U.S. patent application number 10/027422 was filed with the patent office on 2003-06-19 for partially preloaded pump diaphragms.
This patent application is currently assigned to Ingersoll-Rand Company. Invention is credited to Able, Stephen D., Distel, Gerald M., Headley, Thomas R..
Application Number | 20030110939 10/027422 |
Document ID | / |
Family ID | 21837647 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030110939 |
Kind Code |
A1 |
Able, Stephen D. ; et
al. |
June 19, 2003 |
Partially preloaded pump diaphragms
Abstract
A partially preloaded diaphragm having an outer attachment
portion defining a first plane (P) and disposed about an axis
substantially perpendicular to the first plane. An inner attachment
portion is disposed substantially perpendicular to the axis of the
outer attachment portion and defines a second plane (C). The inner
attachment portion is movable away from the outer attachment
portion into a fully extended pumping position defining a third
plane (F). The first plane and the second plane are spaced at a
distance to define a preload distance (PC) when the diaphragm is at
rest, and the first and third plane are spaced to define a pump
stroke distance (PF) when the diaphragm is fully extended. The
preload distance is from about 25 percent to about 85 percent of
the pump stroke distance.
Inventors: |
Able, Stephen D.; (Bryan,
OH) ; Distel, Gerald M.; (Bryan, OH) ;
Headley, Thomas R.; (Bryan, OH) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
3773 CORPORATE PARKWAY
SUITE 360
CENTER VALLEY
PA
18034-8217
US
|
Assignee: |
Ingersoll-Rand Company
Woodcliff Lake
NJ
|
Family ID: |
21837647 |
Appl. No.: |
10/027422 |
Filed: |
December 19, 2001 |
Current U.S.
Class: |
92/98R |
Current CPC
Class: |
F04B 43/0054
20130101 |
Class at
Publication: |
92/98.00R |
International
Class: |
F01B 019/00 |
Claims
Having described the invention, what is claimed is:
1. A partially preloaded diaphragm, comprising: an outer attachment
portion defining a first plane (P) and disposed about an axis
substantially perpendicular to said first plane, and an inner
attachment portion disposed substantially perpendicular to said
axis of said outer attachment portion and defining a second plane
(C), said inner attachment portion being movable away from said
outer attachment portion into a fully extended pumping position
defining a third plane (F), said first plane and said second plane
being spaced at a distance to define a preload distance (PC) when
said diaphragm is at rest, and said first and third plane being
spaced to define a pump stroke distance (PF) when said diaphragm is
fully extended, said preload distance being from about 25 percent
to about 85 percent of said pump stroke distance.
2. The partially preloaded diaphragm according to claim 1, wherein
said preload distance being from about 50 percent to about 75
percent of said pump stroke distance.
3. The partially preloaded diaphragm according to claim 2, wherein
said preload distance being about 50 percent of said pump stroke
distance.
4. The partially preloaded diaphragm according to claim 2, wherein
said preload distance being about 67 percent of said pump stroke
distance.
5. The partially preloaded diaphragm according to claim 1, wherein
said outer and inner attachment portions are adapted for attachment
to a pump and further comprise an annular working portion
connecting said outer and inner attachment portions.
6. The partially preloaded diaphragm according to claim 5, further
comprising a peripheral portion formed annularly between said inner
attachment portion and said annular working portion when said inner
attachment portion is moved into a fully extended pumping
position.
7. The partially preloaded diaphragm according to claim 1, wherein
said diaphragm comprises a thermoplastic elastomer.
8. The partially preloaded diaphragm according to claim 1, wherein
said diaphragm comprises a thermoplastic elastomer selected from
the group consisting of an EPDM rubber and polypropylene blend and
a thermoplastic urethane.
9. The partially preloaded diaphragm according to claim 1, wherein
said diaphragm comprises a thermoplastic elastomer selected from
the group consisting of SANTOPRENE, ESTANE, HYLENE, HYTREL,
GEOLAST, SARLINK elastomers, and combinations thereof.
10. The partially preloaded diaphragm according to claim 1, wherein
said diaphragm comprises a fluoropolymer.
11. The partially preloaded diaphragm according to claim 10,
wherein said fluoropolymer is polytetrafluoroethylene.
12. The partially preloaded diaphragm according to claim 1, wherein
said outer attachment portion comprises a bead.
13. The partially preloaded diaphragm according to claim 1, wherein
said outer attachment portion comprises a dovetailed portion.
