CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX
FIELD OF THE INVENTION
This present application claims priority from U.S. provisional application No. 61/520,630 having the same title as the present invention and filed on Jun. 13, 2011.
This invention relates to pumps, and more particularly, to hydraulic injection pumps used in injecting fluid into a vessel, the pressure inside which is controlled within a predetermined range.
BACKGROUND OF THE INVENTION
Air-driven hydraulic pumps use compressed air to drive reciprocating actions in delivering pressurized liquid. With a stepped piston having its large diameter side contacting compressed air in an air cylinder and small diameter side driving liquid in a high pressure injection cylinder, an air-driven hydraulic pump is able to provide high driving pressure, which is multiple times of compressed air pressure, and the multiplication ratio is determined by the ratio of the large diameter to the small diameter. To complete a reciprocation cycle, which includes a suction stroke and a pressing stroke, it needs to control the air pressure inside the air cylinder by filling and releasing compressed air. Normally, the pressure control is realized by using relay valves that use sealed air and switches to fill and release the sealed air in controlling the relay valves (U.S. Pat. Nos. 3,963,383, 4,645,431, and 6,386,841). Therefore, the reciprocating rate is determined by air pressure, air filling and releasing rate, and switch position. As a result, fluctuations in compressed air supply pressure affect both reciprocating rate and driving pressure. Also, in the pressing stroke, compressed air expands and results in pressure drop. The pressure change in compressed air is then amplified by the pump and causes larger change in driving pressure.
To accurately control the driving pressure, a primary object of the present invention is to provide controls means to adjust the driving pressure, thereby with a closed-loop control, the driving pressure can be controlled within a predetermined range.
A further object is to replace the relay valve using the controls means set forth in the foregoing object to provide a simplified pump structure.
A further object is to provide controls means to avoid the effects of the suction stroke in controlling driving pressure.
SUMMARY OF THE INVENTION
In accordance with the present invention, a hydraulically actuated pumping apparatus with driving pressure controlled within a predetermined range is provided.
According to one embodiment of the invention, an air-driven hydraulic injection pump is provided that has a pressure multiplication ratio of 1.0, however, has no piston device inside. The stroke control and pressure control are accomplished by energizing and de-energizing two solenoid valves to control air pressure inside the pump according to pressure sensing values obtained from a pressure sensor.
According to another embodiment of the invention, an air-driven hydraulic injection pump is provided that has a pressure multiplication ratio higher than 1.0. This pump has a piston inside and strokes and pressure are controlled by energizing and de-energizing two solenoid valves to release and fill compressed air according to pressure sensing values obtained from a pressure sensor.
According to another embodiment of the invention, a hydraulic buffer is provided with an air-driven hydraulic injection pump. The hydraulic buffer decreases pressure drops associated with suction strokes in which compressed air is released from the pump.
According to another embodiment of the invention, a hydraulically driven pump system including two air-driven hydraulic injection pumps are provided. These two pumps work alternately to control driving pressure within a predetermined range.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a depicts an air-driven hydraulic pump system with two two-way solenoid valves and a pump without piston;
FIG. 1b depicts an air-driven hydraulic pump system with a two-way solenoid valve, a three-way solenoid valve, and a pump without piston;
FIG. 2 is a flow chart of a control algorithm for controlling strokes and pressure;
FIG. 3 depicts a cross sectional elevation view of a hydraulic pump housing used with the same stroke and pressure controls in a system as shown in FIG. 1;
FIG. 4 depicts a cross sectional elevation view of a hydraulic pump housing and a hydraulic buffer that is to decrease pressure drops associated with suction strokes;
FIG. 5 illustrates a timing chart of pressure changes in systems with and without a hydraulic buffer;
FIG. 6 depicts a system with two hydraulic pumps working together to control driving pressure within a predetermined range;
FIG. 7 is timing chart of control mode changes in a system shown in FIG. 6
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1a, a pump 100 includes a gas port 101, a liquid inlet port 105, a liquid outlet port 102, and a pressure sensor 103. Through a liquid passage 132, the liquid inlet port 105 is fluidly connected to a port 131 of a liquid tank 130, which contains a fluid 133. Inside the inlet port 105, a check valve 106 only allows liquid to flow from the liquid tank 130 to the pump 100. Fluid in the pump 100 flows out through the liquid outlet port 102, which has a check valve 104 included, while pressure inside the pump is measured by the pressure sensor 103 and the sensing value is sent to a controller 110. The gas port 101 of the pump 100 is fluidly coupled to the outlet of a two-way solenoid valve 126 through a Tee connector 127 and an air passage 125, and the inlet of the solenoid valve 126 is connected to a compressed air supply (not shown in FIG. 1a). The Tee connector 127 is also fluidly connected to the inlet of another two way solenoid valve 122 through an air passage 121. To lower down the noise when releasing air, an optional muffler 124 can be connected to the outlet of the solenoid valve 122 through an air passage 123. Both of the solenoid valves 122 and 126 are electrically connected to the controller 110. At normal states, i.e., before the solenoid valves 122 and 126 are energized, the compressed air is disconnected to the gas port 101 and the gas port 101 is fluidly connected to ambient through the solenoid valve 122.
Stroke control and pressure control for the pump 100 are accomplished by using the combination of controls to the solenoid valves 122 and 126. The controls to the two valves have four modes shown in the following table:
Status of the
Status of the