U.S. patent number 3,680,981 [Application Number 05/099,823] was granted by the patent office on 1972-08-01 for pump and method of driving same.
Invention is credited to Josef Wagner.
United States Patent |
3,680,981 |
Wagner |
August 1, 1972 |
PUMP AND METHOD OF DRIVING SAME
Abstract
A fluid transfer device such as a reciprocating pump, preferably
of the diaphragm type suitable for use with an airless spray-gun
for painting and the like, having a pumping side for the fluid to
be pumped and a driving side driven through a piston through a
solution or mixture of liquid and gas, such as oil and air. Under
throttled or standby operation conditions, reduced diaphragm
movement is accommodated without changing the piston stroke by
reducing the volume of the driving liquid and by releasing gas from
the reduced volume of liquid to prevent vaporization and
condensation of the driving fluid itself. A dead space is provided
on the pumping side allowing some diaphragm movement into the
pumping side even when completely closed so that only a small
proportion of driving liquid is released and only a small amount of
gas is freed from the driving liquid to accommodate the reduced
diaphragm movement during the full piston stroke. The loading and
unloading of the driving fluid on the power and suction strokes of
the piston is controlled so that the driving fluid is always above
its vapor pressure. The gas is released from the driving liquid
according to Henry's Law.
Inventors: |
Wagner; Josef
(Friedrichshafen-Spaltenstein, DT) |
Family
ID: |
22276790 |
Appl.
No.: |
05/099,823 |
Filed: |
December 21, 1970 |
Current U.S.
Class: |
417/388;
417/395 |
Current CPC
Class: |
B05B
9/0409 (20130101); F04B 43/0054 (20130101); F04B
43/067 (20130101) |
Current International
Class: |
B05B
9/04 (20060101); F04B 43/06 (20060101); F04B
43/067 (20060101); F04B 43/00 (20060101); F04b
009/08 (); F04b 035/02 (); F15b 007/00 (); F15b
007/08 (); F04b 043/06 (); F04b 045/00 () |
Field of
Search: |
;417/388,387,339,395
;60/54.5R,54.6R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Walker; Robert M.
Claims
I claim as my invention:
1. A driven fluid pump device adapted to be throttled and stopped
without throttling or stopping the driving input which comprises,
means defining a pumping chamber and a driven fluid chamber, a
fluid propelling member separating said chambers, a driving fluid
in said driving fluid chamber actuating said member and composed of
liquid and gas, driving means for alternately pressure loading and
unloading said driving fluid, means for releasing some of said
driving fluid when loaded above a predetermined pressure to provide
a reduced driving volume for reduced actuation of said propelling
member, and means maintaining minimum pressure on the driving fluid
above the vapor pressure of said fluid whereby any expansion of the
reduced driving volume upon unloading will be accommodated by the
remaining liquid and gas released therefrom.
2. The device of claim 1 wherein the driving fluid is a liquid
having a gas dissolved therein which is released therefrom
according to the law of Henry.
3. The device of claim 2 wherein the liquid is a lubricant and the
gas is air.
4. The device of claim 1 wherein the fluid propelling member is a
diaphragm.
5. The device of claim 1 wherein the driving means is a piston.
6. The device of claim 5 wherein the piston has a uniform
stroke.
7. The device of claim 5 wherein the piston is driven by an
eccentric member.
8. The pump device of claim 1 wherein the fluid propelling member
receives pumpage on one side and said driving fluid on the other
side and an inlet valve controls flow of pumpage to maintain a dead
space on the pumpage side of said fluid propelling member
accommodating movement of the member to lessen reduction of the
driving volume of said driving fluid during standby operation when
no flow of pumpage occurs.
9. The device of claim 8 wherein the fluid propelling member is a
diaphragm having a pumpage chamber on one side and a driving fluid
chamber on the other side, an inlet valve controls flow of pumpage
into the pumpage chamber, a check valve controls flow out of the
pumpage chamber, and said two valves cooperate to prevent the
pumpage chamber from being completely filled to maintain a dead
space of compressible fluid accommodating movement of the diaphragm
into the pumpage chamber during throttling or stopping of the
pumping.
10. The device of claim 1 including a supply chamber for driving
fluid and a spring loaded valve controlling release of driving
fluid to said supply chamber.
11. The device of claim 10 wherein a passageway selectively
connects the supply chamber with the driving fluid chamber ahead of
the driving means for replenishing said chamber.