14. The partially preloaded diaphragm according to claim 1, wherein
said outer attachment portion comprises a plurality of holes for
receiving fastening members.
Description
FIELD OF THE INVENTION
[0001] This invention relates to diaphragms for such uses as
air-operated or mechanically operated diaphragm pumps, brake
actuators or other diaphragm-operated devices in which a central
plate or plates is connected to or makes contact with the central
portion of the diaphragm.
DESCRIPTION OF THE PRIOR ART
[0002] Diaphragm pumps are widely used in pumping a wide variety of
materials including materials which are abrasive, have high
viscosity, or consist of slurries that might damage other pump
designs. Diaphragm pumps are often air driven which is advantageous
in pumping flammable liquids or in environments where electrically
driven equipment could otherwise be hazardous. Electrically or
otherwise mechanically driven diaphragm pump designs, however, are
also utilized.
[0003] The pump diaphragm is the critical driving member of the
diaphragm pump and is a relatively flexible membrane that has an
outer attachment portion that is clamped or otherwise held in a
stationary position against the pump housing. Such diaphragms also
include a centrally located portion and a working portion that
joins the inner attachment and outer attachment portions. The inner
attachment portion is clamped between a pair of clamping washers or
the like during operation of the pump. The working and inner
attachment portions of the diaphragm are displaced in a
reciprocating manner along an axis to drive liquid out of the
pump.
[0004] Pump diaphragms have traditionally been made of fabric
reinforced rubber. Shown in FIG. 3 is an example of a conventional
rubber diaphragm 9 shown having a dish shape with an inner
attachment portion 6, an outer attachment portion 2 which may be
dovetailed or beaded for retention in an associated pump housing,
and an innerconnecting flexure sidewall working portion 4. Fabric
reinforcement must be embedded in the body of these diaphragms to
achieve adequate flex fatigue life, which drives up the cost. If
the reinforcing fabric is not uniformly encased inside of the
rubber, however, premature diaphragm failure may still occur. In
certain applications the lack of chemical resistance presents
problems as well.
[0005] Due to the wide nature of the different materials these
pumps are used to move, a correspondingly wide variety of materials
are used in their construction. To a limited extent, plastic
materials with relatively stiff inner attachment portions and
thinner, more flexible sidewall portions have been used in some
diaphragm applications, for instance, as disclosed in U.S. Pat. No.
3,011,758 to McFarland, Jr. thermoplastic polyurethane diaphragms
have also been used as pump diaphragms. These polyurethane
diaphragms have been constructed with a generally curvilinear
flexure sidewall incorporating concentric ribs, terminating in an
outer beaded flange and radially inward bead for mounting to a
split piston plate.
[0006] In all cases the repetitive flexing of the diaphragm
eventually causes failure of the diaphragm. Failure of the
diaphragm may result in materials being pumped contaminating the
pump equipment. A diaphragm failure may also cause the release of
chemicals to an air stream that subsequently gets released into the
environment where it may result in further damage or injury.
Attempts have been made design the diaphragm to minimize these
operating stresses to improve the life of diaphragms. Such attempts
included varying the geometry of the diaphragms to minimize stress
on the working portion during operation of the pump.
[0007] Other materials that are stiffer than rubber have also been
incorporated into diaphragms for a number of reasons, among which
are their low cost and ease of manufacturing by injection molding.
One such group of stiffer materials are thermoplastic elastomers
(TPE's). SANTOPRENE TPE is an example of one type of TPE material
typically used in pump diaphragms and comprises a polypropylene
polymer and an ethylene propylene (EPDM) elastomer. Another group
of stiffer materials are fluoropolymer materials. TEFLON
polytetrafluoroethylene (PTFE) is an example of one type of
fluoropolymer typically used in pump diaphragms.
[0008] In the case of pump diaphragms manufactured using these
stiffer materials such as thermoplastic elastomer and fluoropolymer
materials, however, relatively early fatigue failures are known to
occur in the flexible working portions of these diaphragms.
Attempts at varying geometry to increase flexure life in diaphragms
of such thermoplastic and fluoropolymer diaphragms have been made.
