Variable breadth impeller that provides a specific shutoff head

In accordance with the present invention, an improved variable breadth imler for use in a variable capacity centrifugal pump and a method for adapting a variable capacity centrifugal pump to produce a specific predetermined shutoff head are provided. The variable breadth impeller is a two piece unit comprising an impeller element having a plurality of radially extending impeller vanes thereon and an axially movable shroud having a plurality of radially extending grooves therein for receiving the impeller vanes in a meshing relationship. The movable shroud further includes a plurality of axially extending grooves in its outer peripheral surface which act as a supplemental pumping means between minimum flow rate condition and shutoff condition. The operation of the improved variable breadth impeller results in a specific predetermined pressure head being attained and maintained at pump shutoff operating condition.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
The present invention relates generally to variable breadth centrifugal 
pumps (also referred to as variable capacity centrifugal pumps) and, more 
particularly, to providing an improved shrouded impeller constructed and 
arranged to provide a specific pressure head at pump shutoff operating 
condition. 
2. Brief Description of Related Art 
Standard (fixed geometry) centrifugal pumps are designed to operate at peak 
efficiency at a specific pressure head and flow rate. In a standard 
centrifugal pump, such as for example, a Navy Standard Fire Pump, the 
volume of water within the pump flow passages, i.e., the fluid passages 
between adjacent impeller vanes, is fixed by the area defined by adjacent 
impeller vanes, the impeller wall, and the opposing wall of the pump 
casing. At a constant drive shaft speed (constant impeller speed), as the 
demand on a standard centrifugal pump decreases the flow rate decreases 
causing a corresponding increase in the pressure head. In certain pump 
applications, drive shaft speed, and thus impeller speed, may be varied to 
account for reduced loads. However, pump efficiency decreases with 
decreasing impeller speed. 
Firemain systems aboard surface ships often include multiple centrifugal 
pumps connected in parallel, with one or more of the pumps run continually 
to maintain a specific system pressure and to ensure quick response in the 
event of an emergency. A typical Navy ship firemain system includes six 
Navy Standard Fire Pumps, standard centrifugal pumps each capable of 
producing a constant flow rate of 1000 gallons per minute at a pressure of 
150 pounds per square inch. The continuous demand on the firemain system, 
however, is generally for a flow rate much lower than the design flow rate 
of the individual pumps. Firemain loads can be less than 25 percent of the 
design flow rate of the individual pumps, resulting in firemain pressures 
that are much greater than the design pressures of the pumps. 
Increasing firemain system pressure reduces pump efficiency and 
reliability. Increased pumping pressure results in higher water velocities 
which, in turn, may produce leaks, increase system noise, and cause 
corrosion and erosion damage to connected equipment. On naval vehicles 
powered by gas turbine engines, varying pump shaft speed is not an option. 
Consequently, centrifugal pumps used on such naval vehicles are run at a 
constant impeller speed. When pump demand drops below the pump's design 
flow rate, the result is pressures that are much greater than the design 
pressures of the pumps. Thus, a need exists for centrifugal pumps which 
are capable of varying flow rates at a constant pressure and constant 
impeller speed. Such variable capacity pumps may, therefore, be employed 
in multiple centrifugal pump systems to efficiently and quietly vary flow 
and pressure characteristics to match varying system demands. 
Variable capacity centrifugal pumps (VCCP) have been designed by the U.S. 
Navy for use as the firemain system's lead pump maintaining constant 
system pressure. Variable capacity centrifugal pumps are described, for 
example, by U.S. Pat. Nos. 4,828,454 and 4,417,849, both assigned to the 
U.S. Navy. A typical approach for providing a centrifugal pump with 
variable capacity is to vary the width of the impeller flow passages by 
incorporating axially adjustable impeller sections. 
In U.S. Pat. No. 4,417,849, the variable capacity centrifugal pump 
arrangement includes two intermeshing impeller sections mounted to a 
common pump shaft such that one of the impeller sections is axially 
movable relative to the other impeller section. By axially adjusting the 
relative position of the impeller sections, the width of the impeller flow 
passage is varied to increase or decrease flow rate in response to system 
requirements. U.S. Pat. No. 4,828,454 describes a variable capacity 
centrifugal pump wherein the flow rate (capacity) is controlled by a 
shroud movably attached to the impeller drive shaft. The axially movable 
shroud has grooves for receiving individual impeller vanes. By axially 
adjusting the the relative position of the impeller and shroud, the width 
of the impeller flow passage is varied to increase or decrease flow rate 
in response to system requirements. 
