Reversible centrifugal pump

A centrifugal pump capable of rotating in a normal direction while enabling a fluid to flow in a normal direction and rotating in a reverse direction while enabling the fluid to flow in the reverse direction without having its pumping efficiency dropping to a lower level in a reverse rotation mode than in a normal rotation mode. The pump includes two pump casings each having an inlet and outlet portion extending tangentially of each pump casing and connected together through an intermediate casing to provide a unitary structure in which the two pump casings are located concentrically in face-to-face relation, and an impeller having a helical blade extending axially from one zone in one pump casing into another zone in the other pump casing for rotation along the center axis of the pump. The impeller has a minimum outer diameter at the center of its center axis and includes portions each flaring in one of axial opposite directions in the form of a cone. The impeller has an outer periphery cooperating with an inner periphery of the intermediate casing to define a small clearance therebetween. The inlet and outlet portions of the two pump casings are arranged such that when the two pump casings alternately act as a suction casing at the time of normal rotation and reverse rotation, the influx direction of the fluid through the inlet and outlet portion of the pump casing acting as a suction casing is opposed to the direction of rotation of the impeller means.

BACKGROUND OF THE INVENTION 
This invention relates to centrifugal pumps, and more particularly it is 
concerned with a centrifugal pump of the type which is capable of rotating 
in a normal direction while enabling a fluid to flow in the normal 
direction and rotating in a reverse direction while enabling the fluid to 
flow in the reverse direction. 
Generally, when a centrifugal pump is let to rotate in the reverse 
direction, the fluid handled flows in the normal direction and the 
performance of the pump is greatly reduced. Thus, in centrifugal pumps of 
the prior art, no flow of fluid takes place in the reverse direction when 
the pump is rotating in the reverse direction. 
SUMMARY OF THE INVENTION 
This invention has as its object the provision of a novel centrifugal pump 
in which an impeller having a helical blade is used to eliminate the 
aforesaid characteristic of the centrifugal pump of the prior art obtained 
when the pump rotates in the reverse direction, whereby the centrifugal 
pump can rotate in the normal direction while enabling a fluid to flow in 
the normal direction and rotate in the reverse direction while enabling 
the fluid to flow in the reverse direction without having pumping 
efficiency dropping to a lower level in a reverse rotation mode than in a 
normal rotation mode. 
To accomplish the aforesaid object, the invention provides a centrifugal 
pump capable of rotating in a normal direction while enabling a fluid to 
flow in the normal direction and rotating in a reverse direction while 
enabling the fluid to flow in the reverse direction, comprising pump 
casing means including a first pump casing member and a second pump casing 
member each having an inlet and outlet portion entending tangentially of 
an outer periphery of each pump casing member, and an intermediate casing 
member interposed between the first pump casing member and second pump 
casing member and coupled thereto to provide a unitary structure in which 
the two pump casing members are located concentrically in faceto-face 
relation, and impeller means including a helical blade member extending 
axially from one zone in the first pump casing member into another zone in 
the second pump casing member for rotation along the center axis of the 
pump, said impeller means having a minimum outer diameter at the center of 
its center axis and including portions each flaring in one of axial 
opposite directions in the form of a cone, said impeller means having an 
outer periphery cooperating with an inner periphery of said intermediate 
casing member to define a small clearance therebetween, said inlet and 
outlet portions of said two pump casing members being arranged such that 
when said two pump casing members alternately act as a suction casing at 
the time of normal direction and reverse direction of the impeller, the 
influx direction of the fluid through the inlet and outlet portion of the 
pump casing acting as a suction casing is opposed to the direction of 
rotation of the impeller.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows in a vertical sectional view as seen in an axial direction of 
a centrifugal pump 10 comprising one embodiment of the invention which is 
capable of rotating in a normal direction while enabling a fluid to flow 
in the normal direction and rotating in a reverse direction while enabling 
the fluid to flow in the reverse direction. The centrifugal pump 10 
comprises a first pump casing member 14 and a second pump casing member 16 
locate concentrically in face-to-face relation and bolted together through 
an intermediate casing member 12. As can be clearly seen in FIGS. 2 and 3, 
the first pump casing member 14 and second pump casing member 16 may be 
each circular in cross section or a volute casing of ordinary centrifugal 
pumps. As can be clearly seen in FIG. 3, the two pump casings 14 and 16 
have nozzles or inlet and outlet portions 14a and 16a respectively which 
are located parallel to each other and extend tangentially from opposite 
sides of the outer peripheries of the two pump casing members 14 and 16 
disposed on opposite ends of the pump 10 and facing each other. A shaft 18 
connected to a motor extends through the two pump casing members 14 and 16 
along their center axis and has an impeller 20 secured thereto by a nut 
22. The shaft 18 may be a motor shaft. The impeller 20 includes a boss 20a 
having portions each flaring in one of axially opposite directions in the 
form of a cone, and a helical blade member 20b located on the peripheral 
surface of the boss 20a and extending axially from one zone in the first 
pump casing member 14 into another zone in the second pump casing member 
16. Thus, the impeller 20 is configured such that its outer diameter is 
minimized at its central portion and successively increases in going from 
its central portion in opposite axial directions in the form of a cone. 