For example, shown in U.S. Pat. No. 4,864,918 to Martin is a
diaphragm for pumps or the like of a dish-shaped body of
non-reinforced thermoplastic elastomer. The diaphragms have a
curvilinear flexure sidewall portion of substantially less
thickness than the inner attachment and outer attachment portions
to which it connects. Shown in U.S. Pat. No. 5,349,896 to Delaney,
III et al. is a flexible pump diaphragm of PTFE having a number of
ribs or troughs located radially across its flexure portion. In
such stiffer diaphragms, however, the inner and outer attachment
portions of the diaphragms are preloaded (i.e., not in the same
plane) in the fully extended position thus subjecting the diaphragm
to flexure problems as discussed further in detail below.
[0009] The foregoing illustrates limitations known to exist in
present diaphragms and devices incorporating them. Thus, it is
apparent that it would be advantageous to provide an improved
diaphragm that has a longer useful life. Accordingly, a suitable
alternative is provided including features more fully disclosed
hereinafter.
SUMMARY OF THE INVENTION
[0010] According to the present invention, a partially preloaded
diaphragm is provided having an outer attachment portion defining a
first plane (P) and disposed about an axis substantially
perpendicular to the first plane. An inner attachment portion is
disposed substantially perpendicular to the axis of the outer
attachment portion and defines a second plane (C). The inner
attachment portion is movable away from the outer attachment
portion into a fully extended pumping position defining a third
plane (F). The first plane and the second plane are spaced at a
distance to define a preload distance (PC) when the diaphragm is at
rest, and the first and third plane are spaced to define a pump
stroke distance (PF) when the diaphragm is fully extended. The
preload distance is from about 25 percent to about 85 percent of
the pump stroke distance.
[0011] The foregoing and other aspects will become apparent from
the following detailed description of the invention when considered
in conjunction with the accompanying drawing figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0012] FIG. 1 is a cross-sectional view of a conventional pump
diaphragm having coplanar inner and outer attachment portions;
[0013] FIG. 2 is a cross-sectional view of a first embodiment of a
preloaded pump diaphragm according to one embodiment of the present
invention and taken along line 2-2 in FIG. 4;
[0014] FIG. 3 is a cross-sectional view of a conventional preloaded
pump diaphragm;
[0015] FIG. 4 is a planar view of the preloaded pump diaphragm
shown in FIG. 2;
[0016] FIGS. 5-7 are cross-sectional, sequential views of the pump
diaphragm of FIG. 2 and 4 shown with immediately adjacent parts of
a driven diaphragm pump during operation of the pump through a
pumping stroke; and
[0017] FIG. 8 is a graph illustrating the output fluid pressure
curves obtained for a given motive (input) air pressure curve
comparing a conventional coplanar diaphragm configuration shown in
FIG. 1 with a partially preloaded configuration according to the
present invention and shown in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] As used herein, the term "diaphragm" means a flexible
barrier that divides two fluid containing chambers or compartments.
Typically, such barriers are useful with diaphragm pumps, however,
these diaphragms may also be employed as a barrier layer between
two compartments in any application where a fluid exists in one
compartment and would cause deleterious effects if present in the
other compartment. The term "preloaded diaphragms" means a
diaphragm that in a free state has inner and outer attachment
portions that are not substantially coplanar.
[0019] The invention is best understood by reference to the
accompanying drawings in which like reference numbers refer to like
parts. It is emphasized that, according to common practice, the
various dimensions of the diaphragms and the associated pump parts
as shown in the drawings are not to scale and have been enlarged or
reduced for clarity.
[0020] To evaluate the effect of geometry on the failure mode of
diaphragms made using materials stiffer than prior art rubber
diaphragms, the present inventors tested competitor's benchmark
diaphragms made of SANTOPRENE.RTM. TPE having conventional
preloaded configurations like those shown in FIG. 3. The present
inventors found that utilizing these stiffer materials with
preloaded configurations created problems, however, because
thermoplastic elastomers (TPE's) are substantially stiffer than
fabric reinforced rubber used in traditional diaphragms. One such
problem encountered was during mechanical assembly of a pump using
diaphragms made of stiffer materials. Unlike fabric-reinforced
rubber diaphragms that can be easily inverted by hand, preloaded
TPE diaphragms generally require the use of assembly fixtures such
as a chain fall or press to overcome the preload in the diaphragm
in order to clamp the outer attachment portion between housing
portions. Another problem encountered when using stiff preloaded
diaphragms was buckling of the diaphragm when inverted during
installation. This buckling caused the formation of typically six
or eight radial wrinkles in the working portion of the diaphragm.
Because each fold or wrinkle in the working portion is known to be
a natural place for the premature formation of a crack, the
buckling that occurs is believed to have a detrimental effect on
diaphragm life.
