Pumps – Processes
Reexamination Certificate
2000-06-14
2001-10-09
Freay, Charles G. (Department: 3746)
Pumps
Processes
C417S440000, C417S534000, C092S182000, C092S183000
Reexamination Certificate
active
06299413
ABSTRACT:
DESCRIPTION OF THE RELATED ART
The present invention relates to the field of pumps, generally, and more specifically to pumps driven by a reciprocating piston.
FIELD OF THE INVENTION
Four-ball pumps have been used in spraying applications for many years, in such diverse applications as spraying furniture and automobiles. A typical four ball pump has a reciprocating piston, which may be pneumatically powered. Fluid is drawn up into the inlet and propelled from the outlet, both on the upstroke and downstroke of the piston. On the upstroke of the piston, fluid is drawn up beneath the piston, and fluid above the piston is propelled out of the fluid outlet. On the downstroke of the piston, fluid beneath the piston is forced into a first tube that is fluidly coupled to the fluid outlet, and a second tube coupled to the cavity above the piston. The fluid in the first tube is propelled out of the outlet. Meanwhile, a partial vacuum is formed on top of the piston, drawing the fluid from the second tube into the cavity above the top of the piston. This flow is regulated by four ball-type check valves.
The piston of a conventional four ball pump is connected to a pneumatic pressure source, even when no spray is required, and the fluid flow is cut off by closing the fluid outlet (for example, by closing a nozzle attached to the fluid outlet). When the fluid outlet is closed, fluid can no longer pass between the cavities above and below the piston, and the motion of the piston stops. This conserves pneumatically supplied power.
When the pump is first started up (also known as priming), air becomes trapped under the piston. Because the air rises above the liquid under the piston, the air cannot escape. Unlike liquids, air is compressible. When the pump transitions from the upstroke to the downstroke of the piston, the air beneath the piston is compressed, causing a pressure pulse. This change in the pressure at the fluid outlet causes an uneven finish in the article being sprayed.
In an attempt to eliminate the trapped air and reduce the pressure changes and uneven finish caused by the trapped air, others have located a small orifice in the piston, connecting the cavities above and below the piston. The trapped air below the piston can bleed through the hole, and escape through the cavity above the piston and the fluid outlet. Although this hole allows the trapped air to escape, it has not been a satisfactory solution. Because fluid can now pass between the cavities above and below the piston, the piston continues its reciprocating motion, even when the fluid outlet is closed. Thus, the pump continues to consume air power, even when not in use. Another problem is that particles forced through the small orifice can break down. For example, metallic particles in metallic paint break down, so that after several hours, the paint has a different appearance. Further, over time, the continuous flow through the orifice enlarges the hole, bypassing an increasing amount of fluid.
An improved pump is desired.
SUMMARY OF THE INVENTION
A pump comprises a housing having a fluid inlet and a fluid outlet. A piston is mounted for reciprocating motion in first and second directions within the housing. The housing has first and second cavities on first and second sides of the piston, respectively. The first and second cavities are fluidly coupled to the fluid inlet and fluid outlet, so that fluid is pumped to the fluid outlet when the piston moves in either of the first and second directions.
A bleed valve is coupled between the first and second cavities. The bleed valve has first and second closed states and an open state. The bleed valve changes from the first closed state through the open state to the second closed state when the piston moves in the first direction. The bleed valve changes from the second closed state through the open state to the first closed state when the piston moves in the second direction.
REFERENCES:
patent: Re. 34301 (1993-07-01), Brooks
patent: 3698182 (1972-10-01), Knoos
patent: 3768932 (1973-10-01), Svercl et al.
patent: 4825752 (1989-05-01), Kiffmeyer
patent: 5079997 (1992-01-01), Hong
patent: 5832727 (1998-11-01), Stanley
Operator's Manual #6695X-X, entitledFour-Ball Style Lower Pump End, released Feb. 12, 1991, revised Nov. 22, 1996, issued by Ingersoll-Rand Fluid Products, pp 1-4.
Carter Raymond
Stahlman David
Freay Charles G.
Hayes E O
Ingersoll-Rand Company
Koffs Steven E.
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