U.S. patent application number 13/658588 was filed with the patent office on 2013-10-31 for low flow-high pressure centrifugal pump.
The applicant listed for this patent is Frederic W. Buse. Invention is credited to Frederic W. Buse.
Application Number | 20130287558 13/658588 |
Document ID | / |
Family ID | 49477446 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130287558 |
Kind Code |
A1 |
Buse; Frederic W. |
October 31, 2013 |
LOW FLOW-HIGH PRESSURE CENTRIFUGAL PUMP
Abstract
Low flow centrifugal pump that develops more than 25 percent
greater pressure than equivalent standard type spiral impellers
with circular casings.
Inventors: |
Buse; Frederic W.;
(Allentown, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Buse; Frederic W. |
Allentown |
PA |
US |
|
|
Family ID: |
49477446 |
Appl. No.: |
13/658588 |
Filed: |
October 23, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61550640 |
Oct 24, 2011 |
|
|
|
Current U.S.
Class: |
415/203 ;
416/235 |
Current CPC
Class: |
F04D 5/002 20130101;
F04D 29/2255 20130101; F04D 1/02 20130101; F04D 1/06 20130101; F04D
29/2238 20130101 |
Class at
Publication: |
415/203 ;
416/235 |
International
Class: |
F04D 29/22 20060101
F04D029/22 |
Claims
1. A low flow centrifugal-regenerative pump having an impeller
disk, said impeller disk having radial grooves on the face of said
impeller disk and radial peripheral teeth on a peripheral edge of
said impeller disk to increase pressure of fluid exiting said pump
due to corkscrew circulation within a volute of said pump and a dam
to push said liquid into a discharge nozzle in said pump.
2. A low flow centrifugal-regenerative pump according to claim 1
wherein said dam is a replaceable cutwater to increase developed
pressure.
3. A low flow centrifugal-regenerative pump according to claim 2
wherein said replaceable cutwater Tater has a shape to provide
optimal increase in performance of said pump.
4. A low flow centrifugal-regenerative pump according to claim 1
having a single entrance impeller with passages communicating with
an entrance to said radial grooves to effect a double suction
impeller.
5. A pump impeller disk having radial grooves to reduce internal
flow which results in less internal heat build up at low fluid flow
through a pump fitted with said impeller.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit of the earlier
filing date of U.S. Provisional Application No. 61/550,640, filed
on Oct. 24, 2011, the contents of which are incorporated herein by
reference as if set forth in their entirety.
BACKGROUND OF THE INVENTION
[0002] There has been a market for very low flow centrifugal pumps
used on low viscosity liquids such as water, chemicals or
hydrocarbons, but these products have not been available.
[0003] The centrifugal pump basically consists of a rotating
impeller within a volute as shown in FIG. 1. The majority of the
volutes are designed like a logarithmic spiral as shown in FIG. 1a.
The shape of the impeller and volute depends on the combination of
desired flow, pressure and speed. In the industry of centrifugal
pumps, the combination of the three criteria in a specific equation
known throughout the industry is called specific speed (Ns). The
range of this dimensionless number is 500 to over 4000. Pumps with
Ns of 500 have a casing that has a narrow width and spiral shape
that for all intents and purpose is a circle. In contrast, a pump
with Ns of 4000, has a casing width that is relatively wide and the
spiral is similar to Nautilus shell as shown in FIG. 2. To obtain
this shaped casing, it is usually made from a casting. Within the
spiral, as the impeller rotates, 25% of the pumped liquid is
collected in the first 90 degrees of the spiral, 50% is collected
by 180 degrees, 75% at 270 degrees and 100% at the 360 degrees or
end of the spiral. Where the spiral ends, is called the throat.
This is where, in theory, 100% of the liquid goes into the
discharge nozzle. The bottom of the throat is called the cutwater.
This is also the beginning of the spiral, hence the name. The
casing of a 4000 Ns pump has the biggest spiral, but the least
circular leakage. At the other end of the range, a pump with 500 Ns
speed or less has so little spiral that the inside of the casing is
made circular as shown in FIG. 3. By making the volute circular,
the inside surface can be machined resulting in a smooth surface,
which increases the efficiency.