During the low demand periods typical for Navy firemain systems, only the 
variable capacity centrifugal pump (VCCP) is needed to satisfy demand. The 
VCCP maintains a system pressure of 150 pounds per square inch over a flow 
range of approximately 250 to 1000 gallons per minute. During intermittent 
operations requiring additional capacity, such as during deck wash down, 
pumping of bilges, or in emergency situations, one or more of the stock 
centrifugal pumps is brought on line to satisfy the increased demand. 
During periods of increased demand, the stock pumps operate at their 
design point (1000 gallons per minute at a head of 150 pounds per square 
inch for Navy Standard Fire Pumps) with the VCCP adjusting its flow rate 
to provide the balance of the flow demanded while maintaining a head of 
150 pounds per square inch. When the increased demand subsides (e.g., dick 
wash down hoses are turned off), the flow rate will decrease and, ideally, 
the stock pump(s) will be taken off line and the VCCP will adjust its flow 
rate to satisfy the reduced demand. 
However, it is often the case that, as demand subsides, the stock pump 
continues to operate resulting in increased system pressure. As long as 
the VCCP can adjust its flow characteristics to match the increased system 
pressure, the VCCP and the stock pump share the load. As required flow 
rate decreases, pump head increases, until a maximum head is reached at 
shutoff, i.e., zero flow for a standard centrifugal pump. If the VCCP has 
a lower value of shutoff head than the stock pump then at some point along 
the head-capacity curve the head of the VCCP will fall below the head of 
the stock pump. At this point, the stock pump will begin to provide all 
the flow demanded by the system. As the VCCP continues to operate, undue 
heating of the fluid within the VCCP will occur ultimately resulting in 
failure of the VCCP. Thus, in multiple pump systems, there exists a need 
for a VCCP capable of being adapted to a specific shutoff head that 
matches the shutoff head of the stock pumps in the system. 
The pumps disclosed in U.S. Pat. Nos. 4,828,454 and 4,417,849 were intended 
to meet operational requirements for Navy variable capacity centrifugal 
pumps. The pumps were designed to provide constant discharge pressure over 
a wide operating range, typically on the order of 250 to 1000 gallons per 
minute. However, an additional requirement for Navy variable capacity 
centrifugal pumps includes a constantly rising head-capacity curve such 
that the shutoff head of the variable capacity centrifugal pump matches 
the shutoff head of a Navy Stock Fire Pump. Present variable capacity 
centrifugal pump designs do not provide the capability of adapting to and 
matching the shutoff head of a specific stock pump and, therefore, do not 
meet the full operational requirements for Navy 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an improved variable breadth 
impeller unit for use in a variable capacity centrifugal pump and a method 
for adapting a variable capacity centrifugal pump to produce a specific 
predetermined shutoff head are provided. The variable breadth impeller of 
the present invention is a two piece unit comprising an impeller element 
having a plurality of radially extending impeller vanes thereon and an 
axially movable shroud having a plurality of radially extending grooves 
therein for receiving the impeller vanes in a meshing relationship. The 
movable shroud further includes a plurality of axially extending grooves 
in its outer peripheral surface which act as a supplemental pumping means 
between minimum flow rate condition and shutoff condition. The operation 
of the improved variable breadth impeller results in a specific 
predetermined pressure head being attained and maintained at pump shutoff 
operating condition. 
More specifically the variable breadth impeller unit of the present 
invention comprises an impeller element adapted to be rotationally mounted 
within a variable capacity centrifugal pump, the impeller element having a 
plurality of radially extending impeller vanes projecting axially 
therefrom and defining flow passages therebetween, and a substantially 
solid annular movable shroud adapted to be rotationally mounted coaxially 
with said impeller element. The movable shroud is adapted for continuous 
axial movement between a fully open position defining a constant pressure 
maximum flow rate operating condition and a fully closed position defining 
a constant pressure minimum flow rate operating condition whereby the 
volume of said flow passages is varied. The movable shroud has first and 
second surfaces disposed axially from one another in a plane substantially 
orthogonal to the axis of rotation of said impeller element. The first 
surface of the movable shroud has a plurality of grooves formed therein 
for receiving the vanes of the impeller element in a meshing relationship. 