12. A driven pump adapted to be throttled or stopped without
throttling or stopping the driving imput comprising a housing
defining a pumping chamber and a driving liquid chamber, a fluid
propelling member separating said chambers, driving means acting on
liquid in the driving liquid chamber to actuate said propelling
member for pumping fluid through the pumping chamber, a relief
valve controlling maximum pressure in said driving liquid chamber
and releasing excess liquid from the chamber to accommodate
throttled movement of the diaphragm, and means controlling the
driving means to maintain pressure on the remaining liquid in the
driving liquid chamber above the vapor pressure of the liquid.
13. The pump of claim 12 having a source of driving liquid
containing gas dissolved therein communicating with said relief
valve to receive excess driving liquid from the driving liquid
chamber, and means connecting said source with the driving liquid
chamber to replenish the chamber whenever pressure therein is below
the pressure of the source.
14. The pump of claim 12 wherein the pumping chamber is fed through
an inlet valve biased to closed position to maintain a dead space
accommodating movement of the fluid propelling member into the
pumping chamber even when the chamber is closed.
15. The pump of claim 12 wherein the fluid propelling member is a
diaphragm and the driving means is a constant stroke piston.
16. A driven diaphragm pump adapted to be throttled and stopped
without throttling or stopping the driving input which comprises a
housing having a diaphragm chamber, a diaphragm in said housing
spanning said chamber and dividing the chamber into a pumping
chamber and an opposed driving liquid chamber, a spring biased
inlet valve for admitting pumpage to said pumping chamber, an
outlet valve controlling flow of pumpage from said pumping chamber,
a source of lubricating liquid having air dissolved therein, means
bleeding liquid from said source to said driving chamber, a relief
valve controlling flow of liquid from the driving chamber back to
the source, a piston acting on liquid in said driving chamber to
load and unload said liquid for reciprocating said diaphragm to
draw pumpage through the inlet valve into said pumping chamber and
to discharge pumpage from the pumping chamber through the outlet
valve, means driving said piston through a stroke to act through
the liquid for forcing a full stroke of the diaphragm whenever
pressure in the pumping chamber is below the pressure of the
driving liquid, said relief valve releasing driving liquid from the
driving chamber back to the source when pressure in the pumping
chamber exceeds pressure on the driving liquid, the spring load on
said inlet valve to the pumping chamber being effective to maintain
a dead space in the pumping chamber accommodating movement of the
diaphragm into the pumping chamber even when the outlet valve is
closed thereby minimizing release of driving liquid through the
relief valve upon throttled operation of the pump, and means
limiting the stroke of the piston to maintain the driving liquid
volume less than a volume occupied by the liquid and available air
from the liquid to always sustain the liquid above its vapor
pressure whereby reduced throttled diaphragm strokes are
accommodated by reducing the volume of driving liquid and releasing
air from the reduced volume of liquid to prevent vaporization of
the liquid.
17. The pump of claim 16 wherein the piston closes the bleeding
means except at the end of its suction stroke.
18. The pump of claim 16 wherein the piston is spring biased
against a wobble plate providing the driving input.
19. The pump of claim 16 wherein the outlet valve is in a spraygun
receiving pumpage from the pumping chamber.
20. A diaphragm pump comprising a housing defining a chamber for a
source of lubricating liquid containing dissolved air, a driving
chamber for said liquid and a pumping chamber, a diaphragm
separating said driving and pumping chambers, a piston separating
said source and driving chambers, means reciprocating said piston
to load and unload liquid in said driving chamber, a passageway
venting the source chamber to the driving chamber only when the
piston unloads the liquid in the driving chamber, a relief valve
releasing liquid from the driving chamber to the source chamber
when pressure in the pumping chamber exceeds pressure in the
driving chamber, means biasing the piston in an unloading direction
to reduce pressure in the driving chamber following release of
liquid therefrom, and means limiting the unloading stroke of the
piston to maintain a volume in the driving chamber filled only by
the liquid therein and the air released from said liquid.
21. The diaphragm pump of claim 20 having an inlet valve limiting
liquid flow into the pumping chamber on the suction stroke of the
diaphragm to maintain a dead space in the pumping chamber
accommodating some movement of the diaphragm into the pumping
chamber even when said pumping chamber is closed.
22. The diaphragm pump of claim 20 wherein the means limiting the
unloading stroke of the piston maintains a pressure in the driving
chamber substantially above the vapor pressure of the liquid
therein so that any air released from said liquid follows the law
of Henry.
23. A method of pumping fluids under variable flow conditions
without varying or stopping the driving input which comprises
driving a fluid pumping member with a driving fluid composed of
liquid and gas, alternately pressure loading and unloading said
driving fluid, releasing some of the driving fluid to provide a
reduced driving volume for reduced actuation of said pumping
member, and maintaining the pressure on the reduced volume of
driving liquid above the vapor pressure thereof to accommodate any
expansion of the reduced volume by separation of gas from the
liquid.