[0004] The intersection of the circular shape casing with the
tangential discharge hole has no defined cutwater, just a
tangential hole to the circle. This produces a lot of circular
leakage; resulting in low hydraulic efficiency. However, even with
the low efficiency there is still a market for a low flow pump.
[0005] Similarly, the impellers of a specific speed range change
shape with a change in number. A 4000 Ns impeller is relatively
wide and with a swooping profile from the inlet to the periphery;
while one with a 500 or less Ns is very narrow with the passage
ways almost radial to the shaft centerline (FIG. 4). Traditionally,
the impellers of 4000 Ns may have 7 to 8 spiral vanes that include
100 to 120 degrees of the circumferential profile. 500 or less Ns
have only 3 to 4 vanes with long spiral vanes that may encompass
270 degrees of the profile. In the design of a pump there are
hydraulic force that are produced that create hydraulic forces that
react on the support bearing of the shaft. These are axial forces
that are parallel to the shaft, radial forces that act
perpendicular to the shaft and coupling forces that acts as a
twisting torque on the end of the shaft.
[0006] The axial force can be the greatest force. To reduce it, a
designer may employ an enclosed impeller, which means that the
hydraulic vanes of the impeller are between two disks, called
shrouds. As the liquid exits the vane the hydraulic pressure goes
down the sides of the shrouds and counter acts the axial thrust one
either side, reducing the thrust. This is a good solution for pumps
that have Ns above 1000. Below that, the ratio of width to impeller
diameter, number of vanes and wrap around of the vanes makes it
very difficult to make a casting. Sometimes a two piece impeller
can be molded from a polymer and then attached together. The cost
of the molds, cleaning techniques, and quality of the attachment
cannot always justify the costs. Another option is to design the
impeller as an open impeller. This utilizes only one shroud, which
has an open thee so the cast or molded vanes are fully exposed.
Because there is only one shroud, a high portion of the developed
pressure of the vanes only is on back side of the impeller and
results in high axial thrust. Designers reduce the pressure acting
on the shroud by scalloping (cutting out material of the shroud).
This does results in negative features; mechanically it is
difficult to maintain the flatness of the impeller, it also weakens
the support of the vanes, hydraulically it reduces the efficiency
of the pump. The open face of the vanes is normally machined to
have a flat surface. This surface is matched to a flat
corresponding stationary surface. The clearance between the
rotating impeller and stationary surface is about 0.10''. When this
clearance is not maintained the hydraulic performance and
efficiency is reduced.
[0007] This whole process gas more difficult to produce when the Ns
is 500 or less.
BRIEF DESCRIPTION OF THE INVENTION
[0008] This present invention relates to pumps with a specific
speed of less than 500. A pump according to the invention has a
circular casing with replaceable cutwater with close clearance to
the periphery of the impeller that increases the developed
pressure. The inlet for the casing has a singular suction, with a
double suction impeller. The double suction impeller reduces axial
thrust. However, a singular suction casing is less expensive and
easier to install than a casing designed specifically for a double
suction impeller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will hereinafter be described in
conjunction with the appended drawing figures wherein like numerals
denote like elements.
[0010] FIG. 1 shows a volute and spiral vane impeller;
[0011] FIG. 1a shows the basic profile of a spiral volute;
[0012] FIG. 2 shows the profile and end shape of volutes for
various specific speeds;
[0013] FIG. 3 shows the profile of a circular volute;
[0014] FIG. 4 shows the change in impeller profile with change in
specific speed;
[0015] FIG. 5 are left side and front views of the double suction
impeller;
[0016] FIG. 6 is a composite view of the replaceable cutwater and
its various features;
[0017] FIG. 7 shows the assembly of the circular volute with a
replaceable cutwater and single inlet, double suction, radial slot
with recirculation slots impeller;
[0018] FIG. 8a shows an impeller with spiral vanes;
[0019] FIG. 8b shows an impeller using slots;
[0020] FIG. 9 is a photograph of a test set-up using an apparatus
according to the present invention
[0021] FIG. 10a and FIG. 10b are photographs respectively of the
back and the front surface an impeller according to the present
invention;
[0022] FIG. 11a and FIG. 11b are respective side views of the
replaceable cutwater according to the present invention; and
[0023] FIG. 11c is a top view of a replaceable cut water according
to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention pertains to pumps in the Ns range of
300 to 400, which is below previous limit of 500, requiring the
invention of a new type of volute, discharge nozzle, and
impeller.