The movable shroud further includes a third surface orthogonally disposed 
between said first and second surfaces and defining the outer radial 
perimeter of the movable shroud. The outer peripheral third surface of the 
movable shroud has a plurality of recessed grooves formed therein 
extending axially over a portion of the third surface between the first 
and second surfaces. The recessed grooves act as a supplemental pumping 
means for energizing the fluid within the variable capacity centrifugal 
pump during operation between the constant pressure minimum flow rate 
condition and the shutoff condition of the variable capacity centrifugal 
pump whereby below a specific flow rate a constantly rising head-capacity 
curve and a specific shutoff head are achieved. 
The method for adapting a variable capacity centrifugal pump to produce a 
specific predetermined shutoff head comprises the steps of: rotatably 
mounting an impeller element within a variable capacity centrifugal pump, 
said impeller element having a plurality of radially extending impeller 
vanes projecting axially therefrom and defining flow passages 
therebetween; rotatably mounting a substantially solid annular movable 
shroud in coaxial alignment with said impeller element, said movable 
shroud having at least three surfaces including first and second surfaces 
disposed axially from one another in a plane substantially orthogonal to 
the axis of rotation of said impeller element and a third surface 
orthogonally disposed between said first and second surfaces and defining 
an outer radial perimeter of said movable shroud; providing said first 
surface of said movable shroud with a plurality of grooves formed for 
receiving said vanes of said impeller element in a meshing relationship; 
adapting said movable shroud for continuous axial movement between a fully 
open position defining a constant pressure maximum flow rate operating 
condition and a fully closed position defining a constant presure minimum 
flow rate operating condition whereby the volume of said flow passages is 
varied; and providing said third surface of said movable shroud with a 
plurality of recessed grooves extending axially over a portion of said 
third surface between said first and second surfaces wherein said recessed 
grooves act as a supplemental pumping means for increasing the fluid 
pressure head within the variable capacity centrifugal pump during 
operation between the constant pressure minimum flow rate condition and 
the shutoff condition of the variable capacity centrifugal pump whereby 
below a specific flow rate a constantly rising head-capacity curve and a 
specific shutoff head are achieved. 
OBJECTS OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved variable breadth impeller for a variable capacity centrifugal 
pump that is easily adaptable to and capable of matching the shutoff head 
of an adjoining stock pump. 
It is a further object of the present invention to provide a variable 
breadth impeller for a variable capacity centrifugal pump that will meet 
the full operational requirements of a Navy variable capacity centrifugal 
pump 
It is still a further object of the present invention to provide a variable 
breadth impeller for a variable capacity centrifugal pump that is 
relatively inexpensive to manufacture and is inherently reliable due to 
simplicity of design. 
Other objects and advantages of the present invention will become apparent 
to those skilled in the art upon a reading of the following detailed 
description taken in conjunction with the drawings and the claims 
supported thereby.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1 through 4, any typical variable capacity 
centrifugal pump, generally shown as item 10, may incorporate the variable 
breadth impeller unit in accordance with the present invention. A typical 
variable capacity pump includes pump casing 12 with casing axial inlet 14 
and casing radial outlet 16. Rotating impeller element 20, mounted, by 
conventional means, to rotating pump drive shaft 21, has a plurality of 
impeller vanes 22 projecting axially therefrom. Pump shaft 21 may be 
journalled in bearings and caused to be rotated by a prime mover such as, 
for example, an electric motor or, in the case of a typical naval vehicle, 
a gas turbine. Impeller element 20 may be of a hollow conical shape with 
impeller axial inlet 24 at its forward extending portion 26 and impeller 
radial outlet 28 at its outer radially extending portions. Axial inlet 24 
and radial outlet 28 are internally connected by a plurality of impeller 
vanes 22. Impeller flow passages 30, located between adjacent impeller 
vanes 22, provide flow passage means for channelling fluid entering 
impeller element 20 through axial inlet 24 and exiting impeller element 20 
through radial outlet 28. 
During the operation of a standard centrifugal pump, fluid is introduced 
into the casing axial inlet 14, is channeled through impeller axial inlet 
24 and along impeller flow passages 30 by the action of rotating impeller 
element 20, is output through impeller radial outlet 28 into casing 12 
which defines the radial output surrounding the tips of impeller vanes 22, 
and is collected, at an operating pressure, in toroidal collector 32. A 
standard centrifugal pump is designed to operate at peak efficiency at a 
specific head and flow rate. 