24. The method of pumping a liquid through full flow, throttled and
intermittently stopped conditions without throttling or stopping
the driving input which comprises driving a liquid propelling
member with a driving fluid composed of liquid and gas, releasing
some of the driving fluid to accommodate throttling and
intermittent stopping of the pumping, and maintaining minimum
pressure on the driving fluid above the vapor pressure of the
liquid.
25. The method of pumping through a wide range of flow rates and
intermittent stopping of flow without changing driving input which
comprises thrusting a driving liquid against a pumping diaphragm,
unloading said liquid whenever pumping pressures exceed a
predetermined level, and maintaining the liquid at all times above
its vapor pressure.
26. The method of diaphragm pumping throughout a wide flow range
without changing the driving input which comprises driving a
diaphragm with a liquid containing a gas dissolved therein and
releasing gas from the liquid under the law of Henry to accommodate
throttled and intermittent stoppage of the pumping operation.
27. The method of diaphragm pumping a liquid throughout a wide
range of flow and intermittent stopped conditions without
throttling the driving input which comprises driving the diaphragm
with a liquid containing a dissolved gas, controlling the flow of
liquid into the diaphragm pumping chamber to maintain a dead space
in the chamber accommodating movement of the diaphragm into the
chamber even when the chamber is sealed, loading and unloading the
driving liquid to reciprocate the diaphragm, releasing driving
liquid to accommodate reduced reciprocation of the diaphragm during
throttling and intermittent stopping of the pumping, and releasing
air from the driving liquid on the suction stroke following the
release of excess driving liquid to maintain pressure of the
driving liquid always above its boiling point.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the art of pumping and particularly to
diaphragm pumps for paint spraying and the like usage.
2. Description of the Prior Art
Diaphragm pumps driven by liquids which vaporize during the suction
stroke of the pump are known in the art, for example in the Paul W.
Schlosser U.S. Pat. No. 3,254,845 granted June 7, 1966. These pumps
utilize cavitation to effect vaporization and condensation of the
driving liquid. The repeated vaporization and condensation causes
rapid erosion and corrosion of the pump parts and useful driving
fluids are limited to low boiling liquids.
SUMMARY OF THE INVENTION
The deficiencies of the prior art liquid driven diaphragm pumps are
completely eliminated and improved pumping efficiency and useful
pump life are provided by this invention which eliminates
vaporization and condensation of driving liquid in a liquid driven
diaphragm pump. According to this invention, the pump diaphragm is
variably driven from a reciprocating piston having a constant
stroke through a variable volume of liquid having a gas dissolved
therein under conditions which never allow the liquid to vaporize
and which operate according to Henry's Law. While it is preferred
that the driving liquid have the gas dissolved therein under one
phase of operation, it is possible to use a driving liquid composed
of a mixture of liquid and undissolved gas which expand under
certain operating conditions.
An important feature of this invention is the complete elimination
of vaporization of driving liquid in the operation of a liquid
driven diaphragm pump and the maintenance of the liquid phase of
the driving liquid at all times.
Another important feature of this invention is the provision of a
dead space occupied only by air, paint solvent vapor or the like
compressible material, on the pumping side of the diaphragm which
allows the diaphragm to move to prevent vaporization of driving
liquid even under conditions where the flow of liquid being pumped
is throttled or completely stopped. In spray-gun usage of the pumps
of this invention, interruption of the flow of paint or the like
being pumped is sudden and may be quite frequent. Displacement of
the diaphragm at least partially into the pumping chamber during
these sudden stop periods provides for an enlarged volume in the
driving liquid chamber with a reduced overflow of driving liquid on
the first power stroke following throttling or shut-off so that the
next suction stroke cannot result in vaporization of any driving
liquid because sufficient gas will be released from the liquid to
fill the chamber without reducing pressure sufficient to
accommodate boiling of the liquid.
More particularly, according to this invention, the driving liquid
is preferably a lubricant such as oil and the gas is preferably air
dissolved in this oil. Under atmospheric temperature and pressure
conditions, about 4-8 % by volume of air is dissolved in a
lubricating oil of relatively low viscosity and relatively high
boiling point. A light hydraulic oil is satisfactory. Gases other
than air might be dissolved in a suitable driving liquid, such as
for example, nitrogen, oxygen, hydrogen, carbon dioxide and the
like. Where lubrication is not a problem, the driving liquid may be
water.
In general, the gas containing driving liquid is maintained under
temperature and pressure conditions which will allow release of the
dissolved or entrained gas only on the suction stroke of the pump
following the throttling or stoppage of the pumping operation. The
released gas is reintroduced into the driving liquid upon
resumption of the pumping operation.
