Dual piston pump
First Claim
1. A pump for producing a continuous outflow of liquid at relatively high pressure and comprising,pressure piston means for pressurizing the liquid,said pressure piston means including a pressure piston movable through suction and expulsion strokes,damper piston means for storing some of the liquid displaced by the pressure piston during the expulsion stroke of the pressure piston and for delivering the stored pressurized liquid to an outlet of the pump during the suction stroke of the pressure piston,said damper piston means including a damper piston movable through storage and expulsion strokes,connecting means connecting the pressure piston means and the damper piston means in series with the flow outlet from the pressure piston means connected to the flow inlet to the damper piston means,drive means for driving the pressure piston and damper piston in cooperation to produce a continuous outflow of pressurized liquid from the damper piston during all conditions of movement of the pistons,said drive means including a rotatable cam shaft, a pressure piston drive cam mounted on the cam shaft, and a damper piston drive cam mounted on the cam shaft,the cams being contoured to produce, at a constant speed of rotation of the cam shaft, a constant amount of outflow of pressurized liquid from the damper piston at all points in the cycle of rotation of the cam shaft except for a short interval at the beginning of the expulsion stroke of the pressure piston and an increased amount of outflow during said short interval,control means for slowing down the speed of rotation of the cam shaft during said short interval to produce the same amount of outflow as produced during the rest of the cycle of rotation of the cam shaft,sensing means for sensing the increase of outflow from the damper piston during said short interval and for supplying a feedback control signal to the control means, andwherein the control means include a first digitally operated control loop which controls the speed of rotation of the cam shaft except during said short interval and wherein the control means include an analog operated control loop which controls the speed of rotation of the cam shaft during said short interval at the beginning of the expulsion stroke of the pressure piston.
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0 Petitions
Accused Products
Abstract
A pump for producing a substantially smooth and continuous outflow of liquid at relatively high pressure has two piston assemblies flow connected in series. The first piston assembly includes a pressure piston having a long suction stroke and a relatively short and abrupt expulsion stroke. A valve at the inlet of the pressurization piston allows flow to enter (but not exit), and a valve at the outlet of the pressurization piston allows flow to exit (but not enter). The second piston assembly includes a damper piston which functions as a mechanically driven damper to smooth the outflow from the pressure piston. This smoothing is accomplished by storing of the liquid displaced by the expulsion stroke of the pressure piston and then delivering the stored pressurized liquid to the pump outlet during the suction stroke of the pressure piston.
The drive for the pistons is constructed to produce an increased outflow of pressurized liquid for a short interval at the beginning of the expulsion stroke of the pressure piston to compensate for compressibility of the liquid at high pressure. At low pressure, the stepper motor drive is slowed down in response to the sensing of the increase of the outflow during this short interval to maintain the outflow smooth and continuous during this part of the cycle of operation.
74 Citations
23 Claims
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1. A pump for producing a continuous outflow of liquid at relatively high pressure and comprising,
pressure piston means for pressurizing the liquid, said pressure piston means including a pressure piston movable through suction and expulsion strokes, damper piston means for storing some of the liquid displaced by the pressure piston during the expulsion stroke of the pressure piston and for delivering the stored pressurized liquid to an outlet of the pump during the suction stroke of the pressure piston, said damper piston means including a damper piston movable through storage and expulsion strokes, connecting means connecting the pressure piston means and the damper piston means in series with the flow outlet from the pressure piston means connected to the flow inlet to the damper piston means, drive means for driving the pressure piston and damper piston in cooperation to produce a continuous outflow of pressurized liquid from the damper piston during all conditions of movement of the pistons, said drive means including a rotatable cam shaft, a pressure piston drive cam mounted on the cam shaft, and a damper piston drive cam mounted on the cam shaft, the cams being contoured to produce, at a constant speed of rotation of the cam shaft, a constant amount of outflow of pressurized liquid from the damper piston at all points in the cycle of rotation of the cam shaft except for a short interval at the beginning of the expulsion stroke of the pressure piston and an increased amount of outflow during said short interval, control means for slowing down the speed of rotation of the cam shaft during said short interval to produce the same amount of outflow as produced during the rest of the cycle of rotation of the cam shaft, sensing means for sensing the increase of outflow from the damper piston during said short interval and for supplying a feedback control signal to the control means, and wherein the control means include a first digitally operated control loop which controls the speed of rotation of the cam shaft except during said short interval and wherein the control means include an analog operated control loop which controls the speed of rotation of the cam shaft during said short interval at the beginning of the expulsion stroke of the pressure piston.
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2. A pump for producing a continuous outflow of liquid at relatively high pressure and comprising,
pressure piston means for pressurizing the liquid, said pressure piston means including a pressure piston movable through suction and expulsion strokes, damper piston means for storing some of the liquid displaced by the pressure piston during the expulsion stroke of the pressure piston and for delivering the stored pressurized liquid to an outlet of the pump during the suction stroke of the pressure piston, said damper piston means including a damper piston movable through storage and expulsion strokes, connecting means connecting the pressure piston means and the damper piston means in series with the flow outlet from the pressure piston means connected to the flow inlet to the damper piston means, and drive means for driving the pressure piston and damper piston in cooperation to produce a continuous outflow of pressurized liquid from the damper piston during all conditions of movement of the pistons, said drive means including a rotatable cam shaft, a pressure piston drive cam mounted on the cam shaft, and a damper piston drive cam mounted on the cam shaft, and wherein the cams are contoured to produce, at a constant speed of rotation of the cam shaft, a constant amount of outflow of pressurized liquid from the damper piston at all points in the cycle of rotation of the cam shaft except for a short interval at the beginning of the expulsion stroke of the pressure piston and an increased amount of outflow during said short interval to compensate for the compressibility of liquids at high pressure by producing a flow positive pulse and to permit a motor control system to slow down the pump to maintain a smooth flow rather than requiring a motor control system to speed up the pump to eliminate a negative pulse resulting from the compressibility of the liquid.
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16. A method of producing a continuous flow of liquid at relatively high pressure from a pump and comprising,
connecting a pressure piston assembly and a damper piston assembly in series with the outlet of the pressure piston assembly connected to the inlet of the damper piston assembly, pressurizing the liquid by moving a pressure piston through a long inlet stroke and a relatively short expulsion stroke, and smoothing out the outflow from the pressure piston by moving a damper piston in cooperation with the movement of the pressure piston, said smoothing out step comprising, storing some of the liquid displaced by the expulsion stroke of the pressure piston in the damper piston assembly during the inlet stroke of the damper piston and delivering the stored pressurized liquid to the outlet of the pump during the expulsion stroke of the damper piston.
Specification