In a standard centrifugal pump, such as for example, a Navy Standard Fire 
Pump, the width of flow passages 30 are fixed by the distance between 
impeller element 20 and the opposing wall of casing 12. At a constant pump 
shaft/impeller speed, as the demand on the pump decreases, the flow rate 
decreases and the head increases correspondingly. In certain pump 
application shaft speed may be varied to account for reduced load, 
however, pump efficiency decreases with decreasing impeller speed. On 
naval vehicles powered by gas turbine engines, varying pump shaft speed is 
not an option. Thus, centrifugal pumps used on such naval vehicles are run 
at a constant impeller speed. Consequently, a need exists for a 
centrifugal pump which is capable of varying flow rates at a constant 
pressure and constant impeller speed. 
In order to convert a standard (fixed geometry) centrifugal pump into a 
variable capacity centrifugal pump, impeller element 20 is fitted with an 
axially movable shroud 33. Movable shroud 33 is generally annular shaped 
and mounted coaxially with impeller element 20 around the forwardly 
extending portion 26 of impeller element 20. Movable shroud 33 is caused 
to rotate with pump drive shaft 21 by torque transmitted to movable shroud 
33 via impeller element 20. Impeller element 20 and movable shroud 33 are 
telescopingly related. Movable shroud 33 is a substantially solid ring 
like member with female grooves 34 on a first surface 36, which faces 
opposing impeller element 20, for receiving impeller vanes 22 and for 
forming a fluid tight seal with impeller vanes 22 and impeller flow 
passages 30 of impeller element 20. 
Rear impeller wear ring 40 and rear casing wear ring 41 are disposed about 
a rearwardly extending portion of impeller element 20, between impeller 
element 20 and casing 12, in order to seal and maintain fluid discharge 
pressure in toroidal collector 32. Impeller wear ring 40 is fixedly 
attached to impeller element 20 and casing wear ring 41 is fixedly 
attached to casing 12 and coaxial with and surrounding impeller wear ring 
40. Alternatively, other standard sealing means may be employed. 
Forward impeller wear ring 42 and forward casing wear ring 43 are disposed 
about forwardly extending portion 26 of impeller element 20, between 
impeller element 20 and casing 12, in order to seal and maintain fluid 
back pressure to a second surface 38 of movable shroud 33. Impeller wear 
ring 42 is fixedly attached to impeller element 20 and casing wear ring 43 
is fixedly attached to casing 12 and coaxial with and surrounding impeller 
wear ring 42. Impeller wear ring 42 is stepped on its outer diameter to 
slidingly engage movable shroud 33 and is threaded on its inner diameter 
to threadedly engage threads provided on the outer peripheral surface of 
the forward extending portion 26 of impeller element 20, thereby forming a 
shroud retaining means for retaining movable shroud 33 on impeller 20. 
As shown in FIG. 2, impeller wear ring 42 has a first outer diameter 44 and 
a second outer diameter 45 smaller than first outer diameter 44 thus 
forming step 46. First outer diameter 44 rotates in a close relationship 
with casing wear ring 43. Second outer diameter 45 slidingly engages 
inwardly facing surface 47 of movable shroud 33. Thus, step 46 and second 
outer diameter 45 of impeller wear ring 42 form a shroud retaining means 
for retaining movable shroud 33 on impeller element 20. 
During operation of variable capacity centrifugal pump 10, the width of 
flow passages 30, and hence of the flow capacity of the pump, are varied 
by means of axially movable shroud 33. Axially movable shroud 33 is 
adapted for continuous axial movement between a fully open position 
defining a constant pressure maximum flow rate operating condition and a 
fully closed position defining a constant pressure minimum flow rate 
operating condition whereby the volume of flow passages 30 is varied. To 
change the width of impeller flow passages 30, movable shroud 33 moves 
axially relative to axially fixed impeller element 20. As shown in FIG. 2, 
movable shroud 33 is inserted to the maximum depth of impeller flow 
passages 30 for minimum impeller flow passage width (fully closed 
position). As shown in FIG. 1, for maximum impeller flow passage width, 
movable shroud 33 is withdrawn axially from impeller flow passages 30 
until forwardly extending portion 48 of movable shroud 33 abuts step 46 of 
impeller wear ring 42 (fully open position). 