To ensure against possible vaporization of the driving liquid, the
pressure of the driving liquid is never released to a point even
close to the vapor pressure of the liquid and the pressure is
maintained from 10 to 100 times the pressure at which vaporization
could occur.
Temperatures of the driving fluid are maintained sufficiently low
to avoid vaporization even at the lowest operating pressures by
reducing any required recirculating of the driving fluid to a
minimum.
After throttling or complete stoppage of flow of the liquid being
pumped, the remaining volume in the driving liquid chamber is
harmonized with the piston stroke so that the lowest pressure
produced on the suction stroke of the piston remains above the
boiling pressure of the driving liquid and the return stroke volume
of the chamber is completed with gas freed or expanded from the
driving liquid thereby preventing vaporization. At the end of the
suction stroke the driving liquid chamber is completely filled with
a mixture of the driving liquid and the released gas.
To ensure that this remaining volume of the driving liquid is
sufficiently great to contain enough gas for completely filling the
driving liquid chamber, the aforementioned dead space is provided
in the pumping chamber even during full pumping operation so that
diaphragm movement into the pumping chamber is not completely
stopped even upon full throttled no-flow standby conditions.
The pumping chamber is fed through an inlet check valve and the
pumped liquid is withdrawn through an outlet check valve and a
control valve such as a spray-gun. The chamber on the opposite side
of the diaphragm containing the driving liquid and the driving
piston is connected to a source chamber through a bypass with a
pressure limiting valve and through a refill passage for
replenishing the pumping liquid. The pressure limiting valve is
adjustable to control the delivery pressure of the pump.
The pump piston must not be retracted during the suction stroke
with too great a velocity since the gas dissolved or entrapped in
the liquid may not be given enough time to be freed from the
liquid. If the suction stroke proceeds at a rate slow enough to
release the dissolved or entrapped gas, only enough gas will be
freed to maintain a constant stroke without ever releasing the
pressure sufficient to permit boiling of the driving liquid. The
gas separation thus obeys the law of Henry, and it is only when the
pump piston is withdrawn with too great a velocity that a hollow
space created ahead of the piston may be filled with vapor of the
driving liquid which during the next pressure stroke, of course,
leads to the undesirable cavitation. The maximum pump velocity is
chosen so that the law of Henry may apply to the freeing of the
gas. Preferably, the piston should not have a retracting velocity
above 1.0 to 1.5 meters per second.
To prevent the dead space in the pumping chamber from becoming
filled with the pumping liquid during the subsequent suction
strokes after a throttling or stoppage of flow of pumping liquid, a
spring loaded inlet valve is preferably provided such that the
spring characteristic and the mass inertia of the valve will not
permit the valve to be opened by reduced pressure in the dead space
of the pumping chamber. A spring having a rate of 75 grams per
millimeter and a closing load of 300 grams is sufficient to
maintain the dead space.
It is then an object of this invention to provide an improved
diaphragm pump capable of being fully throttled and method of
pumping through a driving liquid without vaporizing the driving
liquid.
Another object of this invention is to provide a liquid driven
diaphragm pump, useful for spray painting, having a wide range of
delivery pressures and delivery rates without bypassing the
material being pumped and without effecting vaporization of the
driving liquid.
A further object of this invention is to provide a method of
driving a diaphragm or the like through a liquid containing a
dissolved or admixed gas freed during a throttling of the diaphragm
stroke to prevent vaporization of the driving liquid.
A still further object of the invention is to provide a liquid
driven diaphragm pump operating according to the law of Henry.
Another object of the invention is to provide a diaphragm pump with
a dead space on the pumping side of the diaphragm which will
accommodate movement of the diaphragm even when flow of the pumping
liquid is stopped.
Another object of the invention is to provide a diaphragm type
paint spray pump with an inlet valve so correlated with a liquid
driven diaphragm as to maintain a void filled only with
compressible air, vapors or the like in the pumping chamber during
all conditions of operation.
A still further object of the invention is to provide a diaphragm
pump driven by a constant stroke reciprocating piston through a
lubricating liquid having a gas dissolved therein which is released
from the liquid when the pumping operation is throttled or
stopped.
Another object of the invention is to provide a diaphragm pump
driven by a constant stroke reciprocating piston through a
lubricating liquid having a gas dissolved therein and a dead space
on the pumping side of the diaphragm so correlated with an inlet
valve as to accommodate limited movement of the diaphragm when flow
of the pump material is stopped so that only a small amount of the
driving liquid need be released to accommodate the limited stroke
of the diaphragm.
