Note: Descriptions are shown in the official language in which they were submitted.
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PULSELESS PIST~N PU~P
BA~K(~OI JND OF T~ D~V13~11ON
A myriad cf different types of pumps are known for use in
pumping various materials. When it is desired to pump difficult
5 materials, i.e., those that are highly viscous and/or abrasive, the
number of choices of pumps suitable for such applications drops
substantially, particularly when it is desired to pump such materials
at relatively elevated pressures and/or at predetermined flow ra~es.
While reciprocating piston pumps have been widely used in such
10 applications, such pumps suffer from having pulses in the pressure
output of the pumps during piston reversal. Such pumps also suffer
to a certain extent from leakage and seepage of pumped material
past t~2e seals which is particularly critical when the materîal is air-
sensitive such as isocyana~es. This leakage is in both directions and
15 can cause environmental contamination, pumped fluid contamination
and regenerative abrasive wear damage to the pump. The reduction
and/or elin~ination of pulses in the output is particularly impor~ant
for circulating systems, fine spray applicat;ons and proportional
metering to produce eonstant output.
2 0 Centrifugal pumps are capable of pumping abrasive materials
without pressure pulses but suffer from the problems of not being
positive displacement type (flow rate is not directl~y related to
speed), inefficiency, shaft seal leakage and impose a high degree of
shear on materials which may be shear-sensitive.
Gear pumps are commonly used for metering and
proportioning apparatus due their ease in synchronizing with other
pumps. Such products, however, are ill-suited for purnping of
abrasive materials which cause unacceptable wear.
It is therefore an object of this invention to provide a pump
capable of handling such ma~erials while providing substantially
pulseless operation. It is further an object of this invention to
provide such a pump which is ~asily manufactured and which is
capable of being operated at varying speeds, flow rates and
pressures in an efficient manner. It is yet a further object of this
invention to provide such a pump which has lealc-proof operation to
avoid contamination of the environment in which the pump is
located or contamination of the pumped lluid by the environment.
1 5 SUMMARY OF T~ INVENTION
A multi-piston/cylinder pump is driven by a cam. The use of
pistons in conjunction with diaphragms allows a much higher
pressure output capability that a simple diaphragm pump and a
more positive displacemen$ action than diaphragm pumps. The cam
2 0 is powered by a DC moto`r or other type of conventional variable
speed rotary driving mechanism ~electric, hydraulic or the like).
When used with these drives, the pump can be stalled against
pressure just like a typical air-operated reciprocating piston pump.
This mode allows adjustable constant flow. A constant speed motor
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driving the pump would use a pressure switch to turn the motor on
and off. Because ~he motion input to the pump is rotary, it can be
easily synchronized with another pump(s) to provide a plural
component material proportioning system or with a conveyor to
5 more fully automate production.
The cam profile is designed so that the reciprocating pistons
(which alternate between pumping and intake strokes) have a net
velocity sum of their pumping strokes which is generally constant.
By doing so, one essentially can eliminate pressure losses that create
10 pulses which result from the piston reversal of a conventional piston
pump. In the preferred embodiment, two pistons are used although
it can be appreciated that more pistons may be used if desired.
As shown in this application9 intake flow is controlled by check
valves which typically take a discreet amount of time to seat. Fluid
15 can flow backwards during this time causing small pump output
pressure variations during the valve seating but such can be
compensated for by shaping the cam profile to provide a nearly
totally pulseless operation.
Each piston is sealed in its respective cylinder by a relatively
2 0 conventional type seal rnechanism. Attached to the piston OII ~he low
pressure intake side of th`e seal is a diaphragm which serves to
isolate the fluid from the environment and assure a leak proof
device. As used in this application, the term "diaphragm" is
understood to include membranes, b~llows or other such structures
2 ~ performing a similar function. An intalce passage provides flow
2 ~ 2
directly over ~he piston between the main seal and the diaphragm to
prevent the build-up and hardening of material in the intake section
and on the piston. The intake flow then passes through the in take
check and into ~he pumping chamber and then exits through an
S outlet passage which also has a check valve. This flow path
minimizes stagnant areas of non-flowing fluid where fluids may
settle out and/or harden. The passage is oriented to minimize air
entrapment and continually replenish the fluid in the intake area.
The cam can either be of a push-pull type, that is, where the
10 roller rides in a track or can be a conventional outer profile cam
wherein the piston assembly roller is spring loaded against the cam
to maintain it in position.
These and other objects and advantages of the invention will
appear more fully from the following description made in
15 conjunction ~ith the accompanying drawings wherein like reference
characters refer to the same or similar parts throughout the several
views.
