolts. ~owever,
on small compressors incurring a flow path clearance on the
order of one-half inch or less, casting of the diaphragm
sections becomes impractical because of prohibitively costly
coring problems normally associated with a-ttempting to main-
tain such a minimal clearance. Consequently, it has become
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c~lstomary, particularly on small compressors having one half
inch or less Elow path clearance requirements, to avoid the
coring expense by construc-ting the diaphragm sections via
machining and brazing as a substitu-te for the otherwise less
costly casting. Despite recognizing the cost advantages of
casting, it has not been known heretofore how to effectively
exploit the use thereof under conditions oE close clearance
requirements.
The present invention resides in a multi-stage
barrel type centrifugal compressor for compressing fluid flow
including a vertically split housing defining a flow path
from an inlet to an outlet, a multi-stage impeller in the
flow path, and an annular stationary diaphragm encircling
the multi-stage impeller in axially contiguous portions at
each intermediate stage thereof for providing continuity
of the flow path between successive of the stages and comprised
of oppositely positioned confronting sections which between
at least one stage constrict the -transverse flow dimensions
at a selected location of the flow path to less than about
2~ one-half inch. An axially extending tie bolt means secures
the axially contiguous portions of the diaphragm. Each
annular portion of the diaphragm of the at least one stage
is supported by the tie bolt means independent of the housing
and is comprised of the confronting sections being joined
interfitted together in a rail fit at a location along the
flow path displaced from the constricted flow dimension with
at least the larger of the confronting sections being of a
cast metal composition.
By means of the invention, the low cost advantage
of diaphragm casting for a multi-stage centrifugal compressor
has been largely retained, even under conditions of close
dimensional clearances in the flow path. Where the prior
art constructions dictated substitution of the more expensive
coring and/or machine-brazing approaches in order to meet
dimensional requirements, it is possible by means hereof to
construct the diaphragm in a manner largely preser~ing the
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use of a casting without the need for -the more costly coring.
By fabricating the diaphraym in this manner, the
need for expensive coring in the constricted flow area is
ellminated while still enabling the bulkier of the components,
including -the vane section thereon, to be cas-t. The remain-
ing return bend section can -then be machined from plate and
assembled -thereto. The entire diaphragm when ultimately
assembled results in a significant reduc-tion in labor cost
on the order oE fifty percent as compared to similar purpose
constructions of the prior art, yet wi~hout adversely
affecting the critical dimensional tolerances sought to be
maintained.
It is therefore an object of the invention to
provide a novel cons-truction for the diaphragm component of a
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multi-stage centrifugal compressor.
It is a further object of the invention to effect
the foregoing object in a manner which results in
substantial cost reduction as compared to otherwise
similar purpose constructions utilized in -the prior
art for constricted flow area relationships.
Brief Description of the Drawings
. ... .
Fig. 1 is a longitudinal cross section of -the top half
of a multi-stage centrifugal compressor in accordance
herewith;
Fig. 2 is a fragmentary elevation of the diaphragm
hereof as seen substantially along the lines 2-2 of Fig. l;
Fig. 3 is an enlarged and exploded sectional elevation
of the diaphragm construction illustrated in Fig. l; and
Fig. 4 is a fragmentary sectional view taken sub-
stantially along the lines 4-4 of Fig. 3.
Referring now to the drawings, there is illustrated
in FigO 1 a centrifugal compressor generally comprising a
housing 10 defining a flow path extending from an inlet
12 communicating with a plurality of stages 14 in turn
leading to an outlet 16. Comprising s-tages 14 are a
plurality of spaced impellers 18 secured to a rotatable
shaft 15 and arranged in series flow communication with
each other with each stage discharging a hlgh velocity
gas at its periphery. Energy transmitted to the gas
creates a pressure rise as the flow velocity decreases
in the diffuser section 20 immediately downstream of the
impeller. From the diffuser, stationary guide vanes 22
turn the flow for proper entry into the succeeding impeller
18.
Betwee~ each impeller stage is a stationary diaphragm
here designated 24, 26, 28, 30 and 32, as will be described,
providing support for the stationary elements utilized
between impellers such as the diffuser faces, guide vanes,
return bend, labyrinths, etc. Associated with each
diaphragm in the flow path entering the succeeding vane 22
about bulb section 23 is a clearance 33, the dimension of
which is determinative of whether the specific diaphragm
construction can be all cast as in the prior art or
constructed in -the manner hereof~
As previously explained supra, a conventional all-
cast construction of -the diaphragm can be u~ilized where
clearance 33 to be encountered is on the order of one-half
inch or greater. For purposes of illustration in Fig. 1,
di.aphragms 24, 26, 28 and 32 are assumed -to have a clearance
33 thereat of greater -than one-half inch enabling them to be
:Eabricated all cast in the manner of the prior art. Typically,
these diaphragms are spli-t into semi-annular sections at
their horizontal center ]ine which are later located with
rabbet fits 34 and secured together via tie bolt 36.
Contrasting with those diaphragms, the clearance 33
i.mmediately preceding diaphragm 30 is assumed to be on the
order of one-half inch or less such that the customary cast
diaphragm construction of the remaining diaphragms become too
cost prohibitive to be practical. Instead, diaphragm 30
utilizes a construction in accordance with the invention as
will now be described with further reference to the remain:ing
figures.
As specifically shown in Figs. 3 and 4, each semi-
annular diaphragm construction thereof is comprised of return
bend section 38 formed machined from plate and defining a
horizontal split at center line 35 (Fig. 2). For joinder
therewith is a vane section 22 cast per se in a conventional
manner leaving the vanes freestanding on one side down to
diameter 40. secause of the side exposure any need to core
for effecting clearance 33 is eliminated while the clearance
at diameter 40 being much larger than clearance 33 can be
easily cored in a conventional manner. Joinder of vane
section 22 with return bend section 38 is by means of a
mutual. offset rail fit 42 at which the two are secured by screws
44 in order to render the installation permanent.
By the above description there is disclosed a novel
construction for the diaphragm component of a multi-stage
centrifugal compressor. The diaphragm is comprised of
semi-annular sections, each of which is in turn comprised
of a pair of separate sections that includes a cast vane
section 22 joined by split screws and a rail fit to a
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machined return bend section 380 By this means, close
flow clearance can be readily accommodated by more
economical casting of at least the major component of
the diaphragm as to eliminate need for the relatively
uneconomical brazing fabrication i.n the manner of the
prior art. Not only does this approach allow the vane
section to be mostly cast, but it additionally affords
incidental advantages such as allowing most of the flow
path between vanes to be open for inspection or for finish
grinding if necessary. ~oreover, the return bend section
can be of any configuration which connects the diaphragms
at the outside diameter that can even include portions of
the preceding or following return bends or parts thereof
or no return bend as in diaphragm 32 if desired. It
should be apparent therefore that the construction hereof
constitutes a significant advance in the art in solving
a long-standing problem with constructing such diaphragms
where minimum flow clearances have been encountered.
Since many changes could be made in the above construc-
tion and many apparently widely different embodiments of
this invention could be made without departing from the
scope thereof, it is intended that all matter contained
in the drawings and specification shall be interpreted
as illustrative and not in a limiting sense.
