Pumps – Expansible chamber type – Having pumping chamber pressure responsive distributor
Reexamination Certificate
1999-10-18
2001-02-20
Freay, Charles G. (Department: 3746)
Pumps
Expansible chamber type
Having pumping chamber pressure responsive distributor
C417S501000
Reexamination Certificate
active
06190143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to piston-type vacuum pumps. More particularly, the present invention relates to an improved piston-type vacuum pump with a zero or negative clearance valve for allowing more complete evacuation of the vacuum chamber, and hence more efficient pumping.
2. State of the Art
Piston-type vacuum pumps are well known. Such pumps typically comprise a reciprocating piston disposed within a cylinder, the cylinder having inlet and outlet ports or valves. Uncompressed air is drawn into an evacuated cylinder through an inlet port, then compressed and forced to flow out through an outlet valve by the forward motion of the piston. As the piston retracts, the outlet valve closes, allowing the retraction of the piston to create a vacuum within the cylinder. When the piston reaches or passes the inlet port, the vacuum formed within the cylinder draws gas into the cylinder, and the process repeats itself.
However, one drawback of typical piston-type vacuum pumps is that the cylinder never completely evacuates at the end of the compression cycle. When the piston extends to the forward position, clearances between component parts allow a small amount of gas to remain in the cylinder. For example, if the pump utilizes a pressure activated outlet valve, such as a spring-loaded valve, some residual pressure will normally remain in the cylinder when the valve closes because a minimum pressure is required to open the valve in the first place due to the spring-biased configuration. Additionally, the clearance between the end of the piston and the inside of the end of the cylinder or outlet valve normally defines a volume of space in which some air will naturally remain.
In order to create a piston-type vacuum pump with increased vacuum pressure capability, it would be desirable to have a piston pump configured to allow no residual gas to remain in the cylinder after.compression. It would also be desirable to have a piston-type vacuum pump which requires very low power to operate.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a piston-type vacuum pump that is simple in design and operation.
It is another object of this invention to provide a compact piston-type vacuum pump with increased vacuum capability.
It is still another object of the invention to provide a compact piston-type vacuum pump which operates at very low power.
It is yet another object of the invention to provide a spring-biased poppet valve which allows full escape of compressed gas from a pump cylinder, without allowing any gas to flow back into the cylinder before resealing.
The above and other objects are realized in a low power piston-type vacuum pump having zero or negative clearance between the piston head and the inside of the cylinder/outlet valve at the end of the compression stroke. The pump comprises a reciprocating piston disposed within a cylinder having a proximal end and a distal end, an inlet port formed in the side of the cylinder near the proximal end, and a spring-biased outlet valve disposed at the distal end of the cylinder. The outlet valve may be either a poppet type valve, or a rocker valve. The piston is configured to reciprocate within the cylinder from a first position wherein the top end of the piston is proximal of the inlet port, to a second position wherein the top end of the piston extends beyond the distal end of the cylinder, so as to contact the face of the outlet valve in its open position. The piston top and valve face remain in contact until the piston has retracted into the distal end of the cylinder, allowing the valve to seal the distal end of the cylinder prior to the beginning of the expansion stroke.
These and other objects are also realized in an embodiment of a piston-type vacuum pump having a pair of oppositely oriented cylinders with encased pistons operating in tandem. The coupled piston pairs allow the pump to achieve very low power operation. Alternatively, a single piston with a sealed motor may also be used to achieve low power operation. Other objects and features of the present invention will be apparent to those skilled in the art, based on the following description, taken in combination with the accompanying drawings.
REFERENCES:
patent: 4125176 (1978-11-01), Thrasher, Jr.
patent: 5253984 (1993-10-01), Gruett et al.
patent: 5638920 (1997-06-01), Gruett
patent: 6071097 (2000-06-01), Gruett et al.
Davis Clark C.
Jacobsen Stephen C.
Morrison Michael G.
Oliver Marc
Evora Robert Z.
Freay Charles G.
Sarcos L.C.
Thorpe North & Western, LLC
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