Other and further objects of this invention will become apparent to
those skilled in this art from the following detailed descriptions
of the annexed sheets of drawings which, by way of a preferred
embodiment, show one form of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a somewhat diagrammatic longitudinal sectional view with
parts in elevation of a diaphragm pump according to this invention
for pumping paint to a spray-gun and illustrating the positions of
the parts at the end of a suction stroke;
FIG. 2 is a view similar to FIG. 1 but illustrating the positions
of the parts at the end of a pressure stroke;
FIG. 3 is a view similar to FIGS. 1 and 2 but illustrating the
position of the parts during a pressure stroke following full
throttling of the pumping operation;
FIG. 4 is a view similar to FIGS. 1 to 3 but illustrating the
positions of the parts and the condition of the driving fluid at
the end of a suction stroke following a pressure stroke after full
throttling, as shown in FIG. 3;
FIG. 5 is a longitudinal cross-sectional view, with parts in
elevation and with parts broken away, of one form of diaphragm pump
according to this invention;
FIG. 6 is an enlarged longitudinal sectional view of the pumping
side of the pump of FIG. 4;
FIG. 7 is an enlarged longitudinal sectional view of the driving
side of the pump of FIG. 4;
FIG. 8 is an enlarged side elevational detail view with parts shown
in cross-section of the diaphragm and support plate of the pump of
FIG. 4;
FIG. 9 is a plan view of the support plate taken along the line
IX--IX of FIG. 8.
DETAILED DESCRIPTION OF THE DRAWINGS
In FIG. 1 there is schematically illustrated a diaphragm pump 1
according to this invention having a casing defining a first or
pumping chamber 2 fed from a supply container 3 with liquid to be
pumped such as paint or the like. Liquid from the container 3 is
supplied to the chamber 2 through an inlet pipe 4 and inlet check
valve 5. The pressurized liquid or pumpage is discharged through an
outlet check valve 6 to a supply hose 7 to a paint spray-gun 8
having a control valve 9 throttling or completely stopping flow
from the pumping chamber 2.
The pump 1 has an axially movable diaphragm 10 forming one wall of
the chamber 2 and separating this chamber from a driving liquid
chamber 11 to which driving pressure is intermittently applied and
relieved by means of a piston pump generally identified at 12 and
including a cylindrical chamber 13 slidably mounting a cylindrical
piston 14 driven by a wobble plate 15 rotated by a driving motor
16.
The wobble plate 15 rotates in a container 17 for the driving
liquid which communicates with the driving liquid chamber 11 behind
the diaphragm 10 by means of an overflow passage 18 containing an
adjustable pressure limiting valve 19. A refill passage 20 also
joins the bottom portion of the container 17 with a refill slot 21
in the cylindrical chamber 13 receiving the piston 14. The slot 21
is uncovered by the piston 14 only at the end of the suction stroke
of the piston and is otherwise closed by the piston.
The container 17 is partially filled with the driving liquid L to a
liquid level LL, and the top of the chamber 17 may be vented to the
atmosphere as at V. A spring S urges the piston 14 against the
wobble plate 15. The wobble plate 15 in the container 17 agitates
the liquid L insuring aeration with air from vent V.
The wobble plate 15 drives the piston 14 through a relatively short
stroke from the rearmost suction stroke illustrated in FIG. 1 to
the forward end of the power stroke illustrated in FIG. 2, and this
reciprocation of the piston drives the liquid L ahead of the piston
forcing the diaphragm 10 from its rearmost position in the chamber
11 as shown in FIG. 1 to its foremost position in the chamber 2, as
illustrated in FIG. 2. The loss of driving liquid by leakage past
the piston 14 is replenished on each driving stroke through the
refill slot 21.
When the valve 9 of the spray-gun 8 throttles the full discharge
through the outlet hose 7, the displacement of the diaphragm 10 is
reduced and since at the moment of throttling the driving liquid
behind the diaphragm in the chamber 11 is sufficient to force a
full diaphragm stroke or displacement, some of the driving liquid
must be displaced from the chamber so that the remaining portion
will permit the reduced stroke of the diaphragm. For this purpose,
the pressure limiting valve 19 in the return or overflow passage 18
is a spring loaded needle valve which is unseated on the first
pressure stroke of the piston 14 following throttling or stoppage
of flow from the pumping chamber 2.
