Regenerative turbine having predetermined clearance relationship between channel ring and impeller

A regenerative turbine pump apparatus which includes a housing having an inlet and an outlet and an impeller mounted for rotation within the housing. The impeller has an outer diameter and a channel ring is disposed around the impeller. The channel ring has a first arcuate portion that has a first radius to provide a substantially uniform first clearance with respect to the outer diameter of the impeller and the first arcuate portion extends throughout a major part of the channel ring. The channel ring includes a second arcuate portion proximate to the inlet having a second clearance with respect to the outer diameter of the impeller that is greater than the first clearance.

BACKGROUND OF THE INVENTION 
The invention relates to regenerative turbine pumps which in some cases are 
also referred to as turbine pumps, periphery pumps, turbulence pumps, or 
friction pumps. The turbine pump name has been used because of the 
plurality of vanes, resembling those of a steam turbine, that are machined 
into the periphery of the impeller that is rotated at high speed. Two 
basic types are known. One type has inclined vanes on only one side of an 
impeller. The more commonly used type has radial vane impellers. While the 
invention will be described in terms of the latter type it will be 
understood by those skilled in the art that the invention has application 
to both forms. 
Regenerative turbine pumps are particularly suitable for air conditioning, 
refrigeration, and heating applications. Regenerative turbine pumps will 
move a relatively low flow of fluid at a relatively high head. More 
specifically, such pumps have a relatively steep head capacity curve. The 
regenerative turbine pump has higher efficiencies at low flows than a 
centrifugal pump. A regenerative turbine type pump typically will produce 
several times the pressure produced by a centrifugal pump having an 
impeller of equal diameter and operating at the same speed. 
Conventional regenerative turbine pumps utilize close running tolerances. 
More particularly, the impeller vanes usually run at very close axial 
clearances within machined channel rings disposed within the pump housing 
to minimize recirculation losses. The channel ring around each impeller 
provides a circular channel around the vane area of the impeller from the 
inlet to the outlet. It is known in the prior art to provide greater axial 
clearance between the vanes and the adjacent channel ring wall near the 
inlet of the pump than at parts of the channel ring. It is also known in 
the prior art to gradually decrease that axial clearance between the sides 
of the vanes and the side walls of the channel ring from a point near the 
inlet through an angular sector. 
In a single stage regenerative turbine pump the fluid enters the channel on 
both sides of the impeller adjacent to a first circumferential part of the 
impeller. The vanes carry the fluid within the channel for almost a full 
revolution. A blocker or splitter directs the fluid through an outlet. 
Some forms of regenerative turbine pumps may be multistage structures. Two 
stage regenerative turbine pumps direct a fluid from a first stage to a 
second stage. If the respective discharges are offset by 180 degrees the 
radial loads on the bearings are nearly balanced and shaft deflection is 
minimized. 
Pumps of this type having a top center line discharge are self venting and 
have the ability to handle vapors without vapor lock. This characteristic 
allows handling of boiling liquids and liquified gases at suction heads 
slightly over the vapor pressure. 
Regenerative turbine pumps have many advantages including even a 
characteristic of superior suction lift. More particularly, they are 
preferred for lifting liquids from lower levels and particularly for hot 
liquids and liquids that vaporize at normal temperatures. 
Although regenerative turbine pumps are desirable for superior suction lift 
there are still many applications where there is insufficient net positive 
suction head to operate conventional regenerative turbine pumps. Net 
positive suction head is the absolute pressure, above the vapor pressure 
of the liquid being pumped, at the pump suction flange. 
If the net positive suction head pressure available to the pump is 
insufficient, the pump will cavitate and serious operational difficulties 
may develop. These troubles can include reduction in capacity and 
efficiency, excessive vibration, reduced life of pump parts due to 
cavitation erosion, and damage to the pump from possible vapor lock and 
running dry. 
One way to solve the problem is to set up the pumping system so that the 
NPSH (net positive suction head pressure) available from the system is 
greater than the NPSH required by the pump. In some pump systems this has 
been achieved by an elevated inlet tank or other costly design 
considerations. For example, it may be necessary to lower the pump with 
respect to a supply tank by providing a pit in which the pump is disposed. 
For other installations multiple pumps in parallel or a discrete booster 
pump in series or large pipelines to decrease friction losses. Discrete 
rotating impellers have also been used in series with another impeller to 
overcome the pressure drop between the suction flange of the pump and the 
entrance to the impeller vanes. 
The change of the physical arrangement is often inconvenient, expensive or 
even impossible. Therefore, when a pump is selected for a particular 
application the NPSH requirement of the pump is an important 
characteristic. 
It is an object of the invention to provide a construction that will have a 
lower net positive suction head pressure requirement. 
It is an object of the invention to provide apparatus that will have a 
longer service life because of the elimination of operating problems such 
as cavitation. 
It is an object of the invention to provide apparatus which is inexpensive 
to manufacture. 
Still another object of the invention is to provide apparatus that will not 
increase the assembly time in any way. 