[0025] A single end suction casing, overhung close coupled
centrifugal pump with an open impeller was obtained. The 1.25''
suction nozzle was reduced to 0.625'' to accommodate a garden hose.
The 1'' discharge was reduced to a 0.25'' tube. The axial position
of the tube in the nozzle could be adjusted.
[0026] An impeller was made from a disk that had a width to
diameter ratio of 0.052. It had four radial slots from the inlet
diameter to periphery machined on the front face and then 60
quarter inch deep radial slots put around the periphery. The
feature of radial slots to develop head is new, but usually there
is a thin membrane in the middle of the slot to guide the liquid
from both sides up to the middle of the volute. This is expensive
and is accomplished with a gear cutter. This is method of
increasing pressure is call regeneration. This developed a head a
little greater than the standard impeller with a flow 2 gpm. There
was a relatively large gap between the front and back of the disk
and the mating surfaces of the casing and casing cover, resulting
in internal slippage and leakage of the liquid. These surfaces were
built up with disks of polymer so the front and back clearances
were in the range of 0.020 to 0.040''. The developed pressure
increased. At this point the impeller was an open front with 60
slotted teeth. This was developing substantial axial thrust
resulting in the impeller rubbing the casing causing the motor to
trip out. Some balance holes were added in the disk, but there was
a significant drop in pressure. A new impeller of the same width
and diameter was made. This one had four radial holes drilled into
the body of the disk. These replace the four radial slots. This
made it a closed impeller and eliminated the axial thrust. The
small diameter- long holes are difficult to drill without breaking
out into the outer surface of the disk. In addition to the holes
the 60 slots were replace with 20 special shaped slots that looked
like the teeth of a circular saw. This is similar to U.S. Pat. No.
3,746,467 dated Jul. 17, 1973. The developed head was less than the
60 slots, but the flow doubled. A circumferential groove half the
width of the impeller was put in the middle of the teeth. The
groove was deep as the bottom of the teeth. The teeth now looked
somewhat like the teeth in the '467 patent. The pressure did not
increase. The groove was refilled with epoxy. The tube in the
discharge was pushed forward so it was 0.010'' from the impeller
periphery. The pressure increased. The end of the tube was cut on a
bias; this too resulted in an increase in head. The circular saw
teeth were filled back to look like radial teeth. The pressure
increased.
[0027] Since the radial holes are difficult to make, open radial
slots were selected but with a change. The front face of two
opposite holes were machined and then the impeller was turned over
and machined to open the other two opposing holes. These last two
terminated at the circumference of the back hub. Where they
terminated, axial holes were drilled into the suction inlet in the
front resulting in a double suction impeller with radial slots that
was basically axially balanced. It also put the mechanical seal
under suction pressure. The resulting pressure was a little less
than with the closed impeller. The flow was greater.
[0028] The difference between 20 degree spiral vanes and radial
vanes was tested. Four radial slots were filled in with an epoxy
resin and four spiral slots were machined into the impeller. The
spiral slots ran quieter but produced less pressure resulting in a
return to the radial slots. More radial slots were added which
increased the pressure. The number of teeth was doubled by
vertically band sawing the existing teeth. This resulted in a large
increase in pressure.
[0029] The resulting impeller is a suction double suction, double
sided open impeller with radial slots on the periphery as shown in
FIG. 5.
[0030] The casing also went through a number of changes and
additions. The tube in the discharge nozzle was replaced with a
replaceable cutwater that is set screwed into position. The
replaceable cutwater can be adjusted to maintain the close
clearance between it and the periphery of the impeller as shown in
FIG. 6. It is made of a material that resists erosion and
corrosion.