Movable shroud wear ring 50 and center casing wear ring 51 are disposed 
about the outer periphery of movable shroud 33, between movable shroud 33 
and casing 12, in order to seal and maintain fluid back pressure to second 
surface 38 of movable shroud 33 thus forming a control cavity 52 between 
movable shroud wear ring 50 and center casing wear ring 51 and forward 
impeller wear ring 42 and forward casing wear ring 43. Movable shroud wear 
ring 50 is fixedly attached to movable shroud 33 and casing wear ring 51 
is fixedly attached to casing 12. Casing wear ring 51 is wide enough to 
remain coaxial with and surround movable shroud 33 for the entire axial 
travel of movable shroud 33. 
In operation, fluid discharged radially outward from impeller flow passages 
30, defined by impeller vanes 22 of impeller element 20 and mating movable 
shroud 33, is received in toroidal collector 32 under fluid discharge 
pressure. Toroidal collector 32 is in fluid communication with radial 
outlet 16 under fluid back pressure. Pipe means 53 puts fluid under back 
pressure within radial outlet 16 in communication with control cavity 52, 
thereby putting the fluid back pressure in fluid communication with second 
surface 38 of movable shroud 33. When demand on the pump decreases the 
fluid back pressure increases and the fluid pressure in control cavity 52 
increases forcing movable shroud 33 to close, i.e., move axially toward 
impeller element 20 thus decreasing the width of impeller flow passages 
30. When demand on the pump increases the fluid back pressure decreases 
and the fluid pressure in control cavity 52 decreases whereby movable 
shroud 33 opens, i.e., is biased toward a maximum impeller flow passage 
width, by means of biasing means 54, such as coil springs situated between 
movable shroud female grooves 34 and impeller vanes 22. Thus, by sensing 
the back pressure in control cavity 52, movable shroud 33 can be 
positioned to control the pump flow rate and head. 
When a variable capacity centrifugal pump (VCCP) operates in parallel with 
one or more standard centrifugal pumps, the pumps must share the load. In 
order for pumped fluid to flow through all active pumps in the system, the 
pumps must maintain equal pumping heads. As shown in FIG. 5, a standard 
centrifugal pump (curve 1) operates along a constantly rising 
head-capacity curve. A VCCP in accordance with the present invention 
(curve 3) operates at a constant head over a large flow rate range, e.g., 
between the constant pressure maximum flow rate condition (point A on 
curve 3) with shroud 33 fully open and the constant pressure minimum flow 
rate condition (point B on curve 3) with shroud 33 fully closed. However, 
below the constant pressure minimum flow rate condition, as demand on the 
system decrease the VCCP will experience a constantly increasing head 
(i.e., a constantly rising head-capacity curve) culminating at shutoff 
condition (point C on curve 3). 
As shown in FIG. 5, if the shutoff head of the standard VCCP (curve 2) does 
not match the shutoff head of the standard (fixed geometry) centrifugal 
pump (curve 1), there comes a point where the head of the VCCP falls below 
that of the standard centrifugal pump. At this point, the stock pump 
provides all the flow demanded by the system. As the VCCP continues to 
operate, undue heating of the fluid within the VCCP will occur ultimately 
resulting in failure of the VCCP. Thus, in multiple pump systems, there 
exists a need for a VCCP capable of being adapted to a specific shutoff 
head that matches the shutoff head of the stock pumps in the system. The 
variable breadth impeller and method in accordance with the present 
invention (curve 3) satisfies such a need. 
In accordance with the present invention, movable shroud 33 is provided 
with a supplemental pumping means for providing a specific predetermined 
shutoff head during shutoff operating condition of the variable capacity 
centrifugal pump. The supplemental pumping means is a means for energizing 
the fluid within the variable capacity centrifugal pump during operation 
between the constant pressure minimum flow rate condition and the shutoff 
condition of the variable capacity centrifugal pump (zero flow condition) 
whereby below a specific flow rate a constantly rising head-capacity curve 
culminating in a specific shutoff head is achieved. Movable shroud 33 
includes third surface 55 orthogonally disposed between first surface 36 
and second surfaces 38 and defining an outer radial perimeter of movable 
shroud 33. A constantly rising head-capacity curve below a specific flow 
rate culminating in a specific shutoff head is achieved by forming a 
plurality of recessed grooves 56 in third surface 55 of movable shroud 33. 
