Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1997-04-04
2001-03-20
Thorpe, Timothy S. (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C417S322000, C417S413200, C417S542000, C137S833000
Reexamination Certificate
active
06203291
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a displacement pump of the type comprising a pump housing with a variable volume pumping chamber having an inlet and an outlet for a fluid to be pumped, and a flow control arrangement for controlling the direction of flow through the pump.
BACKGROUND OF THE INVENTION
Displacement pumps of this general type are usually called diaphragm pumps. Such a pump has a pump housing which contains a pump chamber (pump cavity) of variable volume. The pump chamber is defined by walls including at least one elastically deformable wall portion, for example in the form of a flexible diaphragm, which by means of a suitable type of actuator can be provided with an oscillating movement. On the suction side of the pump, there is a fluid inlet to the pump chamber, and, on its pressure side, a fluid outlet from the pump chamber. The fluid flow through the inlet and outlet is controlled by check valves. These check valves can be of many different types. For example, a check valve can be used where the flow-preventing element is a ball or a hinged flap. The check valves are so arranged in the fluid inlet and fluid outlet that the check valve at the inlet is open and the check valve at the outlet is closed during the intake phase (when the volume of the pump chamber is increasing), while the inlet check valve is closed and the outlet check valve is open during the pumping phase (when the volume of the pump chamber is decreasing). The movement and change in shape of the flexible diaphragm causes the volume of the pump chamber to vary, and thus creates the displacement effect, which, thanks to the check valves, is translated into a net flow from the fluid inlet to the fluid outlet, and thus a pulsating flow at the pressure side of the pump (the outlet side).
Pumps with check valves passively controlled by the flow direction and pressure of the pump fluid have, however, certain characteristics which can be disadvantageous, especially in certain applications or fields of use for such pumps.
One example of such disadvantages is the excessively great drop in pressure over the check valves and the risk of wear and fatigue damage to the moving, flow-preventing elements of the valves, which can result in reduced life and reduced reliability of the pump. For pumping, especially sensitive fluids, primarily liquids, there is also the risk that the moving valve elements can damage the fluid or negatively affect its properties.
OBJECTS OF THE INVENTION
For the above applications and special fields of use, there is a pronounced need for pumps which completely lack moving parts, such as check valves, or have only extremely few such moving parts.
The primary purpose of the present invention is therefore to provide a displacement pump of the type described by way of introduction, which can be made completely without valves in the fluid inlet and/or fluid outlet.
The pump is to be a fluid pump which can be used and optimized for pumping both liquids and gases. It must also be able to be used for pumping fluids containing fluid borne particles, e.g. liquids containing solid particles.
SUMMARY OF THE INVENTION
The above mentioned purposes are achieved according to the invention by virtue of the fact that at least one of the fluid inlet and the fluid outlet comprises a constricting element which, for the same flow, has a greater pressure drop over the element in one flow direction, the nozzle direction, than in its opposite, other flow direction, the diffuser direction.
Particularly characteristic for the new type of displacement pump, is that constricting elements with “fixed” geometry are used instead of the check valve(s) used in previously known types of diaphragm pumps, for example.
For the pump according to the invention, in general the wall portion, which through its movement and/or change in shape causes the volume of the pump chamber to vary, can suitably be elastic in itself (i.e. cause its own spring action), but it is also quite possible instead to use a plastically deformable wall portion with a spring or a spring device coupled thereto, which returns the wall portion to its original position. The wall portion can even be the end surface of a reciprocating rigid piston. A pump according to the invention can be made of metal, polymer material, silicon or another suitable material.
In practice, it is suitable that both the fluid inlet and the fluid outlet are made of individual constricting elements of the type described. Both the constricting element of the fluid inlet and the constricting element of the fluid outlet are preferably arranged so that their diffuser direction agrees with the flow direction for the pulse volume flow from the fluid inlet to the fluid outlet.
In general, it can be said that the displacement pump of the invention is given its flow-directing effect by virtue of the fact that the selected type of constricting element has lower pressure losses when the element functions as a diffuser than when it functions as a nozzle. In this connection, it can be pointed out that the term diffuser refers to a flow-affecting element or means which converts kinetic energy of a flowing fluid into pressure energy in the fluid. A nozzle is, in turn, an element or means which, while utilizing a pressure difference (over the nozzle), converts pressure energy in the flowing fluid into kinetic energy.
During the intake phase of the displacement pump (when the pump chamber volume increases), the constricting element on the intake side of the pump of the invention functions as a diffuser with lower flow resistance than the constricting element, functioning at the same time as a nozzle on the outlet side of the pump.
It follows therefrom, that a larger fluid volume is sucked into the pump chamber via the inlet diffuser than via the outlet nozzle during the same suction phase. During the subsequent displacement phase (“pumping phase”) of the pump, the constricting element on the inlet side will, instead, function as a nozzle with higher flow resistance than the constricting element on the outlet side of the pump functioning at the same time as the diffuser. This means that a larger volume of fluid is forced out of the pump chamber via the outlet diffuser than via the inlet nozzle during the last mentioned displacement or pumping phase. The result during a complete period (work cycle for the pump) will thus be that a net volume has been moved through the pump, i.e. pumped, from the inlet side to the outlet side, despite the fact that both constricting elements permit a fluid flow in both possible flow directions.
The constriction elements at the inlet and outlet of the pump chamber are preferably directed so that the diffuser directions of the elements agree with the flow direction for the pulsed flow from the fluid inlet and the fluid outlet. The elastically deformable wall portion of the pump chamber consists suitably of one or more flexible membranes, the movement and changing shape of which are achieved by suitable drive means which imparts an oscillating movement to the membrane(s) which causes the fluid volume enclosed in the pump chamber to pulsate. Such a drive means can, for example, be a part of a piezo-electric, electro-static, electromagnetic or electro-dynamic drive unit. It is also possible to use thermally excited membranes.
The pump housing itself, with associated constricting elements, can be made so that they constitute integral parts of an integral piece. The displacement pump according to the invention can also be made by a micro-working process; the pump structure can, for example, be made of silicon.
A pump according to the invention can suitably be made with the aid of micro working methods, especially if the pump is made flat with the constricting elements and the cavity is lying in the same plane. The constricting elements should then be planar, i.e. have a rectangular cross-section.
Micro-working methods refer essentially to those techniques which are used in the manufacture of micro-electronics components. This manufacturing concept
Stemme Erik
Stemme Goran
Birch & Stewart Kolasch & Birch, LLP
Thorpe Timothy S.
Tyler Cheryl J.
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