SUMMARY OF THE INVENTION 
It has now been found that these and other objects of the invention may be 
attained in a regenerative turbine pump apparatus which includes a housing 
having an inlet and an outlet and an impeller mounted for rotation within 
the housing. The impeller has an outer diameter. A channel ring is 
disposed around the impeller. The channel ring has a first arcuate portion 
that has a first radius to provide a substantially uniform first clearance 
with respect to the outer diameter of the impeller and the first arcuate 
portion extends throughout a major part of the channel ring. The channel 
ring includes a second arcuate portion proximate to the inlet having a 
second clearance with respect to the outer diameter of the impeller that 
is greater than the first clearance. 
In some forms of the invention the second clearance is greater nearer to 
the inlet than at parts thereof remote from the inlet. The second 
clearance may taper from the first clearance to a maximum at a point 
proximate to the inlet. 
The second arcuate portion may extend through an arc of up to 90 degrees 
and may have an arc shape having a radius greater than an arc defining the 
first arcuate portion. The second arcuate portion may have a center of 
curvature that is different from the center of curvature of the first 
arcuate portion.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1-8 there is shown a regenerative turbine pump 10. 
In FIG. 1 the view is taken in a direction parallel to the pump shaft 12, 
broken away. The pump 10 is shown in partial section in the region of the 
inlet 22 and outlet 24 of a pump housing 26. The direction of rotation of 
the impeller 14 is indicated by an arrow A. 
The inlet/outlet region of the pump 10 is shown in greater detail in FIG. 2 
that more clearly shows the details of the invention. The impeller 14 is 
disposed in a channel or channel ring 16 which is a part of the housing 
26. 
The impeller 14 has parallel sides 14A, 14B and includes a plurality of 
vanes 18 that are disposed on both sides of the impeller 14 as best seen 
in FIGS. 3-8. The vanes 18 are offset from one axial side of the impeller 
14 to the other as best seen in FIG. 8. The vanes are uniformly spaced 
within the channel ring 16. As best seen in FIGS. 3-7 the channel ring 16 
is machined into the housing 26 which is cast as two axial sections. The 
parting line 40 indicates the plane in which the two axial portions of the 
housing join together. Those skilled in the art will recognize that the 
channel ring 16 is partly in one axial section of the housing 26 and 
partly in another axial section of the housing 26. The sides of the vanes 
18 of the impeller 14 have increased side clearance with respect to the 
sides of the channel ring 16 in an arcuate portion near the inlet 22. This 
arcuate portion is approximately 45 degrees in extent as best seen in 
FIGS. 2 & 8. This axial clearance tapers from a maximum proximate to the 
inlet 22 to a uniform and smaller axial clearance at a location between 
section O-C and O-D shown in FIG. 2. The angular quadrant or arcuate 
portion of the channel ring 16 intermediate the section O-B and the outlet 
24 has a uniform internal radius. Accordingly, the tips 32 of the vanes 18 
in the angular sector between the section O-B and the outlet 24 have a 
uniform radial clearance. 
In the single stage regenerative turbine pump in accordance with one form 
of the invention the fluid enters through the inlet 22 and passes into the 
channel 16 on both sides of the impeller 14 adjacent to a first 
circumferential part of the impeller 14. The vanes 18 carry the fluid 
within the channel 16 for almost a full revolution of the impeller 14. A 
blocker or splitter 20 directs the fluid through an outlet 24. Ordinarily 
the splitter 20 is disposed much closer to the impeller 14 than the 
channel ring 16. This is necessary to separate the inlet 22 fluid stream 
from the outlet 24 fluid stream. 
The prior art channel ring 16 as best seen in FIGS. 2-5 has a wall defining 
the radial clearance between the channel ring 16 and the circumferential 
tips 32 of the vanes 18 indicated by the numeral 34. More specifically the 
line showing the prior art channel ring 16 contour is a dotted line. In 
this prior art construction the impeller 14 has vanes 18 that are disposed 
in a channel ring 16 that has a constant internal diameter (except at the 
location of the stripper 20 which must separate the high pressure region 
at the outlet 24 from the low pressure region 22 at the inlet). 
As best seen in FIGS. 2-6 the pump 10 in accordance with the invention 
provides an entrance region extending through an angular quadrant between 
the inlet 22 to the section O-B shown in FIG. 6. In the apparatus of the 
invention the channel ring 16 has a larger radial clearance between the 
tips 32 of the vanes 18 and the channel ring 16 in this angular quadrant. 
The entrance region of the channel ring 16, in accordance with the 
invention, gradually decreases throughout an angular quadrant of the 
channel ring 16 as best seen in FIGS. 2-6. In a preferred form of the 
invention, the inside diameter of the channel ring 16 is uniform except at 
the splitter 20 and the angular extent of the entrance region. This 
angular extent may be up to 90 degrees. 
The entrance region 36 is arcuate and has a radius that is somewhat larger 
than the existing channel internal surface radius and has a center that 
lies slightly above and to the left of the centerline O of the channel 16. 
The invention has been described with reference to its illustrated 
preferred embodiment. Persons skilled in the art of such devices may upon 
exposure to the teachings herein, conceive other variations. Such 
variations are deemed to be encompassed by the disclosure, the invention 
being delimited only by the following claims.