As shown in FIGS. 1 and 2, the volume of the driving liquid behind
the diaphragm remains constant when the pump is operated at
capacity under a full stroke of the diaphragm. However, as shown in
FIG. 3, when flow from the pumping chamber 2 is throttled or
stopped, the diaphragm movement is reduced and the volume of the
driving fluid behind the diaphragm must be reduced because the
stroke of the piston remains the same. Thus, the needle valve 19
will open, allowing escape of driving fluid back to the container
17 only in an amount sufficient to reduce the volume of liquid
behind the diaphragm for accommodating the reduced displacement of
the diaphragm into the pumping chamber caused by the throttling of
the discharge from the pumping chamber. The valve 19 will only open
under the increased pressure created in the pumping chamber 2 and
in turn on the driving liquid by the throttling. Then, on the
suction or return stroke of the piston 14 the valve 19 will
immediately close and since the piston 14 moves through a full
stroke, there will be insufficient driving liquid remaining between
the piston and diaphragm to fill the chamber 11 and the cylinder
space ahead of the piston. Under these conditions, as shown in FIG.
4, the pressure on the driving liquid is reduced and the gas
dissolved in the liquid is released according to the law of Henry
to fill the chamber with gas G and liquid L without ever allowing
the liquid L to vaporize. Thus, the remaining volume of the mixture
of gas and driving liquid is automatically adjusted during the
suction stroke to fill the reduced chamber caused by the reduced
movement of the diaphragm.
If leakage should occur during further working strokes of the
piston pump following initial throttling since the pressure in the
chamber 11 at the end of the suction stroke of the pump piston as
illustrated in FIG. 1 will be lower than the pressure in the supply
container, 17, a small amount of replacement driving liquid is fed
to the chamber through the passageway 20 only during the short time
when the slot 21 is uncovered by the piston. In the event excess
liquid is supplied through the refill passage 20, it will be
returned to the container 17 through the passageway 18 since the
resulting increased pressure in the chamber 11 will reopen the
spring loaded needle valve 19 for this purpose.
When the throttle valve 9 of the spray-gun 8 is again fully opened
so that full pumping performance of the pump 11 is permitted, the
outlet check valve 6 will open reducing the pressure in the pumping
chamber 2 and again allowing the diaphragm 10 to resume its full
stroke. The driving liquid behind the diaphragm is then replenished
from the container 17 via the passage 20 and slot 21 until the
volume of the driving liquid again fills the chamber 11 and the gas
is again dissolved into the driving liquid. Each working stroke of
the piston 14 decreases the amount of freed gas in the chamber 11
until full pumping operation is again achieved.
To minimize return of pumping liquid from the chamber 11 back to
the container 17 and to thereby decrease freeing of gas from the
driving liquid to fill the chamber behind the diaphragm, the
diaphragm is arranged so that it will always have some movement on
a pressure stroke even when the throttle valve 9 of the spray-gun
is completely closed and no discharge is permitted from the pumping
chamber 2. To accomplish this movement of the diaphragm 10 into the
pumping chamber 2 even under complete stoppage of discharge from
the pumping chamber, the inlet check valve 5 is sufficiently biased
to a closed position and the walls of the pumping chamber are so
shaped that the pumping chamber 2 will never be completely filled
and a dead space or void will be provided in the pumping chamber as
illustrated at D around the periphery of the pumping chamber. Then,
even though the valves 5 and 6 are completely closed trapping
incompressible pumpage such as liquid paint in the chamber 2, the
air or paint solvent vapor in the dead space D can still be
compressed on the pressure stroke of the diaphragm to permit some
displacement of the diaphragm into the pumping chamber. This
displacement of the diaphragm even under fully closed outlet
operation of the pump maintains the volume in the driving liquid
chamber 11 closer to the volume of the chamber under fully opened
pumping operation so that only a small overflow of liquid through
the passage 18 will be needed to accommodate the reduced volume in
the driving liquid chamber from the full pumping volume of the
chamber. This, of course, reduces the amount of gas freed from the
liquid required to fill the remaining volume of the driving
chamber.
It will be understood that the pressure stroke of the pump piston
14 following a complete closing of the throttle valve 9 urges the
diaphragm 10 through a complete stroke and this compresses the
pumping liquid present in the chamber 2 an amount permitted by the
dead space or void. If this pressure in the chamber 2 exceeds the
pressure of the limiting valve 19 on the driving side of the
diaphragm, some driving liquid will be returned to the supply
container 17. Then on the following suction stroke, the pump piston
14 moves the diaphragm to rest against a support plate 22 as shown
in FIG. 4, and the continued suction stroke decreases the pressure
on the driving liquid to release the gas therefrom. When the
pressure at the end of the suction stroke has decreased the
pressure in the driving chamber 11 to a point where it is below the
pressure of the supply container 17, additional liquid will be
supplied through the refill passage 20 when the slot 21 is
uncovered by the piston. Then in a subsequent pressure stroke, the
previously freed air in the chamber 11 is re-dissolved into the
driving liquid and the diaphragm is moved into the pumping chamber
2 an amount permitted by the dead space until the pressure of the
driving liquid is again increased sufficiently to open the pressure
limiting valve. Then, on the next suction stroke the diaphragm 10
is again caused to bottom on the support disc 22 which will reduce
the pressure in chamber 2 a small amount insufficient to open the
check valve 5. Any leakage during the following strokes of the pump
piston 14 is replenished from the supply container 17 through the
refill passage 20 and slot 21.