[0021] In early investigations by ARO Fluid Products, a subsidiary
of Ingersoll-Rand Company, it was learned that upon cycling
preloaded diaphragms (i.e., diaphragms having inner and outer
attachment portions in different planes) made of stiff materials
such as PTFE, failures appearing as radial or "wagon-wheel" cracks
occurred in the working portion of diaphragms. With these radial
cracks, it was observed that the working portion of the diaphragm
was formed into a convoluted shape. To alleviate this radial
cracking problem, a diaphragm 7 shown in FIG. 1 was provided having
no preload with substantially coplanar inner and outer attachment
portions (6,2) and a convoluted working portion 3 provided to join
the attachment portions. This diaphragm having an improved flex
life is available today from ARO Fluid Products as the Model PD20
series diaphragm.
[0022] In an attempt to prevent the buckling that occurred with a
preloaded TPE diaphragm, the present inventors similarly considered
molding a diaphragm with the inner and outer attachment portions in
a coplanar configuration, i.e., without a preload, like that shown
in FIG. 1. With the use of stiffer materials such as TPE, however,
the extra force required to deform such a diaphragm as it
approaches the fully extended position becomes significant and can
result in a pressure loss from the air to the liquid side of the
pump. Parenthetically, the diaphragm performs work on the fluid
being pumped by force transfer. The force transferred to the liquid
side of the diaphragm is the air pressure times the area of the
diaphragm minus frictional losses, minus the force to extend each
diaphragm. Thus, as the stiffness of the diaphragms increases, the
pressure loss of the air causes a decreasing output fluid pressure
as the diaphragm moves into its forward pumping position.
[0023] According to the present invention and as described in
greater detail below, to alleviate the problems associated
described above, the present inventors have developed a partially
preloaded diaphragm having outer and inner attachment portions
spaced at a distance to define a preload distance when the
diaphragm is at rest, of from about 25 percent to about 85 percent
of the pump stroke distance. Shown in FIG. 8 is a graph
illustrating the output fluid pressure curves obtained for a given
motive (input) air pressure curve for a forward pumping stroke
using two SANTOPRENE.RTM. TPE diaphragms, one having a conventional
configuration with coplanar inner and outer attachment portions
shown in FIG. 1, and the other having a partially preloaded
configuration shown in FIG. 2 according to the present invention.
As can be seen from the graph, the output fluid pressure obtained
using the partially preloaded configuration results in an output
fluid pressure that substantially corresponds to the motive air
(input) pressure while the prior art coplanar configuration has a
decreasing output fluid pressure as the diaphragm moves to the
forward position in its stroke. This pressure loss is due to the
air pressure needed to extend the inner attachment portion from its
coplanar position with the outer attachment portion.
[0024] Referring now to the drawings, shown in FIGS. 2, 4, and 5-7
is a pump diaphragm 10 that is partially preloaded according to the
present invention. Diaphragm 10 includes a outer attachment portion
12 that is clamped or otherwise attached and held stationary
between pump housing sections 50 and 53 during operation of the
pump as shown sequentially in FIGS. 5-7. Preferably, outer
attachment portion 12 is adapted for attachment to a pump. For
instance, outer attachment portion 12 can be formed with an
enlarged bead, or a dovetailed portion as shown or may alternately
be provided with a plurality of holes for receiving fastening
members to retain the diaphragm in the pump housing.
[0025] Diaphragm 10 also includes an inner attachment portion 16
having an opening 18 located at approximately the center of the
diaphragm. Preferably, an annular working portion 20 connects the
outer and inner attachment portions.
[0026] As shown in FIGS. 5-7, inner attachment portion 16 is
attached to a pump to define a motive fluid chamber 49 and a
pumping fluid chamber 54 by clamping between a pair of clamping
washers 51, 52 each having a centrally positioned opening to be
aligned with diaphragm opening 18. The openings in clamping washers
51, 52 and inner attachment portion 16 are adapted to attach to an
end of a diaphragm rod 36 or other member for moving the annular
working portion 20 and the inner attachment portion 16 in a
reciprocating manner, relative to the fixed outer attachment
portion 12, along axis 21. Preferably, one end of diaphragm rod 36
is connected to clamping washers 51, 52 at diaphragm inner
attachment portion 16 by a threaded bolt 37 passing therethrough as
shown. Diaphragm rod 36 may also be either operatively connected to
a mechanical driving means or may be connected to a second
diaphragm.