The intermediate casing member 12 has an inner periphery which extends 
along and cooperates with an outer periphery of the helical blade 20b of 
the impeller 20 to define therebetween a small clearance. In the 
embodiment shown and described, the impeller 20 is formed as a unitary 
structure. Thus, to facilitate assembling, the intermediate casing member 
12 is split into two halves along a horizontal plane including its axis, 
and they are bolted together. The reference numeral 24 designates a 
mechanical seal. A first pump casing cover 26 is bolted to the first pump 
casing member 14, and a second pump casing cover 28 is bolted to the 
second pump casing member 16. 
In the embodiment shown and described, the impeller 20 is formed as a 
unitary structure. However, this is not restrictive, and the impeller 20 
may be split at its center in a plane perpendicular to its axis into two 
half impeller portions each having a conical shape which may be connected 
together at the center of the impeller 20. When the impeller 20 is formed 
in this way, the pump casing members 14 and 16 may be formed as one-piece 
structure with the intermediate casing member 12. However, when the pump 
casing members 14 and 16 are formed as one-piece structure, the structures 
formed at the outer peripheries on opposite axial ends of the pump casing 
members for the casing covers to be fitted therein should have a diameter 
which is slightly larger than the maximum outer diameter of the impeller. 
Operation of the centrifugal pump constructed as described hereinabove 
according to the invention will be described by referring to FIGS. 4-7. 
FIGS. 4 and 5 are schematic sectional views of the first pump casing member 
14 and second casing member 16 respectively obtained when the central 
transverse cross sections of the two pump casing members are viewed from 
the same direction in a normal rotation mode, and FIGS. 6 and 7 are views 
similar to FIGS. 4 and 5 respectively but obtained in a reverse rotation 
mode. These figures show the relation between the suction casing and 
discharge casing of the pump to which the first pump casing member 14 and 
second pump casing member 16 alternately become as the impeller switches 
its direction of rotation from normal to reverse and vice versa. That is, 
when the impeller 20 rotates in the normal direction, the first pump 
casing member 14 becomes a suction casing as shown in FIG. 4 and the 
direction of flow of the fluid through the inlet and outlet portion 14a is 
opposed to the direction of rotation of the impeller 20 at the pump inlet. 
The second pump casing member 16 becomes a discharge casing, as shown in 
FIG. 5, and the fluid under pressure is discharged through the inlet and 
outlet portion 16a. When the direction of rotation of the impeller 20 is 
reversed, the second pump casing member 16 becomes a suction casing, as 
shown in FIG. 7, and the direction of flow of the fluid through the inlet 
and outlet portion 16a is opposed to the direction of rotation of the 
impeller 20. The first pump casing member 14 becomes a discharge casing, 
as shown in FIG. 6, and the fluid under pressure is discharged through the 
inlet and outlet portion 14a. In the centrifugal pump according to the 
invention, it is an important feature that, regardless of whether the pump 
is rotating in a normal direction or in a reverse direction, the direction 
of flow of a fluid at the inlet port or suction port of the suction casing 
is opposed to the direction of rotation of the impeller. Experiments 
conducted on the operation of the centrifugal pump according to the 
invention have produced results which show that the pump has the total 
head H represented by a curve A shown in FIG. 8, both in a normal rotation 
mode and in a reverse rotation mode. 