In no event during the operation of the pump as illustrated in
FIGS. 1 to 4 can vaporization occur in the pumping chamber 11, nor
will the diaphragm movement be completely arrested even during
standby operation where the throttle valve is completely closed.
Thus, the pumping chamber 2 is never completely filled with the
pumping liquid and the diaphragm never rests firmly against the
wall of this chamber. In this manner, the remaining volume of the
driving liquid in the chamber 11 may be maintained at a maximum and
more than a sufficient supply of air from the driving liquid is
available to prevent vaporization in the chamber 11. The heretofore
encountered erosion and corrosion caused by vaporization in liquid
driven diaphragm pumps is thus completely eliminated.
In the detailed drawings of FIGS. 5 through 8, parts corresponding
with parts illustrated in FIGS. 1 to 4 have been marked with the
same reference numerals.
The casing for the pump 1 as shown in FIG. 5 is formed from two
half sections 30 and 31 shown separately in FIGS. 6 and 7. The half
section 30 as best shown in FIG. 6 has a recess 32 in the face
thereof mating with the opposing face of the section 31. This
recess 32 receives an insert 33 preferably composed of corrosion
and erosion resisting plastic material such as "Teflon"
(polytetrafluoroethylene) or polypropylene. The exposed face of the
plastic ring 33 is contoured around its inner peripheral portion
33a to provide a seat for the diaphragm 10 as hereinafter more
fully explained and is recessed around its outer peripheral face
portion as at 33b to provide for the aforementioned dead space.
The inlet valve 5 includes a poppet valve 34 with a head 34a
seating on a valve seat insert ring 35 and with a stem 34b slidably
mounted in the bore of a plastic bearing 36 which has radiating
fins or webs 36a pressed in the inlet bore 37 of the casing part
30. A coil spring 38 surrounds the plastic bearing 36 and is
bottomed at one end against the fins 36a and at the other end
against a washer 39 backed by a nut 40 threaded on the valve stem
34b. Liquid such as paint from the inlet 4 flows around the bearing
36 through the spaces between the ribs 36a thereof to the head 34a
which when seated on the ring 35 will seal off the inlet of paint
to the pumping chamber 2 and which when opened will allow flow of
paint into this pumping chamber.
The outlet check valve 6 as shown includes a spring pressed ball 41
cooperating with a seat 42.
The casing 30 has a passage 43 from the pumping chamber to the
spring pressed ball 41.
The pump casing part 31 shown in FIG. 7 has a recess 44 in the face
thereof mating with the casing half 30 and this recess receives a
diaphragm support plate as hereinafter described.
The cylinder bore 13 receiving the piston 14 is lined with a sleeve
45 slidably supporting the piston which is in the form of a hollow
cup 46, the closed or head end of which has a projecting nose 46a
for engaging the wobble plate 15 and the hollow interior 46b of
which receives a spring 47 bottomed at one end against a plastic
spacer 48 seated against the head and at the other end against a
metal spring retaining collar 49 held in abutted relation against
the end of the sleeve 45 by a fastener 50 threaded into the casing
31.
The piston cup 46 has a groove 51 around the periphery thereof and
holes 52 through the bottom of the groove connect the groove to the
interior of the cup 46b. The cylinder sleeve 45 has holes 53 at
spaced intervals therearound adapted to register with the groove 51
when the piston reaches the end of its suction stroke as above
described. These holes 53 through the sleeve 45 communicate with
the refill slot 21 described above and the refill passage 20 to the
container 17. A cylindrical filter screen 54 is provided in the
passage 20 and may conveniently be carried in a casing 55 threaded
into the casing part 31 and easily removed therefrom for
cleaning.
The container 17 shown in FIG. 7 is defined by an integral
cylindrical wall 31a of the casing part 31. The overflow passage 18
as shown in FIG. 7 is provided by two drilled holes in the casing
connected through a well 56 receiving the spring loaded needle
valve 19 described above.
