Pumps – Processes
Reexamination Certificate
2001-05-04
2003-02-04
Freay, Charles G. (Department: 3746)
Pumps
Processes
C417S413100, C417S415000, C417S044100, C417S045000
Reexamination Certificate
active
06514047
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of Invention
This invention relates generally to apparatus and methods for the pumping of gases and liquids and more specifically to the field of linear pumps and compressors.
2) Description of Related Art
Over the years, efforts have been undertaken for pump and compressor designs to yield desired ideal characteristics of operation such as operation free of oils of other external lubricants, commonly known as “oil-free operation”, variable pumping capacity, few moving parts, compatibility with a wide range of toxic or chemically reactive gases, manufacturing simplicity, size, low cost, energy efficiency, and long life. The term “pump” is used herein consistent with its use by those skilled in the art to refer to both compressors and liquid pumps. The term “compressor” is typically used to designate machines that compress and discharge gases such as air or refrigerants. “Liquid pumps” are similar structures that typically compress the flow of a liquid. Pumps and compressors with such desired ideal characteristics have been sought for use in applications including the general compression of gases such as air, hydrocarbons, process gases, high-purity gases, hazardous and corrosive gases, as well as the compression of phase-change refrigerants for refrigeration, air conditioning and heat pumps, and other specialty vapor-compression heat transfer applications.
Prior pump design efforts have provided a diversity of pump designs that can be roughly defined in two classes of operation: positive displacement and kinetic compressors. Positive displacement compressors have been devised in two categories: (1) rotary compressors such as screws, scrolls, and rotary vanes; and (2) reciprocating compressors operating with crank-driven pistons, free-pistons, and diaphragms. Examples of kinetic compressors that have been provided are centrifugal and acoustic compressors. The operating principles of each of these compressors requires the designer to compromise or sacrifice many of the above-mentioned desired ideal characteristics in order to promote a specific characteristic in a particular design. Of particular present interest are efforts relating to free-piston compressors, diaphragm compressors and acoustic compressors.
Free-piston pumps and compressors have been designed with the hope of achieving conceptual simplicity by using a linear motor to move a reciprocating piston back and forth in its cylinder, thus eliminating crankshafts, connecting rods and bearings. However, in practice, the desired conceptual simplicity of such free-piston compressors has not been realized as other complex subsystems have been required for the operation of such free-piston compressors. For example, free-piston compressors have attempted to utilize variable capacity since the piston has no fixed displacement. With the intent of improving efficiency and capacity, such free-piston pumps have sought to operate at a resonance frequency that is defined by the piston mass and the spring stiffness of the gas-filled cylinder. However, such free-piston compressors, as with all piston compressors, require the piston to be moved very close to the head to minimize the clearance volume in the interest of volumetric efficiency. This requirement has resulted in such free-piston compressor designs experiencing undesired damage or diminished operation if the piston strikes the head during operation or during any transients that might occur. Thus, to attempt to achieve the desired characteristics in these free-piston compressor designs, elaborate and complicated controls have been required to keep the piston from striking the head during operation or during any transients that might occur. However, such controls have not satisfactorily performed under varying operational conditions.
Further, such free-piston compressors have sought to achieve oil-free operation by allowing the piston to float on a gas bearing. Unfortunately, the gas bearing has required very small clearances between the piston and cylinder, and thus high-precision machining has been required which is difficult and costly. The gas bearing also requires a network of small gas feed drillings that have a low tolerance for the moisture and particulate contamination often found in operation of such pumps and compressors. Under use conditions, such moisture and particulate contamination have caused obstructions in the small gas feed drillings that have resulted in failure or inferior performance of the gas bearings. Due to these complex subsystems that are required for operation and other reasons known in the art, these free-piston compressors have not realized certain of the desired ideal characteristics and have lacked the desired conceptual simplicity for a variety of commercial applications.
Further, attempts have been made to operate free-piston compressors at their resonance. The elements of the mass-spring resonance of certain of such free-piston compressors operated at their resonance are the compressed gas as the spring and the free piston as the mass. To take advantage of this mechanical resonance, free piston compressors must be able to accommodate the instabilities related to varying flow rates and varying compression ratios. Variations in both compression ratios and flow rates cause large variations in the spring constant of the gas. Also, low compression ratios provide little restoring force to the piston, thus causing the resonant frequency to drop below the operating frequencies needed for a given flow rate. Electromechanical and/or fluidic controls have been required in such free-piston compressors to compensate for these instabilities, thus adding complexity to the pump or compressor. Further, changing operating conditions have created an additional instability in these free-piston compressors. In operation, as the compression ratio changes, the average force exerted on the piston by the gas spring changes, thus causing the mean position of the oscillating piston to undesirably creep. This instability has also necessitated the use of various electromechanical and/or fluidic controls to stabilize the mean piston position.
In addition to free-piston compressors, diaphragm pumps and compressors have also been provided using a moving diaphragm to provide fluid compression. Attempts have been made to use such diaphragm compressors for oil-free operation by actuating such diaphragm pumps by a motor. Unfortunately, to provide the displacement needed for adequate flow rates, diaphragm compressors have typically required a non-metallic, elastic member, such as rubber, to be attached to the diaphragm. These flexible members of rubber, or other organic compounds, have been susceptible, in prior designs, to cracking, weakening, breakage or other failures of the elastic member under high pressure conditions that are necessary for the high compression ratios needed for many consumer, commercial, and industrial applications. Such susceptibility of the elastic rubber members to cracking, weakening, breakage or other failures under high pressures have reduced the reliability and life of these elastic rubber diaphragm members. Further, such elastic rubber members have not been compatible with certain fluids, such as fuels, oils, lubricants, coolants, solvents, and various chemicals, due to susceptibility of the diaphragm to cracking, weakening, degradation or failure when exposed to the fluid during operation. Certain rubber diaphragms have been used that were permeable to certain gases resulting in a flow of gas through the diaphragm and a pressure build up on the backside of the diaphragm. Also, such permeable rubber diaphragms have resulted in the contamination of the gas with rubber odors that are problematic in applications where individuals are exposed to the gas and may be allergic to the rubber odor absorbed by the gas. As such, these efforts to provide diaphragm compressors have also failed to provide the simplicity of a diaphragm design with desired characteristics in view of the required compromise in compression ratio
Burr Ronald Frederick
Lawrenson Christopher Charles
Popham Vernon Wade
Shelley Franz Joseph
Freay Charles G.
Gray Michael K.
Haynes Michael N.
Macrosonix Corporation
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