Recessed grooves 56 act as supplemental pumping means for increasing the 
flow head within the variable capacity centrifugal pump when movable 
shroud 33 is fully closed. During open shroud operation, however, recessed 
grooves 56 contribute only marginally to the pump head. 
Recessed grooves 56 extend axially over a portion of third surface 55 
between first surface 36 and second surfaces 38. The exact number, shape 
and location of recessed grooves 56 for a particular pump are fixed, 
however, the number, shape and location may be tailored to satisfy the 
specific operating conditions required for a particular pump application. 
As shown in FIG. 3, female grooves 34 on first surface 36 of the annular 
shaped movable shroud 33 may extend partially from near the central 
opening of movable shroud 33, which is adjacent to and coaxial with 
impeller axial inlet 24, to near the outer periphery of movable shroud 33 
such that third surface 55 of movable shroud 33 is a continuous unbroken 
surface. In such a case, recessed grooves 56 may be located at any point 
along third surface 56 of movable shroud 33. Alternatively, as shown in 
FIG. 4, female grooves 34 may extend completely from adjacent axial inlet 
24 to the outer periphery of movable shroud 33 such that third surface 55 
of movable shroud 33 is a discontinuous surface having gaps at the outer 
radial ends of female grooves 34 in first surface 36. In such a case, 
recessed grooves 56 formed in third surface 55 of movable shroud 33 are 
located between the gaps at the outer radial ends of female grooves 34. 
A number of specific embodiments of the present invention have been reduced 
to practice and applied to a Navy Variable Capacity Centrifugal Pump 
design. Navy Variable Capacity Centrifugal Pumps designs are intended for 
use in shipboard firemain systems connected in parallel to multiple Navy 
Standard Fire Pumps. In such a system, a Navy Variable Capacity 
Centrifugal Pump will provide a constant system pressure of 150 pounds per 
square inch over a flow range of approximately 250 to 1000 gallons per 
minute. Navy Standard Fire Pumps, standard centrifugal pumps capable of 
producing a constant flow rate of 1000 gallons per minute at a pressure of 
150 pounds per square inch, have a shutoff head of 182 pounds per square 
inch at 1.03 specific gravity. In contrast, as shown in FIG. 5, the 
shutoff head of a Navy Variable Capacity Centrifugal Pump design at the 
fully closed position of a variable breadth impeller without recessed 
perimeter grooves 56 (curve 2 of FIG. 5) is 174 pounds per square inch at 
1.03 specific gravity. As shown by curve 3 of FIG. 5, raising the shutoff 
head of a Navy Variable Capacity Centrifugal Pump design to match that of 
the Navy Standard Fire Pumps was accomplished by machining six sets of 
seven recessed grooves 56 around the perimeter (third surface 55) of 
movable shroud 33. As shown in FIG. 4, recessed grooves 56 were formed in 
third surface 55 of movable shroud 33 between the gaps at the outer radial 
ends of female grooves 34. 
The advantages of the present invention are numerous. 
Any typical variable capacity centrifugal pump may incorporate the variable 
breadth impeller that provides a specific shutoff head in accordance with 
the present invention. 
In multiple pump systems, there exists a need for a variable capacity 
centrifugal pump capable of being adapted to a specific shutoff head that 
matches the shutoff head of the stock pumps in the system. The variable 
breadth impeller and method in accordance with the present invention 
satisfies such a need. 
Accordingly, the present invention provides an improved variable breadth 
impeller for a variable capacity centrifugal pump that is easily adaptable 
to and capable of matching the shutoff head of an adjoining stock pump. 
Furthermore, the present invention provides a variable breadth impeller for 
a variable capacity centrifugal pump that will meet the full operational 
requirements of a Navy variable capacity centrifugal pump by incorporating 
a variable breadth impeller that is relatively inexpensive to manufacture 
and is inherently reliable due to simplicity of design. 
The present invention and many of its attendant advantages will be 
understood from the foregoing description and it will be apparent to those 
skilled in the art to which the invention relates that various 
modifications may be made in the form, construction and arrangement of the 
elements of the invention described herein without departing from the 
spirit and scope of the invention or sacrificing all of its material 
advantages. The forms of the present invention herein described are not 
intended to be limiting but are merely preferred or exemplary embodiments 
thereof.