As shown in FIG. 8, the diaphragm 10 is a molded plastic unit 57
having a thick rigid central portion 57a surrounded by a thin
flexible peripheral membrane portion 57b. A cylindrical stem 57c
extends from the center of the thick portion 57a and has a threaded
end 58. One face of the thick portion 57a is stepped to mate with
the step portion 33a on the inner periphery of the insert ring 33
shown in FIG. 6. The opposite face of this central portion 57a is
contoured to mate with the face of a metal backup or support plate
ring 59 which in turn is seated in and mates with the recess 44 of
the casing part 31 shown in FIG. 7. This support plate 59 has a
central aperture 59a slidably receiving the stem 57c therethrough
and this aperture 59a is surrounded by a ring of apertures 59b as
shown in FIG. 9 for passage of driving liquid through the support
plate 59.
As shown in FIG. 8, a coil spring 60 surrounds the stem 57c and a
nut 61 threaded on the end 58 of the stem compresses the spring 60
against the support plate 59, thereby drawing the diaphragm 57 into
seated relation on this support plate.
As shown in FIG. 5, the stem 57a and spring 60 extend into the
spring 47 in the cup portion 46b of the piston. In this manner, the
piston is biased against the wobble plate 15 while the diaphragm is
biased against the support plate 59. The diaphragm 10 is thus
always biased away from the insert ring 33.
The motor 16, as illustrated in FIG. 5, is in the form of an
electric motor 62 driving a shaft 63 on which is keyed a flywheel
64 in the container 17. A thrust bearing 65 rotatably supports the
flywheel 64 in the container and the wobble plate 15 is mounted in
angled relation on this flywheel through radial bearing 66 and
thrust bearing 67. A seal 68 is provided around the shaft 63 to
stop leakage between the motor and container 17.
When the motor is driven to rotate the wobble plate 15, the piston
14 will be moved forwardly from its rearmost position shown in FIG.
5 against the bias of the spring 47 and will act through the
driving liquid to force the diaphragm 10 off of the seating plate
59. The forward movement of the diaphragm in the pumping chamber 2
will discharge paint from the pumping chamber past the check valve
6 to the spray-gun outlet. Then, on the return stroke the diaphragm
10 will be biased back to the position shown in FIG. 5 enlarging
the pumping chamber 2 and drawing paint from the inlet 4 through
the inlet valve 5. The load of the spring 38 on this inlet valve 5
is such that the valve will not open on the initial retraction of
the diaphragm so that the pumping chamber 2 is never filled with a
liquid material and the dead space D will be preserved. The contour
33b of the insert ring 33 and the thin membrane portion 57b
overlying this contoured portion cooperate with the spring load on
the inlet valve to maintain this small dead space D.
In one commercial embodiment of a diaphragm pump for airless spary
painting usage according to this invention, the pump chamber 2 of
the pump has a capacity of about 19 c.c., the outlet check valve 6
is spring loaded at about 150 grams with the spring having a rate
of 60 grams/m.m. and the inlet valve 5 is spring loaded at about
300 grams with a spring rate of 75 grams/m.m. The diaphragm 10 is
spring biased into the chamber 11 by spring 60 at 23.4 kilograms
with a rate of 2.93 kg/m.m. When the relief valve 19 is set to open
at 240 kg, this pump will deliver a pressure of about 150
kg/cc.sup.2 to a spray-gun 8 having a delivery orifice diameter of
0.31 inches. The relief valve 19 may be varied to open at different
pressures with a resultant variation in delivery pressure. The
orifice size on the spraygun 8 may be changed to vary the delivery
pressure at the same relief valve setting. The piston 14 has a
stroke of about 8 m.m. and the wobble plate 15 is driven at about
1,480 RPM. When such a pump is fully throttled to stop flow from
the pumping chamber 2, the amount of driving fluid released through
the valve 19 will not be more than about 6 percent of the volume of
driving liquid in the chamber 11. Then, when the spray-gun 8 is
opened for full delivery, the driving liquid will be replenished
through the passage 20 at the rate of about 0.45 c.c. on each
stroke of the piston 14 until the chamber is again filled with the
driving liquid and the gas is re-dissolved in this liquid. The
wobble plate drive has a wide speed range and is driven slow enough
so that the piston cannot retract at a faster rate than the gas can
be released.
It should be understood that the pump form of FIGS. 5 through 9
represents only one embodiment of the pump of this invention, and
details of construction may be widely varied from this illustrated
form without departing from the principles and scope of this
invention.
It should be understood that the herein described diaphragm is a
preferred fluid propelling member but it could be replaced with a
piston, a bellows or the like fluid propelling device without
departing from the principles and scope of this invention.
It should also be understood that while the invention is
particularly described as embodied in a pump, the principles of the
invention are generally useful in fluid power transfer machines
including motors as well as fluid propelling machines and such
usage is included within the scope of this invention.
* * * * *