[0027] As best seen in FIG. 6, in which the diaphragm is shown
moving through the at rest position shown in FIG. 2, outer
attachment portion 12 defines a first plane (P) and is disposed
about an axis 21 that is substantially perpendicular to the first
plane. Inner attachment portion 16 is disposed substantially
perpendicular to axis 21 of the outer attachment portion 12 and
defines a second plane (C). Inner attachment portion 16 is movable
away from the outer attachment portion 12 into a fully extended
pumping position defining a third plane (F). The first plane (P)
and the second plane (C) are spaced at a distance to define a
preload distance (PC) when the diaphragm is at rest. The first
plane (P) and third plane (F) are spaced to define a pump stroke
distance (PF) when the diaphragm is fully extended with the preload
distance (PC) being from about 25 percent to about 85 percent of
the pump stroke distance. Preferably the preload distance is from
about 50 percent to about 75 percent of the pump stroke distance
with most preferred loading being at 67 percent.
[0028] Preferably, annular working portion 20 is provided in a
convoluted form shown in FIGS. 2 and 6 comprising empirically
derived radii such that when inner attachment portion 16 is moved
to the fully extended position (shown in FIG. 7), the annular
working portion 20 is stretched to form a linear wall. Most
preferably, the radii of annular working portion 20 are provided
such that, when inner attachment portion 16 is in the fully
extended position, a peripheral portion 17 forms annularly between
the inner attachment portion 16 and the annular working portion 20.
Additionally, the convoluted portion of annular working portion 20
is preferably spaced from outer attachment portion 12 as shown to
reduce wear caused by pump housing sections 50 and 53 during
operation of the pump. In this manner, excess material at the
juncture between the inner attachment portion 16 and the annular
working portion 20 is eliminated and wear of the juncture between
the annular working portion 20 and the outer attachment portion 12
is reduced, thereby prolonging the flex life of diaphragm 10.
[0029] Although not intending to be bound by or otherwise limited
to any theory, it is believed that the useful life of the partially
preloaded diaphragm may be further enhanced by reducing the amount
of excess material to reduce the tendency of the diaphragm to
buckle during mid-stroke. The chord length of annular working
portion 20 is, preferably, the minimum that is needed to prevent
overstressing at the end of the stroke. Thus, diaphragms having an
annular working portion 20 that stretches to form peripheral
portion 17, described above and shown in FIG. 7, is most preferred
because it achieves this reduction in diaphragm material.
[0030] Suitable thermoplastic elastomers which may be employed
include SANTOPRENE.RTM. blend of EPDM rubber and polypropylene
(available from Advanced Elastomer Systems, Akron, Ohio),
HYLENE.RTM. diisocyanate and HYTREL.RTM. polyester elastomers
(available from DuPont Company, Wilmington, Del.), GEOLAST.RTM.
polypropylene and nitrile rubber blend (available from Advanced
Elastomer Systems, Akron, Ohio), SARLINK.RTM. elastomer (available
from DSM Elastomers, The Netherlands), and various thermoplastic
urethanes including polyether and polyester based polyurethanes,
such as ESTANE.RTM. thermoplastic polyurethane (available from B F
Goodrich, Cleveland, Ohio). A suitable listing of usable
thermoplastic elastomers is given in "Elastomerics," October 1986,
v. 118, no. 10. pp. 13-19. Although the polyurethanes yield
superior abrasion resistance and have excellent flexing properties,
SANTOPRENE.RTM. thermoplastic elastomer is preferred for many
applications because of lower cost, and long flex life when
employing the preferred wall design in accordance with this
invention. The thermoplastic elastomers of the invention provide
advantages of both thermoplastics and elastomers separately.
Additionally, fluoropolymers such as TEFLON.RTM.
polytetrafluoro-ethylene (available from DuPont Company,
Wilmington, Del.) may also be employed in diaphragms according to
the present invention.
[0031] While embodiments and applications of this invention have
been shown and described, it will be apparent to those skilled in
the art that many more modifications are possible without departing
from the inventive concepts herein described. For example, although
described above with respect to thermoplastic elastomers, it is
envisioned that diaphragms of other materials with similar or
greater stiffnesses may be utilized according to the present
invention to improve their useful flexure lives. It is understood,
therefore, that the invention is capable of modification, and
therefore is not to be limited to the precise details set forth.
Rather, various modifications may be made in the details within the
scope and range of equivalents of the claims and without departing
from the spirit of the invention.
* * * * *