A centrifugal pump having two inlet and outlet portions located on the same 
side of the two pump casing with respect to the axis of the pump will be 
described in comparison with the centrifugal pump according to the 
invention. FIGS. 9 and 10 show two pump casings 114 and 116 having inlet 
and outlet portions 114a and 116a respectively located on the same side, 
in which the pump casing 114 serves as a suction casing and the pump 
casing 116 as a discharge casing in a normal rotation mode. FIGS. 11 and 
12 are similar to FIGS. 9 and 10 respectively but show the pump casings in 
a reverse rotation mode, in which the pump casing 114 serves as a 
discharge casing and the pump casing 116 as a suction casing. It will be 
seen that, in FIG. 9 in which the pump casing 114 serves as a suction 
casing, the direction of flow of a fluid through the inlet and outlet 
portion 114a is opposed to the direction of rotation of an impeller 120 at 
the pump inlet. In FIG. 10 in which the pump casing 116 serves as a 
discharge casing, the fluid under pressure is discharged through the inlet 
and outlet portion 116a. The results of experiments conducted on this type 
of centrifugal pump are as follows. When the pump rotated in the normal 
direction in which the direction of flow of the fluid through the inlet 
and outlet portion of the suction casing was opposed to the direction of 
rotation of the impeller at the pump inlet, the pump had the head curve 
similar to the curve A obtained in the experiments on the centrifugal pump 
10 in which the inlet and outlet portions of the two pump casing members 
are located at sides opposed to each other with respect to the axis of the 
pump. When the direction of rotation of the impeller of the centrifugal 
pump having the arrangement of the pump casings shown in FIGS. 9, 10, 11 
and 12 was reversed, the fluid flowed through the inlet and outlet portion 
116a into the pump casing 116 serving as a suction casing as shown in FIG. 
12 in the same direction as the rotation of the impeller 120 and the fluid 
was discharged through the inlet and outlet portion 114a of the pump 
casing 114 serving as a discharge casing as shown in FIG. 11. In the 
reverse rotation mode, the pump had the head represented by a curve B 
shown in FIG. 8 which was reduced as compared with the head represented by 
the curve A. This is because the fluid flows into the suction casing 
through the inlet and outlet portion thereof in the same direction as the 
direction of rotation of the impeller at the pump inlet. 
The results of the experiments described hereinabove show that it is 
important that the inlet and outlet portions of the first pump casing 
member and the second pump casing member be located tangentially of the 
impeller in such a manner that when the two pump casing members 
alternately act as a suction casing at the time of normal rotation and 
reverse rotation of the impeller, the influx direction of the fluid 
through the inlet and outlet portion of the pump casing acting as a 
suction casing is opposed to the direction of rotation of the impeller. 
This arrangement of the inlet and outlet portions of the first and second 
pump casing members enables a centrifugal pump according to the invention 
to be obtained which is capable of rotating in a normal direction while 
enabling a fluid to flow in the normal direction and rotating in a reverse 
direction while enabling the fluid to flow in the reverse direction and 
which has the head of practical value both in the normal rotation mode and 
in the reverse rotation mode. 
The reason why it is important to let the fluid flow into the pump through 
the inlet and outlet portion of the suction casing in a direction opposed 
to the direction of rotation of the impeller will be described by 
referring to FIGS. 13 and 14. FIG. 13 is a diagram showing a vector of 
velocities obtained at the inlet of a centrifugal pump when a normal 
operation is performed. In the diagram shown in FIG. 13, U.sub.1, W.sub.1, 
C.sub.m1 .alpha. designate the inlet peripheral velocity of the impeller, 
the relative velocity of the fluid particles with respect to the impeller, 
meridional component of absolute velocity C.sub.1 of the fluid particles, 
and the inlet angle of the fluid, respectively. It is C.sub.m1 that 
decides the head of the pump. When a prerotation occurs in the vicinity of 
the pump inlet in this inlet velocity triangle, the inlet angle .alpha. 
changes to .alpha.' (see FIG. 14) and the meridional component of absolute 
velocity of the fluid particles C.sub.m1 is reduced to C.sub.m1'. As a 
result, the flow rate is greatly reduced. 
When a centrifugal pump capable of rotating in a normal direction while 
enabling a fluid to flow in the normal direction and rotating in a reverse 
direction while enabling the fluid to flow in the reverse direction is 
designed by connecting two pump casings in face-toface relation, each pump 
casing is required to perform the functions of suction and discharge. 
However, in an ordinary centrifual pump, the position of inlet and outlet 
portion of each casing is designed with a view to improving the discharge 
performance of the pump. Thus, when each casing of this design functions 
as a suction casing, a prerotation of an extremely great magnitude is 
produced, resulting in a marked reduction in pumping efficiency. To avoid 
this trouble, one only has to design the pump casings in such a manner 
that the influx direction of the fluid flow through each of the inlet and 
outlet portions of the pump casing members alternately acting as a suction 
casing at the time of normal rotation and reverse rotation is opposed to 
the direction of rotation of the impeller, as stated above. 
When provided with the aforesaid feature according to the invention, a 
centrifugal pump can be made to rotate in a normal direction while 
allowing a fluid to flow in the normal direction and to rotate in a 
reverse direction while enabling the fluid to flow in the reverse 
direction without having its pumping efficiency dropping to a lower level 
in a reverse rotation mode than in a normal rotation mode.