[0031] The side profile of the volute has dimensions and shape to
guide the liquid from the impeller to split to both sides of the
volute and guide it back into the impeller to regenerate the
pressure of the liquid as shown in FIG. 7.
[0032] The impeller according to the present invention has three by
features, namely:
[0033] a. Slots vs. vanes: Traditionally centrifugal impellers used
wide spaced a spiral shaped passage ways with thin vanes along or
within the impeller disk to develop pressure from the inlet to
periphery of the impeller as shown in FIG. 8. When used in an
enclosed impeller it is very difficult to produce. In an open
impeller, the thin vanes are can be cast, machined or molded. The
open space between the vanes results in a lot of internal slippage.
This pump uses radial slots instead of vanes. Therefore, there is
less internal slippage (FIG. 8b). Testing of this pump showed that
there was little performance difference between radial and spiral
grooves. The radial groove produced slightly higher pressure. The
pump seemed to be quieter with spiral grooves;
[0034] b. Double suction vs. single suction: The impeller has a
singular inlet that matches the casing inlet. There are radial
pumping slots on both sides of the impeller disk. The front slots
are directly connected to the periphery of the inlet. The back
slots terminate at the back hub of the impeller. There are axial
holes the same width as the slots adjacent to the hub that
communicate the back slots to the impeller inlet. This allows
liquid to be pumped up the back slots. The amount of liquid pumped
of the front are about equal, resulting in a minimum of residual
axial thrust.
[0035] c Radial grooves vs. spiral vanes: As the impeller rotates
it adds energy to the moving liquid. Some of the liquid is
re-circulated within the impeller passages. With the discharge
valve fully open most of the energy passes through the pump. As the
valve is closed to reduce flow, energy is trapped within the casing
and impeller. When the valve is fully or almost closed this energy
is changes to heat. The rise of temperature of the casing and
internal parts can result in catastrophic mechanical failure. An
impeller with only radial grooves rather than spiral vanes has much
less contained water and absorbed energy, resulting lower internal
heat build.
[0036] d. Dam vs. no cutwater: The placement of a dam (replaceable
cutwater in this design) in the volute passage where the tangential
discharge meets the circular volute increases the developed
pressure. This principal of a dam is employed in what is referred
to as a regenerative pump. These pumps have a circular volute. A
regenerative pump has tine teeth along the periphery of the
impeller. There may be from 40 to over 80 teeth. There is usually a
thin radial web between the teeth to act as a guide for the liquid
and a support between the teeth. The present invention does not
employ a web. In a regenerative pump the inlet and discharge
connections are usually adjacent (located at the same diameter) as
the teeth. A close fitting permanent dam separates the two
connections. The principal is that the liquid comes into the teeth
it is discharged radial into the volute, but is forced back into
other passing teeth. This cork screwing of the liquid in and out of
the teeth continuously increases the pressure of the liquid as it
goes around to the volute and exits out the discharge. These pumps
required dose side and dam clearances. The dam wears down from
erosion caused by the pressure break down from discharge to suction
ports. Since this pump has a circular volute with a dam
(replaceable cutwater), radial teeth without a radial web were
added to the periphery of the impeller. These teeth are fed by the
liquids coming from the radial grooves are both sides of the
impeller as shown in FIGS. 5 and 7.
[0037] The assembly of the impeller in the casing is shown in FIG.
7. It shows the single inlet in the casing, the liquid going into
both sides of the impeller, the radial teeth on the periphery and
the replaceable cutwater in the casing.
[0038] A pump according to the present invention was constructed
and tested as shown in FIG. 9. After all adjustments were made, the
increase in pressure was from 10 to 30 percent over a standard
design centrifugal impeller.
[0039] FIGS. 10a and 10b are photographs of the back and front
surfaces of an impeller according to the invention.
[0040] FIGS. 11a and 11b are side views and FIG. 11e is a top view
of a replaceable cut water according to the present invention.
[0041] While the principles of the invention have been described
above in connection with preferred embodiments, it is to be dearly
understood that this description is made only by way of example and
not as a limitation of the scope of the invention.
* * * * *