A BRIEF DESCRIPI~ON QF 1~ DRAWINGS
Figure 1 is a general cross section of the purnp of the instant
invention.
Figure 2 is a cross section talcen along 2-2 of Figure 1 showing
5 the cam of the instant invention.
Figure 3 is an alternate embodiment of the cam of Figure 2.
Figure 3a is a chart showing the velocities and outputs of a two
piston pump.
DESCRIP~ION OF THE PREFERRE EMBODIMENT
The pump of the instant inYention, generally designated 10, is
comprised of a main housing 12 in which runs a shaft 14 having a
gear 16 rnounted thereon. A motor (not shown) which may be a DC
brushless type motor7 drives gear 16 and shaft 14 to turn cam 18
15 mounted on the end thereof. A cam follower assembly 20 rides on
cam 18 and is comprised of a follower housing 22 having a follower
24 mounted thereto via shaft 26. Follower housing 22 h~s guide
rollers 28 mounted on the outside thereof which run in slots 30 in
housing 12. Follower assembly 20 is spring loaded against cam 18
2 0 by means of a spring 32.
Follower assembly 20 is attached to a piston 34 and located in
between follower 22 and piston 34 is a diaphragm 36. Those three
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parts are fastened together by a bolt 38 which passes consecutively
therethrough. An initial inlet passage 40 leads iIltO a flushing
chamber 42 located about piston 34 between diaphragm 36 and
main pressure se~l 44 in cylinder 46. Flushing chamber 42 runs
5 circurnferentially around piston 34 thus inlet flow therethrough
serves to flush material through which might potentially harden off
the surface of piston 34. Inlet flow thence passes through passage
48 in to main inlet passage 50 which has located in series therein a
check valve 52 of a conventional nature.
Pumping chamber 54 is loca~ed in the end of cylinder 46 over
piston 34 and also has connected thereto outlet passage 56 having an
outlet check 5~ of conventional design therein. When the device is
positioned as oriented in Figure 1, that is with the inlet and outlet
ports 40 and 56 respectively facing upwardly, the product is
15 designed so as to prevent the accumulation of air or other gas within
pockets of the pump, that is, all such bubbles and gas may freely
flow upwardly and out of the pump thereby reducing problems of
priming and assuring full volumetric flow without air entrapment. It
can be seen as piston 34 moves upwardly into pumping chamber 34,
2 0 diaphragm 36 flexes upwardly to the point of nearly touching the
upper surface 42a of flushing chamber 42 thereby continually
assuring a fresh flow of material through the pump and th~
prevention of stagnant flow zones therein.
While the embodiment shown in the drawing figures utilizes a
2 5 spring loaded follower and cam~ it can also be appreciated that the
cam drive may be of a different type wherein no such spring is
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necessary. Such a type of cam is often referred to as a desmodromic
type cam, and an example of such a cam is shown in Figure 3
wherein the roller is guided in a track 60 and is driven in both its
pumping and inta~e strokes. It can also be appreciated ~hat seal 44
S may be of any conventional type which is capable of performing a
proper sealing function, however, it carl be appreciated that because
diaphragm 36 is subjected to relatively low pressures, its service life
will be dramatically increased to maintain the pump in a
substantially leak-free state. It can also be seen that if seal 44
10 should leak, its leakage is from the high pressure side back into ~he
inlet rather than into the çnvironment.
Up to this point, the description has been of a theoretically
perfect pump. In reality, check valve physics (closing time, etc.),
fluid compressibility and viscosity preclude perfect pulseless output.
15 Satisfactory pulseless output may be obtained by modifying the cam
profile to compensate for the above factors. By increasing the
velocity of the opposite piston during check valve closing time by
putting a "blip" in the cam to change the veloeity profile, the
pumping action can be slightly increased near the point of chec~
2 0 valve seating to compensate for the decreased output during the
seating time. The required net velocity profile for pulseless output
may be different for any material which is pumped. Using a
representative fluid such as oil for the purposes of optimizing the
velocity profile of the pump results in a solueion which is satisfactory
2 5 for most other fluids.
Additional]y, it can :,e appreciated that such a pump is easily
adaptable to power operated valving, that is, valving which could be
operated electrica]ly and/or through a mechanical linkage not unli}~e
an automotive engine such that the valve opening and closing time
S can be selected as desired.
It is conternplated that various changes and modifications may
be made tO the pump without departing from the spiriè and scope of
the invention as defined by the following claims.
